stubgen: preserve string arguments in annotations (python#11292)

Fixes python#11222

Author: 0x000A

mypy/stubgen.py

@@ -255,7 +255,7 @@ def visit_unbound_type(self, t: UnboundType) -> str:
         s = t.name
         self.stubgen.import_tracker.require_name(s)
         if t.args:
-            s += '[{}]'.format(self.list_str(t.args))
+            s += '[{}]'.format(self.args_str(t.args))
         return s
 
     def visit_none_type(self, t: NoneType) -> str:
@@ -264,6 +264,22 @@ def visit_none_type(self, t: NoneType) -> str:
     def visit_type_list(self, t: TypeList) -> str:
         return '[{}]'.format(self.list_str(t.items))
 
+    def args_str(self, args: Iterable[Type]) -> str:
+        """Convert an array of arguments to strings and join the results with commas.
+
+        The main difference from list_str is the preservation of quotes for string
+        arguments
+        """
+        types = ['builtins.bytes', 'builtins.unicode']
+        res = []
+        for arg in args:
+            arg_str = arg.accept(self)
+            if isinstance(arg, UnboundType) and arg.original_str_fallback in types:
+                res.append("'{}'".format(arg_str))
+            else:
+                res.append(arg_str)
+        return ', '.join(res)
+
 
 class AliasPrinter(NodeVisitor[str]):
     """Visitor used to collect type aliases _and_ type variable definitions.

test-data/unit/stubgen.test

@@ -64,6 +64,25 @@ def g(x: Foo = Foo()) -> Bar: ...
 def f(x: Foo) -> Bar: ...
 def g(x: Foo = ...) -> Bar: ...
 
+[case testPreserveFunctionAnnotationWithArgs]
+def f(x: foo['x']) -> bar: ...
+def g(x: foo[x]) -> bar: ...
+def h(x: foo['x', 'y']) -> bar: ...
+def i(x: foo[x, y]) -> bar: ...
+def j(x: foo['x', y]) -> bar: ...
+def k(x: foo[x, 'y']) -> bar: ...
+def lit_str(x: Literal['str']) -> Literal['str']: ...
+def lit_int(x: Literal[1]) -> Literal[1]: ...
+[out]
+def f(x: foo['x']) -> bar: ...
+def g(x: foo[x]) -> bar: ...
+def h(x: foo['x', 'y']) -> bar: ...
+def i(x: foo[x, y]) -> bar: ...
+def j(x: foo['x', y]) -> bar: ...
+def k(x: foo[x, 'y']) -> bar: ...
+def lit_str(x: Literal['str']) -> Literal['str']: ...
+def lit_int(x: Literal[1]) -> Literal[1]: ...
+
 [case testPreserveVarAnnotation]
 x: Foo
 [out]