[flake8-type-checking] Adds implementation for TC006 (#14511)

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_linter/resources/test/fixtures/flake8_type_checking/TC006.py

@@ -0,0 +1,62 @@
+def f():
+    from typing import cast
+
+    cast(int, 3.0)  # TC006
+
+
+def f():
+    from typing import cast
+
+    cast(list[tuple[bool | float | int | str]], 3.0)  # TC006
+
+
+def f():
+    from typing import Union, cast
+
+    cast(list[tuple[Union[bool, float, int, str]]], 3.0)  # TC006
+
+
+def f():
+    from typing import cast
+
+    cast("int", 3.0)  # OK
+
+
+def f():
+    from typing import cast
+
+    cast("list[tuple[bool | float | int | str]]", 3.0)  # OK
+
+
+def f():
+    from typing import Union, cast
+
+    cast("list[tuple[Union[bool, float, int, str]]]", 3.0)  # OK
+
+
+def f():
+    from typing import cast as typecast
+
+    typecast(int, 3.0)  # TC006
+
+
+def f():
+    import typing
+
+    typing.cast(int, 3.0)  # TC006
+
+
+def f():
+    import typing as t
+
+    t.cast(t.Literal["3.0", '3'], 3.0)  # TC006
+
+
+def f():
+    from typing import cast
+
+    cast(
+        int  # TC006 (unsafe, because it will get rid of this comment)
+        | None,
+        3.0
+    )

crates/ruff_linter/src/checkers/ast/mod.rs

@@ -1280,6 +1280,10 @@ impl<'a> Visitor<'a> for Checker<'a> {
                         let mut args = arguments.args.iter();
                         if let Some(arg) = args.next() {
                             self.visit_type_definition(arg);
+
+                            if self.enabled(Rule::RuntimeCastValue) {
+                                flake8_type_checking::rules::runtime_cast_value(self, arg);
+                            }
                         }
                         for arg in args {
                             self.visit_expr(arg);

crates/ruff_linter/src/codes.rs

@@ -856,6 +856,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8TypeChecking, "003") => (RuleGroup::Stable, rules::flake8_type_checking::rules::TypingOnlyStandardLibraryImport),
         (Flake8TypeChecking, "004") => (RuleGroup::Stable, rules::flake8_type_checking::rules::RuntimeImportInTypeCheckingBlock),
         (Flake8TypeChecking, "005") => (RuleGroup::Stable, rules::flake8_type_checking::rules::EmptyTypeCheckingBlock),
+        (Flake8TypeChecking, "006") => (RuleGroup::Preview, rules::flake8_type_checking::rules::RuntimeCastValue),
         (Flake8TypeChecking, "010") => (RuleGroup::Stable, rules::flake8_type_checking::rules::RuntimeStringUnion),
 
         // tryceratops

crates/ruff_linter/src/rules/flake8_type_checking/helpers.rs

@@ -269,6 +269,23 @@ pub(crate) fn quote_annotation(
         }
     }
 
+    quote_type_expression(expr, semantic, stylist)
+}
+
+/// Wrap a type expression in quotes.
+///
+/// This function assumes that the callee already expanded expression components
+/// to the minimum acceptable range for quoting, i.e. the parent node may not be
+/// a [`Expr::Subscript`], [`Expr::Attribute`], `[Expr::Call]` or `[Expr::BinOp]`.
+///
+/// In most cases you want to call [`quote_annotation`] instead, which provides
+/// that guarantee by expanding the expression before calling into this function.
+pub(crate) fn quote_type_expression(
+    expr: &Expr,
+    semantic: &SemanticModel,
+    stylist: &Stylist,
+) -> Result<Edit> {
+    // Quote the entire expression.
     let quote = stylist.quote();
     let mut quote_annotator = QuoteAnnotator::new(semantic, stylist);
     quote_annotator.visit_expr(expr);

crates/ruff_linter/src/rules/flake8_type_checking/mod.rs

@@ -17,6 +17,7 @@ mod tests {
     use crate::{assert_messages, settings};
 
