Implement import sorting (#633)

README.md

@@ -27,9 +27,10 @@ An extremely fast Python linter, written in Rust.
 
 Ruff aims to be orders of magnitude faster than alternative tools while integrating more
 functionality behind a single, common interface. Ruff can be used to replace Flake8 (plus a variety
-of plugins), [`pydocstyle`](https://pypi.org/project/pydocstyle/), [`yesqa`](https://github.com/asottile/yesqa),
+of plugins), [`isort`](https://pypi.org/project/isort/), [`pydocstyle`](https://pypi.org/project/pydocstyle/),
-and even a subset of [`pyupgrade`](https://pypi.org/project/pyupgrade/) and [`autoflake`](https://pypi.org/project/autoflake/)
+[`yesqa`](https://github.com/asottile/yesqa), and even a subset of [`pyupgrade`](https://pypi.org/project/pyupgrade/)
-all while executing tens or hundreds of times faster than any individual tool.
+and [`autoflake`](https://pypi.org/project/autoflake/) all while executing tens or hundreds of times
+faster than any individual tool.
 
 (Coming from Flake8? Try [`flake8-to-ruff`](https://pypi.org/project/flake8-to-ruff/) to
 automatically convert your existing configuration.)
@@ -285,16 +286,16 @@ Ruff supports several workflows to aid in `noqa` management.
 
 First, Ruff provides a special error code, `M001`, to enforce that your `noqa` directives are
 "valid", in that the errors they _say_ they ignore are actually being triggered on that line (and
-thus suppressed). **You can run `ruff /path/to/file.py --extend-select M001` to flag unused `noqa`
+thus suppressed). You can run `ruff /path/to/file.py --extend-select M001` to flag unused `noqa`
-directives.**
+directives.
 
 Second, Ruff can _automatically remove_ unused `noqa` directives via its autofix functionality.
-**You can run `ruff /path/to/file.py --extend-select M001 --fix` to automatically remove unused
+You can run `ruff /path/to/file.py --extend-select M001 --fix` to automatically remove unused
-`noqa` directives.**
+`noqa` directives.
 
 Third, Ruff can _automatically add_ `noqa` directives to all failing lines. This is useful when
-migrating a new codebase to Ruff. **You can run `ruff /path/to/file.py --add-noqa` to automatically
+migrating a new codebase to Ruff. You can run `ruff /path/to/file.py --add-noqa` to automatically
-add `noqa` directives to all failing lines, with the appropriate error codes.**
+add `noqa` directives to all failing lines, with the appropriate error codes.
 
 ## Supported Rules
 
@@ -365,6 +366,14 @@ For more, see [pycodestyle](https://pypi.org/project/pycodestyle/2.9.1/) on PyPI
 | W292 | NoNewLineAtEndOfFile | No newline at end of file |  |
 | W605 | InvalidEscapeSequence | Invalid escape sequence: '\c' |  |
 
+### isort
+
+For more, see [isort](https://pypi.org/project/isort/5.10.1/) on PyPI.
+
+| Code | Name | Message | Fix |
+| ---- | ---- | ------- | --- |
+| I001 | UnsortedImports | Import block is un-sorted or un-formatted | 🛠 |
+
 ### pydocstyle
 
 For more, see [pydocstyle](https://pypi.org/project/pydocstyle/6.1.1/) on PyPI.
@@ -681,7 +690,7 @@ Today, Ruff can be used to replace Flake8 when used with any of the following pl
 - [`flake8-comprehensions`](https://pypi.org/project/flake8-comprehensions/)
 - [`flake8-bugbear`](https://pypi.org/project/flake8-bugbear/) (19/32)
 
-Ruff also implements the functionality that you get from [`yesqa`](https://github.com/asottile/yesqa),
+Ruff can also replace [`isort`](https://pypi.org/project/isort/), [`yesqa`](https://github.com/asottile/yesqa),
 and a subset of the rules implemented in [`pyupgrade`](https://pypi.org/project/pyupgrade/) (14/34).
 
 If you're looking to use Ruff, but rely on an unsupported Flake8 plugin, free to file an Issue.
@@ -702,6 +711,31 @@ on Rust at all.
 Ruff does not yet support third-party plugins, though a plugin system is within-scope for the
 project. See [#283](https://github.com/charliermarsh/ruff/issues/283) for more.
 
+### How does Ruff's import sorting compare to [`isort`](https://pypi.org/project/isort/)?
+
+Ruff's import sorting is intended to be equivalent to `isort` when used `profile = "black"` and
+`combine_as_imports = true`. Like `isort`, Ruff's import sorting is compatible with Black.
+
+Ruff is less configurable than `isort`, but supports the `known-first-party`, `known-third-party`,
+`extra-standard-library`, and `src` settings, like so:
+
+```toml
+[tool.ruff]
+select = [
+    # Pyflakes
+    "F",
+    # Pycodestyle
+    "E",
+    "W",
+    # isort
+    "I"
+]
+src = ["src", "tests"]
+
+[tool.ruff.isort]
+known-first-party = ["my_module1", "my_module2"]
+```
+
 ### Does Ruff support NumPy- or Google-style docstrings?
 
 Yes! To enable a specific docstring convention, start by enabling all `pydocstyle` error codes, and

flake8_to_ruff/src/converter.rs

@@ -208,6 +208,7 @@ mod tests {
         let actual = convert(&HashMap::from([]), None)?;
         let expected = Pyproject::new(Options {
             line_length: None,
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -224,6 +225,7 @@ mod tests {
             target_version: None,
             flake8_annotations: None,
             flake8_quotes: None,
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);
@@ -239,6 +241,7 @@ mod tests {
         )?;
         let expected = Pyproject::new(Options {
             line_length: Some(100),
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -255,6 +258,7 @@ mod tests {
             target_version: None,
             flake8_annotations: None,
             flake8_quotes: None,
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);
@@ -270,6 +274,7 @@ mod tests {
         )?;
         let expected = Pyproject::new(Options {
             line_length: Some(100),
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -286,6 +291,7 @@ mod tests {
             target_version: None,
             flake8_annotations: None,
             flake8_quotes: None,
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);
@@ -301,6 +307,7 @@ mod tests {
         )?;
         let expected = Pyproject::new(Options {
             line_length: None,
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -317,6 +324,7 @@ mod tests {
             target_version: None,
             flake8_annotations: None,
             flake8_quotes: None,
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);
@@ -332,6 +340,7 @@ mod tests {
         )?;
         let expected = Pyproject::new(Options {
             line_length: None,
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -353,6 +362,7 @@ mod tests {
                 docstring_quotes: None,
                 avoid_escape: None,
             }),
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);
@@ -371,6 +381,7 @@ mod tests {
         )?;
         let expected = Pyproject::new(Options {
             line_length: None,
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -422,6 +433,7 @@ mod tests {
             target_version: None,
             flake8_annotations: None,
             flake8_quotes: None,
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);
@@ -437,6 +449,7 @@ mod tests {
         )?;
         let expected = Pyproject::new(Options {
             line_length: None,
+            src: None,
             fix: None,
             exclude: None,
             extend_exclude: None,
@@ -459,6 +472,7 @@ mod tests {
                 docstring_quotes: None,
                 avoid_escape: None,
             }),
+            isort: None,
             pep8_naming: None,
         });
         assert_eq!(actual, expected);

pyproject.toml

@@ -32,3 +32,7 @@ build-backend = "maturin"
 bindings = "bin"
 sdist-include = ["Cargo.lock"]
 strip = true
+
+[tool.isort]
+profile = "black"
+known_third_party = ["fastapi", "pydantic", "starlette"]

resources/test/fixtures/isort/combine_import_froms.py

@@ -0,0 +1,5 @@
+from collections import Awaitable
+from collections import AsyncIterable
+from collections import Collection
+from collections import ChainMap
+from collections import MutableSequence, MutableMapping

