feat: let params of internal functions be mutable

tests/parser/features/test_assignment.py

@@ -39,7 +39,39 @@ def augmod(x: int128, y: int128) -> int128:
     print("Passed aug-assignment test")
 
 
-def test_invalid_assign(assert_compile_failed, get_contract_with_gas_estimation):
+def test_internal_assign(get_contract_with_gas_estimation):
+    code = """
+@internal
+def foo(x: int128) -> int128:
+    x = 77
+    return x
+
+@external
+def bar(x: int128) -> int128:
+    return self.foo(x)
+    """
+    c = get_contract_with_gas_estimation(code)
+
+    assert c.bar(123) == 77
+
+
+def test_internal_augassign(get_contract_with_gas_estimation):
+    code = """
+@internal
+def foo(x: int128) -> int128:
+    x += 77
+    return x
+
+@external
+def bar(x: int128) -> int128:
+    return self.foo(x)
+    """
+    c = get_contract_with_gas_estimation(code)
+
+    assert c.bar(123) == 200
+
+
+def test_invalid_external_assign(assert_compile_failed, get_contract_with_gas_estimation):
     code = """
 @external
 def foo(x: int128):
@@ -48,7 +80,7 @@ def foo(x: int128):
     assert_compile_failed(lambda: get_contract_with_gas_estimation(code), ImmutableViolation)
 
 
-def test_invalid_augassign(assert_compile_failed, get_contract_with_gas_estimation):
+def test_invalid_external_augassign(assert_compile_failed, get_contract_with_gas_estimation):
     code = """
 @external
 def foo(x: int128):

vyper/codegen/function_definitions/internal_function.py

@@ -41,8 +41,8 @@ def generate_ir_for_internal_function(
 
     for arg in func_t.arguments:
         # allocate a variable for every arg, setting mutability
-        # to False to comply with vyper semantics, function arguments are immutable
-        context.new_variable(arg.name, arg.typ, is_mutable=False)
+        # to True to allow internal function arguments to be mutable
+        context.new_variable(arg.name, arg.typ, is_mutable=True)
 
     nonreentrant_pre, nonreentrant_post = get_nonreentrant_lock(func_t)
 

vyper/semantics/analysis/local.py

@@ -173,9 +173,13 @@ def __init__(
         self.func = fn_node._metadata["type"]
         self.annotation_visitor = StatementAnnotationVisitor(fn_node, namespace)
         self.expr_visitor = _LocalExpressionVisitor()
+
+        # allow internal function params to be mutable
+        location = DataLocation.MEMORY if self.func.is_internal else DataLocation.CALLDATA
+        is_immutable = False if self.func.is_internal else True
         for arg in self.func.arguments:
             namespace[arg.name] = VarInfo(
-                arg.typ, location=DataLocation.CALLDATA, is_immutable=True
+                arg.typ, location=location, is_immutable=is_immutable
             )
 
         for node in fn_node.body: