[cfe-users] warning/error issues
David Blaikie
dblaikie at gmail.com
Sat Oct 12 18:07:00 PDT 2013
This is just a matter of ordering:
$ clang++-tot unused.cpp -Werror -Wno-error=unused-parameter
-Wunused-parameter
unused.cpp:2:17: error: unused parameter 'i' [-Werror,-Wunused-parameter]
void func(int i) {
^
1 error generated.
$ clang++-tot unused.cpp -Wextra -Werror -Wno-error=unused-parameter
unused.cpp:2:17: warning: unused parameter 'i' [-Wunused-parameter]
void func(int i) {
^
1 warning generated.
Which differs from GCC, which warns in both cases. This is arguably (not
sure if the Clang behavior is intentional) a bug in Clang. Feel free to
file it at llvm.org/bugs - in the mean time you can workaround it by
putting the -Werror related flags last.
On Fri, Oct 11, 2013 at 7:13 PM, Eric Levy <contact at ericlevy.name> wrote:
> Evidently my build is not behaving the same way, as demonstrated below.
> Version information is also shown.
>
>
> % clang -c -m64 -pipe -std=c++0x -Werror -Wno-error=unused-parameter -g
> -fPIC -Wall -W -D_REENTRANT -DQT_XMLPATTERNS_LIB -DQT_CONCURRENT_LIB
> -DQT_NETWORK_LIB -DQT_XML_LIB -DQT_CORE_LIB -I/opt/qt-5.0.0-linux64-**
> ubuntu1204-gcc/mkspecs/linux-**g++-64 -I../src -I/opt/qt-5.0.0-linux64-**ubuntu1204-gcc/include
> -I/opt/qt-5.0.0-linux64-**ubuntu1204-gcc/include/**QtXmlPatterns
> -I/opt/qt-5.0.0-linux64-**ubuntu1204-gcc/include/**QtConcurrent
> -I/opt/qt-5.0.0-linux64-**ubuntu1204-gcc/include/**QtNetwork
> -I/opt/qt-5.0.0-linux64-**ubuntu1204-gcc/include/QtXml
> -I/opt/qt-5.0.0-linux64-**ubuntu1204-gcc/include/QtCore -I. -I. -o
> ../obj/QDavResource.o ../src/QDavResource.cpp
> ../src/QDavResource.cpp:12:60: error: unused parameter 'propList'
> [-Werror,-Wunused-parameter]
> void QDavResource::setPropertyList(**const QDavPropertyList* propList) {
> ^
> 1 error generated.
>
>
> % clang -v
> Ubuntu clang version 3.0-6ubuntu3 (tags/RELEASE_30/final) (based on LLVM
> 3.0)
> Target: x86_64-pc-linux-gnu
> Thread model: posix
>
>
>
> On 10/11/2013 10:00 PM, David Blaikie wrote:
>
>>
>>
>>
>> On Fri, Oct 11, 2013 at 6:58 PM, Eric Levy <contact at ericlevy.name
>> <mailto:contact at ericlevy.name>**> wrote:
>>
>> I stand corrected on the -Werror/-Wall issue.
>>
>> With respect to unused parameters, I do have -Wall enabled, however,
>> the documentation states I can override it on particular types of
>> warnings using -Wno-error=foo (this part is definitely different
>> from gcc), however, I have been unsuccessful in doing so.
>>
>>
>> I demonstrated that in my example:
>>
>> $ clang++-tot unused.cpp -Wextra -Werror -Wno-error=unused-parameter
>> unused.cpp:2:17: warning: unused parameter 'i' [-Wunused-parameter]
>> void func(int i) {
>> ^
>> 1 warning generated.
>>
>> demoting the unused-parameter warning back from an error to a warning,
>> worked for me. You do need to use the exact warning name, not a warning
>> group (eg: -Wno-error=unused or -Wno-error=all won't work).
