Consider all TYPE_CHECKING symbols for type-checking blocks (#16669)

## Summary

This PR stabilizes the preview behavior introduced in
#15719 to recognize all symbols
named `TYPE_CHECKING` as type-checking
checks in `if TYPE_CHECKING` conditions. This ensures compatibility with
mypy and pyright.

This PR also stabilizes the new behavior that removes `if 0:` and `if
False` to be no longer considered type checking blocks.
Since then, this syntax has been removed from the typing spec and was
only used for Python modules that don't have a `typing` module
([comment](#15719 (comment))).

The preview behavior was first released with Ruff 0.9.5 (6th of
February), which was about a month ago. There are no open issues or PRs
for the changed behavior


## Test Plan

The snapshots for `SIM108` change because `SIM108` ignored type checking
blocks but it can no
simplify `if 0` or `if False` blocks again because they're no longer
considered type checking blocks.

The changes in the `TC005` snapshot or only due to that `if 0` and `if
False` are no longer recognized as type checking blocks

<!-- How was it tested? -->

Author: MichaReiser

crates/ruff_linter/resources/test/fixtures/flake8_type_checking/TC005.py

@@ -4,13 +4,6 @@
     pass  # TC005
 
 
-if False:
-    pass  # TC005
-
-if 0:
-    pass  # TC005
-
-
 def example():
     if TYPE_CHECKING:
         pass  # TC005
@@ -32,13 +25,6 @@ class Test:
     x: List
 
 
-if False:
-    x: List
-
-if 0:
-    x: List
-
-
 from typing_extensions import TYPE_CHECKING
 
 if TYPE_CHECKING:

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

@@ -246,11 +246,7 @@ impl<'a> Checker<'a> {
         notebook_index: Option<&'a NotebookIndex>,
         target_version: PythonVersion,
     ) -> Checker<'a> {
-        let mut semantic = SemanticModel::new(&settings.typing_modules, path, module);
-        if settings.preview.is_enabled() {
-            // Set the feature flag to test `TYPE_CHECKING` semantic changes
-            semantic.flags |= SemanticModelFlags::NEW_TYPE_CHECKING_BLOCK_DETECTION;
-        }
+        let semantic = SemanticModel::new(&settings.typing_modules, path, module);
         Self {
             parsed,
             parsed_type_annotation: None,

crates/ruff_linter/src/rules/flake8_simplify/snapshots/ruff_linter__rules__flake8_simplify__tests__SIM108_SIM108.py.snap

@@ -226,6 +226,33 @@ SIM108.py:167:1: SIM108 [*] Use ternary operator `z = 1 if True else other` inst
 172 169 | if False:
 173 170 |     z = 1
 
+SIM108.py:172:1: SIM108 [*] Use ternary operator `z = 1 if False else other` instead of `if`-`else`-block
+    |
+170 |       z = other
+171 |
+172 | / if False:
+173 | |     z = 1
+174 | | else:
+175 | |     z = other
+    | |_____________^ SIM108
+176 |
+177 |   if 1:
+    |
+    = help: Replace `if`-`else`-block with `z = 1 if False else other`
+
+ℹ Unsafe fix
+169 169 | else:
+170 170 |     z = other
+171 171 | 
+172     |-if False:
+173     |-    z = 1
+174     |-else:
+175     |-    z = other
+    172 |+z = 1 if False else other
+176 173 | 
+177 174 | if 1:
+178 175 |     z = True
+
 SIM108.py:177:1: SIM108 [*] Use ternary operator `z = True if 1 else other` instead of `if`-`else`-block
     |
 175 |       z = other

crates/ruff_linter/src/rules/flake8_type_checking/snapshots/ruff_linter__rules__flake8_type_checking__tests__empty-type-checking-block_TC005.py.snap

@@ -16,102 +16,64 @@ TC005.py:4:5: TC005 [*] Found empty type-checking block
 4   |-    pass  # TC005
 5 3 | 
 6 4 | 
-7 5 | if False:
+7 5 | def example():
 
-TC005.py:8:5: TC005 [*] Found empty type-checking block
+TC005.py:9:9: TC005 [*] Found empty type-checking block
    |
- 7 | if False:
- 8 |     pass  # TC005
-   |     ^^^^ TC005
- 9 |
-10 | if 0:
-   |
-   = help: Delete empty type-checking block
-
-ℹ Safe fix
-4 4 |     pass  # TC005
-5 5 | 
-6 6 | 
-7   |-if False:
-8   |-    pass  # TC005
-9 7 | 
-10 8 | if 0:
-11 9 |     pass  # TC005
-
-TC005.py:11:5: TC005 [*] Found empty type-checking block
-   |
-10 | if 0:
-11 |     pass  # TC005
-   |     ^^^^ TC005
+ 7 | def example():
+ 8 |     if TYPE_CHECKING:
+ 9 |         pass  # TC005
+   |         ^^^^ TC005
+10 |     return
    |
    = help: Delete empty type-checking block
 
 ℹ Safe fix
-7  7  | if False:
-8  8  |     pass  # TC005
-9  9  | 
-10    |-if 0:
-11    |-    pass  # TC005
+5  5  | 
+6  6  | 
+7  7  | def example():
+8     |-    if TYPE_CHECKING:
+9     |-        pass  # TC005
+10 8  |     return
+11 9  | 
 12 10 | 
-13 11 | 
-14 12 | def example():
 
-TC005.py:16:9: TC005 [*] Found empty type-checking block
+TC005.py:15:9: TC005 [*] Found empty type-checking block
    |
-14 | def example():
-15 |     if TYPE_CHECKING:
-16 |         pass  # TC005
+13 | class Test:
+14 |     if TYPE_CHECKING:
+15 |         pass  # TC005
    |         ^^^^ TC005
-17 |     return
+16 |     x = 2
    |
    = help: Delete empty type-checking block
 
 ℹ Safe fix
+11 11 | 
 12 12 | 
-13 13 | 
-14 14 | def example():
-15    |-    if TYPE_CHECKING:
-16    |-        pass  # TC005
-17 15 |     return
+13 13 | class Test:
+14    |-    if TYPE_CHECKING:
+15    |-        pass  # TC005
+16 14 |     x = 2
+17 15 | 
 18 16 | 
-19 17 | 
-
-TC005.py:22:9: TC005 [*] Found empty type-checking block
-   |
-20 | class Test:
-21 |     if TYPE_CHECKING:
-22 |         pass  # TC005
-   |         ^^^^ TC005
-23 |     x = 2
-   |
-   = help: Delete empty type-checking block
-
-ℹ Safe fix
-18 18 | 
-19 19 | 
-20 20 | class Test:
-21    |-    if TYPE_CHECKING:
-22    |-        pass  # TC005
-23 21 |     x = 2
-24 22 | 
-25 23 | 
 
-TC005.py:45:5: TC005 [*] Found empty type-checking block
+TC005.py:31:5: TC005 [*] Found empty type-checking block
    |
-44 | if TYPE_CHECKING:
-45 |     pass  # TC005
+30 | if TYPE_CHECKING:
+31 |     pass  # TC005
    |     ^^^^ TC005
-46 |
-47 | # https://github.com/astral-sh/ruff/issues/11368
+32 |
+33 | # https://github.com/astral-sh/ruff/issues/11368
    |
    = help: Delete empty type-checking block
 
 ℹ Safe fix
-41 41 | 
-42 42 | from typing_extensions import TYPE_CHECKING
-43 43 | 
-44    |-if TYPE_CHECKING:
-45    |-    pass  # TC005
-46 44 | 
-47 45 | # https://github.com/astral-sh/ruff/issues/11368
-48 46 | if TYPE_CHECKING:
+27 27 | 
+28 28 | from typing_extensions import TYPE_CHECKING
+29 29 | 
+30    |-if TYPE_CHECKING:
+31    |-    pass  # TC005
+32 30 | 
+33 31 | # https://github.com/astral-sh/ruff/issues/11368
+34 32 | if TYPE_CHECKING:

crates/ruff_python_semantic/src/analyze/typing.rs

@@ -1,10 +1,10 @@
 //! Analysis rules for the `typing` module.
 
