[Bug c++/57170] Diagnostic for a negative case when switching over unsigned comes from -Wsign-conversion instead of -Wpedantic or -Wnarrowing
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 --- Comment #7 from Eric Gallager --- (In reply to Jonathan Wakely from comment #6) > It should be an error, not a warning. For other narrowing conversions > involving constants we do actually use -Wnarrowing (but still defaulting to > an error) so I guess my last comment was wrong. > > Or it could just be an unconditional error. Or a permerror, so -fpermissive > would allow it. I'd prefer the permerror so -fpermissive would allow it, but... > > The code that handles this is in gcc/c-family/c-common.c so isn't > C++-specific. I'm not sure if that code has enough context to know if the > conversion happens in a constant expression where narrowing conversions are > disallowed. ...if it's in c-common.c... are permerrors allowed to come from there even though -fpermissive is only for C++? > > > #0 unsafe_conversion_p (loc=, loc@entry=267203, > type=type@entry=0x7013c690, expr=expr@entry=0x701401f8, > result=result@entry=0x70140048, produce_warns=produce_warns@entry=true) > at /home/jwakely/src/gcc/gcc/gcc/c-family/c-common.c:1261 > #1 0x008cdb27 in conversion_warning (loc=267203, > type=type@entry=0x7013c690, expr=expr@entry=0x701401f8, > result=result@entry=0x70140048) at > /home/jwakely/src/gcc/gcc/gcc/c-family/c-warn.c:1127 > #2 0x008d11d1 in warnings_for_convert_and_check (loc= out>, loc@entry=267203, type=type@entry=0x7013c690, > expr=expr@entry=0x701401f8, result=result@entry=0x70140048) at > /home/jwakely/src/gcc/gcc/gcc/c-family/c-warn.c:1278 > #3 0x0085df41 in convert_and_check (loc=loc@entry=267203, > type=type@entry=0x7013c690, expr=0x701401f8) at > /home/jwakely/src/gcc/gcc/gcc/c-family/c-common.c:1548 > #4 0x00886a55 in c_add_case_label (loc=loc@entry=267203, > cases=0x24ad5e0, cond=cond@entry=0x77ff6cf0, > orig_type=orig_type@entry=0x7013c690, low_value=, > low_value@entry=0x701401f8, high_value=, > high_value@entry=0x0, outside_range_p=0x24abff0) > at /home/jwakely/src/gcc/gcc/gcc/c-family/c-common.c:4780 > #5 0x0066b1fa in finish_case_label (loc=267203, > low_value=, low_value@entry=0x701401f8, > high_value=) at /home/jwakely/src/gcc/gcc/gcc/cp/decl.c:3669 > #6 0x007309e9 in cp_parser_label_for_labeled_statement > (parser=parser@entry=0x77ff6ab0, attributes=attributes@entry=0x0) at > /home/jwakely/src/gcc/gcc/gcc/cp/parser.c:11072
[Bug c++/57170] Diagnostic for a negative case when switching over unsigned comes from -Wsign-conversion instead of -Wpedantic or -Wnarrowing
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 --- Comment #6 from Jonathan Wakely --- It should be an error, not a warning. For other narrowing conversions involving constants we do actually use -Wnarrowing (but still defaulting to an error) so I guess my last comment was wrong. Or it could just be an unconditional error. Or a permerror, so -fpermissive would allow it. The code that handles this is in gcc/c-family/c-common.c so isn't C++-specific. I'm not sure if that code has enough context to know if the conversion happens in a constant expression where narrowing conversions are disallowed. #0 unsafe_conversion_p (loc=, loc@entry=267203, type=type@entry=0x7013c690, expr=expr@entry=0x701401f8, result=result@entry=0x70140048, produce_warns=produce_warns@entry=true) at /home/jwakely/src/gcc/gcc/gcc/c-family/c-common.c:1261 #1 0x008cdb27 in conversion_warning (loc=267203, type=type@entry=0x7013c690, expr=expr@entry=0x701401f8, result=result@entry=0x70140048) at /home/jwakely/src/gcc/gcc/gcc/c-family/c-warn.c:1127 #2 0x008d11d1 in warnings_for_convert_and_check (loc=, loc@entry=267203, type=type@entry=0x7013c690, expr=expr@entry=0x701401f8, result=result@entry=0x70140048) at /home/jwakely/src/gcc/gcc/gcc/c-family/c-warn.c:1278 #3 0x0085df41 in convert_and_check (loc=loc@entry=267203, type=type@entry=0x7013c690, expr=0x701401f8) at /home/jwakely/src/gcc/gcc/gcc/c-family/c-common.c:1548 #4 0x00886a55 in c_add_case_label (loc=loc@entry=267203, cases=0x24ad5e0, cond=cond@entry=0x77ff6cf0, orig_type=orig_type@entry=0x7013c690, low_value=, low_value@entry=0x701401f8, high_value=, high_value@entry=0x0, outside_range_p=0x24abff0) at /home/jwakely/src/gcc/gcc/gcc/c-family/c-common.c:4780 #5 0x0066b1fa in finish_case_label (loc=267203, low_value=, low_value@entry=0x701401f8, high_value=) at /home/jwakely/src/gcc/gcc/gcc/cp/decl.c:3669 #6 0x007309e9 in cp_parser_label_for_labeled_statement (parser=parser@entry=0x77ff6ab0, attributes=attributes@entry=0x0) at /home/jwakely/src/gcc/gcc/gcc/cp/parser.c:11072
[Bug c++/57170] Diagnostic for a negative case when switching over unsigned comes from -Wsign-conversion instead of -Wpedantic or -Wnarrowing
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 --- Comment #5 from Eric Gallager --- (In reply to Jonathan Wakely from comment #4) > Diagnostics for narrowing conversions involving non-constants are controlled > by -Wnarrowing (allowing them to be either warnings or errors). But > narrowing conversions involving constants are always errors. Case labels > must be constants, so making this depend on -Wnarrowing wouldn't seem > appropriate to me. So -Wpedantic instead? Or -fpermissive?
[Bug c++/57170] Diagnostic for a negative case when switching over unsigned comes from -Wsign-conversion instead of -Wpedantic or -Wnarrowing
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 --- Comment #4 from Jonathan Wakely --- Diagnostics for narrowing conversions involving non-constants are controlled by -Wnarrowing (allowing them to be either warnings or errors). But narrowing conversions involving constants are always errors. Case labels must be constants, so making this depend on -Wnarrowing wouldn't seem appropriate to me.
[Bug c++/57170] Diagnostic for a negative case when switching over unsigned comes from -Wsign-conversion instead of -Wpedantic or -Wnarrowing
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57170 Eric Gallager changed: What|Removed |Added Keywords||accepts-invalid Status|RESOLVED|NEW Last reconfirmed||2017-08-24 Resolution|INVALID |--- Summary|No diagnostic for a |Diagnostic for a negative |negative case when |case when switching over |switching over unsigned |unsigned comes from ||-Wsign-conversion instead ||of -Wpedantic or ||-Wnarrowing Ever confirmed|0 |1 --- Comment #3 from Eric Gallager --- (In reply to TC from comment #2) > As comment #0 alluded to - perhaps a bit opaquely - this code is ill-formed > in C++11 and later. [stmt.switch] requires the case expression to be "a > converted constant expression ([expr.const]) of the promoted type of the > switch condition", and a narrowing conversion cannot be used in a converted > constant expression. The standard requires a diagnostic, which GCC fails to > provide even with -pedantic. > > (Meanwhile, using unsigned char or unsigned short there is actually > well-formed if they get promoted to int as they usually do.) > > So, unless you are saying that GCC's full conformance mode requires > -Wsign-conversion, I don't see how this bug is invalid. OK, reopening and retitling to make it clearer.
