[gcc r13-101] c++: Don't emit deprecated warnings or unavailable errors on lambda declarations

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:1c8e9bed9b9d46d479b83ae05b334543f66961fb

commit r13-101-g1c8e9bed9b9d46d479b83ae05b334543f66961fb
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed May 4 10:07:36 2022 +0200

    c++: Don't emit deprecated warnings or unavailable errors on lambda declarations
    
    On the following testcase, we emit deprecated warnings or unavailable errors
    even on merge declarations of those lambdas (the dg-bogus directives), while
    IMHO we should emit them only when something actually calls those lambdas.
    
    The following patch temporarily disables that diagnostics during
    maybe_add_lambda_conv_op.
    
    PR2173R1 also says that ambiguity between attribute-specifier-seq at the
    end of requires-clause and attribute-specifier-seq from lambda-expression
    should be resolved to attribute-specifier-seq for the latter.  Do we need
    to do anything about that?  I mean, can a valid requires-clause end with
    an attribute-specifier-seq?  Say operator int [[]] is valid primary
    expression, but requires operator int [[]] isn't valid, nor is
    requires operator int, no?
    
    2022-05-04  Jakub Jelinek  <jakub@redhat.com>
    
            * lambda.cc: Include decl.h.
            (maybe_add_lambda_conv_op): Temporarily override deprecated_state to
            UNAVAILABLE_DEPRECATED_SUPPRESS.
    
            * g++.dg/cpp23/lambda-attr1.C: New test.
            * g++.dg/cpp23/lambda-attr2.C: New test.

Diff:
---
 gcc/cp/lambda.cc                          | 12 +++++++---
 gcc/testsuite/g++.dg/cpp23/lambda-attr1.C | 37 +++++++++++++++++++++++++++++++
 gcc/testsuite/g++.dg/cpp23/lambda-attr2.C | 19 ++++++++++++++++
 3 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index 10834d6b143..afac53b6d7c 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "toplev.h"
 #include "gimplify.h"
 #include "target.h"
+#include "decl.h"
 
 /* Constructor for a lambda expression.  */
 
@@ -1192,9 +1193,14 @@ maybe_add_lambda_conv_op (tree type)
 	}
     }
   else
-    call = build_call_a (callop,
-			 direct_argvec->length (),
-			 direct_argvec->address ());
+    {
+      /* Don't warn on deprecated or unavailable lambda declarations, unless
+	 the lambda is actually called.  */
+      auto du = make_temp_override (deprecated_state,
+				    UNAVAILABLE_DEPRECATED_SUPPRESS);
+      call = build_call_a (callop, direct_argvec->length (),
+			   direct_argvec->address ());
+    }
 
   CALL_FROM_THUNK_P (call) = 1;
   SET_EXPR_LOCATION (call, UNKNOWN_LOCATION);
diff --git a/gcc/testsuite/g++.dg/cpp23/lambda-attr1.C b/gcc/testsuite/g++.dg/cpp23/lambda-attr1.C
new file mode 100644
index 00000000000..a653c732fca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/lambda-attr1.C
@@ -0,0 +1,37 @@
+// P2173R1 - Attributes on Lambda-Expressions
+// { dg-do compile { target c++11 } }
+
+void
+foo (bool x, bool y)
+{
+  auto a = [][[noreturn]] () {};	// { dg-warning "'noreturn' function does return" }
+  if (x)
+    a ();
+  auto b = [][[noreturn]] {};		// { dg-warning "'noreturn' function does return" }
+  if (y)
+    b ();
+  auto c = [] [[ deprecated ]] () {};	// { dg-bogus "is deprecated" }
+  c ();					// { dg-warning "'foo\\\(bool, bool\\\)::<lambda\\\(\\\)>' is deprecated" }
+  auto d = [][[deprecated]] {};		// { dg-bogus "is deprecated" }
+  d ();					// { dg-warning "'foo\\\(bool, bool\\\)::<lambda\\\(\\\)>' is deprecated" }
+#if __cpp_generic_lambdas >= 201304
+  auto e = [] [[deprecated]] (auto x) {};	// { dg-bogus "is deprecated" }
+  e (0.0);				// { dg-warning "'foo\\\(bool, bool\\\)::<lambda\\\(auto:1\\\)>\[^\n\r]*' is deprecated" "" { target c++14 } }
+#endif
+#if __cpp_generic_lambdas >= 201707
+  auto f = [] <typename T> [[deprecated]] (T) {};	// { dg-bogus "is deprecated" }
+  f (1);				// { dg-warning "'foo\\\(bool, bool\\\)::<lambda\\\(T\\\)>\[^\n\r]*' is deprecated" "" { target c++20 } }
+#endif
+  auto g = [][[nodiscard]](int) { return 1; };
+  g (1);				// { dg-warning "ignoring return value of 'foo\\\(bool, bool\\\)::<lambda\\\(int\\\)>', declared with attribute 'nodiscard'" }
+  auto h = [] [[nodiscard]] { return 0; };
+  h ();					// { dg-warning "ignoring return value of 'foo\\\(bool, bool\\\)::<lambda\\\(\\\)>', declared with attribute 'nodiscard'" }
+  auto i = [] [[ gnu::unavailable ]] () {};
+  auto j = [][[gnu::unavailable]] {};
+#if __cpp_generic_lambdas >= 201304
+  auto k = [] [[gnu::unavailable]] (auto x) {};	// { dg-bogus "is unavailable" }
+#endif
+#if __cpp_generic_lambdas >= 201707
+  auto l = [] <typename T> [[gnu::unavailable]] (T) {};	// { dg-bogus "is unavailable" }
+#endif
+}
diff --git a/gcc/testsuite/g++.dg/cpp23/lambda-attr2.C b/gcc/testsuite/g++.dg/cpp23/lambda-attr2.C
new file mode 100644
index 00000000000..0392b179b86
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/lambda-attr2.C
@@ -0,0 +1,19 @@
+// P2173R1 - Attributes on Lambda-Expressions
+// { dg-do compile { target c++11 } }
+
+void
+foo (bool x, bool y)
+{
+  auto i = [] [[ gnu::unavailable ]] () {};
+  i ();			// { dg-error "'foo\\\(bool, bool\\\)::<lambda\\\(\\\)>' is unavailable" }
+  auto j = [][[gnu::unavailable]] {};
+  j ();			// { dg-error "'foo\\\(bool, bool\\\)::<lambda\\\(\\\)>' is unavailable" }
+#if __cpp_generic_lambdas >= 201304
+  auto k = [] [[gnu::unavailable]] (auto x) {};	// { dg-bogus "is unavailable" }
+  k (0.0);		// { dg-error "'foo\\\(bool, bool\\\)::<lambda\\\(auto:1\\\)>\[^\n\r]*' is unavailable" "" { target c++14 } }
+#endif
+#if __cpp_generic_lambdas >= 201707
+  auto l = [] <typename T> [[gnu::unavailable]] (T) {};	// { dg-bogus "is unavailable" }
+  l (1);		// { dg-error "'foo\\\(bool, bool\\\)::<lambda\\\(T\\\)>\[^\n\r]*' is unavailable" "" { target c++20 } }
+#endif
+}