Move Literal flag detection into recurse phase (#5768)

## Summary

The AST pass is broken up into three phases: pre-visit (which includes
analysis), recurse (visit all members), and post-visit (clean-up). We're
not supposed to edit semantic model flags in the pre-visit phase, but it
looks like we were for literal detection. This didn't matter in
practice, but I'm looking into some AST refactors for which this _does_
cause issues.

No behavior changes expected.

## Test Plan

Good test coverage on these.

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

@@ -2222,9 +2222,6 @@ where
                     }
                 }
 
-                if self.semantic.match_typing_expr(value, "Literal") {
-                    self.semantic.flags |= SemanticModelFlags::LITERAL;
-                }
                 if self.any_enabled(&[
                     Rule::SysVersionSlice3,
                     Rule::SysVersion2,
@@ -3810,14 +3807,21 @@ where
                     ) {
                         Some(subscript) => {
                             match subscript {
+                                // Ex) Literal["Class"]
+                                typing::SubscriptKind::Literal => {
+                                    self.semantic.flags |= SemanticModelFlags::LITERAL;
+                                    self.visit_expr(value);
+                                    self.visit_type_definition(slice);
+                                    self.visit_expr_context(ctx);
+                                }
                                 // Ex) Optional[int]
-                                typing::SubscriptKind::AnnotatedSubscript => {
+                                typing::SubscriptKind::Generic => {
                                     self.visit_expr(value);
                                     self.visit_type_definition(slice);
                                     self.visit_expr_context(ctx);
                                 }
                                 // Ex) Annotated[int, "Hello, world!"]
-                                typing::SubscriptKind::PEP593AnnotatedSubscript => {
+                                typing::SubscriptKind::PEP593Annotation => {
                                     // First argument is a type (including forward references); the
                                     // rest are arbitrary Python objects.
                                     self.visit_expr(value);
@@ -3836,8 +3840,7 @@ where
                                         }
                                     } else {
                                         error!(
-                                            "Found non-Expr::Tuple argument to PEP 593 \
-                                             Annotation."
+                                            "Found non-Expr::Tuple argument to PEP 593 Annotation."
                                         );
                                     }
                                 }

crates/ruff_python_semantic/src/analyze/typing.rs

@@ -7,9 +7,9 @@ use ruff_python_ast::call_path::{from_qualified_name, from_unqualified_name, Cal
 use ruff_python_ast::helpers::is_const_false;
 use ruff_python_stdlib::typing::{
     as_pep_585_generic, has_pep_585_generic, is_immutable_generic_type,
-    is_immutable_non_generic_type, is_immutable_return_type, is_mutable_return_type,
-    is_pep_593_generic_member, is_pep_593_generic_type, is_standard_library_generic,
-    is_standard_library_generic_member,
+    is_immutable_non_generic_type, is_immutable_return_type, is_literal_member,
+    is_mutable_return_type, is_pep_593_generic_member, is_pep_593_generic_type,
+    is_standard_library_generic, is_standard_library_generic_member, is_standard_library_literal,
 };
 
 use crate::model::SemanticModel;
@@ -27,8 +27,12 @@ pub enum Callable {
 
 #[derive(Copy, Clone)]
 pub enum SubscriptKind {
-    AnnotatedSubscript,
-    PEP593AnnotatedSubscript,
+    /// A subscript of the form `typing.Literal["foo", "bar"]`, i.e., a literal.
+    Literal,
+    /// A subscript of the form `typing.List[int]`, i.e., a generic.
+    Generic,
+    /// A subscript of the form `typing.Annotated[int, "foo"]`, i.e., a PEP 593 annotation.
+    PEP593Annotation,
 }
 
 pub fn match_annotated_subscript<'a>(
@@ -38,28 +42,35 @@ pub fn match_annotated_subscript<'a>(
     extend_generics: &[String],
 ) -> Option<SubscriptKind> {
     semantic.resolve_call_path(expr).and_then(|call_path| {
+        if is_standard_library_literal(call_path.as_slice()) {
+            return Some(SubscriptKind::Literal);
+        }
+
         if is_standard_library_generic(call_path.as_slice())
             || extend_generics
                 .iter()
                 .map(|target| from_qualified_name(target))
                 .any(|target| call_path == target)
         {
-            return Some(SubscriptKind::AnnotatedSubscript);
+            return Some(SubscriptKind::Generic);
         }
 
         if is_pep_593_generic_type(call_path.as_slice()) {
-            return Some(SubscriptKind::PEP593AnnotatedSubscript);
+            return Some(SubscriptKind::PEP593Annotation);
         }
 
         for module in typing_modules {
             let module_call_path: CallPath = from_unqualified_name(module);
             if call_path.starts_with(&module_call_path) {
                 if let Some(member) = call_path.last() {
+                    if is_literal_member(member) {
+                        return Some(SubscriptKind::Literal);
+                    }
                     if is_standard_library_generic_member(member) {
-                        return Some(SubscriptKind::AnnotatedSubscript);
+                        return Some(SubscriptKind::Generic);
                     }
                     if is_pep_593_generic_member(member) {
-                        return Some(SubscriptKind::PEP593AnnotatedSubscript);
+                        return Some(SubscriptKind::PEP593Annotation);
                     }
                 }
             }

crates/ruff_python_stdlib/src/typing.rs

@@ -182,6 +182,11 @@ pub fn is_pep_593_generic_type(call_path: &[&str]) -> bool {
     matches!(call_path, ["typing" | "typing_extensions", "Annotated"])
 }
 
+/// Returns `true` if a call path is `Literal`.
+pub fn is_standard_library_literal(call_path: &[&str]) -> bool {
+    matches!(call_path, ["typing" | "typing_extensions", "Literal"])
+}
+
 /// Returns `true` if a name matches that of a generic from the Python standard library (e.g.
 /// `list` or `Set`).
 ///
@@ -267,6 +272,11 @@ pub fn is_pep_593_generic_member(member: &str) -> bool {
     matches!(member, "Annotated")
 }
 
+/// Returns `true` if a name matches that of the `Literal` generic.
+pub fn is_literal_member(member: &str) -> bool {
+    matches!(member, "Literal")
+}
+
 /// Returns `true` if a call path represents that of an immutable, non-generic type from the Python
 /// standard library (e.g. `int` or `str`).
 pub fn is_immutable_non_generic_type(call_path: &[&str]) -> bool {