Implement B021 (#719)

README.md

@@ -526,6 +526,7 @@ For more, see [flake8-bugbear](https://pypi.org/project/flake8-bugbear/22.10.27/
 | B017 | NoAssertRaisesException | `assertRaises(Exception)` should be considered evil |  |
 | B018 | UselessExpression | Found useless expression. Either assign it to a variable or remove it. |  |
 | B019 | CachedInstanceMethod | Use of `functools.lru_cache` or `functools.cache` on methods can lead to memory leaks |  |
+| B021 | FStringDocstring | f-string used as docstring. This will be interpreted by python as a joined string rather than a docstring. |  |
 | B025 | DuplicateTryBlockException | try-except block with duplicate exception `Exception` |  |
 | B026 | StarArgUnpackingAfterKeywordArg | Star-arg unpacking after a keyword argument is strongly discouraged |  |
 

resources/test/fixtures/B021.py

@@ -0,0 +1,76 @@
+f"""
+Should emit:
+B021 - on lines 14, 22, 30, 38, 46, 54, 62, 70, 73
+"""
+
+VARIABLE = "world"
+
+
+def foo1():
+    """hello world!"""
+
+
+def foo2():
+    f"""hello {VARIABLE}!"""
+
+
+class bar1:
+    """hello world!"""
+
+
+class bar2:
+    f"""hello {VARIABLE}!"""
+
+
+def foo1():
+    """hello world!"""
+
+
+def foo2():
+    f"""hello {VARIABLE}!"""
+
+
+class bar1:
+    """hello world!"""
+
+
+class bar2:
+    f"""hello {VARIABLE}!"""
+
+
+def foo1():
+    "hello world!"
+
+
+def foo2():
+    f"hello {VARIABLE}!"
+
+
+class bar1:
+    "hello world!"
+
+
+class bar2:
+    f"hello {VARIABLE}!"
+
+
+def foo1():
+    "hello world!"
+
+
+def foo2():
+    f"hello {VARIABLE}!"
+
+
+class bar1:
+    "hello world!"
+
+
+class bar2:
+    f"hello {VARIABLE}!"
+
+
+def baz():
+    f"""I'm probably a docstring: {VARIABLE}!"""
+    print(f"""I'm a normal string""")
+    f"""Don't detect me!"""

src/check_ast.rs

@@ -875,6 +875,9 @@ where
         let prev_visible_scope = self.visible_scope.clone();
         match &stmt.node {
             StmtKind::FunctionDef { body, .. } | StmtKind::AsyncFunctionDef { body, .. } => {
+                if self.settings.enabled.contains(&CheckCode::B021) {
+                    flake8_bugbear::plugins::f_string_docstring(self, body);
+                }
                 let definition = docstrings::extraction::extract(
                     &self.visible_scope,
                     stmt,
@@ -894,6 +897,9 @@ where
                 ));
             }
             StmtKind::ClassDef { body, .. } => {
+                if self.settings.enabled.contains(&CheckCode::B021) {
+                    flake8_bugbear::plugins::f_string_docstring(self, body);
+                }
                 let definition = docstrings::extraction::extract(
                     &self.visible_scope,
                     stmt,
@@ -2245,6 +2251,9 @@ impl<'a> Checker<'a> {
     where
         'b: 'a,
     {
+        if self.settings.enabled.contains(&CheckCode::B021) {
+            flake8_bugbear::plugins::f_string_docstring(self, python_ast);
+        }
         let docstring = docstrings::extraction::docstring_from(python_ast);
         self.definitions.push((
             Definition {

