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{ "id": 2222804, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2222804/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/ad00nW_wFL_TxjW6@redhat.com/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/1.2/projects/17/?format=api", "name": "GNU Compiler Collection", "link_name": "gcc", "list_id": "gcc-patches.gcc.gnu.org", "list_email": "gcc-patches@gcc.gnu.org", "web_url": null, "scm_url": null, "webscm_url": null, "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<ad00nW_wFL_TxjW6@redhat.com>", "list_archive_url": null, "date": "2026-04-13T18:23:25", "name": "[v2] c++/reflection: fn call with splice in decltype rejected [PR124835]", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "15362cd3d76d1c2d31abd0a994383c13c85166a8", "submitter": { "id": 14370, "url": "http://patchwork.ozlabs.org/api/1.2/people/14370/?format=api", "name": "Marek Polacek", "email": "polacek@redhat.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/ad00nW_wFL_TxjW6@redhat.com/mbox/", "series": [ { "id": 499738, "url": "http://patchwork.ozlabs.org/api/1.2/series/499738/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=499738", "date": "2026-04-13T18:23:25", "name": "[v2] c++/reflection: fn call with splice in decltype rejected [PR124835]", "version": 2, "mbox": "http://patchwork.ozlabs.org/series/499738/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2222804/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2222804/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=UuCgEMn0;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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charset=us-ascii", "Content-Disposition": "inline", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "On Fri, Apr 10, 2026 at 03:05:18PM -0400, Jason Merrill wrote:\n> On 4/9/26 8:27 PM, Marek Polacek wrote:\n> > I found this while working on the mangling patch and this bug\n> > blocks that patch.\n> > \n> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?\n> > \n> > -- >8 --\n> > Here we reject the valid\n> > \n> > decltype([:^^foo<int>:](42))\n> > \n> > saying that a ')' is expected. [dcl.type.decltype] says \"if E is an\n> > unparenthesized splice-expression, decltype(E) is...\" and we handle it\n> > by calling _splice_expression and setting id_expression_or_member_access_p.\n> > \n> > But for the code above we shouldn't do this, because the [: :] isn't\n> > the sole operand of decltype. _nth_token_starts_splice_without_nns_p\n> > checks that there's no :: after the :] but here we want to check that\n> > the [: :] is followed by a ')'.\n> > \n> > \tPR c++/124835\n> > \n> > gcc/cp/ChangeLog:\n> > \n> > \t* parser.cc (cp_parser_decltype_expr): Check that [: :] is\n> > \tfollowed by a ')' before declaring it an unparenthesized\n> > \tsplice-expression.\n> > \n> > gcc/testsuite/ChangeLog:\n> > \n> > \t* g++.dg/reflect/decltype2.C: New test.\n> > ---\n> > gcc/cp/parser.cc | 11 ++++++++++-\n> > gcc/testsuite/g++.dg/reflect/decltype2.C | 12 ++++++++++++\n> > 2 files changed, 22 insertions(+), 1 deletion(-)\n> > create mode 100644 gcc/testsuite/g++.dg/reflect/decltype2.C\n> > \n> > diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc\n> > index fe27a15a283..6493a26a149 100644\n> > --- a/gcc/cp/parser.cc\n> > +++ b/gcc/cp/parser.cc\n> > @@ -19387,7 +19387,16 @@ cp_parser_decltype_expr (cp_parser *parser,\n> > /* [dcl.type.decltype] \"if E is an unparenthesized splice-expression,\n> > \t decltype(E) is the type of the entity, object, or value designated\n> > \t by the splice-specifier of E\" */\n> > - if (cp_parser_nth_token_starts_splice_without_nns_p (parser, 1))\n> > + const bool unparenthesized_splice_expr_p = [&] {\n> > +\t/* The next token must be '[:'. */\n> > +\tif (cp_lexer_next_token_is_not (parser->lexer, CPP_OPEN_SPLICE))\n> > +\t return false;\n> \n> What about a splice-expression with leading 'template'? I think we can just\n> drop this check and rely on _skip_entire_.\n\nI think we can't have a valid leading 'template' here: in \"template [:X:]\"\nthe X must designate a function template, and\n\n decltype(template [:^^foo:])\n\nresults in \"cannot resolve address of overloaded function\". But let's\ndrop the first check anyway.\n \n> Optionally, I wonder about using tentative parsing like for member access\n> just above, rather than token scanning and then parsing.