Avoid if-else simplification for TYPE_CHECKING blocks

crates/ruff_linter/resources/test/fixtures/flake8_simplify/SIM108.py

@@ -126,3 +126,12 @@ def f():
         x = yield 3
     else:
         x = yield 5
+
+
+from typing import TYPE_CHECKING
+
+# OK
+if TYPE_CHECKING:
+    x = 3
+else:
+    x = 5

crates/ruff_linter/src/checkers/ast/analyze/statement.rs

@@ -1050,7 +1050,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 flake8_simplify::rules::manual_dict_lookup(checker, if_);
             }
             if checker.enabled(Rule::IfElseBlockInsteadOfIfExp) {
-                flake8_simplify::rules::use_ternary_operator(checker, stmt);
+                flake8_simplify::rules::use_ternary_operator(checker, if_);
             }
             if checker.enabled(Rule::IfElseBlockInsteadOfDictGet) {
                 flake8_simplify::rules::use_dict_get_with_default(checker, if_);

crates/ruff_linter/src/rules/flake8_simplify/rules/if_else_block_instead_of_if_exp.rs

@@ -2,6 +2,7 @@ use ruff_diagnostics::{Diagnostic, Edit, Fix, FixAvailability, Violation};
 use ruff_macros::{derive_message_formats, violation};
 use ruff_python_ast::helpers::any_over_expr;
 use ruff_python_ast::{self as ast, ElifElseClause, Expr, Stmt};
+use ruff_python_semantic::analyze::typing::is_type_checking_block;
 use ruff_python_semantic::SemanticModel;
 use ruff_text_size::{Ranged, TextRange};
 
@@ -51,16 +52,14 @@ impl Violation for IfElseBlockInsteadOfIfExp {
 }
 
 /// SIM108
-pub(crate) fn use_ternary_operator(checker: &mut Checker, stmt: &Stmt) {
-    let Stmt::If(ast::StmtIf {
+pub(crate) fn use_ternary_operator(checker: &mut Checker, if_: &ast::StmtIf) {
+    let ast::StmtIf {
         test,
         body,
         elif_else_clauses,
         range: _,
-    }) = stmt
-    else {
-        return;
-    };
+    } = if_;
+
     // `test: None` to only match an `else` clause
     let [ElifElseClause {
         body: else_body,
@@ -99,13 +98,6 @@ pub(crate) fn use_ternary_operator(checker: &mut Checker, stmt: &Stmt) {
         return;
     }
 
-    // Avoid suggesting ternary for `if sys.version_info >= ...`-style and
-    // `if sys.platform.startswith("...")`-style checks.
-    let ignored_call_paths: &[&[&str]] = &[&["sys", "version_info"], &["sys", "platform"]];
-    if contains_call_path(test, ignored_call_paths, checker.semantic()) {
-        return;
-    }
-
     // Avoid suggesting ternary for `if (yield ...)`-style checks.
     // TODO(charlie): Fix precedence handling for yields in generator.
     if matches!(
@@ -121,14 +113,26 @@ pub(crate) fn use_ternary_operator(checker: &mut Checker, stmt: &Stmt) {
         return;
     }
 
+    // Avoid suggesting ternary for `if sys.version_info >= ...`-style and
+    // `if sys.platform.startswith("...")`-style checks.
+    let ignored_call_paths: &[&[&str]] = &[&["sys", "version_info"], &["sys", "platform"]];
+    if contains_call_path(test, ignored_call_paths, checker.semantic()) {
+        return;
+    }
+
+    // Avoid suggesting ternary for `if TYPE_CHECKING:`-style checks.
+    if is_type_checking_block(if_, checker.semantic()) {
+        return;
+    }
+
     let target_var = &body_target;
     let ternary = ternary(target_var, body_value, test, else_value);
     let contents = checker.generator().stmt(&ternary);
 
     // Don't flag if the resulting expression would exceed the maximum line length.
     if !fits(
         &contents,
-        stmt.into(),
+        if_.into(),
         checker.locator(),
         checker.settings.line_length,
         checker.settings.tab_size,
@@ -140,12 +144,12 @@ pub(crate) fn use_ternary_operator(checker: &mut Checker, stmt: &Stmt) {
         IfElseBlockInsteadOfIfExp {
             contents: contents.clone(),
         },
-        stmt.range(),
+        if_.range(),
     );
-    if !checker.indexer().has_comments(stmt, checker.locator()) {
+    if !checker.indexer().has_comments(if_, checker.locator()) {
         diagnostic.set_fix(Fix::unsafe_edit(Edit::range_replacement(
             contents,
-            stmt.range(),
+            if_.range(),
         )));
     }
     checker.diagnostics.push(diagnostic);