bpo-38605: Make 'from __future__ import annotations' the default (GH-20434)

The hard part was making all the tests pass; there are some subtle issues here, because apparently the future import wasn't tested very thoroughly in previous Python versions.

For example, `inspect.signature()` returned type objects normally (except for forward references), but strings with the future import. We changed it to try and return type objects by calling `typing.get_type_hints()`, but fall back on returning strings if that function fails (which it may do if there are future references in the annotations that require passing in a specific namespace to resolve).

1 files changed, 0 insertions, 24 deletions

diff --git a/Python/ast_opt.c b/Python/ast_opt.c
index 5efaac4..22ca6f2 100644
--- a/Python/ast_opt.c
+++ b/Python/ast_opt.c
@@ -392,7 +392,6 @@ static int astfold_expr(expr_ty node_, PyArena *ctx_, _PyASTOptimizeState *state
 static int astfold_arguments(arguments_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
 static int astfold_comprehension(comprehension_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
 static int astfold_keyword(keyword_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
-static int astfold_arg(arg_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
 static int astfold_withitem(withitem_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
 static int astfold_excepthandler(excepthandler_ty node_, PyArena *ctx_, _PyASTOptimizeState *state);
 #define CALL(FUNC, TYPE, ARG) \
@@ -595,26 +594,12 @@ astfold_comprehension(comprehension_ty node_, PyArena *ctx_, _PyASTOptimizeState
 static int
 astfold_arguments(arguments_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
 {
-    CALL_SEQ(astfold_arg, arg, node_->posonlyargs);
-    CALL_SEQ(astfold_arg, arg, node_->args);
-    CALL_OPT(astfold_arg, arg_ty, node_->vararg);
-    CALL_SEQ(astfold_arg, arg, node_->kwonlyargs);
     CALL_SEQ(astfold_expr, expr, node_->kw_defaults);
-    CALL_OPT(astfold_arg, arg_ty, node_->kwarg);
     CALL_SEQ(astfold_expr, expr, node_->defaults);
     return 1;
 }
 
 static int
-astfold_arg(arg_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
-{
-    if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
-        CALL_OPT(astfold_expr, expr_ty, node_->annotation);
-    }
-    return 1;
-}
-
-static int
 astfold_stmt(stmt_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
 {
     switch (node_->kind) {
@@ -622,17 +607,11 @@ astfold_stmt(stmt_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
         CALL(astfold_arguments, arguments_ty, node_->v.FunctionDef.args);
         CALL(astfold_body, asdl_seq, node_->v.FunctionDef.body);
         CALL_SEQ(astfold_expr, expr, node_->v.FunctionDef.decorator_list);
-        if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
-            CALL_OPT(astfold_expr, expr_ty, node_->v.FunctionDef.returns);
-        }
         break;
     case AsyncFunctionDef_kind:
         CALL(astfold_arguments, arguments_ty, node_->v.AsyncFunctionDef.args);
         CALL(astfold_body, asdl_seq, node_->v.AsyncFunctionDef.body);
         CALL_SEQ(astfold_expr, expr, node_->v.AsyncFunctionDef.decorator_list);
-        if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
-            CALL_OPT(astfold_expr, expr_ty, node_->v.AsyncFunctionDef.returns);
-        }
         break;
     case ClassDef_kind:
         CALL_SEQ(astfold_expr, expr, node_->v.ClassDef.bases);
@@ -656,9 +635,6 @@ astfold_stmt(stmt_ty node_, PyArena *ctx_, _PyASTOptimizeState *state)
         break;
     case AnnAssign_kind:
         CALL(astfold_expr, expr_ty, node_->v.AnnAssign.target);
-        if (!(state->ff_features & CO_FUTURE_ANNOTATIONS)) {
-            CALL(astfold_expr, expr_ty, node_->v.AnnAssign.annotation);
-        }
         CALL_OPT(astfold_expr, expr_ty, node_->v.AnnAssign.value);
         break;
     case For_kind: