From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id B6DC13858D39 for ; Fri, 1 Mar 2024 15:08:18 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org B6DC13858D39 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org B6DC13858D39 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1709305701; cv=none; b=hy9R09OToCiPfMrY4iuQqYhzpA2RwEF97dMHkt7JH3lvD2RxFuR3dhdo4CQGQRnKtAJw17rPtqcI7p8PwXYIcGEH9xf9ZdbrV0Os7TQEuvhSQw2Am6/Lnt0mPj0VDVdjTCcFdTYBrh/Gv7gy64YThMgEiAo0ZgFV72i+4SgqX7Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1709305701; c=relaxed/simple; bh=K257Oc5y6U4K9yjLqErR5KfjX0AC8m275OSxbyZKHEY=; h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version; b=bntOFbmfLgWzQUchXMvyXdRvv86rokdSEppBWjLKxBMKrZnJ9WPMvXu9Bl6jZUVNF2GwWdtpttp8cRsjpjwdIH6un/0c/+V0P3hRfPDbpEdrCe+5/iIkZmM7XQwdcV6QcK+RegIA3cUuM877CSTVX3hVXAfaVp818100j0+IVtI= ARC-Authentication-Results: i=1; server2.sourceware.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709305698; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=JRNJMSwa5L6hKsysSP+X9YFhYAk9l+7vvGv2AEKYepM=; b=KJQrM23i77c1B1QCNOypjiLeAzcarY8ox5cOcY5tgJWNykpoYYPldsGt8DwnsaXgBA7Ega qQXP/B+a121Wjq3drxOBWBbgSW1ayd6IRqAADAR/1aMeiuFG+QXvJF2rrF2XAMcYtM1Li8 kW2KQpHZmzLVOsgYbnxgqf/uuIIj3Sk= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-622-7HgALrUhPHCszxcgBEDgRA-1; Fri, 01 Mar 2024 10:08:14 -0500 X-MC-Unique: 7HgALrUhPHCszxcgBEDgRA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 00C7D280640F; Fri, 1 Mar 2024 15:08:14 +0000 (UTC) Received: from localhost (unknown [10.42.28.150]) by smtp.corp.redhat.com (Postfix) with ESMTP id 921671121312; Fri, 1 Mar 2024 15:08:13 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [PATCH] libstdc++: Better diagnostics for std::format errors Date: Fri, 1 Mar 2024 14:44:30 +0000 Message-ID: <20240301150812.95213-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Does the text of these new diagnostics look good? There are of course other ways for a type to be not-formattable (e.g. the formatter::format member doesn't return the right type or has some other kind of incorrect signature, or the formatter::parse member isn't constexpr) but we can't predict/detect them all reliably. This just attempts to give a user-friendly explanation for a couple of common mistakes. It should not have any false positives, because the basic_format_arg constructor requires __formattable_with<_Tp, _Context> so if either of these assertions fails, constructing __arg will fail too. The static_assert only adds a more readable error for a compilation that's going to fail anyway. Tested x86_64-linux. -- >8 -- This adds two new static_assert messages to the internals of std::make_format_args to give better diagnostics for invalid format args. Rather than just getting an error saying that basic_format_arg cannot be constructed, we get more specific errors for the cases where std::formatter isn't specialized for the type at all, and where it's specialized but only meets the BasicFormatter requirements and so can only format non-const arguments. Also add a test for the existing static_assert when constructing a format_string for non-formattable args. libstdc++-v3/ChangeLog: * include/std/format (_Arg_store::_S_make_elt): Add two static_assert checks to give more user-friendly error messages. * testsuite/lib/prune.exp (libstdc++-dg-prune): Prune another form of "in requirements with" note. * testsuite/std/format/arguments/args_neg.cc: Check for user-friendly diagnostics for non-formattable types. * testsuite/std/format/string_neg.cc: Likewise. --- libstdc++-v3/include/std/format | 13 +++++++ libstdc++-v3/testsuite/lib/prune.exp | 1 + .../std/format/arguments/args_neg.cc | 34 ++++++++++++++++++- .../testsuite/std/format/string_neg.cc | 4 +++ 4 files changed, 51 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format index ee189f9086c..1e839e88db4 100644 --- a/libstdc++-v3/include/std/format +++ b/libstdc++-v3/include/std/format @@ -3704,6 +3704,19 @@ namespace __format static _Element_t _S_make_elt(_Tp& __v) { + using _Tq = remove_const_t<_Tp>; + using _CharT = typename _Context::char_type; + static_assert(is_default_constructible_v>, + "std::formatter must be specialized for the type " + "of each format arg"); + using __format::__formattable_with; + if constexpr (is_const_v<_Tp>) + if constexpr (!__formattable_with<_Tp, _Context>) + if constexpr (__formattable_with<_Tq, _Context>) + static_assert(__formattable_with<_Tp, _Context>, + "format arg must be non-const because its " + "std::formatter specialization has a " + "non-const reference parameter"); basic_format_arg<_Context> __arg(__v); if constexpr (_S_values_only) return __arg._M_val; diff --git a/libstdc++-v3/testsuite/lib/prune.exp b/libstdc++-v3/testsuite/lib/prune.exp index 24a15ccad22..071dcf34c1e 100644 --- a/libstdc++-v3/testsuite/lib/prune.exp +++ b/libstdc++-v3/testsuite/lib/prune.exp @@ -54,6 +54,7 @@ proc libstdc++-dg-prune { system text } { regsub -all "(^|\n)\[^\n\]*: . skipping \[0-9\]* instantiation contexts \[^\n\]*" $text "" text regsub -all "(^|\n)\[^\n\]*: in .constexpr. expansion \[^\n\]*" $text "" text regsub -all "(^|\n)\[^\n\]*: in requirements .with\[^\n\]*" $text "" text + regsub -all "(^|\n)\[^\n\]*: in requirements with\[^\n\]*" $text "" text regsub -all "(^|\n) inlined from \[^\n\]*" $text "" text # Why doesn't GCC need these to strip header context? regsub -all "(^|\n)In file included from \[^\n\]*" $text "" text diff --git a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc index 16ac3040146..ded56fe63ab 100644 --- a/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc +++ b/libstdc++-v3/testsuite/std/format/arguments/args_neg.cc @@ -6,7 +6,39 @@ std::string rval() { return "path/etic/experience"; } -void f() +void test_rval() { (void)std::make_format_args(rval()); // { dg-error "cannot bind non-const lvalue reference" } } + +void test_missing_specialization() +{ + struct X { }; + X x; + (void)std::make_format_args(x); // { dg-error "here" } +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 } +} + +struct Y { }; +template<> class std::formatter { +public: + constexpr typename format_parse_context::iterator + parse(format_parse_context& c) + { return c.begin(); } + + template + typename C::iterator format(Y&, C&) const; +}; + +void test(std::formatter& f, std::format_parse_context& pc) { + f.parse(pc); +} + +void test_const_arg() +{ + const Y y; + (void)std::make_format_args(y); // { dg-error "here" } +// { dg-error "format arg must be non-const" "" { target *-*-* } 0 } +} + +// { dg-prune-output "no matching function for call to .*::basic_format_arg<" } diff --git a/libstdc++-v3/testsuite/std/format/string_neg.cc b/libstdc++-v3/testsuite/std/format/string_neg.cc index 69bcc736cff..d5963145b18 100644 --- a/libstdc++-v3/testsuite/std/format/string_neg.cc +++ b/libstdc++-v3/testsuite/std/format/string_neg.cc @@ -4,3 +4,7 @@ auto s = std::format(" {9} "); // { dg-error "call to consteval function" } // { dg-error "invalid.arg.id" "" { target *-*-* } 0 } + +struct X { }; +std::format_string str(""); // dg-error "here" } +// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 } -- 2.43.2