[gcc r15-7347] c++: Fix up pedwarn for capturing structured bindings in lambdas [PR118719]

[Jakub Jelinek via Gcc-cvs]

https://gcc.gnu.org/g:4b2726a62ddfe958302d6790725503ac09b28f11

commit r15-7347-g4b2726a62ddfe958302d6790725503ac09b28f11
Author: Jakub Jelinek <ja...@redhat.com>
Date:   Tue Feb 4 09:23:15 2025 +0100

    c++: Fix up pedwarn for capturing structured bindings in lambdas [PR118719]
    
    As mentioned in the PR, this pedwarni is desirable for the implicit or
    explicit capturing of structured bindings in C++17, but in the case of
    init-captures the initializer is just some expression and that can include
    structured bindings.
    
    So, the following patch limits the warning to non-explicit_init_p.
    
    2025-02-04  Jakub Jelinek  <ja...@redhat.com>
    
            PR c++/118719
            * lambda.cc (add_capture): Only pedwarn about capturing structured
            binding if !explicit_init_p.
    
            * g++.dg/cpp1z/decomp63.C: New test.

Diff:
---
 gcc/cp/lambda.cc                      |  2 +-
 gcc/testsuite/g++.dg/cpp1z/decomp63.C | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index 5593636eaf8e..2d86e9892f99 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -613,7 +613,7 @@ add_capture (tree lambda, tree id, tree orig_init, bool 
by_reference_p,
            return error_mark_node;
        }
 
-      if (cxx_dialect < cxx20)
+      if (cxx_dialect < cxx20 && !explicit_init_p)
        {
          auto_diagnostic_group d;
          tree stripped_init = tree_strip_any_location_wrapper (initializer);
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp63.C 
b/gcc/testsuite/g++.dg/cpp1z/decomp63.C
new file mode 100644
index 000000000000..50049255efb1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp63.C
@@ -0,0 +1,18 @@
+// PR c++/118719
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+int
+main ()
+{
+  int a[] = { 42 };
+  auto [x] = a;                                        // { dg-warning 
"structured bindings only available with" "" { target c++14_down } }
+                                               // { dg-message "declared here" 
"" { target c++17_down } .-1 }
+  [=] () { int b = x; (void) b; };             // { dg-warning "captured 
structured bindings are a C\\\+\\\+20 extension" "" { target c++17_down } }
+  [&] () { int b = x; (void) b; };             // { dg-warning "captured 
structured bindings are a C\\\+\\\+20 extension" "" { target c++17_down } }
+  [x] () { int b = x; (void) b; };             // { dg-warning "captured 
structured bindings are a C\\\+\\\+20 extension" "" { target c++17_down } }
+  [&x] () { int b = x; (void) b; };            // { dg-warning "captured 
structured bindings are a C\\\+\\\+20 extension" "" { target c++17_down } }
+  [x = x] () { int b = x; (void) b; };         // { dg-warning "lambda capture 
initializers only available with" "" { target c++11_only } }
+  [y = x] () { int b = y; (void) b; };         // { dg-warning "lambda capture 
initializers only available with" "" { target c++11_only } }
+  [y = x * 2] () { int b = y; (void) b; };     // { dg-warning "lambda capture 
initializers only available with" "" { target c++11_only } }
+}