flake8-pyi: fix PYI015 false positive on assignment of TypeVar & friends (#3861)

crates/ruff/resources/test/fixtures/flake8_pyi/PYI015.pyi

@@ -1,6 +1,6 @@
 import builtins
 import typing
-from typing import TypeAlias, Final
+from typing import TypeAlias, Final, NewType, TypeVar, TypeVarTuple, ParamSpec
 
 # We shouldn't emit Y015 for simple default values
 field1: int
@@ -26,6 +26,10 @@ field9 = None  # Y026 Use typing_extensions.TypeAlias for type aliases, e.g. "fi
 Field95: TypeAlias = None
 Field96: TypeAlias = int | None
 Field97: TypeAlias = None | typing.SupportsInt | builtins.str | float | bool
+Field98 = NewType('MyInt', int)
+Field99 = TypeVar('Field99')
+Field100 = TypeVarTuple('Field100')
+Field101 = ParamSpec('Field101')
 field19 = [1, 2, 3]  # Y052 Need type annotation for "field19"
 field191: list[int] = [1, 2, 3]
 field20 = (1, 2, 3)  # Y052 Need type annotation for "field20"

crates/ruff/src/rules/flake8_pyi/rules/simple_defaults.rs

@@ -221,6 +221,23 @@ fn is_valid_default_value_with_annotation(
     false
 }
 
+pub fn is_type_var_call(checker: &Checker, expr: &Expr) -> bool {
+    let ExprKind::Call {func, ..} = &expr.node else {
+        return false;
+    };
+    checker
+        .ctx
+        .resolve_call_path(func)
+        .map_or(false, |call_path| {
+            call_path.as_slice() == ["typing", "TypeVar"]
+                || call_path.as_slice() == ["typing", "TypeVarTuple"]
+                || call_path.as_slice() == ["typing_extensions", "TypeVarTuple"]
+                || call_path.as_slice() == ["typing", "NewType"]
+                || call_path.as_slice() == ["typing", "ParamSpec"]
+                || call_path.as_slice() == ["typing_extensions", "ParamSpec"]
+        })
+}
+
 /// PYI011
 pub fn typed_argument_simple_defaults(checker: &mut Checker, args: &Arguments) {
     if !args.defaults.is_empty() {
@@ -342,6 +359,9 @@ pub fn assignment_default_in_stub(checker: &mut Checker, value: &Expr, annotatio
     }) {
         return;
     }
+    if is_type_var_call(checker, value) {
+        return;
+    }
     if !is_valid_default_value_with_annotation(value, checker, true) {
         let mut diagnostic = Diagnostic::new(AssignmentDefaultInStub, Range::from(value));
 

crates/ruff/src/rules/flake8_pyi/snapshots/ruff__rules__flake8_pyi__tests__PYI015_PYI015.pyi.snap

@@ -8,19 +8,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 40
+    row: 44
     column: 22
   end_location:
-    row: 40
+    row: 44
     column: 57
   fix:
     edits:
       - content: "..."
         location:
-          row: 40
+          row: 44
           column: 22
         end_location:
-          row: 40
+          row: 44
           column: 57
   parent: ~
 - kind:
@@ -29,19 +29,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 41
+    row: 45
     column: 22
   end_location:
-    row: 41
+    row: 45
     column: 34
   fix:
     edits:
       - content: "..."
         location:
-          row: 41
+          row: 45
           column: 22
         end_location:
-          row: 41
+          row: 45
           column: 34
   parent: ~
 - kind:
@@ -50,19 +50,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 42
+    row: 46
     column: 22
   end_location:
-    row: 42
+    row: 46
     column: 37
   fix:
     edits:
       - content: "..."
         location:
-          row: 42
+          row: 46
           column: 22
         end_location:
-          row: 42
+          row: 46
           column: 37
   parent: ~
 - kind:
@@ -71,19 +71,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 43
+    row: 47
     column: 25
   end_location:
-    row: 43
+    row: 47
     column: 35
   fix:
     edits:
       - content: "..."
         location:
-          row: 43
+          row: 47
           column: 25
         end_location:
-          row: 43
+          row: 47
           column: 35
   parent: ~
 - kind:
@@ -92,19 +92,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 44
+    row: 48
     column: 46
   end_location:
-    row: 44
+    row: 48
     column: 69
   fix:
     edits:
       - content: "..."
         location:
-          row: 44
+          row: 48
           column: 46
         end_location:
-          row: 44
+          row: 48
           column: 69
   parent: ~
 - kind:
@@ -113,19 +113,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 45
+    row: 49
     column: 30
   end_location:
-    row: 45
+    row: 49
     column: 53
   fix:
     edits:
       - content: "..."
         location:
-          row: 45
+          row: 49
           column: 30
         end_location:
-          row: 45
+          row: 49
           column: 53
   parent: ~
 - kind:
@@ -134,19 +134,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 46
+    row: 50
     column: 36
   end_location:
-    row: 46
+    row: 50
     column: 47
   fix:
     edits:
       - content: "..."
         location:
-          row: 46
+          row: 50
           column: 36
         end_location:
-          row: 46
+          row: 50
           column: 47
   parent: ~
 - kind:
@@ -155,19 +155,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 48
+    row: 52
     column: 27
   end_location:
-    row: 48
+    row: 52
     column: 43
   fix:
     edits:
       - content: "..."
         location:
-          row: 48
+          row: 52
           column: 27
         end_location:
-          row: 48
+          row: 52
           column: 43
   parent: ~
 - kind:
@@ -176,19 +176,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 49
+    row: 53
     column: 10
   end_location:
-    row: 49
+    row: 53
     column: 23
   fix:
     edits:
       - content: "..."
         location:
-          row: 49
+          row: 53
           column: 10
         end_location:
-          row: 49
+          row: 53
           column: 23
   parent: ~
 - kind:
@@ -197,19 +197,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 50
+    row: 54
     column: 10
   end_location:
-    row: 50
+    row: 54
     column: 25
   fix:
     edits:
       - content: "..."
         location:
-          row: 50
+          row: 54
           column: 10
         end_location:
-          row: 50
+          row: 54
           column: 25
   parent: ~
 - kind:
@@ -218,19 +218,19 @@ expression: diagnostics
     suggestion: "Replace default value with `...`"
     fixable: true
   location:
-    row: 51
+    row: 55
     column: 10
   end_location:
-    row: 51
+    row: 55
     column: 15
   fix:
     edits:
       - content: "..."
         location:
-          row: 51
+          row: 55
           column: 10
         end_location:
-          row: 51
+          row: 55
           column: 15
   parent: ~