Avoid UP028 false negatives with non-reference shadowed bindings of loop variables (#13504)

Closes https://github.com/astral-sh/ruff/issues/13266

Avoids false negatives for shadowed bindings that aren't actually
references to the loop variable. There are some shadowed bindings we
need to support still, e.g., `del` requires the loop variable to exist.

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP028_0.py

@@ -81,3 +81,85 @@ def _serve_method(fn):
             .markup(highlight=args.region)
     ):
         yield h
+
+
+# UP028: The later loop variable is not a reference to the earlier loop variable
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with another loop
+    for x in (1, 2, 3):
+        yield x
+
+
+# UP028: The exception binding is not a reference to the loop variable
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with an `except`
+    try:
+        pass
+    except Exception as x:
+        pass
+
+
+# UP028: The context binding is not a reference to the loop variable
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with `with`
+    with contextlib.nullcontext() as x:
+        pass
+
+
+
+# UP028: The type annotation binding is not a reference to the loop variable
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with a type annotation
+    x: int
+
+
+# OK: The `del` statement requires the loop variable to exist
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with `del`
+    del x
+
+
+# UP028: The exception bindings are not a reference to the loop variable
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with multiple `except` blocks
+    try:
+        pass
+    except Exception as x:
+        pass
+    try:
+        pass
+    except Exception as x:
+        pass
+
+
+# OK: The `del` statement requires the loop variable to exist
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with multiple `del` statements
+    del x
+    del x
+
+
+# OK: The `print` call requires the loop variable to exist
+def f():
+    for x in (1, 2, 3):
+        yield x
+    # Shadowing with a reference and non-reference binding
+    print(x)
+    try:
+        pass
+    except Exception as x:
+        pass

crates/ruff_linter/src/rules/pyupgrade/rules/yield_in_for_loop.rs

@@ -101,7 +101,9 @@ pub(crate) fn yield_in_for_loop(checker: &mut Checker, stmt_for: &ast::StmtFor)
             .semantic()
             .current_scope()
             .get_all(name.id.as_str())
-            .any(|binding_id| {
+            // Skip unbound bindings like `del x`
+            .find(|&id| !checker.semantic().binding(id).is_unbound())
+            .is_some_and(|binding_id| {
                 let binding = checker.semantic().binding(binding_id);
                 binding.references.iter().any(|reference_id| {
                     checker.semantic().reference(*reference_id).range() != name.range()

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP028_0.py.snap

@@ -298,5 +298,102 @@ UP028_0.py:79:5: UP028 [*] Replace `yield` over `for` loop with `yield from`
 82    |-    ):
 83    |-        yield h
    82 |+    )
+84 83 | 
+85 84 | 
+86 85 | # UP028: The later loop variable is not a reference to the earlier loop variable
 
+UP028_0.py:97:5: UP028 [*] Replace `yield` over `for` loop with `yield from`
+    |
+ 95 |   # UP028: The exception binding is not a reference to the loop variable
+ 96 |   def f():
+ 97 |       for x in (1, 2, 3):
+    |  _____^
+ 98 | |         yield x
+    | |_______________^ UP028
+ 99 |       # Shadowing with an `except`
+100 |       try:
+    |
+    = help: Replace with `yield from`
 
+ℹ Unsafe fix
+94 94 | 
+95 95 | # UP028: The exception binding is not a reference to the loop variable
+96 96 | def f():
+97    |-    for x in (1, 2, 3):
+98    |-        yield x
+   97 |+    yield from (1, 2, 3)
+99 98 |     # Shadowing with an `except`
+100 99 |     try:
+101 100 |         pass
+
+UP028_0.py:108:5: UP028 [*] Replace `yield` over `for` loop with `yield from`
+    |
+106 |   # UP028: The context binding is not a reference to the loop variable
+107 |   def f():
+108 |       for x in (1, 2, 3):
+    |  _____^
+109 | |         yield x
+    | |_______________^ UP028
+110 |       # Shadowing with `with`
+111 |       with contextlib.nullcontext() as x:
+    |
+    = help: Replace with `yield from`
+
+ℹ Unsafe fix
+105 105 | 
+106 106 | # UP028: The context binding is not a reference to the loop variable
+107 107 | def f():
+108     |-    for x in (1, 2, 3):
+109     |-        yield x
+    108 |+    yield from (1, 2, 3)
+110 109 |     # Shadowing with `with`
+111 110 |     with contextlib.nullcontext() as x:
+112 111 |         pass
+
+UP028_0.py:118:5: UP028 [*] Replace `yield` over `for` loop with `yield from`
+    |
+116 |   # UP028: The type annotation binding is not a reference to the loop variable
+117 |   def f():
+118 |       for x in (1, 2, 3):
+    |  _____^
+119 | |         yield x
+    | |_______________^ UP028
+120 |       # Shadowing with a type annotation
+121 |       x: int
+    |
+    = help: Replace with `yield from`
+
+ℹ Unsafe fix
+115 115 | 
+116 116 | # UP028: The type annotation binding is not a reference to the loop variable
+117 117 | def f():
+118     |-    for x in (1, 2, 3):
+119     |-        yield x
+    118 |+    yield from (1, 2, 3)
+120 119 |     # Shadowing with a type annotation
+121 120 |     x: int
+122 121 | 
+
+UP028_0.py:134:5: UP028 [*] Replace `yield` over `for` loop with `yield from`
+    |
+132 |   # UP028: The exception bindings are not a reference to the loop variable
+133 |   def f():
+134 |       for x in (1, 2, 3):
+    |  _____^
+135 | |         yield x
+    | |_______________^ UP028
+136 |       # Shadowing with multiple `except` blocks
+137 |       try:
+    |
+    = help: Replace with `yield from`
+
+ℹ Unsafe fix
+131 131 | 
+132 132 | # UP028: The exception bindings are not a reference to the loop variable
+133 133 | def f():
+134     |-    for x in (1, 2, 3):
+135     |-        yield x
+    134 |+    yield from (1, 2, 3)
+136 135 |     # Shadowing with multiple `except` blocks
+137 136 |     try:
+138 137 |         pass