Macros active in error messages

Macros active in error messages

[emre brookes]

I was compiling a project and received an odd message that took some 
digging.
e.g.

file.cpp:#:#: error: expected unqualified-id before numeric constant
# | if ( inttype == MyClass::ERROR )
                              ^~~~~
where MyClass::ERROR is an enum.

Took some digging to find out ERROR was somewhere #define'd and the cure 
was to #undef ERROR
Could never find out *where* it was defined - recursively searched all 
include files of the project and /usr/include etc.
Regardless, it would have been very helpful to know in the error 
messages that a #define was active or to have the ERROR replaced by the 
macro substitution.

Is it possible to get any macro expansion information in error messages?
I didn't see a compiler flag for to get this information, but I might 
have missed it.
If not, it would be a nice feature to have.

Cheers,
Emre.

Re: Macros active in error messages

[Jonathan Wakely]

On Sun, 22 Nov 2020, 15:35 emre brookes, <brookes@uthscsa.edu> wrote:

> I was compiling a project and received an odd message that took some
> digging.
> e.g.
>
> file.cpp:#:#: error: expected unqualified-id before numeric constant
> # | if ( inttype == MyClass::ERROR )
>                               ^~~~~
> where MyClass::ERROR is an enum.
>
> Took some digging to find out ERROR was somewhere #define'd and the cure
> was to #undef ERROR
> Could never find out *where* it was defined - recursively searched all
> include files of the project and /usr/include etc.
>


I know it's not your main question, but ...

g++ -E -dD foo.cc will show all the macro definitions.

Re: Macros active in error messages

[Martin Sebor]

On 11/22/20 8:34 AM, emre brookes wrote:
> I was compiling a project and received an odd message that took some 
> digging.
> e.g.
> 
> file.cpp:#:#: error: expected unqualified-id before numeric constant
> # | if ( inttype == MyClass::ERROR )
>                               ^~~~~
> where MyClass::ERROR is an enum.
> 
> Took some digging to find out ERROR was somewhere #define'd and the cure 
> was to #undef ERROR
> Could never find out *where* it was defined - recursively searched all 
> include files of the project and /usr/include etc.
> Regardless, it would have been very helpful to know in the error 
> messages that a #define was active or to have the ERROR replaced by the 
> macro substitution.
> 
> Is it possible to get any macro expansion information in error messages?
> I didn't see a compiler flag for to get this information, but I might 
> have missed it.
> If not, it would be a nice feature to have.

I'd expect to see output similar to the below where the error points
to the macro.  I'm not sure under what conditions it won't (with some
specific options perhaps?)  If you can create an isolated test case
showing it doesn't I'd recommend to open a bug in Bugzilla (or just
follow up here).

Martin

$ cat a.C && gcc -S a.C
struct MyClass { enum { ERROR = 1 }; };

#define ERROR 1

int f (int inttype)
{
   if (inttype == MyClass::ERROR)
     return 0;
   return 1;
}
a.C: In function ‘int f(int)’:
a.C:3:15: error: expected unqualified-id before numeric constant
     3 | #define ERROR 1
       |               ^
a.C:7:27: note: in expansion of macro ‘ERROR’
     7 |   if (inttype == MyClass::ERROR)
       |                           ^~~~~
a.C:7:25: error: expected ‘)’ before numeric constant
     7 |   if (inttype == MyClass::ERROR)
       |      ~                  ^
       |                         )

Re: Macros active in error messages

[Florian Weimer]

* emre brookes:

> I was compiling a project and received an odd message that took some
> digging.
> e.g.
>
> file.cpp:#:#: error: expected unqualified-id before numeric constant
> # | if ( inttype == MyClass::ERROR )
>                              ^~~~~
> where MyClass::ERROR is an enum.
>
> Took some digging to find out ERROR was somewhere #define'd and the
> cure was to #undef ERROR
> Could never find out *where* it was defined - recursively searched all
> include files of the project and /usr/include etc.
> Regardless, it would have been very helpful to know in the error
> messages that a #define was active or to have the ERROR replaced by
> the macro substitution.

Do you use distcc or ccache to build your project?