resources/test/fixtures/isort/deduplicate_imports.py

@@ -0,0 +1,4 @@
+import os
+import os
+import os as os1
+import os as os2

resources/test/fixtures/isort/fit_line_length.py

@@ -0,0 +1 @@
+from collections import Collection

resources/test/fixtures/isort/import_from_after_import.py

@@ -0,0 +1,2 @@
+from collections import Collection
+import os

resources/test/fixtures/isort/leading_prefix.py

@@ -0,0 +1,6 @@
+x = 1; import sys
+import os
+
+if True:
+    x = 1; import sys
+    import os

resources/test/fixtures/isort/no_reorder_within_section.py

@@ -0,0 +1,3 @@
+# OK
+import os
+import sys

resources/test/fixtures/isort/preserve_indentation.py

@@ -0,0 +1,6 @@
+if True:
+    import sys
+    import os
+else:
+    import sys
+    import os

resources/test/fixtures/isort/reorder_within_section.py

@@ -0,0 +1,2 @@
+import sys
+import os

resources/test/fixtures/isort/separate_first_party_imports.py

@@ -0,0 +1,5 @@
+import sys
+import leading_prefix
+import numpy as np
+import os
+from leading_prefix import Class

resources/test/fixtures/isort/separate_future_imports.py

@@ -0,0 +1,3 @@
+import sys
+import os
+from __future__ import annotations

resources/test/fixtures/isort/separate_third_party_imports.py

@@ -0,0 +1,4 @@
+import pandas as pd
+import sys
+import numpy as np
+import os

resources/test/fixtures/isort/trailing_suffix.py

@@ -0,0 +1,6 @@
+import sys
+import os; x = 1
+
+if True:
+    import sys
+    import os; x = 1

src/check_ast.rs

@@ -23,6 +23,7 @@ use crate::ast::{helpers, operations, visitor};
 use crate::autofix::fixer;
 use crate::checks::{Check, CheckCode, CheckKind};
 use crate::docstrings::definition::{Definition, DefinitionKind, Documentable};
+use crate::isort::track::ImportTracker;
 use crate::python::builtins::{BUILTINS, MAGIC_GLOBALS};
 use crate::python::future::ALL_FEATURE_NAMES;
 use crate::python::typing;
@@ -77,6 +78,7 @@ pub struct Checker<'a> {
     deferred_functions: Vec<(&'a Stmt, Vec<usize>, Vec<usize>, VisibleScope)>,
     deferred_lambdas: Vec<(&'a Expr, Vec<usize>, Vec<usize>)>,
     deferred_assignments: Vec<usize>,
+    import_tracker: ImportTracker<'a>,
     // Internal, derivative state.
     visible_scope: VisibleScope,
     in_f_string: Option<Range>,
@@ -115,6 +117,8 @@ impl<'a> Checker<'a> {
             deferred_functions: Default::default(),
             deferred_lambdas: Default::default(),
             deferred_assignments: Default::default(),
+            import_tracker: ImportTracker::new(),
+            // Internal, derivative state.
             visible_scope: VisibleScope {
                 modifier: Modifier::Module,
                 visibility: module_visibility(path),
@@ -181,6 +185,9 @@ where
     'b: 'a,
 {
     fn visit_stmt(&mut self, stmt: &'b Stmt) {
+        // Call-through to any composed visitors.
+        self.import_tracker.visit_stmt(stmt);
+
         self.push_parent(stmt);
 
         // Track whether we've seen docstrings, non-imports, etc.
@@ -1657,6 +1664,9 @@ where
     }
 
     fn visit_excepthandler(&mut self, excepthandler: &'b Excepthandler) {
+        // Call-through to any composed visitors.
+        self.import_tracker.visit_excepthandler(excepthandler);
+
         match &excepthandler.node {
             ExcepthandlerKind::ExceptHandler { type_, name, .. } => {
                 if self.settings.enabled.contains(&CheckCode::E722) && type_.is_none() {
@@ -2591,5 +2601,8 @@ pub fn check_ast(
     // Check docstrings.
     checker.check_definitions();
 
+    // Check import blocks.
+    // checker.check_import_blocks();
+
     checker.checks
 }

src/check_imports.rs

@@ -0,0 +1,41 @@
+//! Lint rules based on import analysis.
+
+use rustpython_parser::ast::Suite;
+
+use crate::ast::visitor::Visitor;
+use crate::autofix::fixer;
+use crate::checks::Check;
+use crate::isort;
+use crate::isort::track::ImportTracker;
+use crate::settings::Settings;
+use crate::source_code_locator::SourceCodeLocator;
+
+fn check_import_blocks(
+    tracker: ImportTracker,
+    locator: &SourceCodeLocator,
+    settings: &Settings,
+    autofix: &fixer::Mode,
+) -> Vec<Check> {
+    let mut checks = vec![];
+    for block in tracker.into_iter() {
+        if !block.is_empty() {
+            if let Some(check) = isort::plugins::check_imports(block, locator, settings, autofix) {
+                checks.push(check);
+            }
+        }
+    }
+    checks
+}
+
+pub fn check_imports(
+    python_ast: &Suite,
+    locator: &SourceCodeLocator,
+    settings: &Settings,
+    autofix: &fixer::Mode,
+) -> Vec<Check> {
+    let mut tracker = ImportTracker::new();
+    for stmt in python_ast {
+        tracker.visit_stmt(stmt);
+    }
+    check_import_blocks(tracker, locator, settings, autofix)
+}

src/checks.rs

@@ -204,6 +204,8 @@ pub enum CheckCode {
     N816,
     N817,
     N818,
+    // isort
+    I001,
     // Ruff
     RUF001,
     RUF002,
@@ -216,6 +218,7 @@ pub enum CheckCode {
 pub enum CheckCategory {
     Pyflakes,
     Pycodestyle,
+    Isort,
     Pydocstyle,
     Pyupgrade,
     PEP8Naming,
@@ -234,6 +237,7 @@ impl CheckCategory {
         match self {
             CheckCategory::Pycodestyle => "pycodestyle",
             CheckCategory::Pyflakes => "Pyflakes",
+            CheckCategory::Isort => "isort",
             CheckCategory::Flake8Builtins => "flake8-builtins",
             CheckCategory::Flake8Bugbear => "flake8-bugbear",
             CheckCategory::Flake8Comprehensions => "flake8-comprehensions",
@@ -252,6 +256,7 @@ impl CheckCategory {
         match self {
             CheckCategory::Pycodestyle => Some("https://pypi.org/project/pycodestyle/2.9.1/"),
             CheckCategory::Pyflakes => Some("https://pypi.org/project/pyflakes/2.5.0/"),
+            CheckCategory::Isort => Some("https://pypi.org/project/isort/5.10.1/"),
             CheckCategory::Flake8Builtins => {
                 Some("https://pypi.org/project/flake8-builtins/2.0.1/")
             }
@@ -281,6 +286,7 @@ pub enum LintSource {
     FileSystem,
     Lines,
     Tokens,
+    Imports,
 }
 