     #[test_case(Rule::EmptyTypeCheckingBlock, Path::new("TC005.py"))]
+    #[test_case(Rule::RuntimeCastValue, Path::new("TC006.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_1.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_10.py"))]
     #[test_case(Rule::RuntimeImportInTypeCheckingBlock, Path::new("TC004_11.py"))]

crates/ruff_linter/src/rules/flake8_type_checking/rules/mod.rs

@@ -1,9 +1,11 @@
 pub(crate) use empty_type_checking_block::*;
+pub(crate) use runtime_cast_value::*;
 pub(crate) use runtime_import_in_type_checking_block::*;
 pub(crate) use runtime_string_union::*;
 pub(crate) use typing_only_runtime_import::*;
 
 mod empty_type_checking_block;
+mod runtime_cast_value;
 mod runtime_import_in_type_checking_block;
 mod runtime_string_union;
 mod typing_only_runtime_import;

crates/ruff_linter/src/rules/flake8_type_checking/rules/runtime_cast_value.rs

@@ -0,0 +1,69 @@
+use ruff_python_ast::Expr;
+
+use ruff_diagnostics::{Diagnostic, Fix, FixAvailability, Violation};
+use ruff_macros::{derive_message_formats, violation};
+use ruff_text_size::Ranged;
+
+use crate::checkers::ast::Checker;
+use crate::rules::flake8_type_checking::helpers::quote_type_expression;
+
+/// ## What it does
+/// Checks for an unquoted type expression in `typing.cast()` calls.
+///
+/// ## Why is this bad?
+/// `typing.cast()` does not do anything at runtime, so the time spent
+/// on evaluating the type expression is wasted.
+///
+/// ## Example
+/// ```python
+/// from typing import cast
+///
+/// x = cast(dict[str, int], foo)
+/// ```
+///
+/// Use instead:
+/// ```python
+/// from typing import cast
+///
+/// x = cast("dict[str, int]", foo)
+/// ```
+///
+/// ## Fix safety
+/// This fix is safe as long as the type expression doesn't span multiple
+/// lines and includes comments on any of the lines apart from the last one.
+#[violation]
+pub struct RuntimeCastValue;
+
+impl Violation for RuntimeCastValue {
+    const FIX_AVAILABILITY: FixAvailability = FixAvailability::Sometimes;
+
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        "Add quotes to type expression in `typing.cast()`".to_string()
+    }
+
+    fn fix_title(&self) -> Option<String> {
+        Some("Add quotes".to_string())
+    }
+}
+
+/// TC006
+pub(crate) fn runtime_cast_value(checker: &mut Checker, type_expr: &Expr) {
+    if type_expr.is_string_literal_expr() {
+        return;
+    }
+
+    let mut diagnostic = Diagnostic::new(RuntimeCastValue, type_expr.range());
+    let edit = quote_type_expression(type_expr, checker.semantic(), checker.stylist()).ok();
+    if let Some(edit) = edit {
+        if checker
+            .comment_ranges()
+            .has_comments(type_expr, checker.source())
+        {
+            diagnostic.set_fix(Fix::unsafe_edit(edit));
+        } else {
+            diagnostic.set_fix(Fix::safe_edit(edit));
+        }
+    }
+    checker.diagnostics.push(diagnostic);
+}

crates/ruff_linter/src/rules/flake8_type_checking/snapshots/ruff_linter__rules__flake8_type_checking__tests__runtime-cast-value_TC006.py.snap