Thanks,
Florian
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Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill

Re: Macros active in error messages

[emre brookes]

Florian Weimer wrote:
> * emre brookes:
>
>> I was compiling a project and received an odd message that took some
>> digging.
>> e.g.
>>
>> file.cpp:#:#: error: expected unqualified-id before numeric constant
>> # | if ( inttype == MyClass::ERROR )
>>                               ^~~~~
>> where MyClass::ERROR is an enum.
>>
>> Took some digging to find out ERROR was somewhere #define'd and the
>> cure was to #undef ERROR
>> Could never find out *where* it was defined - recursively searched all
>> include files of the project and /usr/include etc.
>> Regardless, it would have been very helpful to know in the error
>> messages that a #define was active or to have the ERROR replaced by
>> the macro substitution.
> Do you use distcc or ccache to build your project?
>
> Thanks,
> Florian
No use of distcc or ccache.
$ g++ --version
g++.exe (Rev5, Built by MSYS2 project) 10.2.0
Copyright (C) 2020 Free Software Foundation, Inc.

Thanks,
Emre

Re: Macros active in error messages

[emre brookes]

Martin Sebor wrote:
> On 11/22/20 8:34 AM, emre brookes wrote:
>> I was compiling a project and received an odd message that took some 
>> digging.
>> e.g.
>>
>> file.cpp:#:#: error: expected unqualified-id before numeric constant
>> # | if ( inttype == MyClass::ERROR )
>>                               ^~~~~
>> where MyClass::ERROR is an enum.
>>
>> Took some digging to find out ERROR was somewhere #define'd and the 
>> cure was to #undef ERROR
>> Could never find out *where* it was defined - recursively searched 
>> all include files of the project and /usr/include etc.
>> Regardless, it would have been very helpful to know in the error 
>> messages that a #define was active or to have the ERROR replaced by 
>> the macro substitution.
>>
>> Is it possible to get any macro expansion information in error messages?
>> I didn't see a compiler flag for to get this information, but I might 
>> have missed it.
>> If not, it would be a nice feature to have.
>
> I'd expect to see output similar to the below where the error points
> to the macro.  I'm not sure under what conditions it won't (with some
> specific options perhaps?)  If you can create an isolated test case
> showing it doesn't I'd recommend to open a bug in Bugzilla (or just
> follow up here).
>
> Martin
>
> $ cat a.C && gcc -S a.C
> struct MyClass { enum { ERROR = 1 }; };
>
> #define ERROR 1
>
> int f (int inttype)
> {
>   if (inttype == MyClass::ERROR)
>     return 0;
>   return 1;
> }
> a.C: In function ‘int f(int)’:
> a.C:3:15: error: expected unqualified-id before numeric constant
>     3 | #define ERROR 1
>       |               ^
> a.C:7:27: note: in expansion of macro ‘ERROR’
>     7 |   if (inttype == MyClass::ERROR)
>       |                           ^~~~~
> a.C:7:25: error: expected ‘)’ before numeric constant
>     7 |   if (inttype == MyClass::ERROR)
>       |      ~                  ^
>       |                         )
> .
>
I get the same results for your example code. Here gcc nicely identifies 
the macro expansion :)
Will test later with compiler flags from the project's Makefile add see 
if I can reproduce the issue I observed on a simple case.

Thanks,
Emre

Re: Macros active in error messages

[emre brookes]