-use ruff_python_ast::helpers::{any_over_expr, is_const_false, map_subscript};
+use ruff_python_ast::helpers::{any_over_expr, map_subscript};
 use ruff_python_ast::identifier::Identifier;
 use ruff_python_ast::name::QualifiedName;
 use ruff_python_ast::{
-    self as ast, Expr, ExprCall, ExprName, Int, Operator, ParameterWithDefault, Parameters, Stmt,
+    self as ast, Expr, ExprCall, ExprName, Operator, ParameterWithDefault, Parameters, Stmt,
     StmtAssign,
 };
 use ruff_python_stdlib::typing::{
@@ -391,44 +391,19 @@ pub fn is_mutable_expr(expr: &Expr, semantic: &SemanticModel) -> bool {
 pub fn is_type_checking_block(stmt: &ast::StmtIf, semantic: &SemanticModel) -> bool {
     let ast::StmtIf { test, .. } = stmt;
 
-    if semantic.use_new_type_checking_block_detection_semantics() {
-        return match test.as_ref() {
-            // As long as the symbol's name is "TYPE_CHECKING" we will treat it like `typing.TYPE_CHECKING`
-            // for this specific check even if it's defined somewhere else, like the current module.
-            // Ex) `if TYPE_CHECKING:`
-            Expr::Name(ast::ExprName { id, .. }) => {
-                id == "TYPE_CHECKING"
+    match test.as_ref() {
+        // As long as the symbol's name is "TYPE_CHECKING" we will treat it like `typing.TYPE_CHECKING`
+        // for this specific check even if it's defined somewhere else, like the current module.
+        // Ex) `if TYPE_CHECKING:`
+        Expr::Name(ast::ExprName { id, .. }) => {
+            id == "TYPE_CHECKING"
                 // Ex) `if TC:` with `from typing import TYPE_CHECKING as TC`
                 || semantic.match_typing_expr(test, "TYPE_CHECKING")
-            }
-            // Ex) `if typing.TYPE_CHECKING:`
-            Expr::Attribute(ast::ExprAttribute { attr, .. }) => attr == "TYPE_CHECKING",
-            _ => false,
-        };
-    }
-
-    // Ex) `if False:`
-    if is_const_false(test) {
-        return true;
-    }
-
-    // Ex) `if 0:`
-    if matches!(
-        test.as_ref(),
-        Expr::NumberLiteral(ast::ExprNumberLiteral {
-            value: ast::Number::Int(Int::ZERO),
-            ..
-        })
-    ) {
-        return true;
-    }
-
-    // Ex) `if typing.TYPE_CHECKING:`
-    if semantic.match_typing_expr(test, "TYPE_CHECKING") {
-        return true;
+        }
+        // Ex) `if typing.TYPE_CHECKING:`
+        Expr::Attribute(ast::ExprAttribute { attr, .. }) => attr == "TYPE_CHECKING",
+        _ => false,
     }
-
-    false
 }
 
 /// Returns `true` if the [`ast::StmtIf`] is a version-checking block (e.g., `if sys.version_info >= ...:`).

crates/ruff_python_semantic/src/model.rs

@@ -2014,18 +2014,6 @@ impl<'a> SemanticModel<'a> {
             .intersects(SemanticModelFlags::DEFERRED_CLASS_BASE)
     }
 
-    /// Return `true` if we should use the new semantics to recognize
-    /// type checking blocks. Previously we only recognized type checking
-    /// blocks if `TYPE_CHECKING` was imported from a typing module.
-    ///
-    /// With this feature flag enabled we recognize any symbol named
-    /// `TYPE_CHECKING`, regardless of where it comes from to mirror
-    /// what mypy and pyright do.
-    pub const fn use_new_type_checking_block_detection_semantics(&self) -> bool {
-        self.flags
-            .intersects(SemanticModelFlags::NEW_TYPE_CHECKING_BLOCK_DETECTION)
-    }
-
     /// Return an iterator over all bindings shadowed by the given [`BindingId`], within the
     /// containing scope, and across scopes.
     pub fn shadowed_bindings(
@@ -2557,14 +2545,6 @@ bitflags! {
         /// [#13824]: https://github.com/astral-sh/ruff/issues/13824
         const NO_TYPE_CHECK = 1 << 30;
 
-        /// The model special-cases any symbol named `TYPE_CHECKING`.
-        ///
-        /// Previously we only recognized `TYPE_CHECKING` if it was part of
-        /// one of the configured `typing` modules. This flag exists to
-        /// test out the semantic change only in preview. This flag will go
-        /// away once this change has been stabilized.
-        const NEW_TYPE_CHECKING_BLOCK_DETECTION = 1 << 31;
-
         /// The context is in any type annotation.
         const ANNOTATION = Self::TYPING_ONLY_ANNOTATION.bits() | Self::RUNTIME_EVALUATED_ANNOTATION.bits() | Self::RUNTIME_REQUIRED_ANNOTATION.bits();