diff mbox

Clarify interaction of -Wnarrowing with -std

Message ID 20160223183853.GK3171@redhat.com
State New
Headers show

Commit Message

Jonathan Wakely Feb. 23, 2016, 6:39 p.m. UTC 
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.

Is this better?
diff mbox

Patch

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 490df93..8d56efa 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -2753,10 +2753,17 @@  During the link-time optimization warn about type mismatches in
 global declarations from different compilation units.
 Requires @option{-flto} to be enabled.  Enabled by default.
 
-@item -Wnarrowing @r{(C++ and Objective-C++ only)}
+@item -Wno-narrowing @r{(C++ and Objective-C++ only)}
 @opindex Wnarrowing
 @opindex Wno-narrowing
-With @option{-std=gnu++98} or @option{-std=c++98}, warn when a narrowing
+For C++11 and later standards, 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.
+
+With @option{-Wnarrowing} in C++98, warn when a narrowing
 conversion prohibited by C++11 occurs within
 @samp{@{ @}}, e.g.
 
@@ -2766,14 +2773,6 @@  int i = @{ 2.2 @}; // error: narrowing from double to int
 
 This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
 
-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
 @opindex Wno-noexcept