[mypyc] Generate error on duplicate function definitions (#16309)

Previously we produced duplicate functions in C, which caused C
compiler errors.

mypyc/irbuild/builder.py

@@ -175,6 +175,7 @@ def __init__(
  self.graph = graph
  self.ret_types: list[RType] = []
  self.functions: list[FuncIR] = []
+ self.function_names: set[tuple[str | None, str]] = set()
  self.classes: list[ClassIR] = []
  self.final_names: list[tuple[str, RType]] = []
  self.callable_class_names: set[str] = set()
@@ -1326,6 +1327,14 @@ def error(self, msg: str, line: int) -> None:
  def note(self, msg: str, line: int) -> None:
  self.errors.note(msg, self.module_path, line)
 
+ def add_function(self, func_ir: FuncIR, line: int) -> None:
+ name = (func_ir.class_name, func_ir.name)
+ if name in self.function_names:
+ self.error(f'Duplicate definition of "{name[1]}" not supported by mypyc', line)
+ return
+ self.function_names.add(name)
+ self.functions.append(func_ir)
+
 
 def gen_arg_defaults(builder: IRBuilder) -> None:
  """Generate blocks for arguments that have default values.

mypyc/irbuild/function.py

@@ -103,7 +103,7 @@ def transform_func_def(builder: IRBuilder, fdef: FuncDef) -> None:
  if func_reg:
  builder.assign(get_func_target(builder, fdef), func_reg, fdef.line)
  maybe_insert_into_registry_dict(builder, fdef)
- builder.functions.append(func_ir)
+ builder.add_function(func_ir, fdef.line)
 
 
 def transform_overloaded_func_def(builder: IRBuilder, o: OverloadedFuncDef) -> None:

mypyc/test-data/irbuild-statements.test

@@ -1123,3 +1123,27 @@ L6:
  r14 = CPy_NoErrOccured()
 L7:
  return 1
+
+[case testConditionalFunctionDefinition]
+if int():
+ def foo() -> int:
+ return 0
+else:
+ def foo() -> int: # E
+ return 1
+
+def bar() -> int:
+ return 0
+
+if int():
+ def bar() -> int: # E
+ return 1
+[out]
+main:5: error: Duplicate definition of "foo" not supported by mypyc
+main:12: error: Duplicate definition of "bar" not supported by mypyc
+
+[case testRepeatedUnderscoreFunctions]
+def _(arg): pass
+def _(arg): pass
+[out]
+main:2: error: Duplicate definition of "_" not supported by mypyc

mypyc/test-data/run-misc.test

@@ -1117,10 +1117,6 @@ for _ in range(2):
  except AssertionError:
  pass
 
-[case testRepeatedUnderscoreFunctions]
-def _(arg): pass
-def _(arg): pass
-
 [case testUnderscoreFunctionsInMethods]
 
 class A: