public inbox for gcc-cvs@sourceware.org
help / color / mirror / Atom feed
* [gcc r11-9391] c++: redundant explicit 'this' capture before C++20 [PR100493]
@ 2021-12-15 19:55 Patrick Palka
0 siblings, 0 replies; only message in thread
From: Patrick Palka @ 2021-12-15 19:55 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:d33f68865f6f71c28cfee5dfd91765e86d471ef1
commit r11-9391-gd33f68865f6f71c28cfee5dfd91765e86d471ef1
Author: Patrick Palka <ppalka@redhat.com>
Date: Mon Nov 29 07:52:47 2021 -0500
c++: redundant explicit 'this' capture before C++20 [PR100493]
As described in detail in the PR, in C++20 implicitly capturing 'this'
via a '=' capture default is deprecated, and in C++17 adding an explicit
'this' capture alongside a '=' capture default is diagnosed as redundant
(and is strictly speaking ill-formed). This means it's impossible to
write, in a forward-compatible way, a C++17 lambda that has a '=' capture
default and that also captures 'this' (implicitly or explicitly):
[=] { this; } // #1 deprecated in C++20, OK in C++17
// GCC issues a -Wdeprecated warning in C++20 mode
[=, this] { } // #2 ill-formed in C++17, OK in C++20
// GCC issues an unconditional warning in C++17 mode
This patch resolves this dilemma by downgrading the warning for #2 into
a -pedantic one. In passing, move it into the -Wc++20-extensions class
of warnings and adjust its wording accordingly.
PR c++/100493
gcc/cp/ChangeLog:
* parser.c (cp_parser_lambda_introducer): In C++17, don't
diagnose a redundant 'this' capture alongside a by-copy
capture default unless -pedantic. Move the diagnostic into
-Wc++20-extensions and adjust wording accordingly.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1z/lambda-this1.C: Adjust expected diagnostics.
* g++.dg/cpp1z/lambda-this8.C: New test.
* g++.dg/cpp2a/lambda-this3.C: Compile with -pedantic in C++17
to continue to diagnose redundant 'this' captures.
(cherry picked from commit 1420ff3efcff98df0e8c6f021a7ff24b5fc65043)
Diff:
---
gcc/cp/parser.c | 8 +++++---
gcc/testsuite/g++.dg/cpp1z/lambda-this1.C | 8 ++++----
gcc/testsuite/g++.dg/cpp1z/lambda-this8.C | 9 +++++++++
gcc/testsuite/g++.dg/cpp2a/lambda-this3.C | 2 +-
4 files changed, 19 insertions(+), 8 deletions(-)
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 8aac2d1803c..af10caa48be 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -11023,10 +11023,12 @@ cp_parser_lambda_introducer (cp_parser* parser, tree lambda_expr)
if (cp_lexer_next_token_is_keyword (parser->lexer, RID_THIS))
{
location_t loc = cp_lexer_peek_token (parser->lexer)->location;
- if (cxx_dialect < cxx20
+ if (cxx_dialect < cxx20 && pedantic
&& LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (lambda_expr) == CPLD_COPY)
- pedwarn (loc, 0, "explicit by-copy capture of %<this%> redundant "
- "with by-copy capture default");
+ pedwarn (loc, 0,
+ "explicit by-copy capture of %<this%> "
+ "with by-copy capture default only available with "
+ "%<-std=c++20%> or %<-std=gnu++20%>");
cp_lexer_consume_token (parser->lexer);
if (LAMBDA_EXPR_THIS_CAPTURE (lambda_expr))
pedwarn (input_location, 0,
diff --git a/gcc/testsuite/g++.dg/cpp1z/lambda-this1.C b/gcc/testsuite/g++.dg/cpp1z/lambda-this1.C
index b13ff8b9fc6..e12330a8291 100644
--- a/gcc/testsuite/g++.dg/cpp1z/lambda-this1.C
+++ b/gcc/testsuite/g++.dg/cpp1z/lambda-this1.C
@@ -18,7 +18,7 @@ struct A {
auto i = [=] { return a; }; // { dg-warning "implicit capture" "" { target c++2a } }
auto j = [&] { return a; };
// P0409R2 - C++2A lambda capture [=, this]
- auto k = [=, this] { return a; };// { dg-error "explicit by-copy capture of 'this' redundant with by-copy capture default" "" { target c++17_down } }
+ auto k = [=, this] { return a; };// { dg-error "explicit by-copy capture of 'this' with by-copy capture default only available with" "" { target c++17_down } }
auto l = [&, this] { return a; };
auto m = [=, *this] { return a; };// { dg-error "'*this' capture only available with" "" { target c++14_down } }
auto n = [&, *this] { return a; };// { dg-error "'*this' capture only available with" "" { target c++14_down } }
@@ -27,12 +27,12 @@ struct A {
// { dg-error "'*this' capture only available with" "" { target c++14_down } .-1 }
auto q = [=, this, *this] { return a; };// { dg-error "already captured 'this'" }
// { dg-error "'*this' capture only available with" "" { target c++14_down } .-1 }
- // { dg-error "explicit by-copy capture of 'this' redundant with by-copy capture default" "" { target c++17_down } .-2 }
+ // { dg-error "explicit by-copy capture of 'this' with by-copy capture default only available with" "" { target c++17_down } .-2 }
auto r = [=, this, this] { return a; };// { dg-error "already captured 'this'" }
- // { dg-error "explicit by-copy capture of 'this' redundant with by-copy capture default" "" { target c++17_down } .-1 }
+ // { dg-error "explicit by-copy capture of 'this' with by-copy capture default only available with" "" { target c++17_down } .-1 }
auto s = [=, *this, this] { return a; };// { dg-error "already captured 'this'" }
// { dg-error "'*this' capture only available with" "" { target c++14_down } .-1 }
- // { dg-error "explicit by-copy capture of 'this' redundant with by-copy capture default" "" { target c++17_down } .-2 }
+ // { dg-error "explicit by-copy capture of 'this' with by-copy capture default only available with" "" { target c++17_down } .-2 }
auto t = [=, *this, *this] { return a; };// { dg-error "already captured 'this'" }
// { dg-error "'*this' capture only available with" "" { target c++14_down } .-1 }
auto u = [&, this, *this] { return a; };// { dg-error "already captured 'this'" }
diff --git a/gcc/testsuite/g++.dg/cpp1z/lambda-this8.C b/gcc/testsuite/g++.dg/cpp1z/lambda-this8.C
new file mode 100644
index 00000000000..4542cbd8506
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/lambda-this8.C
@@ -0,0 +1,9 @@
+// PR c++/100493
+// { dg-do compile { target c++17 } }
+// { dg-options "" }
+
+struct A {
+ void f() {
+ [=, this] { };
+ }
+};
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-this3.C b/gcc/testsuite/g++.dg/cpp2a/lambda-this3.C
index 3e00e68e906..bc54a4c895d 100644
--- a/gcc/testsuite/g++.dg/cpp2a/lambda-this3.C
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-this3.C
@@ -1,6 +1,6 @@
// P0806R2
// { dg-do compile { target c++17 } }
-// { dg-options "" }
+// { dg-options "-pedantic" }
struct X {
int x;
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2021-12-15 19:55 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-12-15 19:55 [gcc r11-9391] c++: redundant explicit 'this' capture before C++20 [PR100493] Patrick Palka
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).