Respect runtime-required decorators for function signatures (#10091)

## Summary

The original implementation of this applied the runtime-required context
to definitions _within_ the function, but not the signature itself. (We
had test coverage; the snapshot was just correctly showing the wrong
outcome.)

Closes https://github.com/astral-sh/ruff/issues/10089.

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

@@ -1,3 +1,4 @@
+use ruff_python_ast::StmtFunctionDef;
 use ruff_python_semantic::{ScopeKind, SemanticModel};
 
 use crate::rules::flake8_type_checking;
@@ -26,6 +27,8 @@ pub(super) enum AnnotationContext {
 }
 
 impl AnnotationContext {
+    /// Determine the [`AnnotationContext`] for an annotation based on the current scope of the
+    /// semantic model.
     pub(super) fn from_model(semantic: &SemanticModel, settings: &LinterSettings) -> Self {
         // If the annotation is in a class scope (e.g., an annotated assignment for a
         // class field) or a function scope, and that class or function is marked as
@@ -71,4 +74,23 @@ impl AnnotationContext {
 
         Self::TypingOnly
     }
+
+    /// Determine the [`AnnotationContext`] to use for annotations in a function signature.
+    pub(super) fn from_function(
+        function_def: &StmtFunctionDef,
+        semantic: &SemanticModel,
+        settings: &LinterSettings,
+    ) -> Self {
+        if flake8_type_checking::helpers::runtime_required_function(
+            function_def,
+            &settings.flake8_type_checking.runtime_required_decorators,
+            semantic,
+        ) {
+            Self::RuntimeRequired
+        } else if semantic.future_annotations() {
+            Self::TypingOnly
+        } else {
+            Self::RuntimeEvaluated
+        }
+    }
 }

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

@@ -584,7 +584,8 @@ where
 
                 // Function annotations are always evaluated at runtime, unless future annotations
                 // are enabled.
-                let runtime_annotation = !self.semantic.future_annotations();
+                let annotation =
+                    AnnotationContext::from_function(function_def, &self.semantic, self.settings);
 
                 // The first parameter may be a single dispatch.
                 let mut singledispatch =
@@ -608,10 +609,18 @@ where
                     if let Some(expr) = &parameter_with_default.parameter.annotation {
                         if singledispatch {
                             self.visit_runtime_required_annotation(expr);
-                        } else if runtime_annotation {
-                            self.visit_runtime_evaluated_annotation(expr);
                         } else {
+                            match annotation {
+                                AnnotationContext::RuntimeRequired => {
+                                    self.visit_runtime_required_annotation(expr);
+                                }
+                                AnnotationContext::RuntimeEvaluated => {
+                                    self.visit_runtime_evaluated_annotation(expr);
+                                }
+                                AnnotationContext::TypingOnly => {
                                     self.visit_annotation(expr);
+                                }
+                            }
                         };
                     }
                     if let Some(expr) = &parameter_with_default.default {
@@ -621,28 +630,46 @@ where
                 }
                 if let Some(arg) = &parameters.vararg {
                     if let Some(expr) = &arg.annotation {
-                        if runtime_annotation {
+                        match annotation {
+                            AnnotationContext::RuntimeRequired => {
+                                self.visit_runtime_required_annotation(expr);
+                            }
+                            AnnotationContext::RuntimeEvaluated => {
                                 self.visit_runtime_evaluated_annotation(expr);
-                        } else {
+                            }
+                            AnnotationContext::TypingOnly => {
                                 self.visit_annotation(expr);
-                        };
+                            }
+                        }
                     }
                 }
                 if let Some(arg) = &parameters.kwarg {
                     if let Some(expr) = &arg.annotation {
-                        if runtime_annotation {
+                        match annotation {
+                            AnnotationContext::RuntimeRequired => {
+                                self.visit_runtime_required_annotation(expr);
+                            }
+                            AnnotationContext::RuntimeEvaluated => {
                                 self.visit_runtime_evaluated_annotation(expr);
-                        } else {
+                            }
+                            AnnotationContext::TypingOnly => {
                                 self.visit_annotation(expr);
-                        };
+                            }
+                        }
                     }
                 }
                 for expr in returns {
-                    if runtime_annotation {
+                    match annotation {
+                        AnnotationContext::RuntimeRequired => {
+                            self.visit_runtime_required_annotation(expr);
+                        }
+                        AnnotationContext::RuntimeEvaluated => {
                             self.visit_runtime_evaluated_annotation(expr);
-                    } else {
+                        }
+                        AnnotationContext::TypingOnly => {
                             self.visit_annotation(expr);
-                    };
+                        }
+                    }
                 }
 
                 let definition = docstrings::extraction::extract_definition(

crates/ruff_linter/src/rules/flake8_type_checking/snapshots/ruff_linter__rules__flake8_type_checking__tests__typing-only-standard-library-import_runtime_evaluated_decorators_3.py.snap

@@ -30,31 +30,4 @@ runtime_evaluated_decorators_3.py:6:18: TCH003 [*] Move standard library import
 13 16 | 
 14 17 | @attrs.define(auto_attribs=True)
 
-runtime_evaluated_decorators_3.py:7:29: TCH003 [*] Move standard library import `collections.abc.Sequence` into a type-checking block
-  |
-5 | from dataclasses import dataclass
-6 | from uuid import UUID  # TCH003
-7 | from collections.abc import Sequence
-  |                             ^^^^^^^^ TCH003
-8 | from pydantic import validate_call
-  |
-  = help: Move into type-checking block
-
-ℹ Unsafe fix
-4  4  | from array import array
-5  5  | from dataclasses import dataclass
-6  6  | from uuid import UUID  # TCH003
-7     |-from collections.abc import Sequence
-8  7  | from pydantic import validate_call
-9  8  | 
-10 9  | import attrs
-11 10 | from attrs import frozen
-   11 |+from typing import TYPE_CHECKING
-   12 |+
-   13 |+if TYPE_CHECKING:
-   14 |+    from collections.abc import Sequence
-12 15 | 
-13 16 | 
-14 17 | @attrs.define(auto_attribs=True)
-