@@ -0,0 +1,138 @@
+---
+source: crates/ruff_linter/src/rules/flake8_type_checking/mod.rs
+---
+TC006.py:4:10: TC006 [*] Add quotes to type expression in `typing.cast()`
+  |
+2 |     from typing import cast
+3 | 
+4 |     cast(int, 3.0)  # TC006
+  |          ^^^ TC006
+  |
+  = help: Add quotes
+
+ℹ Safe fix
+1 1 | def f():
+2 2 |     from typing import cast
+3 3 | 
+4   |-    cast(int, 3.0)  # TC006
+  4 |+    cast("int", 3.0)  # TC006
+5 5 | 
+6 6 | 
+7 7 | def f():
+
+TC006.py:10:10: TC006 [*] Add quotes to type expression in `typing.cast()`
+   |
+ 8 |     from typing import cast
+ 9 | 
+10 |     cast(list[tuple[bool | float | int | str]], 3.0)  # TC006
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TC006
+   |
+   = help: Add quotes
+
+ℹ Safe fix
+7  7  | def f():
+8  8  |     from typing import cast
+9  9  | 
+10    |-    cast(list[tuple[bool | float | int | str]], 3.0)  # TC006
+   10 |+    cast("list[tuple[bool | float | int | str]]", 3.0)  # TC006
+11 11 | 
+12 12 | 
+13 13 | def f():
+
+TC006.py:16:10: TC006 [*] Add quotes to type expression in `typing.cast()`
+   |
+14 |     from typing import Union, cast
+15 | 
+16 |     cast(list[tuple[Union[bool, float, int, str]]], 3.0)  # TC006
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ TC006
+   |
+   = help: Add quotes
+
+ℹ Safe fix
+13 13 | def f():
+14 14 |     from typing import Union, cast
+15 15 | 
+16    |-    cast(list[tuple[Union[bool, float, int, str]]], 3.0)  # TC006
+   16 |+    cast("list[tuple[Union[bool, float, int, str]]]", 3.0)  # TC006
+17 17 | 
+18 18 | 
+19 19 | def f():
+
+TC006.py:40:14: TC006 [*] Add quotes to type expression in `typing.cast()`
+   |
+38 |     from typing import cast as typecast
+39 | 
+40 |     typecast(int, 3.0)  # TC006
+   |              ^^^ TC006
+   |
+   = help: Add quotes
+
+ℹ Safe fix
+37 37 | def f():
+38 38 |     from typing import cast as typecast
+39 39 | 
+40    |-    typecast(int, 3.0)  # TC006
+   40 |+    typecast("int", 3.0)  # TC006
+41 41 | 
+42 42 | 
+43 43 | def f():
+
+TC006.py:46:17: TC006 [*] Add quotes to type expression in `typing.cast()`
+   |
+44 |     import typing
+45 | 
+46 |     typing.cast(int, 3.0)  # TC006
+   |                 ^^^ TC006
+   |
+   = help: Add quotes
+
+ℹ Safe fix
+43 43 | def f():
+44 44 |     import typing
+45 45 | 
+46    |-    typing.cast(int, 3.0)  # TC006
+   46 |+    typing.cast("int", 3.0)  # TC006
+47 47 | 
+48 48 | 
+49 49 | def f():
+
+TC006.py:52:12: TC006 [*] Add quotes to type expression in `typing.cast()`
+   |
+50 |     import typing as t
+51 | 
+52 |     t.cast(t.Literal["3.0", '3'], 3.0)  # TC006
+   |            ^^^^^^^^^^^^^^^^^^^^^ TC006
+   |
+   = help: Add quotes
+
+ℹ Safe fix
+49 49 | def f():
+50 50 |     import typing as t
+51 51 | 
+52    |-    t.cast(t.Literal["3.0", '3'], 3.0)  # TC006
+   52 |+    t.cast("t.Literal['3.0', '3']", 3.0)  # TC006
+53 53 | 
+54 54 | 
+55 55 | def f():
+
+TC006.py:59:9: TC006 [*] Add quotes to type expression in `typing.cast()`
+   |
+58 |       cast(
+59 |           int  # TC006 (unsafe, because it will get rid of this comment)
+   |  _________^
+60 | |         | None,
+   | |______________^ TC006
+61 |           3.0
+62 |       )
+   |
+   = help: Add quotes
+
+ℹ Unsafe fix
+56 56 |     from typing import cast
+57 57 | 
+58 58 |     cast(
+59    |-        int  # TC006 (unsafe, because it will get rid of this comment)
+60    |-        | None,
+   59 |+        "int | None",
+61 60 |         3.0
+62 61 |     )

ruff.schema.json

@@ -4003,6 +4003,7 @@
         "TC003",
         "TC004",
         "TC005",
+        "TC006",
         "TC01",
         "TC010",
         "TD",