emre brookes wrote:
> Martin Sebor wrote:
>> On 11/22/20 8:34 AM, emre brookes wrote:
>>> I was compiling a project and received an odd message that took some 
>>> digging.
>>> e.g.
>>>
>>> file.cpp:#:#: error: expected unqualified-id before numeric constant
>>> # | if ( inttype == MyClass::ERROR )
>>>                               ^~~~~
>>> where MyClass::ERROR is an enum.
>>>
>>> Took some digging to find out ERROR was somewhere #define'd and the 
>>> cure was to #undef ERROR
>>> Could never find out *where* it was defined - recursively searched 
>>> all include files of the project and /usr/include etc.
>>> Regardless, it would have been very helpful to know in the error 
>>> messages that a #define was active or to have the ERROR replaced by 
>>> the macro substitution.
>>>
>>> Is it possible to get any macro expansion information in error 
>>> messages?
>>> I didn't see a compiler flag for to get this information, but I 
>>> might have missed it.
>>> If not, it would be a nice feature to have.
>>
>> I'd expect to see output similar to the below where the error points
>> to the macro.  I'm not sure under what conditions it won't (with some
>> specific options perhaps?)  If you can create an isolated test case
>> showing it doesn't I'd recommend to open a bug in Bugzilla (or just
>> follow up here).
>>
>> Martin
>>
>> $ cat a.C && gcc -S a.C
>> struct MyClass { enum { ERROR = 1 }; };
>>
>> #define ERROR 1
>>
>> int f (int inttype)
>> {
>>   if (inttype == MyClass::ERROR)
>>     return 0;
>>   return 1;
>> }
>> a.C: In function ‘int f(int)’:
>> a.C:3:15: error: expected unqualified-id before numeric constant
>>     3 | #define ERROR 1
>>       |               ^
>> a.C:7:27: note: in expansion of macro ‘ERROR’
>>     7 |   if (inttype == MyClass::ERROR)
>>       |                           ^~~~~
>> a.C:7:25: error: expected ‘)’ before numeric constant
>>     7 |   if (inttype == MyClass::ERROR)
>>       |      ~                  ^
>>       |                         )
>> .
>>
> I get the same results for your example code. Here gcc nicely 
> identifies the macro expansion :)
> Will test later with compiler flags from the project's Makefile add 
> see if I can reproduce the issue I observed on a simple case.
>
> Thanks,
> Emre
Followup:
strange error

555 0 mingw [eb@ebwin764] ~/gccerrortest $ gcc --version
gcc.exe (Rev5, Built by MSYS2 project) 10.2.0

key takeway -
on msys2 64 bit
macro expansion information is lost when the #define ERROR is in an 
include file in /mingw64/x86_64-w64-mingw32/include
if i move the include file elsewhere (tested /usr/include and .) - 
normal behavior
linux variants tested did not show this behavior
centos 8 gcc (GCC) 9.2.1 20191120 (Red Hat 9.2.1-2)
centos 8 gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5)
ubuntu 20 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

Should I create a bugzilla for gcc? Might be some msys2 issue. Not sure.

---
Partial evidence:

549 0 mingw [eb@ebwin764] ~/gccerrortest $ cat a.C
struct MyClass { enum { ERROR = 1 }; };

#include <a.h>

int f (int inttype)
{
    if (inttype == MyClass::ERROR)
       return 0;
    return 1;
}
550 0 mingw [eb@ebwin764] ~/gccerrortest $ cat b.C
struct MyClass { enum { ERROR = 1 }; };

#include <b.h>

int f (int inttype)
{
    if (inttype == MyClass::ERROR)
       return 0;
    return 1;
}
551 0 mingw [eb@ebwin764] ~/gccerrortest $ cat a.h
#define ERROR 0
552 0 mingw [eb@ebwin764] ~/gccerrortest $ cat 
/mingw64/x86_64-w64-mingw32/include/b.h
#define ERROR 0
553 0 mingw [eb@ebwin764] ~/gccerrortest $ gcc -I. a.C
In file included from a.C:3:
a.C: In function 'int f(int)':
./a.h:1:15: error: expected unqualified-id before numeric constant
     1 | #define ERROR 0
       |               ^
a.C:7:28: note: in expansion of macro 'ERROR'
     7 |    if (inttype == MyClass::ERROR)
       |                            ^~~~~
a.C:7:26: error: expected ')' before numeric constant
     7 |    if (inttype == MyClass::ERROR)
       |       ~                  ^
       |                          )
554 0 mingw [eb@ebwin764] ~/gccerrortest $ gcc -I 
/mingw64/x86_64-w64-mingw32/include b.C
In file included from b.C:3:
b.C: In function 'int f(int)':
b.C:7:28: error: expected unqualified-id before numeric constant
     7 |    if (inttype == MyClass::ERROR)
       |                            ^~~~~
b.C:7:26: error: expected ')' before numeric constant
     7 |    if (inttype == MyClass::ERROR)
       |       ~                  ^
       |                          )
555 0 mingw [eb@ebwin764] ~/gccerrortest $

