c++: lambda capturing structured bindings [PR85889]
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Commit Message
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for 15? (Or even trunk?)
-- >8 --
<https://wg21.link/p1381r1> clarifies that it's OK to capture structured
bindings.
[expr.prim.lambda.capture]/4 says "The identifier in a simple-capture shall
denote a local entity" and [basic.pre]/3: "An entity is a [...] structured
binding".
It doesn't appear that this was made a DR, so, strictly speaking, we
should have a -Wc++20-extensions warning, like clang++.
PR c++/85889
gcc/cp/ChangeLog:
* lambda.cc (add_capture): Add a pedwarn for capturing structured
bindings.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/decomp3.C: Use -Wno-c++20-extensions.
* g++.dg/cpp1z/decomp60.C: New test.
---
gcc/cp/lambda.cc | 9 +++++++++
gcc/testsuite/g++.dg/cpp1z/decomp60.C | 12 ++++++++++++
gcc/testsuite/g++.dg/cpp2a/decomp3.C | 2 +-
3 files changed, 22 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1z/decomp60.C
base-commit: 574fd1f17f100c7c355ad26bc525ab5a3386bb2d
Comments
On Fri, Mar 01, 2024 at 07:58:24PM -0500, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for 15? (Or even trunk?)
>
> -- >8 --
> <https://wg21.link/p1381r1> clarifies that it's OK to capture structured
> bindings.
>
> [expr.prim.lambda.capture]/4 says "The identifier in a simple-capture shall
> denote a local entity" and [basic.pre]/3: "An entity is a [...] structured
> binding".
>
> It doesn't appear that this was made a DR, so, strictly speaking, we
> should have a -Wc++20-extensions warning, like clang++.
>
> PR c++/85889
>
> gcc/cp/ChangeLog:
>
> * lambda.cc (add_capture): Add a pedwarn for capturing structured
> bindings.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/decomp3.C: Use -Wno-c++20-extensions.
> * g++.dg/cpp1z/decomp60.C: New test.
> ---
> gcc/cp/lambda.cc | 9 +++++++++
> gcc/testsuite/g++.dg/cpp1z/decomp60.C | 12 ++++++++++++
> gcc/testsuite/g++.dg/cpp2a/decomp3.C | 2 +-
> 3 files changed, 22 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp1z/decomp60.C
>
> diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
> index 4b1f9391fee..470f9d2c4f1 100644
> --- a/gcc/cp/lambda.cc
> +++ b/gcc/cp/lambda.cc
> @@ -607,6 +607,15 @@ add_capture (tree lambda, tree id, tree orig_init, bool by_reference_p,
> TCTX_CAPTURE_BY_COPY, type))
> return error_mark_node;
> }
> +
> + if (cxx_dialect < cxx20)
> + {
> + tree stripped_init = tree_strip_any_location_wrapper (initializer);
I was missing an auto_diagnostic_group here. Fixed.
> + if (DECL_DECOMPOSITION_P (stripped_init)
> + && pedwarn (input_location, OPT_Wc__20_extensions,
> + "captured structured bindings are a C++20 extension"))
> + inform (DECL_SOURCE_LOCATION (stripped_init), "declared here");
@@ -607,6 +607,15 @@ add_capture (tree lambda, tree id, tree orig_init, bool by_reference_p,
TCTX_CAPTURE_BY_COPY, type))
return error_mark_node;
}
+
+ if (cxx_dialect < cxx20)
+ {
+ tree stripped_init = tree_strip_any_location_wrapper (initializer);
+ if (DECL_DECOMPOSITION_P (stripped_init)
+ && pedwarn (input_location, OPT_Wc__20_extensions,
+ "captured structured bindings are a C++20 extension"))
+ inform (DECL_SOURCE_LOCATION (stripped_init), "declared here");
+ }
}
/* Add __ to the beginning of the field name so that user code
new file mode 100644
@@ -0,0 +1,12 @@
+// PR c++/85889
+// { dg-do compile { target c++17 } }
+// { dg-options "" }
+
+struct X { int i, j; };
+void f() {
+ X x{};
+ auto [i, j] = x;
+ [&i]() { }; // { dg-warning "captured structured bindings" "" { target c++17_only } }
+ [i]() { }; // { dg-warning "captured structured bindings" "" { target c++17_only } }
+}
+
@@ -1,6 +1,6 @@
// P1381R1
// { dg-do compile { target c++11 } }
-// { dg-options "" }
+// { dg-options "-Wno-c++20-extensions" }
struct Foo { int a : 1; int b; };