[`pylint`] Fix suppression for empty dict without tuple key annotation (`PLE1141`) (#21290)

## Summary

Fixes the PLE1141 (`dict-iter-missing-items`) rule to allow fixes for
empty dictionaries unless they have type annotations indicating 2-tuple
keys. Previously, the fix was incorrectly suppressed for all empty dicts
due to vacuous truth in the `all()` function.

Fixes #21289

## Problem Analysis

The `is_dict_key_tuple_with_two_elements` function was designed to
suppress the fix when a dictionary's keys are all 2-tuples, as unpacking
tuple keys directly would change runtime behavior.

However, for empty dictionaries, `iter_keys()` returns an empty
iterator, and `all()` on an empty iterator returns `true` (vacuous
truth). This caused the function to incorrectly suppress fixes for empty
dicts, even when there was no indication that future keys would be
2-tuples.

## Approach

1. **Detect empty dictionaries**: Added a check to identify when a dict
literal has no keys.

2. **Handle annotated empty dicts**: For empty dicts with type
annotations:
- Parse the annotation to check if it's `dict[tuple[T1, T2], ...]` where
the tuple has exactly 2 elements
- Support both PEP 484 (`typing.Dict`, `typing.Tuple`) and PEP 585
(`dict`, `tuple`) syntax
   - If tuple keys are detected, suppress the fix (correct behavior)
   - Otherwise, allow the fix

3. **Handle unannotated empty dicts**: For empty dicts without
annotations, allow the fix since there's no indication that keys will be
2-tuples.

4. **Preserve existing behavior**: For non-empty dicts, the original
logic is unchanged - check if all existing keys are 2-tuples.

The implementation includes helper functions:
- `is_annotation_dict_with_tuple_keys()`: Checks if a type annotation
specifies dict with tuple keys
- `is_tuple_type_with_two_elements()`: Checks if a type expression
represents a 2-tuple

Test cases were added to verify:
- Empty dict without annotation triggers the error
- Empty dict with `dict[tuple[int, str], bool]` suppresses the error
- Empty dict with `dict[str, int]` triggers the error
- Existing tests remain unchanged

---------

Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>

crates/ruff_linter/resources/test/fixtures/pylint/dict_iter_missing_items.py

@@ -30,3 +30,23 @@ for a, b in d_tuple:
     pass
 for a, b in d_tuple_annotated: 
     pass
+
+# Empty dict cases
+empty_dict = {}
+empty_dict["x"] = 1
+for k, v in empty_dict:
+    pass
+
+empty_dict_annotated_tuple_keys: dict[tuple[int, str], bool] = {}
+for k, v in empty_dict_annotated_tuple_keys:
+    pass
+
+empty_dict_unannotated = {}
+empty_dict_unannotated[("x", "y")] = True
+for k, v in empty_dict_unannotated:
+    pass
+
+empty_dict_annotated_str_keys: dict[str, int] = {}
+empty_dict_annotated_str_keys["x"] = 1
+for k, v in empty_dict_annotated_str_keys:
+    pass

crates/ruff_linter/src/rules/pylint/rules/dict_iter_missing_items.rs

@@ -1,4 +1,4 @@
-use ruff_python_ast::{Expr, Stmt};
+use ruff_python_ast::{self as ast, Expr, Stmt};
 
 use ruff_macros::{ViolationMetadata, derive_message_formats};
 use ruff_python_semantic::analyze::typing::is_dict;
@@ -108,15 +108,77 @@ fn is_dict_key_tuple_with_two_elements(binding: &Binding, semantic: &SemanticMod
         return false;
     };
 
-    let Stmt::Assign(assign_stmt) = statement else {
+    let (value, annotation) = match statement {
+        Stmt::Assign(assign_stmt) => (assign_stmt.value.as_ref(), None),
+        Stmt::AnnAssign(ast::StmtAnnAssign {
+            value: Some(value),
+            annotation,
+            ..
+        }) => (value.as_ref(), Some(annotation.as_ref())),
+        _ => return false,
+    };
+
+    let Expr::Dict(dict_expr) = value else {
         return false;
     };
 
-    let Expr::Dict(dict_expr) = &*assign_stmt.value else {
+    // Check if dict is empty
-        return false;
+    let is_empty = dict_expr.is_empty();
-    };
 