Re: Macros active in error messages

[Jonathan Wakely]

On Fri, 27 Nov 2020 at 15:57, emre brookes <brookes@uthscsa.edu> wrote:
>
> emre brookes wrote:
> > Martin Sebor wrote:
> >> On 11/22/20 8:34 AM, emre brookes wrote:
> >>> I was compiling a project and received an odd message that took some
> >>> digging.
> >>> e.g.
> >>>
> >>> file.cpp:#:#: error: expected unqualified-id before numeric constant
> >>> # | if ( inttype == MyClass::ERROR )
> >>>                               ^~~~~
> >>> where MyClass::ERROR is an enum.
> >>>
> >>> Took some digging to find out ERROR was somewhere #define'd and the
> >>> cure was to #undef ERROR
> >>> Could never find out *where* it was defined - recursively searched
> >>> all include files of the project and /usr/include etc.
> >>> Regardless, it would have been very helpful to know in the error
> >>> messages that a #define was active or to have the ERROR replaced by
> >>> the macro substitution.
> >>>
> >>> Is it possible to get any macro expansion information in error
> >>> messages?
> >>> I didn't see a compiler flag for to get this information, but I
> >>> might have missed it.
> >>> If not, it would be a nice feature to have.
> >>
> >> I'd expect to see output similar to the below where the error points
> >> to the macro.  I'm not sure under what conditions it won't (with some
> >> specific options perhaps?)  If you can create an isolated test case
> >> showing it doesn't I'd recommend to open a bug in Bugzilla (or just
> >> follow up here).
> >>
> >> Martin
> >>
> >> $ cat a.C && gcc -S a.C
> >> struct MyClass { enum { ERROR = 1 }; };
> >>
> >> #define ERROR 1
> >>
> >> int f (int inttype)
> >> {
> >>   if (inttype == MyClass::ERROR)
> >>     return 0;
> >>   return 1;
> >> }
> >> a.C: In function ‘int f(int)’:
> >> a.C:3:15: error: expected unqualified-id before numeric constant
> >>     3 | #define ERROR 1
> >>       |               ^
> >> a.C:7:27: note: in expansion of macro ‘ERROR’
> >>     7 |   if (inttype == MyClass::ERROR)
> >>       |                           ^~~~~
> >> a.C:7:25: error: expected ‘)’ before numeric constant
> >>     7 |   if (inttype == MyClass::ERROR)
> >>       |      ~                  ^
> >>       |                         )
> >> .
> >>
> > I get the same results for your example code. Here gcc nicely
> > identifies the macro expansion :)
> > Will test later with compiler flags from the project's Makefile add
> > see if I can reproduce the issue I observed on a simple case.
> >
> > Thanks,
> > Emre
> Followup:
> strange error
>
> 555 0 mingw [eb@ebwin764] ~/gccerrortest $ gcc --version
> gcc.exe (Rev5, Built by MSYS2 project) 10.2.0
>
> key takeway -
> on msys2 64 bit
> macro expansion information is lost when the #define ERROR is in an
> include file in /mingw64/x86_64-w64-mingw32/include
> if i move the include file elsewhere (tested /usr/include and .) -
> normal behavior
> linux variants tested did not show this behavior
> centos 8 gcc (GCC) 9.2.1 20191120 (Red Hat 9.2.1-2)
> centos 8 gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5)
> ubuntu 20 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
>
> Should I create a bugzilla for gcc? Might be some msys2 issue. Not sure.

I think this is the expected behaviour when the macro is defined in a
system header, although I'm not convinced it's useful. I think there's
already a bugzilla about it.