 #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
@@ -470,6 +476,8 @@ pub enum CheckKind {
     MixedCaseVariableInGlobalScope(String),
     CamelcaseImportedAsAcronym(String, String),
     ErrorSuffixOnExceptionName(String),
+    // isort
+    UnsortedImports,
     // Ruff
     AmbiguousUnicodeCharacterString(char, char),
     AmbiguousUnicodeCharacterDocstring(char, char),
@@ -495,6 +503,7 @@ impl CheckCode {
             | CheckCode::RUF002
             | CheckCode::RUF003 => &LintSource::Tokens,
             CheckCode::E902 => &LintSource::FileSystem,
+            CheckCode::I001 => &LintSource::Imports,
             _ => &LintSource::AST,
         }
     }
@@ -717,6 +726,8 @@ impl CheckCode {
                 CheckKind::CamelcaseImportedAsAcronym("...".to_string(), "...".to_string())
             }
             CheckCode::N818 => CheckKind::ErrorSuffixOnExceptionName("...".to_string()),
+            // isort
+            CheckCode::I001 => CheckKind::UnsortedImports,
             // Ruff
             CheckCode::RUF001 => CheckKind::AmbiguousUnicodeCharacterString('𝐁', 'B'),
             CheckCode::RUF002 => CheckKind::AmbiguousUnicodeCharacterDocstring('𝐁', 'B'),
@@ -895,6 +906,7 @@ impl CheckCode {
             CheckCode::N816 => CheckCategory::PEP8Naming,
             CheckCode::N817 => CheckCategory::PEP8Naming,
             CheckCode::N818 => CheckCategory::PEP8Naming,
+            CheckCode::I001 => CheckCategory::Isort,
             CheckCode::RUF001 => CheckCategory::Ruff,
             CheckCode::RUF002 => CheckCategory::Ruff,
             CheckCode::RUF003 => CheckCategory::Ruff,
@@ -1085,6 +1097,8 @@ impl CheckKind {
             CheckKind::MixedCaseVariableInGlobalScope(..) => &CheckCode::N816,
             CheckKind::CamelcaseImportedAsAcronym(..) => &CheckCode::N817,
             CheckKind::ErrorSuffixOnExceptionName(..) => &CheckCode::N818,
+            // isort
+            CheckKind::UnsortedImports => &CheckCode::I001,
             // Ruff
             CheckKind::AmbiguousUnicodeCharacterString(..) => &CheckCode::RUF001,
             CheckKind::AmbiguousUnicodeCharacterDocstring(..) => &CheckCode::RUF002,
@@ -1644,6 +1658,8 @@ impl CheckKind {
             CheckKind::PEP3120UnnecessaryCodingComment => {
                 "utf-8 encoding declaration is unnecessary".to_string()
             }
+            // isort
+            CheckKind::UnsortedImports => "Import block is un-sorted or un-formatted".to_string(),
             // Ruff
             CheckKind::AmbiguousUnicodeCharacterString(confusable, representant) => {
                 format!(
@@ -1749,12 +1765,13 @@ impl CheckKind {
                 | CheckKind::UnnecessaryGeneratorSet
                 | CheckKind::UnnecessaryLRUCacheParams
                 | CheckKind::UnnecessaryListCall
-                | CheckKind::UnnecessaryListComprehensionSet
                 | CheckKind::UnnecessaryListComprehensionDict
+                | CheckKind::UnnecessaryListComprehensionSet
                 | CheckKind::UnnecessaryLiteralDict(_)
                 | CheckKind::UnnecessaryLiteralSet(_)
                 | CheckKind::UnnecessaryLiteralWithinListCall(_)
                 | CheckKind::UnnecessaryLiteralWithinTupleCall(_)
+                | CheckKind::UnsortedImports
                 | CheckKind::UnusedImport(_, false)
                 | CheckKind::UnusedLoopControlVariable(_)
                 | CheckKind::UnusedNOQA(_)

src/checks_gen.rs

@@ -203,6 +203,10 @@ pub enum CheckCodePrefix {
     F9,
     F90,
     F901,
+    I,
+    I0,
+    I00,
+    I001,
     M,
     M0,
     M00,
@@ -852,6 +856,10 @@ impl CheckCodePrefix {
             CheckCodePrefix::F9 => vec![CheckCode::F901],
             CheckCodePrefix::F90 => vec![CheckCode::F901],
             CheckCodePrefix::F901 => vec![CheckCode::F901],
+            CheckCodePrefix::I => vec![CheckCode::I001],
+            CheckCodePrefix::I0 => vec![CheckCode::I001],
+            CheckCodePrefix::I00 => vec![CheckCode::I001],
+            CheckCodePrefix::I001 => vec![CheckCode::I001],
             CheckCodePrefix::M => vec![CheckCode::M001],
             CheckCodePrefix::M0 => vec![CheckCode::M001],
             CheckCodePrefix::M00 => vec![CheckCode::M001],
@@ -1216,6 +1224,10 @@ impl CheckCodePrefix {
             CheckCodePrefix::F9 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::F90 => PrefixSpecificity::Tens,
             CheckCodePrefix::F901 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::I => PrefixSpecificity::Category,
+            CheckCodePrefix::I0 => PrefixSpecificity::Hundreds,
+            CheckCodePrefix::I00 => PrefixSpecificity::Tens,
+            CheckCodePrefix::I001 => PrefixSpecificity::Explicit,
             CheckCodePrefix::M => PrefixSpecificity::Category,
             CheckCodePrefix::M0 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::M00 => PrefixSpecificity::Tens,

src/docstrings/helpers.rs

@@ -1,4 +1,4 @@
-use rustpython_ast::{Expr, Location};
+use rustpython_ast::{Located, Location};
 
 use crate::ast::types::Range;
 use crate::check_ast::Checker;
@@ -24,9 +24,9 @@ pub fn leading_space(line: &str) -> String {
         .collect()
 }
 
-/// Extract the leading indentation from a docstring.
+/// Extract the leading indentation from a line.
-pub fn indentation<'a>(checker: &'a Checker, docstring: &Expr) -> String {
+pub fn indentation<'a, T>(checker: &'a Checker, located: &Located<T>) -> String {
-    let range = Range::from_located(docstring);
+    let range = Range::from_located(located);
     checker
         .locator
         .slice_source_code_range(&Range {

src/isort/categorize.rs

@@ -0,0 +1,68 @@
+use std::collections::{BTreeMap, BTreeSet};
+use std::fs;
+use std::path::PathBuf;
+
+use once_cell::sync::Lazy;
+
+use crate::python::sys::KNOWN_STANDARD_LIBRARY;
+
+#[derive(Debug, PartialOrd, Ord, PartialEq, Eq, Clone)]
+pub enum ImportType {
+    Future,
+    StandardLibrary,
+    ThirdParty,
+    FirstParty,
+}
+
+pub fn categorize(
+    module_base: &str,
+    src: &[PathBuf],
+    known_first_party: &BTreeSet<String>,
+    known_third_party: &BTreeSet<String>,
+    extra_standard_library: &BTreeSet<String>,
+) -> ImportType {
+    if known_first_party.contains(module_base) {
+        ImportType::FirstParty
+    } else if known_third_party.contains(module_base) {
+        ImportType::ThirdParty
+    } else if extra_standard_library.contains(module_base) {
+        ImportType::StandardLibrary
+    } else if let Some(import_type) = STATIC_CLASSIFICATIONS.get(module_base) {
+        import_type.clone()
+    } else if KNOWN_STANDARD_LIBRARY.contains(module_base) {
+        ImportType::StandardLibrary
+    } else {
+        if find_local(src, module_base) {
+            ImportType::FirstParty
+        } else {
+            ImportType::ThirdParty
+        }
+    }
+}
+
+static STATIC_CLASSIFICATIONS: Lazy<BTreeMap<&'static str, ImportType>> = Lazy::new(|| {
+    BTreeMap::from([
+        ("__future__", ImportType::Future),
+        ("__main__", ImportType::FirstParty),
+        // Force `disutils` to be considered third-party.
+        ("disutils", ImportType::ThirdParty),
+        // Relative imports (e.g., `from . import module`).
+        ("", ImportType::FirstParty),
+    ])
+});
+
+fn find_local(paths: &[PathBuf], base: &str) -> bool {
+    for path in paths {
+        if let Ok(metadata) = fs::metadata(path.join(base)) {
+            if metadata.is_dir() {
+                return true;
+            }
+        }
+        if let Ok(metadata) = fs::metadata(path.join(format!("{base}.py"))) {
+            if metadata.is_file() {
+                return true;
+            }
+        }
+    }
+    false
+}

