[llvm-dev] Why does clang -E - of a header file may have different exit status?

[Harald van Dijk via llvm-dev]

On 30/04/2021 10:21, Harald van Dijk via llvm-dev wrote:
> On 30/04/2021 04:04, Peng Yu via llvm-dev wrote:
>> I see different exit status of clang. Does anybody know why? Should
>> clang be consistent on this aspect no matter what the header file is?
>>
>> $ clang -E - <<< '#include <bfd.h>' | head -n 1
>> # 1 "<stdin>"
>> $ declare -p PIPESTATUS
>> declare -a PIPESTATUS=([0]="141" [1]="0")
> 
> $ kill -l 141
> PIPE
> 
> This happens because clang failed to fully write the preprocessed output 
> because the head command is no longer accepting more input. This is not 
> specific to clang, it happens with many other utilities as well. Once 
> the head command is no longer accepting more input, it's pointless for 
> clang to continue writing output, so it's sent a signal to stop.
> 
> Depending on the contents of the header file, the signal to stop may be 
> sent before or after clang has already fully written its output. If it 

This was so poorly worded that it became wrong. It should be: depending 
on the contents of the header file, head may stop accepting input before 
or after clang has already fully written its output. If it stops 
accepting input afterwards, clang will not be sent any signal to stop.

> has fully written the output already, then clang will not notice any 
> error and exit successfully. This matches GCC, except that you need 
> different header files to show this with GCC. Try a tiny header file 
> such as <stdbool.h> instead.
> 
> Cheers,
> Harald van Dijk