src/checks.rs

@@ -94,6 +94,7 @@ pub enum CheckCode {
     B017,
     B018,
     B019,
+    B021,
     B025,
     B026,
     // flake8-comprehensions
@@ -393,6 +394,7 @@ pub enum CheckKind {
     NoAssertRaisesException,
     UselessExpression,
     CachedInstanceMethod,
+    FStringDocstring,
     DuplicateTryBlockException(String),
     StarArgUnpackingAfterKeywordArg,
     // flake8-comprehensions
@@ -632,6 +634,7 @@ impl CheckCode {
             CheckCode::B017 => CheckKind::NoAssertRaisesException,
             CheckCode::B018 => CheckKind::UselessExpression,
             CheckCode::B019 => CheckKind::CachedInstanceMethod,
+            CheckCode::B021 => CheckKind::FStringDocstring,
             CheckCode::B025 => CheckKind::DuplicateTryBlockException("Exception".to_string()),
             CheckCode::B026 => CheckKind::StarArgUnpackingAfterKeywordArg,
             // flake8-comprehensions
@@ -872,6 +875,7 @@ impl CheckCode {
             CheckCode::B017 => CheckCategory::Flake8Bugbear,
             CheckCode::B018 => CheckCategory::Flake8Bugbear,
             CheckCode::B019 => CheckCategory::Flake8Bugbear,
+            CheckCode::B021 => CheckCategory::Flake8Bugbear,
             CheckCode::B025 => CheckCategory::Flake8Bugbear,
             CheckCode::B026 => CheckCategory::Flake8Bugbear,
             CheckCode::C400 => CheckCategory::Flake8Comprehensions,
@@ -1075,6 +1079,7 @@ impl CheckKind {
             CheckKind::NoAssertRaisesException => &CheckCode::B017,
             CheckKind::UselessExpression => &CheckCode::B018,
             CheckKind::CachedInstanceMethod => &CheckCode::B019,
+            CheckKind::FStringDocstring => &CheckCode::B021,
             CheckKind::DuplicateTryBlockException(_) => &CheckCode::B025,
             CheckKind::StarArgUnpackingAfterKeywordArg => &CheckCode::B026,
             // flake8-comprehensions
@@ -1442,6 +1447,9 @@ impl CheckKind {
             CheckKind::CachedInstanceMethod => "Use of `functools.lru_cache` or `functools.cache` \
                                                 on methods can lead to memory leaks"
                 .to_string(),
+            CheckKind::FStringDocstring => "f-string used as docstring. This will be interpreted \
+                                            by python as a joined string rather than a docstring."
+                .to_string(),
             CheckKind::DuplicateTryBlockException(name) => {
                 format!("try-except block with duplicate exception `{name}`")
             }

src/checks_gen.rs

@@ -55,6 +55,7 @@ pub enum CheckCodePrefix {
     B018,
     B019,
     B02,
+    B021,
     B025,
     B026,
     C,
@@ -380,6 +381,7 @@ impl CheckCodePrefix {
                 CheckCode::B017,
                 CheckCode::B018,
                 CheckCode::B019,
+                CheckCode::B021,
                 CheckCode::B025,
                 CheckCode::B026,
             ],
@@ -401,6 +403,7 @@ impl CheckCodePrefix {
                 CheckCode::B017,
                 CheckCode::B018,
                 CheckCode::B019,
+                CheckCode::B021,
                 CheckCode::B025,
                 CheckCode::B026,
             ],
@@ -442,7 +445,8 @@ impl CheckCodePrefix {
             CheckCodePrefix::B017 => vec![CheckCode::B017],
             CheckCodePrefix::B018 => vec![CheckCode::B018],
             CheckCodePrefix::B019 => vec![CheckCode::B019],
-            CheckCodePrefix::B02 => vec![CheckCode::B025, CheckCode::B026],
+            CheckCodePrefix::B02 => vec![CheckCode::B021, CheckCode::B025, CheckCode::B026],
+            CheckCodePrefix::B021 => vec![CheckCode::B021],
             CheckCodePrefix::B025 => vec![CheckCode::B025],
             CheckCodePrefix::B026 => vec![CheckCode::B026],
             CheckCodePrefix::C => vec![
@@ -1184,6 +1188,7 @@ impl CheckCodePrefix {
             CheckCodePrefix::B018 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B019 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B02 => PrefixSpecificity::Tens,
+            CheckCodePrefix::B021 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B025 => PrefixSpecificity::Explicit,
             CheckCodePrefix::B026 => PrefixSpecificity::Explicit,
             CheckCodePrefix::C => PrefixSpecificity::Category,
@@ -1338,15 +1343,6 @@ impl CheckCodePrefix {
             CheckCodePrefix::I0 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::I00 => PrefixSpecificity::Tens,
             CheckCodePrefix::I001 => PrefixSpecificity::Explicit,
-            CheckCodePrefix::S => PrefixSpecificity::Category,
-            CheckCodePrefix::S1 => PrefixSpecificity::Hundreds,
-            CheckCodePrefix::S10 => PrefixSpecificity::Tens,
-            CheckCodePrefix::S101 => PrefixSpecificity::Explicit,
-            CheckCodePrefix::S102 => PrefixSpecificity::Explicit,
-            CheckCodePrefix::S104 => PrefixSpecificity::Explicit,
-            CheckCodePrefix::S105 => PrefixSpecificity::Explicit,
-            CheckCodePrefix::S106 => PrefixSpecificity::Explicit,
-            CheckCodePrefix::S107 => PrefixSpecificity::Explicit,
             CheckCodePrefix::M => PrefixSpecificity::Category,
             CheckCodePrefix::M0 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::M00 => PrefixSpecificity::Tens,
@@ -1383,6 +1379,15 @@ impl CheckCodePrefix {
             CheckCodePrefix::RUF001 => PrefixSpecificity::Explicit,
             CheckCodePrefix::RUF002 => PrefixSpecificity::Explicit,
             CheckCodePrefix::RUF003 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::S => PrefixSpecificity::Category,
+            CheckCodePrefix::S1 => PrefixSpecificity::Hundreds,
+            CheckCodePrefix::S10 => PrefixSpecificity::Tens,
+            CheckCodePrefix::S101 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::S102 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::S104 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::S105 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::S106 => PrefixSpecificity::Explicit,
+            CheckCodePrefix::S107 => PrefixSpecificity::Explicit,
             CheckCodePrefix::T => PrefixSpecificity::Category,
             CheckCodePrefix::T2 => PrefixSpecificity::Hundreds,
             CheckCodePrefix::T20 => PrefixSpecificity::Tens,