src/isort/mod.rs

@@ -0,0 +1,256 @@
+use std::collections::{BTreeMap, BTreeSet};
+use std::path::PathBuf;
+
+use ropey::RopeBuilder;
+use rustpython_ast::{Stmt, StmtKind};
+
+use crate::isort::categorize::{categorize, ImportType};
+use crate::isort::types::{AliasData, ImportBlock, ImportFromData, Importable};
+
+mod categorize;
+pub mod plugins;
+pub mod settings;
+pub mod track;
+mod types;
+
+// Hard-code four-space indentation for the imports themselves, to match Black.
+const INDENT: &str = "    ";
+
+fn normalize_imports<'a>(imports: &'a [&'a Stmt]) -> ImportBlock<'a> {
+    let mut block: ImportBlock = Default::default();
+    for import in imports {
+        match &import.node {
+            StmtKind::Import { names } => {
+                for name in names {
+                    block.import.insert(AliasData {
+                        name: &name.node.name,
+                        asname: &name.node.asname,
+                    });
+                }
+            }
+            StmtKind::ImportFrom {
+                module,
+                names,
+                level,
+            } => {
+                let targets = block
+                    .import_from
+                    .entry(ImportFromData { module, level })
+                    .or_default();
+                for name in names {
+                    targets.insert(AliasData {
+                        name: &name.node.name,
+                        asname: &name.node.asname,
+                    });
+                }
+            }
+            _ => unreachable!("Expected StmtKind::Import | StmtKind::ImportFrom"),
+        }
+    }
+    block
+}
+
+fn categorize_imports<'a>(
+    block: ImportBlock<'a>,
+    src: &[PathBuf],
+    known_first_party: &BTreeSet<String>,
+    known_third_party: &BTreeSet<String>,
+    extra_standard_library: &BTreeSet<String>,
+) -> BTreeMap<ImportType, ImportBlock<'a>> {
+    let mut block_by_type: BTreeMap<ImportType, ImportBlock> = Default::default();
+    // Categorize `StmtKind::Import`.
+    for alias in block.import {
+        let import_type = categorize(
+            &alias.module_base(),
+            src,
+            known_first_party,
+            known_third_party,
+            extra_standard_library,
+        );
+        block_by_type
+            .entry(import_type)
+            .or_default()
+            .import
+            .insert(alias);
+    }
+    // Categorize `StmtKind::ImportFrom`.
+    for (import_from, aliases) in block.import_from {
+        let classification = categorize(
+            &import_from.module_base(),
+            src,
+            known_first_party,
+            known_third_party,
+            extra_standard_library,
+        );
+        block_by_type
+            .entry(classification)
+            .or_default()
+            .import_from
+            .insert(import_from, aliases);
+    }
+    block_by_type
+}
+
+pub fn sort_imports(
+    block: Vec<&Stmt>,
+    line_length: &usize,
+    src: &[PathBuf],
+    known_first_party: &BTreeSet<String>,
+    known_third_party: &BTreeSet<String>,
+    extra_standard_library: &BTreeSet<String>,
+) -> String {
+    // Normalize imports (i.e., deduplicate, aggregate `from` imports).
+    let block = normalize_imports(&block);
+
+    // Categorize by type (e.g., first-party vs. third-party).
+    let block_by_type = categorize_imports(
+        block,
+        src,
+        known_first_party,
+        known_third_party,
+        extra_standard_library,
+    );
+
+    // Generate replacement source code.
+    let mut output = RopeBuilder::new();
+    let mut first_block = true;
+    for import_type in [
+        ImportType::Future,
+        ImportType::StandardLibrary,
+        ImportType::ThirdParty,
+        ImportType::FirstParty,
+    ] {
+        if let Some(import_block) = block_by_type.get(&import_type) {
+            // Add a blank line between every section.
+            if !first_block {
+                output.append("\n");
+            } else {
+                first_block = false;
+            }
+
+            // Format `StmtKind::Import` statements.
+            for AliasData { name, asname } in import_block.import.iter() {
+                if let Some(asname) = asname {
+                    output.append(&format!("import {} as {}\n", name, asname));
+                } else {
+                    output.append(&format!("import {}\n", name));
+                }
+            }
+
+            // Format `StmtKind::ImportFrom` statements.
+            for (import_from, aliases) in import_block.import_from.iter() {
+                let prelude: String = format!("from {} import ", import_from.module_name());
+                let members: Vec<String> = aliases
+                    .iter()
+                    .map(|AliasData { name, asname }| {
+                        if let Some(asname) = asname {
+                            format!("{} as {}", name, asname)
+                        } else {
+                            name.to_string()
+                        }
+                    })
+                    .collect();
+
+                // Can we fit the import on a single line?
+                let expected_len: usize =
+                    // `from base import `
+                    prelude.len()
+                        // `member( as alias)?`
+                        + members.iter().map(|part| part.len()).sum::<usize>()
+                        // `, `
+                        + 2 * (members.len() - 1);
+
+                if expected_len <= *line_length {
+                    // `from base import `
+                    output.append(&prelude);
+                    // `member( as alias)?(, )?`
+                    for (index, part) in members.into_iter().enumerate() {
+                        if index > 0 {
+                            output.append(", ");
+                        }
+                        output.append(&part);
+                    }
+                    // `\n`
+                    output.append("\n");
+                } else {
+                    // `from base import (\n`
+                    output.append(&prelude);
+                    output.append("(");
+                    output.append("\n");
+
+                    // `    member( as alias)?,\n`
+                    for part in members {
+                        output.append(INDENT);
+                        output.append(&part);
+                        output.append(",");
+                        output.append("\n");
+                    }
+
+                    // `)\n`
+                    output.append(")");
+                    output.append("\n");
+                }
+            }
+        }
+    }
+    output.finish().to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use std::path::Path;
+
+    use anyhow::Result;
+    use rustpython_parser::lexer::LexResult;
+    use test_case::test_case;
+
+    use crate::autofix::fixer;
+    use crate::checks::{Check, CheckCode};
+    use crate::linter::tokenize;
+    use crate::{fs, linter, noqa, Settings, SourceCodeLocator};
+
+    fn check_path(path: &Path, settings: &Settings, autofix: &fixer::Mode) -> Result<Vec<Check>> {
+        let contents = fs::read_file(path)?;
+        let tokens: Vec<LexResult> = tokenize(&contents);
+        let locator = SourceCodeLocator::new(&contents);
+        let noqa_line_for = noqa::extract_noqa_line_for(&tokens);
+        linter::check_path(
+            path,
+            &contents,
+            tokens,
+            &locator,
+            &noqa_line_for,
+            settings,
+            autofix,
+        )
+    }
+
+    #[test_case(Path::new("reorder_within_section.py"))]
+    #[test_case(Path::new("no_reorder_within_section.py"))]
+    #[test_case(Path::new("separate_future_imports.py"))]
+    #[test_case(Path::new("separate_third_party_imports.py"))]
+    #[test_case(Path::new("separate_first_party_imports.py"))]
+    #[test_case(Path::new("deduplicate_imports.py"))]
+    #[test_case(Path::new("combine_import_froms.py"))]
+    #[test_case(Path::new("preserve_indentation.py"))]
+    #[test_case(Path::new("fit_line_length.py"))]
+    #[test_case(Path::new("import_from_after_import.py"))]
+    #[test_case(Path::new("leading_prefix.py"))]
+    #[test_case(Path::new("trailing_suffix.py"))]
+    fn isort(path: &Path) -> Result<()> {
+        let snapshot = format!("{}", path.to_string_lossy());
+        let mut checks = check_path(
+            Path::new("./resources/test/fixtures/isort")
+                .join(path)
+                .as_path(),
+            &Settings {
+                src: vec![Path::new("resources/test/fixtures/isort").to_path_buf()],
+                ..Settings::for_rule(CheckCode::I001)
+            },
+            &fixer::Mode::Generate,
+        )?;
+        checks.sort_by_key(|check| check.location);
+        insta::assert_yaml_snapshot!(snapshot, checks);
+        Ok(())
+    }
+}