+    if is_empty {
+        // For empty dicts, check type annotation
+        return annotation
+            .is_some_and(|annotation| is_annotation_dict_with_tuple_keys(annotation, semantic));
+    }
+
+    // For non-empty dicts, check if all keys are 2-tuples
     dict_expr
         .iter_keys()
         .all(|key| matches!(key, Some(Expr::Tuple(tuple)) if tuple.len() == 2))
 }
+
+/// Returns true if the annotation is `dict[tuple[T1, T2], ...]` where tuple has exactly 2 elements.
+fn is_annotation_dict_with_tuple_keys(annotation: &Expr, semantic: &SemanticModel) -> bool {
+    // Check if it's a subscript: dict[...]
+    let Expr::Subscript(subscript) = annotation else {
+        return false;
+    };
+
+    // Check if it's dict or typing.Dict
+    if !semantic.match_builtin_expr(subscript.value.as_ref(), "dict")
+        && !semantic.match_typing_expr(subscript.value.as_ref(), "Dict")
+    {
+        return false;
+    }
+
+    // Extract the slice (should be a tuple: (key_type, value_type))
+    let Expr::Tuple(tuple) = subscript.slice.as_ref() else {
+        return false;
+    };
+
+    // dict[K, V] format - check if K is tuple with 2 elements
+    if let [key, _value] = tuple.elts.as_slice() {
+        return is_tuple_type_with_two_elements(key, semantic);
+    }
+
+    false
+}
+
+/// Returns true if the expression represents a tuple type with exactly 2 elements.
+fn is_tuple_type_with_two_elements(expr: &Expr, semantic: &SemanticModel) -> bool {
+    // Handle tuple[...] subscript
+    if let Expr::Subscript(subscript) = expr {
+        // Check if it's tuple or typing.Tuple
+        if semantic.match_builtin_expr(subscript.value.as_ref(), "tuple")
+            || semantic.match_typing_expr(subscript.value.as_ref(), "Tuple")
+        {
+            // Check the slice - tuple[T1, T2]
+            if let Expr::Tuple(tuple_slice) = subscript.slice.as_ref() {
+                return tuple_slice.elts.len() == 2;
+            }
+            return false;
+        }
+    }
+
+    false
+}

crates/ruff_linter/src/rules/pylint/snapshots/ruff_linter__rules__pylint__tests__PLE1141_dict_iter_missing_items.py.snap

@@ -39,3 +39,61 @@ help: Add a call to `.items()`
 18 | 
 19 | 
 note: This is an unsafe fix and may change runtime behavior
+
+PLE1141 [*] Unpacking a dictionary in iteration without calling `.items()`
+  --> dict_iter_missing_items.py:37:13
+   |
+35 | empty_dict = {}
+36 | empty_dict["x"] = 1
+37 | for k, v in empty_dict:
+   |             ^^^^^^^^^^
+38 |     pass
+   |
+help: Add a call to `.items()`
+34 | # Empty dict cases
+35 | empty_dict = {}
+36 | empty_dict["x"] = 1
+   - for k, v in empty_dict:
+37 + for k, v in empty_dict.items():
+38 |     pass
+39 | 
+40 | empty_dict_annotated_tuple_keys: dict[tuple[int, str], bool] = {}
+note: This is an unsafe fix and may change runtime behavior
+
+PLE1141 [*] Unpacking a dictionary in iteration without calling `.items()`
+  --> dict_iter_missing_items.py:46:13
+   |
+44 | empty_dict_unannotated = {}
+45 | empty_dict_unannotated[("x", "y")] = True
+46 | for k, v in empty_dict_unannotated:
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+47 |     pass
+   |
+help: Add a call to `.items()`
+43 | 
+44 | empty_dict_unannotated = {}
+45 | empty_dict_unannotated[("x", "y")] = True
+   - for k, v in empty_dict_unannotated:
+46 + for k, v in empty_dict_unannotated.items():
+47 |     pass
+48 | 
+49 | empty_dict_annotated_str_keys: dict[str, int] = {}
+note: This is an unsafe fix and may change runtime behavior
+
+PLE1141 [*] Unpacking a dictionary in iteration without calling `.items()`
+  --> dict_iter_missing_items.py:51:13
+   |
+49 | empty_dict_annotated_str_keys: dict[str, int] = {}
+50 | empty_dict_annotated_str_keys["x"] = 1
+51 | for k, v in empty_dict_annotated_str_keys:
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+52 |     pass
+   |
+help: Add a call to `.items()`
+48 | 
+49 | empty_dict_annotated_str_keys: dict[str, int] = {}
+50 | empty_dict_annotated_str_keys["x"] = 1
+   - for k, v in empty_dict_annotated_str_keys:
+51 + for k, v in empty_dict_annotated_str_keys.items():
+52 |     pass
+note: This is an unsafe fix and may change runtime behavior