>>
>>
>> Eric Levy
>>
>>
>>
>> On 10/11/2013 09:49 PM, David Blaikie wrote:
>>
>>
>>
>>
>> On Fri, Oct 11, 2013 at 6:34 PM, Eric Levy
>> <contact at ericlevy.name <mailto:contact at ericlevy.name>
>> <mailto:contact at ericlevy.name <mailto:contact at ericlevy.name>**
>> >__>
>>
>> wrote:
>>
>> Hello,
>>
>> I began to experiment with clang to build an existing C++
>> (Qt-based)
>> project. I wanted to make warnings into errors in order to
>> ensure
>> that the code is solid. However, there are several issues:
>>
>> 1) Clang is said to be designed to have the same command-line
>> interface as gcc, but the options for warnings and errors are
>> different. The gcc command -Wall is -Werror in clang, and
>> so on.
>>
>>
>> Actually Clang and GCC both have -Wall and -Werror and they do
>> (roughly)
>> the same thing in each. -Wall is the "common likely-good
>> warnings" and
>> -Werror is "whatever warnings are on, make them errors". The
>> specific
>> set of things in -Wall differs somewhat between Clang and GCC
>> since
>> there's no specific definition, but roughly speaking those flags
>> do the
>> same thing.
>>
>>
>> 2) The user documentation states that specific warnings can
>> be made
>> into errors or not errors by using the -Werror=foo and
>> -Wno-error=foo options. However, no list of accepted
>> values for foo
>> is given.
>>
>>
>> This is a flaw in Clang's documentation - we basically don't
>> document
>> our flags, so far as I know. You guess them, or you look at the
>> implementation, or try -Weverything (turns on all warnings) and
>> see what
>> warnings fire and what their flags are called (we print the flag
>> name by
>> default).
>>
>>
>> 3) Finally, gcc/clang both warn on unused variables and
>> parameters.
>> This often undesired, especially in C++ where, due to
>> polymorphism
>> some implementations of a method may not need certain
>> parameters.
>>
>>
>> I don't believe Clang warns on unused parameters by default, if
>> at all.
>> If it does so on virtual functions that's probably a bug to be
>> fixed.
>>
>> When clang produces an error for unused parameters (-Werror
>> enabled), it reports the reason is -Wunused-parameter.
>> However,
>> introducing -Wno-error=unused-parameter has no effect,
>> despite
>> documentation to the contrary. The gcc-style
>> -Wno-unused-parameter
>> is equally ineffective.
>>
>>
>> Could you show examples of this?
>>
>> -Wunused-parameter isn't under -Wall, so you must've passed it
>> explicitly I assume (or perhaps via -Wextra)?
>>
>> All these options seem to work quite well for me with Clang:
>>
>> $ clang++-tot unused.cpp -Wextra
>> unused.cpp:2:17: warning: unused parameter 'i'
>> [-Wunused-parameter]
>> void func(int i) {
>> ^
>> 1 warning generated.
>> $ clang++-tot unused.cpp -Wextra -Werror
>> unused.cpp:2:17: error: unused parameter 'i'
>> [-Werror,-Wunused-parameter]
>> void func(int i) {
>> ^
>> 1 error generated.
>> $ clang++-tot unused.cpp -Wextra -Werror
>> -Wno-error=unused-parameter
>> unused.cpp:2:17: warning: unused parameter 'i'
>> [-Wunused-parameter]
>> void func(int i) {
>> ^
>> 1 warning generated.
>> $ clang++-tot unused.cpp -Wextra -Werror -Wno-unused-parameter
>> $
>>
>> So too is replacing unused-parameter with simply unused,
>> which, at
>> least according to gcc documentation, subsumes unused
>> variables and
>> parameters alike.
>>
>> Whether these observations represent choice or oversight, I
>> would
>> like to know how to make all warnings errors except for
>> unused
>> variables and parameters.
>>
>> Thank you.
>>
>> Sincerely,
>> Eric Levy
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>>
>>
>>
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