src/isort/plugins.rs

@@ -0,0 +1,116 @@
+use rustpython_ast::{Location, Stmt};
+use textwrap::{dedent, indent};
+
+use crate::ast::types::Range;
+use crate::autofix::{fixer, Fix};
+use crate::checks::CheckKind;
+use crate::docstrings::helpers::leading_space;
+use crate::isort::sort_imports;
+use crate::{Check, Settings, SourceCodeLocator};
+
+fn extract_range(body: &[&Stmt]) -> Range {
+    let location = body.first().unwrap().location;
+    let end_location = body.last().unwrap().end_location.unwrap();
+    Range {
+        location,
+        end_location,
+    }
+}
+
+fn extract_indentation(body: &[&Stmt], locator: &SourceCodeLocator) -> String {
+    let location = body.first().unwrap().location;
+    let range = Range {
+        location: Location::new(location.row(), 0),
+        end_location: location,
+    };
+    let existing = locator.slice_source_code_range(&range);
+    leading_space(&existing)
+}
+
+fn match_leading_content(body: &[&Stmt], locator: &SourceCodeLocator) -> bool {
+    let location = body.first().unwrap().location;
+    let range = Range {
+        location: Location::new(location.row(), 0),
+        end_location: location,
+    };
+    let prefix = locator.slice_source_code_range(&range);
+    prefix.chars().any(|char| !char.is_whitespace())
+}
+
+fn match_trailing_content(body: &[&Stmt], locator: &SourceCodeLocator) -> bool {
+    let end_location = body.last().unwrap().end_location.unwrap();
+    let range = Range {
+        location: end_location,
+        end_location: Location::new(end_location.row() + 1, 0),
+    };
+    let suffix = locator.slice_source_code_range(&range);
+    suffix.chars().any(|char| !char.is_whitespace())
+}
+
+/// I001
+pub fn check_imports(
+    body: Vec<&Stmt>,
+    locator: &SourceCodeLocator,
+    settings: &Settings,
+    autofix: &fixer::Mode,
+) -> Option<Check> {
+    let range = extract_range(&body);
+    let indentation = extract_indentation(&body, locator);
+
+    // Special-cases: there's leading or trailing content in the import block.
+    let has_leading_content = match_leading_content(&body, locator);
+    let has_trailing_content = match_trailing_content(&body, locator);
+
+    // Generate the sorted import block.
+    let expected = sort_imports(
+        body,
+        &settings.line_length,
+        &settings.src,
+        &settings.isort.known_first_party,
+        &settings.isort.known_third_party,
+        &settings.isort.extra_standard_library,
+    );
+
+    if has_leading_content || has_trailing_content {
+        let mut check = Check::new(CheckKind::UnsortedImports, range);
+        if autofix.patch() {
+            let mut content = String::new();
+            if has_leading_content {
+                content.push('\n');
+            }
+            content.push_str(&indent(&expected, &indentation));
+            check.amend(Fix::replacement(
+                content,
+                // Preserve leading prefix (but put the imports on a new line).
+                if has_leading_content {
+                    range.location
+                } else {
+                    Location::new(range.location.row(), 0)
+                },
+                // TODO(charlie): Preserve trailing suffixes. Right now, we strip them.
+                Location::new(range.end_location.row() + 1, 0),
+            ));
+        }
+        Some(check)
+    } else {
+        // Expand the span the entire range, including leading and trailing space.
+        let range = Range {
+            location: Location::new(range.location.row(), 0),
+            end_location: Location::new(range.end_location.row() + 1, 0),
+        };
+        let actual = dedent(&locator.slice_source_code_range(&range));
+        if actual != expected {
+            let mut check = Check::new(CheckKind::UnsortedImports, range);
+            if autofix.patch() {
+                check.amend(Fix::replacement(
+                    indent(&expected, &indentation),
+                    range.location,
+                    range.end_location,
+                ));
+            }
+            Some(check)
+        } else {
+            None
+        }
+    }
+}

src/isort/settings.rs

@@ -0,0 +1,32 @@
+//! Settings for the `isort` plugin.
+
+use std::collections::BTreeSet;
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, PartialEq, Eq, Serialize, Deserialize, Default)]
+#[serde(deny_unknown_fields, rename_all = "kebab-case")]
+pub struct Options {
+    pub known_first_party: Option<Vec<String>>,
+    pub known_third_party: Option<Vec<String>>,
+    pub extra_standard_library: Option<Vec<String>>,
+}
+
+#[derive(Debug, Hash, Default)]
+pub struct Settings {
+    pub known_first_party: BTreeSet<String>,
+    pub known_third_party: BTreeSet<String>,
+    pub extra_standard_library: BTreeSet<String>,
+}
+
+impl Settings {
+    pub fn from_options(options: Options) -> Self {
+        Self {
+            known_first_party: BTreeSet::from_iter(options.known_first_party.unwrap_or_default()),
+            known_third_party: BTreeSet::from_iter(options.known_third_party.unwrap_or_default()),
+            extra_standard_library: BTreeSet::from_iter(
+                options.extra_standard_library.unwrap_or_default(),
+            ),
+        }
+    }
+}

src/isort/snapshots/ruff__isort__tests__combine_import_froms.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 6
+    column: 0
+  fix:
+    patch:
+      content: "from collections import (\n    AsyncIterable,\n    Awaitable,\n    ChainMap,\n    Collection,\n    MutableMapping,\n    MutableSequence,\n)\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 6
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__deduplicate_imports.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 5
+    column: 0
+  fix:
+    patch:
+      content: "import os\nimport os as os1\nimport os as os2\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 5
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__fit_line_length.py.snap

@@ -0,0 +1,6 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+[]
+

src/isort/snapshots/ruff__isort__tests__import_from_after_import.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 3
+    column: 0
+  fix:
+    patch:
+      content: "import os\nfrom collections import Collection\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 3
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__leading_prefix.py.snap

@@ -0,0 +1,39 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 7
+  end_location:
+    row: 2
+    column: 9
+  fix:
+    patch:
+      content: "\nimport os\nimport sys\n"
+      location:
+        row: 1
+        column: 7
+      end_location:
+        row: 3
+        column: 0
+    applied: false
+- kind: UnsortedImports
+  location:
+    row: 5
+    column: 11
+  end_location:
+    row: 6
+    column: 13
+  fix:
+    patch:
+      content: "\n    import os\n    import sys\n"
+      location:
+        row: 5
+        column: 11
+      end_location:
+        row: 7
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__no_reorder_within_section.py.snap

@@ -0,0 +1,6 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+[]
+

src/isort/snapshots/ruff__isort__tests__preserve_indentation.py.snap

@@ -0,0 +1,39 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 2
+    column: 0
+  end_location:
+    row: 4
+    column: 0
+  fix:
+    patch:
+      content: "    import os\n    import sys\n"
+      location:
+        row: 2
+        column: 0
+      end_location:
+        row: 4
+        column: 0
+    applied: false
+- kind: UnsortedImports
+  location:
+    row: 5
+    column: 0
+  end_location:
+    row: 7
+    column: 0
+  fix:
+    patch:
+      content: "    import os\n    import sys\n"
+      location:
+        row: 5
+        column: 0
+      end_location:
+        row: 7
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__reorder_within_section.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 3
+    column: 0
+  fix:
+    patch:
+      content: "import os\nimport sys\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 3
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__separate_first_party_imports.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 6
+    column: 0
+  fix:
+    patch:
+      content: "import os\nimport sys\n\nimport numpy as np\n\nimport leading_prefix\nfrom leading_prefix import Class\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 6
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__separate_future_imports.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 4
+    column: 0
+  fix:
+    patch:
+      content: "from __future__ import annotations\n\nimport os\nimport sys\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 4
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__separate_third_party_imports.py.snap

@@ -0,0 +1,22 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 5
+    column: 0
+  fix:
+    patch:
+      content: "import os\nimport sys\n\nimport numpy as np\nimport pandas as pd\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 5
+        column: 0
+    applied: false
+

src/isort/snapshots/ruff__isort__tests__trailing_suffix.py.snap

@@ -0,0 +1,39 @@
+---
+source: src/isort/mod.rs
+expression: checks
+---
+- kind: UnsortedImports
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 2
+    column: 9
+  fix:
+    patch:
+      content: "import os\nimport sys\n"
+      location:
+        row: 1
+        column: 0
+      end_location:
+        row: 3
+        column: 0
+    applied: false
+- kind: UnsortedImports
+  location:
+    row: 5
+    column: 4
+  end_location:
+    row: 6
+    column: 13
+  fix:
+    patch:
+      content: "    import os\n    import sys\n"
+      location:
+        row: 5
+        column: 0
+      end_location:
+        row: 7
+        column: 0
+    applied: false
+

src/isort/track.rs

@@ -0,0 +1,206 @@
+use rustpython_ast::{
+    Alias, Arg, Arguments, Boolop, Cmpop, Comprehension, Constant, Excepthandler,
+    ExcepthandlerKind, Expr, ExprContext, Keyword, MatchCase, Operator, Pattern, Stmt, StmtKind,
+    Unaryop, Withitem,
+};
+
+use crate::ast::visitor::Visitor;
+
+#[derive(Debug)]
+pub struct ImportTracker<'a> {
+    pub blocks: Vec<Vec<&'a Stmt>>,
+}
+impl<'a> ImportTracker<'a> {
+    pub fn new() -> Self {
+        Self {
+            blocks: vec![vec![]],
+        }
+    }
+
+    fn add_import(&mut self, stmt: &'a Stmt) {
+        let index = self.blocks.len() - 1;
+        self.blocks[index].push(stmt);
+    }
+
+    fn finalize(&mut self) {
+        let index = self.blocks.len() - 1;
+        if !self.blocks[index].is_empty() {
+            self.blocks.push(vec![]);
+        }
+    }
+
+    pub fn into_iter(self) -> impl IntoIterator<Item = Vec<&'a Stmt>> {
+        self.blocks.into_iter()
+    }
+}
+
+impl<'a, 'b> Visitor<'b> for ImportTracker<'a>
+where
+    'b: 'a,
+{
+    fn visit_stmt(&mut self, stmt: &'b Stmt) {
+        // Track imports.
+        if matches!(
+            stmt.node,
+            StmtKind::Import { .. } | StmtKind::ImportFrom { .. }
+        ) {
+            self.add_import(stmt);
+        } else {
+            self.finalize();
+        }
+
+        // Track scope.
+        match &stmt.node {
+            StmtKind::FunctionDef { body, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::AsyncFunctionDef { body, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::ClassDef { body, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::For { body, orelse, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+
+                for stmt in orelse {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::AsyncFor { body, orelse, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+
+                for stmt in orelse {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::While { body, orelse, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+
+                for stmt in orelse {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::If { body, orelse, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+
+                for stmt in orelse {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::With { body, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::AsyncWith { body, .. } => {
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            StmtKind::Match { cases, .. } => {
+                for match_case in cases {
+                    self.visit_match_case(match_case);
+                }
+            }
+            StmtKind::Try {
+                body,
+                handlers,
+                orelse,
+                finalbody,
+            } => {
+                for excepthandler in handlers {
+                    self.visit_excepthandler(excepthandler)
+                }
+
+                for stmt in body {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+
+                for stmt in orelse {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+
+                for stmt in finalbody {
+                    self.visit_stmt(stmt);
+                }
+                self.finalize();
+            }
+            _ => {}
+        }
+    }
+
+    fn visit_annotation(&mut self, _: &'b Expr) {}
+
+    fn visit_expr(&mut self, _: &'b Expr) {}
+
+    fn visit_constant(&mut self, _: &'b Constant) {}
+
+    fn visit_expr_context(&mut self, _: &'b ExprContext) {}
+
+    fn visit_boolop(&mut self, _: &'b Boolop) {}
+
+    fn visit_operator(&mut self, _: &'b Operator) {}
+
+    fn visit_unaryop(&mut self, _: &'b Unaryop) {}
+
+    fn visit_cmpop(&mut self, _: &'b Cmpop) {}
+
+    fn visit_comprehension(&mut self, _: &'b Comprehension) {}
+
+    fn visit_excepthandler(&mut self, excepthandler: &'b Excepthandler) {
+        let ExcepthandlerKind::ExceptHandler { body, .. } = &excepthandler.node;
+        for stmt in body {
+            self.visit_stmt(stmt);
+        }
+        self.finalize();
+    }
+
+    fn visit_arguments(&mut self, _: &'b Arguments) {}
+
+    fn visit_arg(&mut self, _: &'b Arg) {}
+
+    fn visit_keyword(&mut self, _: &'b Keyword) {}
+
+    fn visit_alias(&mut self, _: &'b Alias) {}
+
+    fn visit_withitem(&mut self, _: &'b Withitem) {}
+
+    fn visit_match_case(&mut self, match_case: &'b MatchCase) {
+        for stmt in &match_case.body {
+            self.visit_stmt(stmt);
+        }
+        self.finalize();
+    }
+
+    fn visit_pattern(&mut self, _: &'b Pattern) {}
+}

src/isort/types.rs

@@ -0,0 +1,55 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+#[derive(Debug, Hash, Ord, PartialOrd, Eq, PartialEq)]
+pub struct ImportFromData<'a> {
+    pub module: &'a Option<String>,
+    pub level: &'a Option<usize>,
+}
+
+#[derive(Debug, Hash, Ord, PartialOrd, Eq, PartialEq)]
+pub struct AliasData<'a> {
+    pub name: &'a str,
+    pub asname: &'a Option<String>,
+}
+
+pub trait Importable {
+    fn module_name(&self) -> String;
+    fn module_base(&self) -> String;
+}
+
+impl Importable for AliasData<'_> {
+    fn module_name(&self) -> String {
+        self.name.to_string()
+    }
+
+    fn module_base(&self) -> String {
+        self.module_name().split('.').next().unwrap().to_string()
+    }
+}
+
+impl Importable for ImportFromData<'_> {
+    fn module_name(&self) -> String {
+        let mut module_name = String::new();
+        if let Some(level) = self.level {
+            if level > &0 {
+                module_name.push_str(&".".repeat(*level));
+            }
+        }
+        if let Some(module) = self.module {
+            module_name.push_str(module);
+        }
+        module_name
+    }
+
+    fn module_base(&self) -> String {
+        self.module_name().split('.').next().unwrap().to_string()
+    }
+}
+
+#[derive(Debug, Default)]
+pub struct ImportBlock<'a> {
+    // Map from (module, level) to `AliasData`.
+    pub import_from: BTreeMap<ImportFromData<'a>, BTreeSet<AliasData<'a>>>,
+    // Set of (name, asname).
+    pub import: BTreeSet<AliasData<'a>>,
+}

src/lib.rs

@@ -17,6 +17,7 @@ mod ast;
 pub mod autofix;
 pub mod cache;
 pub mod check_ast;
+mod check_imports;
 mod check_lines;
 mod check_tokens;
 pub mod checks;
@@ -32,6 +33,7 @@ mod flake8_comprehensions;
 mod flake8_print;
 pub mod flake8_quotes;
 pub mod fs;
+mod isort;
 mod lex;
 pub mod linter;
 pub mod logging;

src/linter.rs

@@ -16,6 +16,7 @@ use crate::ast::types::Range;
 use crate::autofix::fixer;
 use crate::autofix::fixer::fix_file;
 use crate::check_ast::check_ast;
+use crate::check_imports::check_imports;
 use crate::check_lines::check_lines;
 use crate::check_tokens::check_tokens;
 use crate::checks::{Check, CheckCode, CheckKind, LintSource};
@@ -63,23 +64,32 @@ pub(crate) fn check_path(
     let mut checks: Vec<Check> = vec![];
 
     // Run the token-based checks.
-    if settings
+    let use_tokens = settings
         .enabled
         .iter()
-        .any(|check_code| matches!(check_code.lint_source(), LintSource::Tokens))
+        .any(|check_code| matches!(check_code.lint_source(), LintSource::Tokens));
-    {
+    if use_tokens {
         check_tokens(&mut checks, locator, &tokens, settings, autofix);
     }
 
