fix references to immutable variables in constructor (#2627)

with the internal name as is, it doesn't get inserted into the variable
namespace properly and so a new memory location gets allocated when it
is referenced. this commit changes the key inserted into `context.vars`
so that it will get picked up properly in `parse_Name`.

Author: charles-cooper

tests/parser/features/test_immutable.py

@@ -32,6 +32,29 @@ def get_value() -> {typ}:
     assert c.get_value() == value
 
 
+@pytest.mark.parametrize("val", [0, 1, 2 ** 256 - 1])
+def test_usage_in_constructor(get_contract, val):
+    code = """
+A: immutable(uint256)
+a: public(uint256)
+
+
+@external
+def __init__(_a: uint256):
+    A = _a
+    self.a = A
+
+
+@external
+@view
+def a1() -> uint256:
+    return A
+    """
+
+    c = get_contract(code, val)
+    assert c.a1() == c.a() == val
+
+
 def test_multiple_immutable_values(get_contract):
     code = """
 a: immutable(uint256)

vyper/codegen/expr.py

@@ -326,7 +326,7 @@ def parse_Name(self):
             is_constructor = self.expr.get_ancestor(vy_ast.FunctionDef).get("name") == "__init__"
             if is_constructor:
                 # store memory position for later access in module.py in the variable record
-                memory_loc = self.context.new_variable(f"#immutable_{self.expr.id}", var.typ)
+                memory_loc = self.context.new_variable(self.expr.id, var.typ)
                 self.context.global_ctx._globals[self.expr.id].pos = memory_loc
                 # store the data offset in the variable record as well for accessing
                 data_offset = self.expr._metadata["type"].position.offset