Treat TypeAlias values as annotations (#377)

resources/test/fixtures/F401.py

@@ -67,7 +67,22 @@ c = cast("Vegetable", b)
 Field = lambda default=MISSING: field(default=default)
 
 
+# Test: access a sub-importation via an alias.
 import pyarrow as pa
 import pyarrow.csv
 
 print(pa.csv.read_csv("test.csv"))
+
+
+# Test: referencing an import via TypeAlias.
+import sys
+
+import numpy as np
+
+if sys.version_info >= (3, 10):
+    from typing import TypeAlias
+else:
+    from typing_extensions import TypeAlias
+
+
+CustomInt: TypeAlias = "np.int8 | np.int16"

src/ast/visitor.rs

@@ -1,3 +1,4 @@
+use crate::ast::helpers::match_name_or_attr;
 use rustpython_parser::ast::{
     Alias, Arg, Arguments, Boolop, Cmpop, Comprehension, Constant, Excepthandler,
     ExcepthandlerKind, Expr, ExprContext, ExprKind, Keyword, MatchCase, Operator, Pattern,
@@ -148,8 +149,12 @@ pub fn walk_stmt<'a, V: Visitor<'a> + ?Sized>(visitor: &mut V, stmt: &'a Stmt) {
         } => {
             visitor.visit_annotation(annotation);
             if let Some(expr) = value {
+                if match_name_or_attr(annotation, "TypeAlias") {
+                    visitor.visit_annotation(expr);
+                } else {
                     visitor.visit_expr(expr);
                 }
+            }
             visitor.visit_expr(target);
         }
         StmtKind::For {