\n> \n> > +\t/* Skip to the end of the ':]' and see if the closing ')' follows. */\n> > +\tsaved_token_sentinel toks (parser->lexer, STS_ROLLBACK);\n> > +\treturn (cp_parser_skip_entire_splice_expr (parser)\n> > +\t\t&& cp_lexer_next_token_is (parser->lexer, CPP_CLOSE_PAREN));\n> > + } ();\n> > + if (unparenthesized_splice_expr_p)\n> > \t{\n> > \t cp_id_kind idk;\n> > \t expr = cp_parser_splice_expression (parser, /*template_p=*/false,\n> > diff --git a/gcc/testsuite/g++.dg/reflect/decltype2.C b/gcc/testsuite/g++.dg/reflect/decltype2.C\n> > new file mode 100644\n> > index 00000000000..cc5532c7957\n> > --- /dev/null\n> > +++ b/gcc/testsuite/g++.dg/reflect/decltype2.C\n> > @@ -0,0 +1,12 @@\n> > +// PR c++/124835\n> > +// { dg-do compile { target c++26 } }\n> > +// { dg-additional-options \"-freflection\" }\n> > +\n> > +template<typename T>\n> > +constexpr T foo (T t) { return t; }\n> > +\n> > +int bar (int);\n> > +\n> > +static_assert ([:^^foo<int>:](42) == 42);\n> > +decltype([:^^foo<int>:](42)) a = 42;\n> > +decltype([:^^foo<int>:]) &b = bar;\n> \n> It would be good to check whether decltype gives the right answer.\n\nYes, done. Also let's check decltype((...)).\n\nBootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?\n\n-- >8 --\nHere we reject the valid\n\n decltype([:^^foo<int>:](42))\n\nsaying that a ')' is expected. [dcl.type.decltype] says \"if E is an\nunparenthesized splice-expression, decltype(E) is...\" and we handle it\nby calling _splice_expression and setting id_expression_or_member_access_p.\n\nBut for the code above we shouldn't do this, because the [: :] isn't\nthe sole operand of decltype. _nth_token_starts_splice_without_nns_p\nchecks that there's no :: after the :] but here we want to check that\nthe [: :] is followed by a ')'.\n\n\tPR c++/124835\n\ngcc/cp/ChangeLog:\n\n\t* parser.cc (cp_parser_decltype_expr): Check that [: :] is\n\tfollowed by a ')' before declaring it an unparenthesized\n\tsplice-expression.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/reflect/decltype2.C: New test.\n---\n gcc/cp/parser.cc | 13 ++++++++++--\n gcc/testsuite/g++.dg/reflect/decltype2.C | 25 ++++++++++++++++++++++++\n 2 files changed, 36 insertions(+), 2 deletions(-)\n create mode 100644 gcc/testsuite/g++.dg/reflect/decltype2.C\n\n\nbase-commit: 9c694b3ecd0eb5308e85a0eac69c4b2d008ca83e", "diff": "diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc\nindex fe27a15a283..9dbc2933e7b 100644\n--- a/gcc/cp/parser.cc\n+++ b/gcc/cp/parser.cc\n@@ -19387,10 +19387,19 @@ cp_parser_decltype_expr (cp_parser *parser,\n /* [dcl.type.decltype] \"if E is an unparenthesized splice-expression,\n \t decltype(E) is the type of the entity, object, or value designated\n \t by the splice-specifier of E\" */\n- if (cp_parser_nth_token_starts_splice_without_nns_p (parser, 1))\n+ const bool unparenthesized_splice_expr_p = [&] {\n+\tif (!flag_reflection)\n+\t return false;\n+\t/* Skip to the end of the ':]' and see if the closing ')' follows. */\n+\tsaved_token_sentinel toks (parser->lexer, STS_ROLLBACK);\n+\treturn (cp_parser_skip_entire_splice_expr (parser)\n+\t\t&& cp_lexer_next_token_is (parser->lexer, CPP_CLOSE_PAREN));\n+ } ();\n+ if (unparenthesized_splice_expr_p)\n \t{\n \t cp_id_kind idk;\n-\t expr = cp_parser_splice_expression (parser, /*template_p=*/false,\n+\t const bool template_p = cp_parser_optional_template_keyword (parser);\n+\t expr = cp_parser_splice_expression (parser, template_p,\n \t\t\t\t\t /*address_p=*/false,\n \t\t\t\t\t /*template_arg_p=*/false,\n \t\t\t\t\t /*member_access_p=*/false, &idk);\ndiff --git a/gcc/testsuite/g++.dg/reflect/decltype2.C b/gcc/testsuite/g++.dg/reflect/decltype2.C\nnew file mode 100644\nindex 00000000000..075d490d368\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/decltype2.C\n@@ -0,0 +1,25 @@\n+// PR c++/124835\n+// { dg-do compile { target c++26 } }\n+// { dg-additional-options \"-freflection\" }\n+\n+template <typename T, typename U>\n+constexpr bool is_same_v = false;\n+\n+template <typename T>\n+constexpr bool is_same_v<T, T> = true;\n+\n+template<typename T>\n+constexpr T foo (T t) { return t; }\n+\n+template<typename T>\n+struct S { };\n+\n+static_assert([:^^foo<int>:](42) == 42);\n+static_assert(is_same_v<decltype([:^^foo<int>:]), int(int)>);\n+static_assert(is_same_v<decltype([:^^foo<int>:](42)), int>);\n+static_assert(is_same_v<decltype(template [:^^foo:](0)), int>);\n+static_assert(is_same_v<decltype(template [:^^foo:]<int>(0)), int>);\n+static_assert(is_same_v<decltype(([:^^foo<int>:])), int(&)(int)>);\n+static_assert(is_same_v<decltype(([:^^foo<int>:](42))), int>);\n+static_assert(is_same_v<decltype((template [:^^foo:](0))), int>);\n+static_assert(is_same_v<decltype((template [:^^foo:]<int>(0))), int>);\n", "prefixes": [ "v2" ] }