     // Run the AST-based checks.
-    if settings
+    let use_ast = settings
         .enabled
         .iter()
-        .any(|check_code| matches!(check_code.lint_source(), LintSource::AST))
+        .any(|check_code| matches!(check_code.lint_source(), LintSource::AST));
-    {
+    let use_imports = settings
+        .enabled
+        .iter()
+        .any(|check_code| matches!(check_code.lint_source(), LintSource::Imports));
+    if use_ast || use_imports {
         match parse_program_tokens(tokens, "<filename>") {
             Ok(python_ast) => {
-                checks.extend(check_ast(&python_ast, locator, settings, autofix, path))
+                if use_ast {
+                    checks.extend(check_ast(&python_ast, locator, settings, autofix, path));
+                }
+                if use_imports {
+                    checks.extend(check_imports(&python_ast, locator, settings, autofix));
+                }
             }
             Err(parse_error) => {
                 if settings.enabled.contains(&CheckCode::E999) {

src/python/mod.rs

@@ -1,4 +1,5 @@
 pub mod builtins;
 pub mod future;
 pub mod keyword;
+pub mod sys;
 pub mod typing;

src/python/sys.rs

@@ -0,0 +1,228 @@
+use std::collections::BTreeSet;
+
+use once_cell::sync::Lazy;
+
+// See: https://pycqa.github.io/isort/docs/configuration/options.html#known-standard-library
+pub static KNOWN_STANDARD_LIBRARY: Lazy<BTreeSet<&'static str>> = Lazy::new(|| {
+    BTreeSet::from([
+        "_ast",
+        "_dummy_thread",
+        "_thread",
+        "abc",
+        "aifc",
+        "argparse",
+        "array",
+        "ast",
+        "asynchat",
+        "asyncio",
+        "asyncore",
+        "atexit",
+        "audioop",
+        "base64",
+        "bdb",
+        "binascii",
+        "binhex",
+        "bisect",
+        "builtins",
+        "bz2",
+        "cProfile",
+        "calendar",
+        "cgi",
+        "cgitb",
+        "chunk",
+        "cmath",
+        "cmd",
+        "code",
+        "codecs",
+        "codeop",
+        "collections",
+        "colorsys",
+        "compileall",
+        "concurrent",
+        "configparser",
+        "contextlib",
+        "contextvars",
+        "copy",
+        "copyreg",
+        "crypt",
+        "csv",
+        "ctypes",
+        "curses",
+        "dataclasses",
+        "datetime",
+        "dbm",
+        "decimal",
+        "difflib",
+        "dis",
+        "distutils",
+        "doctest",
+        "dummy_threading",
+        "email",
+        "encodings",
+        "ensurepip",
+        "enum",
+        "errno",
+        "faulthandler",
+        "fcntl",
+        "filecmp",
+        "fileinput",
+        "fnmatch",
+        "formatter",
+        "fpectl",
+        "fractions",
+        "ftplib",
+        "functools",
+        "gc",
+        "getopt",
+        "getpass",
+        "gettext",
+        "glob",
+        "graphlib",
+        "grp",
+        "gzip",
+        "hashlib",
+        "heapq",
+        "hmac",
+        "html",
+        "http",
+        "imaplib",
+        "imghdr",
+        "imp",
+        "importlib",
+        "inspect",
+        "io",
+        "ipaddress",
+        "itertools",
+        "json",
+        "keyword",
+        "lib2to3",
+        "linecache",
+        "locale",
+        "logging",
+        "lzma",
+        "macpath",
+        "mailbox",
+        "mailcap",
+        "marshal",
+        "math",
+        "mimetypes",
+        "mmap",
+        "modulefinder",
+        "msilib",
+        "msvcrt",
+        "multiprocessing",
+        "netrc",
+        "nis",
+        "nntplib",
+        "ntpath",
+        "numbers",
+        "operator",
+        "optparse",
+        "os",
+        "ossaudiodev",
+        "parser",
+        "pathlib",
+        "pdb",
+        "pickle",
+        "pickletools",
+        "pipes",
+        "pkgutil",
+        "platform",
+        "plistlib",
+        "poplib",
+        "posix",
+        "posixpath",
+        "pprint",
+        "profile",
+        "pstats",
+        "pty",
+        "pwd",
+        "py_compile",
+        "pyclbr",
+        "pydoc",
+        "queue",
+        "quopri",
+        "random",
+        "re",
+        "readline",
+        "reprlib",
+        "resource",
+        "rlcompleter",
+        "runpy",
+        "sched",
+        "secrets",
+        "select",
+        "selectors",
+        "shelve",
+        "shlex",
+        "shutil",
+        "signal",
+        "site",
+        "smtpd",
+        "smtplib",
+        "sndhdr",
+        "socket",
+        "socketserver",
+        "spwd",
+        "sqlite3",
+        "sre",
+        "sre_compile",
+        "sre_constants",
+        "sre_parse",
+        "ssl",
+        "stat",
+        "statistics",
+        "string",
+        "stringprep",
+        "struct",
+        "subprocess",
+        "sunau",
+        "symbol",
+        "symtable",
+        "sys",
+        "sysconfig",
+        "syslog",
+        "tabnanny",
+        "tarfile",
+        "telnetlib",
+        "tempfile",
+        "termios",
+        "test",
+        "textwrap",
+        "threading",
+        "time",
+        "timeit",
+        "tkinter",
+        "token",
+        "tokenize",
+        "trace",
+        "traceback",
+        "tracemalloc",
+        "tty",
+        "turtle",
+        "turtledemo",
+        "types",
+        "typing",
+        "unicodedata",
+        "unittest",
+        "urllib",
+        "uu",
+        "uuid",
+        "venv",
+        "warnings",
+        "wave",
+        "weakref",
+        "webbrowser",
+        "winreg",
+        "winsound",
+        "wsgiref",
+        "xdrlib",
+        "xml",
+        "xmlrpc",
+        "zipapp",
+        "zipfile",
+        "zipimport",
+        "zlib",
+        "zoneinfo",
+    ])
+});

src/settings/configuration.rs

@@ -2,16 +2,17 @@
 //! command-line options. Structure mirrors the user-facing representation of
 //! the various parameters.
 
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use anyhow::{anyhow, Result};
 use once_cell::sync::Lazy;
+use path_absolutize::path_dedot;
 use regex::Regex;
 
 use crate::checks_gen::CheckCodePrefix;
 use crate::settings::pyproject::load_options;
 use crate::settings::types::{FilePattern, PerFileIgnore, PythonVersion};
-use crate::{flake8_annotations, flake8_quotes, pep8_naming};
+use crate::{flake8_annotations, flake8_quotes, fs, isort, pep8_naming};
 
 #[derive(Debug)]
 pub struct Configuration {
@@ -25,10 +26,12 @@ pub struct Configuration {
     pub line_length: usize,
     pub per_file_ignores: Vec<PerFileIgnore>,
     pub select: Vec<CheckCodePrefix>,
+    pub src: Vec<PathBuf>,
     pub target_version: PythonVersion,
     // Plugins
     pub flake8_annotations: flake8_annotations::settings::Settings,
     pub flake8_quotes: flake8_quotes::settings::Settings,
+    pub isort: isort::settings::Settings,
     pub pep8_naming: pep8_naming::settings::Settings,
 }
 
@@ -71,6 +74,25 @@ impl Configuration {
                     .map_err(|e| anyhow!("Invalid dummy-variable-rgx value: {e}"))?,
                 None => DEFAULT_DUMMY_VARIABLE_RGX.clone(),
             },
+            src: options
+                .src
+                .map(|src| {
+                    src.iter()
+                        .map(|path| {
+                            let path = Path::new(path);
+                            match project_root {
+                                Some(project_root) => fs::normalize_path_to(path, project_root),
+                                None => fs::normalize_path(path),
+                            }
+                        })
+                        .collect()
+                })
+                .unwrap_or_else(|| {
+                    vec![match project_root {
+                        Some(project_root) => project_root.clone(),
+                        None => path_dedot::CWD.clone(),
+                    }]
+                }),
             target_version: options.target_version.unwrap_or(PythonVersion::Py310),
             exclude: options
                 .exclude
@@ -115,6 +137,10 @@ impl Configuration {
                 .flake8_quotes
                 .map(flake8_quotes::settings::Settings::from_options)
                 .unwrap_or_default(),
+            isort: options
+                .isort
+                .map(isort::settings::Settings::from_options)
+                .unwrap_or_default(),
             pep8_naming: options
                 .pep8_naming
                 .map(pep8_naming::settings::Settings::from_options)

src/settings/mod.rs

@@ -4,14 +4,16 @@
 
 use std::collections::BTreeSet;
 use std::hash::{Hash, Hasher};
+use std::path::PathBuf;
 
