| Message ID | 20230217203209.2141339-1-jason@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC] c++: static_assert (false) in template [DR2518] | expand |
On Fri, Feb 17, 2023 at 03:32:09PM -0500, Jason Merrill via Gcc-patches wrote: > Tested x86_64-pc-linux-gnu. This isn't really a regression fix, but it's very > safe, and fixes a longstanding annoyance, so I'm leaning toward putting it into > GCC 13. Thoughts? I think it is ok for GCC 13. I bet for the testsuite coverage of the whole DR2518 wording we have already tons of testcases which verify we actually error on #error directives and warn on #warning directives and error in failed static_assert unless in uninstantiated templates that it isn't worth repeating them in the dr2518*.C testcase(s). I'm a little bit surprised we didn't check for errors from static_asserts failed asserts in uninstantiated templates... Jakub
On Fri, Feb 17, 2023 at 03:32:09PM -0500, Jason Merrill via Gcc-patches wrote: > Tested x86_64-pc-linux-gnu. This isn't really a regression fix, but it's very > safe, and fixes a longstanding annoyance, so I'm leaning toward putting it into > GCC 13. Thoughts? LGTM. > -- 8< -- > > For a long time, people have expected to be able to write > static_assert (false) in a template and only have it diagnosed if the > template is instantiated, but we (and other implementations) gave an error > about the uninstantiated template because the standard says that if no valid > instantiation of the template is possible, the program is ill-formed, no > diagnostic required, and we try to diagnose IFNDR things when feasible. > > At the meeting last week we were looking at CWG2518, which wanted to specify > that an implementation must not accept a program containing a failing #error > or static_assert. We also looked at P2593, which proposed allowing > static_assert in an uninstantiated template. We ended up combining these > two in order to avoid requiring implementations to reject programs with > static_assert (false) in uninstantiated templates. > > The committee accepted this as a DR, so I'm making the change to all > standard modes. This behavior was also conformant previously, since no > diagnostic was required in this case. > > We continue to diagnose non-constant or otherwise ill-formed conditions, so > no changes to existing tests were needed. > > DR 2518 > PR c++/52809 > PR c++/53638 > PR c++/87389 > PR c++/89741 > PR c++/92099 > PR c++/104041 > PR c++/104691 > > gcc/cp/ChangeLog: > > * semantics.cc (finish_static_assert): Don't diagnose in > template context. > > gcc/testsuite/ChangeLog: > > * g++.dg/DRs/dr2518.C: New test. > --- > gcc/cp/semantics.cc | 17 ++++++++++------- > gcc/testsuite/g++.dg/DRs/dr2518.C | 7 +++++++ > 2 files changed, 17 insertions(+), 7 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/DRs/dr2518.C > > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc > index c2df0b69b30..79b7cc72f21 100644 > --- a/gcc/cp/semantics.cc > +++ b/gcc/cp/semantics.cc > @@ -11232,14 +11232,16 @@ finish_static_assert (tree condition, tree message, location_t location, > if (check_for_bare_parameter_packs (condition)) > condition = error_mark_node; > > + /* Save the condition in case it was a concept check. */ > + tree orig_condition = condition; > + > if (instantiation_dependent_expression_p (condition)) > { > /* We're in a template; build a STATIC_ASSERT and put it in > the right place. */ > - tree assertion; > - > - assertion = make_node (STATIC_ASSERT); > - STATIC_ASSERT_CONDITION (assertion) = condition; > + defer: > + tree assertion = make_node (STATIC_ASSERT); > + STATIC_ASSERT_CONDITION (assertion) = orig_condition; > STATIC_ASSERT_MESSAGE (assertion) = message; > STATIC_ASSERT_SOURCE_LOCATION (assertion) = location; > > @@ -11253,9 +11255,6 @@ finish_static_assert (tree condition, tree message, location_t location, > return; > } > > - /* Save the condition in case it was a concept check. */ > - tree orig_condition = condition; > - > /* Fold the expression and convert it to a boolean value. */ > condition = contextual_conv_bool (condition, complain); > condition = fold_non_dependent_expr (condition, complain, > @@ -11270,6 +11269,10 @@ finish_static_assert (tree condition, tree message, location_t location, > > if (integer_zerop (condition)) > { > + /* CWG2518: static_assert failure in a template is not IFNDR. */ > + if (processing_template_decl) > + goto defer; > + > int sz = TREE_INT_CST_LOW (TYPE_SIZE_UNIT > (TREE_TYPE (TREE_TYPE (message)))); > int len = TREE_STRING_LENGTH (message) / sz - 1; > diff --git a/gcc/testsuite/g++.dg/DRs/dr2518.C b/gcc/testsuite/g++.dg/DRs/dr2518.C > new file mode 100644 > index 00000000000..240186211e6 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/DRs/dr2518.C > @@ -0,0 +1,7 @@ > +// CWG 2518 > +// { dg-do compile { target c++11 } } > + > +template <class T> void f() > +{ > + static_assert (false, ""); > +} > > base-commit: 07f497c2da3600cc99cd7d1b5c6726972fb2b5a1 > -- > 2.31.1 > Marek
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc index c2df0b69b30..79b7cc72f21 100644 --- a/gcc/cp/semantics.cc +++ b/gcc/cp/semantics.cc @@ -11232,14 +11232,16 @@ finish_static_assert (tree condition, tree message, location_t location, if (check_for_bare_parameter_packs (condition)) condition = error_mark_node; + /* Save the condition in case it was a concept check. */ + tree orig_condition = condition; + if (instantiation_dependent_expression_p (condition)) { /* We're in a template; build a STATIC_ASSERT and put it in the right place. */ - tree assertion; - - assertion = make_node (STATIC_ASSERT); - STATIC_ASSERT_CONDITION (assertion) = condition; + defer: + tree assertion = make_node (STATIC_ASSERT); + STATIC_ASSERT_CONDITION (assertion) = orig_condition; STATIC_ASSERT_MESSAGE (assertion) = message; STATIC_ASSERT_SOURCE_LOCATION (assertion) = location; @@ -11253,9 +11255,6 @@ finish_static_assert (tree condition, tree message, location_t location, return; } - /* Save the condition in case it was a concept check. */ - tree orig_condition = condition; - /* Fold the expression and convert it to a boolean value. */ condition = contextual_conv_bool (condition, complain); condition = fold_non_dependent_expr (condition, complain, @@ -11270,6 +11269,10 @@ finish_static_assert (tree condition, tree message, location_t location, if (integer_zerop (condition)) { + /* CWG2518: static_assert failure in a template is not IFNDR. */ + if (processing_template_decl) + goto defer; + int sz = TREE_INT_CST_LOW (TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (message)))); int len = TREE_STRING_LENGTH (message) / sz - 1; diff --git a/gcc/testsuite/g++.dg/DRs/dr2518.C b/gcc/testsuite/g++.dg/DRs/dr2518.C new file mode 100644 index 00000000000..240186211e6 --- /dev/null +++ b/gcc/testsuite/g++.dg/DRs/dr2518.C @@ -0,0 +1,7 @@ +// CWG 2518 +// { dg-do compile { target c++11 } } + +template <class T> void f() +{ + static_assert (false, ""); +}