[committed] c++: Add -std=c++20.

[committed] c++: Add -std=c++20.

[Jason Merrill]

It's probably past time for this, but definitely now that we're done with
the final committee meeting of C++20.  This patch only adds the option and
adjusts the testsuite to recognize it; more extensive changes can wait for
the published standard.

Tested x86_64-pc-linux-gnu, applying to trunk.

gcc/ChangeLog
2020-02-15  Jason Merrill  <jason@redhat.com>

	* doc/invoke.texi (C Dialect Options): Add -std=c++20.

gcc/c-family/ChangeLog
2020-02-15  Jason Merrill  <jason@redhat.com>

	* c.opt: Add -std=c++20.

gcc/testsuite/ChangeLog
2020-02-15  Jason Merrill  <jason@redhat.com>

	* lib/target-supports.exp (check_effective_target_c++2a_only): Also
	look for -std=*++20.
	(check_effective_target_concepts): Use check_effective_target_c++2a.
---
 gcc/doc/invoke.texi                   | 10 ++++++----
 gcc/c-family/c.opt                    |  6 +++++-
 gcc/testsuite/lib/target-supports.exp |  9 ++++++---
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 597151670be..3e47d06f0d5 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -2078,13 +2078,15 @@ The name @samp{c++1z} is deprecated.
 GNU dialect of @option{-std=c++17}.
 The name @samp{gnu++1z} is deprecated.
 
-@item c++2a
-The next revision of the ISO C++ standard, tentatively planned for
+@item c++20
+@itemx c++2a
+The next revision of the ISO C++ standard, planned for
 2020.  Support is highly experimental, and will almost certainly
 change in incompatible ways in future releases.
 
-@item gnu++2a
-GNU dialect of @option{-std=c++2a}.  Support is highly experimental,
+@item gnu++20
+@itemx gnu++2a
+GNU dialect of @option{-std=c++20}.  Support is highly experimental,
 and will almost certainly change in incompatible ways in future
 releases.
 @end table
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 814ed17f7c4..b7e4fe146b2 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -2071,7 +2071,11 @@ Conform to the ISO 2017 C++ standard.
 
 std=c++2a
 C++ ObjC++
-Conform to the ISO 2020(?) C++ draft standard (experimental and incomplete support).
+Conform to the ISO 2020 C++ draft standard (experimental and incomplete support).
+
+std=c++20
+C++ ObjC++ Alias(std=c++2a)
+Conform to the ISO 2020 C++ draft standard (experimental and incomplete support).
 
 std=c11
 C ObjC
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index fb177c54aa8..ec462315860 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -8806,7 +8806,7 @@ proc check_effective_target_c++2a_only { } {
     if ![check_effective_target_c++] {
 	return 0
     }
-    if [check-flags { { } { } { -std=c++2a -std=gnu++2a } }] {
+    if [check-flags { { } { } { -std=c++2a -std=gnu++2a -std=c++20 -std=gnu++20 } }] {
 	return 1
     }
     if { $cxx_default == "c++20" && [check-flags { { } { } { } { -std=* } }] } {
@@ -8818,9 +8818,12 @@ proc check_effective_target_c++2a { } {
     return [check_effective_target_c++2a_only]
 }
 
-# Check for C++ Concepts TS support, i.e. -fconcepts flag.
+# Check for C++ Concepts support, i.e. -fconcepts flag.
 proc check_effective_target_concepts { } {
-    return [check-flags { "" { } { -fconcepts -std=*2a } }]
+    if [check_effective_target_c++2a] {
+	return 1
+    }
+    return [check-flags { "" { } { -fconcepts } }]
 }
 
 # Return 1 if expensive testcases should be run.

base-commit: 0b3c2eed35d608d6541ecf004a9576b4eae0b4ef
-- 
2.18.1

[PATCH] c++: use "C++20" in std header hints

[David Malcolm]

On Sat, 2020-02-15 at 22:21 +0100, Jason Merrill wrote:
> It's probably past time for this, but definitely now that we're done
> with
> the final committee meeting of C++20.  This patch only adds the
> option and
> adjusts the testsuite to recognize it; more extensive changes can
> wait for
> the published standard.

I don't know if this is premature, or too piecemeal, but this patch
improves hints such as:
  note: 'std::source_location' is only available from C++2a onwards
to
  note: 'std::source_location' is only available from C++20 onwards

Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.

OK for master?

gcc/cp/ChangeLog:
	* name-lookup.c (get_cxx_dialect_name): Return "C++20" for cxx2a.

gcc/testsuite/ChangeLog:
	* g++.dg/lookup/missing-std-include-8.C: Add test coverage for
	C++20 hints.
---
 gcc/cp/name-lookup.c                                | 2 +-
 gcc/testsuite/g++.dg/lookup/missing-std-include-8.C | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index e5638d2df91..7a87c3d2eb5 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -5856,7 +5856,7 @@ get_cxx_dialect_name (enum cxx_dialect dialect)
     case cxx17:
       return "C++17";
     case cxx2a:
-      return "C++2a";
+      return "C++20";
     }
 }
 
diff --git a/gcc/testsuite/g++.dg/lookup/missing-std-include-8.C b/gcc/testsuite/g++.dg/lookup/missing-std-include-8.C
index 73532c82968..716479761b4 100644
--- a/gcc/testsuite/g++.dg/lookup/missing-std-include-8.C
+++ b/gcc/testsuite/g++.dg/lookup/missing-std-include-8.C
@@ -43,6 +43,10 @@ std::shared_timed_mutex m; // { dg-error "'shared_timed_mutex' in namespace 'std
 std::string_view sv; // { dg-error "'string_view' in namespace 'std' does not name a type" }
 // { dg-message "'std::string_view' is only available from C\\+\\+17 onwards" "" { target *-*-* } .-1 }
 
+/* Since C++20: */
+std::source_location loc; // { dg-error "'source_location' in namespace 'std' does not name a type" }
+// { dg-message "'std::source_location' is only available from C\\+\\+20 onwards" "" { target *-*-* } .-1 }
+
 /* Verify interaction with "using namespace std;".  */
 using namespace std;
 void test_via_using_directive ()
-- 
2.21.0

Re: [PATCH] c++: use "C++20" in std header hints

[Jason Merrill]

On 2/18/20 2:14 AM, David Malcolm wrote:
> On Sat, 2020-02-15 at 22:21 +0100, Jason Merrill wrote:
>> It's probably past time for this, but definitely now that we're done
>> with
>> the final committee meeting of C++20.  This patch only adds the
>> option and
>> adjusts the testsuite to recognize it; more extensive changes can
>> wait for
>> the published standard.
> 
> I don't know if this is premature, or too piecemeal, but this patch
> improves hints such as:
>    note: 'std::source_location' is only available from C++2a onwards
> to
>    note: 'std::source_location' is only available from C++20 onwards
> 
> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
> 
> OK for master?

Why change this in just this one place?

Jason