| Message ID | 20160219124235.GF3171@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 02/19/2016 07:42 AM, Jonathan Wakely wrote: > In PR69864 Manu suggests improving the docs to explain that > -Wnarrowing sometimes produces errors not warnings. > > I think the right way to do that is clarify how it interacts with > -std. Specifically that the effect of -Wnarrowing listed first in the > manual *only* applies to C++98 modes, For all later modes (not just > with -std=c++11 as it says now), narrowing conversions produce errors > or warnings by default. > > OK for trunk? OK, thanks. Jason
On 02/19/2016 12:01 PM, Jason Merrill wrote: > On 02/19/2016 07:42 AM, Jonathan Wakely wrote: >> In PR69864 Manu suggests improving the docs to explain that >> -Wnarrowing sometimes produces errors not warnings. >> >> I think the right way to do that is clarify how it interacts with >> -std. Specifically that the effect of -Wnarrowing listed first in the >> manual *only* applies to C++98 modes, For all later modes (not just >> with -std=c++11 as it says now), narrowing conversions produce errors >> or warnings by default. >> >> OK for trunk? > > OK, thanks. I suppose the patch is OK as it stands, but I was going to suggest restructuring it so that it talks about the default behavior first and what it does with non-default -std= options after that, instead of vice-versa. Unfortunately I am backlogged on other things right now and it might take me a day or two before I have time to come up with some alternate wording. If we are in a rush, go ahead and commit the existing patch meanwhile, I guess. -Sandra
On 19/02/16 13:17 -0700, Sandra Loosemore wrote: >On 02/19/2016 12:01 PM, Jason Merrill wrote: >>On 02/19/2016 07:42 AM, Jonathan Wakely wrote: >>>In PR69864 Manu suggests improving the docs to explain that >>>-Wnarrowing sometimes produces errors not warnings. >>> >>>I think the right way to do that is clarify how it interacts with >>>-std. Specifically that the effect of -Wnarrowing listed first in the >>>manual *only* applies to C++98 modes, For all later modes (not just >>>with -std=c++11 as it says now), narrowing conversions produce errors >>>or warnings by default. >>> >>>OK for trunk? >> >>OK, thanks. > >I suppose the patch is OK as it stands, but I was going to suggest >restructuring it so that it talks about the default behavior first and >what it does with non-default -std= options after that, instead of >vice-versa. Unfortunately I am backlogged on other things right now >and it might take me a day or two before I have time to come up with >some alternate wording. If we are in a rush, go ahead and commit the >existing patch meanwhile, I guess. I did wonder about that but couldn't come up with wording I liked. I went ahead and committed it after Jason's OK, but I can take another look at it next week.
commit b78b2728d8d946bd92843f6155cdd2415682da09
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Feb 19 12:14:33 2016 +0000
* doc/invoke.texi (C++ Dialect Options): Clarify interaction of
-Wnarrowing with -std.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2bd793d..c1ab788 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -2756,7 +2756,8 @@ Requires @option{-flto} to be enabled. Enabled by default.
@item -Wnarrowing @r{(C++ and Objective-C++ only)}
@opindex Wnarrowing
@opindex Wno-narrowing
-Warn when a narrowing conversion prohibited by C++11 occurs within
+With @option{-std=gnu++98} or @option{-std=c++98}, warn when a narrowing
+conversion prohibited by C++11 occurs within
@samp{@{ @}}, e.g.
@smallexample
@@ -2765,10 +2766,13 @@ int i = @{ 2.2 @}; // error: narrowing from double to int
This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
-With @option{-std=c++11}, @option{-Wno-narrowing} suppresses the diagnostic
-required by the standard. Note that this does not affect the meaning
-of well-formed code; narrowing conversions are still considered
-ill-formed in SFINAE context.
+When a later standard is in effect, e.g. when using @option{-std=c++11},
+narrowing conversions are diagnosed by default, as required by the standard.
+A narrowing conversion from a constant produces an error,
+and a narrowing conversion from a non-constant produces a warning,
+but @option{-Wno-narrowing} suppresses the diagnostic.
+Note that this does not affect the meaning of well-formed code;
+narrowing conversions are still considered ill-formed in SFINAE contexts.
@item -Wnoexcept @r{(C++ and Objective-C++ only)}
@opindex Wnoexcept