src/flake8_bugbear/plugins/f_string_docstring.rs

@@ -0,0 +1,19 @@
+use rustpython_ast::{ExprKind, Stmt, StmtKind};
+
+use crate::ast::types::Range;
+use crate::check_ast::Checker;
+use crate::checks::{Check, CheckKind};
+
+/// B021
+pub fn f_string_docstring(checker: &mut Checker, body: &[Stmt]) {
+    if let Some(stmt) = body.first() {
+        if let StmtKind::Expr { value } = &stmt.node {
+            if let ExprKind::JoinedStr { .. } = value.node {
+                checker.add_check(Check::new(
+                    CheckKind::FStringDocstring,
+                    Range::from_located(stmt),
+                ));
+            }
+        }
+    }
+}

src/flake8_bugbear/plugins/mod.rs

@@ -4,6 +4,7 @@ pub use assignment_to_os_environ::assignment_to_os_environ;
 pub use cached_instance_method::cached_instance_method;
 pub use cannot_raise_literal::cannot_raise_literal;
 pub use duplicate_exceptions::{duplicate_exceptions, duplicate_handler_exceptions};
+pub use f_string_docstring::f_string_docstring;
 pub use function_call_argument_default::function_call_argument_default;
 pub use getattr_with_constant::getattr_with_constant;
 pub use mutable_argument_default::mutable_argument_default;
@@ -23,6 +24,7 @@ mod assignment_to_os_environ;
 mod cached_instance_method;
 mod cannot_raise_literal;
 mod duplicate_exceptions;
+mod f_string_docstring;
 mod function_call_argument_default;
 mod getattr_with_constant;
 mod mutable_argument_default;

src/linter.rs

@@ -343,6 +343,7 @@ mod tests {
     #[test_case(CheckCode::B017, Path::new("B017.py"); "B017")]
     #[test_case(CheckCode::B018, Path::new("B018.py"); "B018")]
     #[test_case(CheckCode::B019, Path::new("B019.py"); "B019")]
+    #[test_case(CheckCode::B021, Path::new("B021.py"); "B021")]
     #[test_case(CheckCode::B025, Path::new("B025.py"); "B025")]
     #[test_case(CheckCode::B026, Path::new("B026.py"); "B026")]
     #[test_case(CheckCode::C400, Path::new("C400.py"); "C400")]

src/snapshots/ruff__linter__tests__B021_B021.py.snap

@@ -0,0 +1,85 @@
+---
+source: src/linter.rs
+expression: checks
+---
+- kind: FStringDocstring
+  location:
+    row: 1
+    column: 0
+  end_location:
+    row: 4
+    column: 3
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 14
+    column: 4
+  end_location:
+    row: 14
+    column: 28
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 22
+    column: 4
+  end_location:
+    row: 22
+    column: 28
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 30
+    column: 4
+  end_location:
+    row: 30
+    column: 28
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 38
+    column: 4
+  end_location:
+    row: 38
+    column: 28
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 46
+    column: 4
+  end_location:
+    row: 46
+    column: 24
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 54
+    column: 4
+  end_location:
+    row: 54
+    column: 24
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 62
+    column: 4
+  end_location:
+    row: 62
+    column: 24
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 70
+    column: 4
+  end_location:
+    row: 70
+    column: 24
+  fix: ~
+- kind: FStringDocstring
+  location:
+    row: 74
+    column: 4
+  end_location:
+    row: 74
+    column: 48
+  fix: ~
+