fix[lang]: allow type expressions inside pure functions (vyperlang#3906)

20432c5 introduced a regression where type expressions like the
following would raise a compiler error instead of successfully
compiling:
```
@pure
def f():
    convert(..., uint256)  # raises `not a variable or literal: 'uint256'`
```

the reason is because `get_expr_info` is called on `uint256`, which
is not a regular expr. this commit introduces a fastpath return to
address the issue. longer-term, we should generalize the rules in
`vyper/semantics/analysis/local.py` so that AST traversal does not
progress into type expressions.

tests/functional/codegen/features/decorators/test_pure.py

@@ -175,6 +175,19 @@ def foo() -> uint256:
         compile_code(code)
 
 
+def test_type_in_pure(get_contract):
+    code = """
+@pure
+@external
+def _convert(x: bytes32) -> uint256:
+    return convert(x, uint256)
+    """
+    c = get_contract(code)
+    x = 123456
+    bs = x.to_bytes(32, "big")
+    assert x == c._convert(bs)
+
+
 def test_invalid_conflicting_decorators():
     code = """
 @pure

vyper/semantics/analysis/local.py

@@ -165,7 +165,10 @@ def _validate_msg_value_access(node: vy_ast.Attribute) -> None:
         raise NonPayableViolation("msg.value is not allowed in non-payable functions", node)
 
 
-def _validate_pure_access(node: vy_ast.Attribute | vy_ast.Name) -> None:
+def _validate_pure_access(node: vy_ast.Attribute | vy_ast.Name, typ: VyperType) -> None:
+    if isinstance(typ, TYPE_T):
+        return
+
     info = get_expr_info(node)
 
     env_vars = CONSTANT_ENVIRONMENT_VARS
@@ -705,7 +708,7 @@ def visit_Attribute(self, node: vy_ast.Attribute, typ: VyperType) -> None:
             _validate_msg_value_access(node)
 
         if self.func and self.func.mutability == StateMutability.PURE:
-            _validate_pure_access(node)
+            _validate_pure_access(node, typ)
 
         value_type = get_exact_type_from_node(node.value)
 
@@ -886,7 +889,7 @@ def visit_List(self, node: vy_ast.List, typ: VyperType) -> None:
 
     def visit_Name(self, node: vy_ast.Name, typ: VyperType) -> None:
         if self.func and self.func.mutability == StateMutability.PURE:
-            _validate_pure_access(node)
+            _validate_pure_access(node, typ)
 
     def visit_Subscript(self, node: vy_ast.Subscript, typ: VyperType) -> None:
         if isinstance(typ, TYPE_T):