Re: Macros active in error messages

[emre brookes]

Jonathan Wakely wrote:
> On Fri, 27 Nov 2020 at 15:57, emre brookes <brookes@uthscsa.edu> wrote:
>> emre brookes wrote:
>>> Martin Sebor wrote:
>>>> On 11/22/20 8:34 AM, emre brookes wrote:
>>>>> I was compiling a project and received an odd message that took some
>>>>> digging.
>>>>> e.g.
>>>>>
>>>>> file.cpp:#:#: error: expected unqualified-id before numeric constant
>>>>> # | if ( inttype == MyClass::ERROR )
>>>>>                                ^~~~~
>>>>> where MyClass::ERROR is an enum.
>>>>>
>>>>> Took some digging to find out ERROR was somewhere #define'd and the
>>>>> cure was to #undef ERROR
>>>>> Could never find out *where* it was defined - recursively searched
>>>>> all include files of the project and /usr/include etc.
>>>>> Regardless, it would have been very helpful to know in the error
>>>>> messages that a #define was active or to have the ERROR replaced by
>>>>> the macro substitution.
>>>>>
>>>>> Is it possible to get any macro expansion information in error
>>>>> messages?
>>>>> I didn't see a compiler flag for to get this information, but I
>>>>> might have missed it.
>>>>> If not, it would be a nice feature to have.
>>>> I'd expect to see output similar to the below where the error points
>>>> to the macro.  I'm not sure under what conditions it won't (with some
>>>> specific options perhaps?)  If you can create an isolated test case
>>>> showing it doesn't I'd recommend to open a bug in Bugzilla (or just
>>>> follow up here).
>>>>
>>>> Martin
>>>>
>>>> $ cat a.C && gcc -S a.C
>>>> struct MyClass { enum { ERROR = 1 }; };
>>>>
>>>> #define ERROR 1
>>>>
>>>> int f (int inttype)
>>>> {
>>>>    if (inttype == MyClass::ERROR)
>>>>      return 0;
>>>>    return 1;
>>>> }
>>>> a.C: In function ‘int f(int)’:
>>>> a.C:3:15: error: expected unqualified-id before numeric constant
>>>>      3 | #define ERROR 1
>>>>        |               ^
>>>> a.C:7:27: note: in expansion of macro ‘ERROR’
>>>>      7 |   if (inttype == MyClass::ERROR)
>>>>        |                           ^~~~~
>>>> a.C:7:25: error: expected ‘)’ before numeric constant
>>>>      7 |   if (inttype == MyClass::ERROR)
>>>>        |      ~                  ^
>>>>        |                         )
>>>> .
>>>>
>>> I get the same results for your example code. Here gcc nicely
>>> identifies the macro expansion :)
>>> Will test later with compiler flags from the project's Makefile add
>>> see if I can reproduce the issue I observed on a simple case.
>>>
>>> Thanks,
>>> Emre
>> Followup:
>> strange error
>>
>> 555 0 mingw [eb@ebwin764] ~/gccerrortest $ gcc --version
>> gcc.exe (Rev5, Built by MSYS2 project) 10.2.0
>>
>> key takeway -
>> on msys2 64 bit
>> macro expansion information is lost when the #define ERROR is in an
>> include file in /mingw64/x86_64-w64-mingw32/include
>> if i move the include file elsewhere (tested /usr/include and .) -
>> normal behavior
>> linux variants tested did not show this behavior
>> centos 8 gcc (GCC) 9.2.1 20191120 (Red Hat 9.2.1-2)
>> centos 8 gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5)
>> ubuntu 20 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
>>
>> Should I create a bugzilla for gcc? Might be some msys2 issue. Not sure.
> I think this is the expected behaviour when the macro is defined in a
> system header, although I'm not convinced it's useful. I think there's
> already a bugzilla about it.
Ah, thank you! system headers, as in 
https://gcc.gnu.org/onlinedocs/gcc-10.2.0/cpp/System-Headers.html
This explains the behavior I am seeing and can duplicate the issue using 
-isystem as evidenced below on all tested versions of gcc.
The world makes sense again :)

It would be useful if involved system header macro expansion were noted 
in compile error output.

Evidence:
$ cat a.h
#define ERROR 0
$ cat a.C
struct MyClass { enum { ERROR = 1 }; };

#include <a.h>

int f (int inttype)
{
    if (inttype == MyClass::ERROR)
       return 0;
    return 1;
}
$ gcc -isystem . a.C
In file included from a.C:3:
a.C: In function ‘int f(int)’:
a.C:7:28: error: expected unqualified-id before numeric constant
if (inttype == MyClass::ERROR)
^~~~~
a.C:7:26: error: expected ‘)’ before numeric constant
if (inttype == MyClass::ERROR)
~                  ^
)