+use path_absolutize::path_dedot;
 use regex::Regex;
 
 use crate::checks::CheckCode;
 use crate::checks_gen::{CheckCodePrefix, PrefixSpecificity};
 use crate::settings::configuration::Configuration;
 use crate::settings::types::{FilePattern, PerFileIgnore, PythonVersion};
-use crate::{flake8_annotations, flake8_quotes, pep8_naming};
+use crate::{flake8_annotations, flake8_quotes, isort, pep8_naming};
 
 pub mod configuration;
 pub mod options;
@@ -27,10 +29,12 @@ pub struct Settings {
     pub extend_exclude: Vec<FilePattern>,
     pub line_length: usize,
     pub per_file_ignores: Vec<PerFileIgnore>,
+    pub src: Vec<PathBuf>,
     pub target_version: PythonVersion,
     // Plugins
     pub flake8_annotations: flake8_annotations::settings::Settings,
     pub flake8_quotes: flake8_quotes::settings::Settings,
+    pub isort: isort::settings::Settings,
     pub pep8_naming: pep8_naming::settings::Settings,
 }
 
@@ -48,9 +52,11 @@ impl Settings {
             extend_exclude: config.extend_exclude,
             flake8_annotations: config.flake8_annotations,
             flake8_quotes: config.flake8_quotes,
+            isort: config.isort,
             line_length: config.line_length,
             pep8_naming: config.pep8_naming,
             per_file_ignores: config.per_file_ignores,
+            src: config.src,
             target_version: config.target_version,
         }
     }
@@ -63,9 +69,11 @@ impl Settings {
             extend_exclude: Default::default(),
             line_length: 88,
             per_file_ignores: Default::default(),
+            src: vec![path_dedot::CWD.clone()],
             target_version: PythonVersion::Py310,
             flake8_annotations: Default::default(),
             flake8_quotes: Default::default(),
+            isort: Default::default(),
             pep8_naming: Default::default(),
         }
     }
@@ -78,9 +86,11 @@ impl Settings {
             extend_exclude: Default::default(),
             line_length: 88,
             per_file_ignores: Default::default(),
+            src: vec![path_dedot::CWD.clone()],
             target_version: PythonVersion::Py310,
             flake8_annotations: Default::default(),
             flake8_quotes: Default::default(),
+            isort: Default::default(),
             pep8_naming: Default::default(),
         }
     }
@@ -101,6 +111,7 @@ impl Hash for Settings {
         // Add plugin properties in alphabetical order.
         self.flake8_annotations.hash(state);
         self.flake8_quotes.hash(state);
+        self.isort.hash(state);
         self.pep8_naming.hash(state);
     }
 }

src/settings/options.rs

@@ -6,7 +6,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::checks_gen::CheckCodePrefix;
 use crate::settings::types::PythonVersion;
-use crate::{flake8_annotations, flake8_quotes, pep8_naming};
+use crate::{flake8_annotations, flake8_quotes, isort, pep8_naming};
 
 #[derive(Debug, PartialEq, Eq, Serialize, Deserialize, Default)]
 #[serde(deny_unknown_fields, rename_all = "kebab-case")]
@@ -21,9 +21,11 @@ pub struct Options {
     pub line_length: Option<usize>,
     pub per_file_ignores: Option<BTreeMap<String, Vec<CheckCodePrefix>>>,
     pub select: Option<Vec<CheckCodePrefix>>,
+    pub src: Option<Vec<String>>,
     pub target_version: Option<PythonVersion>,
     // Plugins
     pub flake8_annotations: Option<flake8_annotations::settings::Options>,
     pub flake8_quotes: Option<flake8_quotes::settings::Options>,
+    pub isort: Option<isort::settings::Options>,
     pub pep8_naming: Option<pep8_naming::settings::Options>,
 }

src/settings/pyproject.rs

@@ -143,9 +143,11 @@ mod tests {
                     extend_ignore: None,
                     per_file_ignores: None,
                     dummy_variable_rgx: None,
+                    src: None,
                     target_version: None,
                     flake8_annotations: None,
                     flake8_quotes: None,
+                    isort: None,
                     pep8_naming: None,
                 })
             })
@@ -172,9 +174,11 @@ line-length = 79
                     extend_ignore: None,
                     per_file_ignores: None,
                     dummy_variable_rgx: None,
+                    src: None,
                     target_version: None,
                     flake8_annotations: None,
                     flake8_quotes: None,
+                    isort: None,
                     pep8_naming: None,
                 })
             })
@@ -201,9 +205,11 @@ exclude = ["foo.py"]
                     extend_ignore: None,
                     per_file_ignores: None,
                     dummy_variable_rgx: None,
+                    src: None,
                     target_version: None,
                     flake8_annotations: None,
                     flake8_quotes: None,
+                    isort: None,
                     pep8_naming: None,
                 })
             })
@@ -230,9 +236,11 @@ select = ["E501"]
                     extend_ignore: None,
                     per_file_ignores: None,
                     dummy_variable_rgx: None,
+                    src: None,
                     target_version: None,
                     flake8_annotations: None,
                     flake8_quotes: None,
+                    isort: None,
                     pep8_naming: None,
                 })
             })
@@ -260,9 +268,11 @@ ignore = ["E501"]
                     extend_ignore: None,
                     per_file_ignores: None,
                     dummy_variable_rgx: None,
+                    src: None,
                     target_version: None,
                     flake8_annotations: None,
                     flake8_quotes: None,
+                    isort: None,
                     pep8_naming: None,
                 })
             })
@@ -336,6 +346,7 @@ other-attribute = 1
                     vec![CheckCodePrefix::F401]
                 ),])),
                 dummy_variable_rgx: None,
+                src: None,
                 target_version: None,
                 flake8_annotations: None,
                 flake8_quotes: Some(flake8_quotes::settings::Options {
@@ -344,6 +355,7 @@ other-attribute = 1
                     docstring_quotes: Some(Quote::Double),
                     avoid_escape: Some(true),
                 }),
+                isort: None,
                 pep8_naming: Some(pep8_naming::settings::Options {
                     ignore_names: Some(vec![
                         "setUp".to_string(),

src/settings/user.rs

@@ -7,7 +7,7 @@ use regex::Regex;
 use crate::checks::CheckCode;
 use crate::checks_gen::CheckCodePrefix;
 use crate::settings::types::{FilePattern, PythonVersion};
-use crate::{flake8_annotations, flake8_quotes, pep8_naming, Configuration};
+use crate::{flake8_annotations, flake8_quotes, isort, pep8_naming, Configuration};
 
 /// Struct to render user-facing exclusion patterns.
 #[derive(Debug)]
@@ -45,10 +45,12 @@ pub struct UserConfiguration {
     pub line_length: usize,
     pub per_file_ignores: Vec<(Exclusion, Vec<CheckCode>)>,
     pub select: Vec<CheckCodePrefix>,
+    pub src: Vec<PathBuf>,
     pub target_version: PythonVersion,
     // Plugins
     pub flake8_annotations: flake8_annotations::settings::Settings,
     pub flake8_quotes: flake8_quotes::settings::Settings,
+    pub isort: isort::settings::Settings,
     pub pep8_naming: pep8_naming::settings::Settings,
     // Non-settings exposed to the user
     pub project_root: Option<PathBuf>,
@@ -89,9 +91,11 @@ impl UserConfiguration {
                 })
                 .collect(),
             select: configuration.select,
+            src: configuration.src,
             target_version: configuration.target_version,
             flake8_annotations: configuration.flake8_annotations,
             flake8_quotes: configuration.flake8_quotes,
+            isort: configuration.isort,
             pep8_naming: configuration.pep8_naming,
             project_root,
             pyproject,