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Please, take '-Wmisleading-indentation' out of -Wall
- From: Antonio Diaz Diaz <antonio at gnu dot org>
- To: gcc at gcc dot gnu dot org
- Cc: Antonio Diaz Diaz <antonio at gnu dot org>
- Date: Wed, 04 May 2016 18:15:37 +0200
- Subject: Please, take '-Wmisleading-indentation' out of -Wall
- Authentication-results: sourceware.org; auth=none
[Please, CC me. I'm not subscribed to email@example.com].
First of all, thank you very much for gcc.
I am not an expert in gcc. Please, forgive any mistakes in this message. :-)
After compiling all my projects with gcc-6.1, I have received warnings
related to -Wmisleading-indentation in four of them for constructs that
I do not consider questionable. (Mainly one-liners inside switch
statements with no indentation involved). As it is now, the name of the
option is misleading, because -Wmisleading-indentation does not limit
itself to warn about misleading indentation.
One of the warnings is a false positive for the following code from GNU
ed (the 'break' is aligned with the 'while', all spaces, no tabs, yet
gcc complains that it is misleadingly indented):
case '#': while( *(*ibufpp)++ != '\n' ) ;
I consider -Wmisleading-indentation an useful addition to gcc, but IMO
there are a number of reasons that make its inclusion in -Wall
inappropriate or at least excessively annoying.
To begin with, the C and C++ standards state clearly that the amount of
whitespace characters separating tokens is not significant. Therefore,
warning about indentation in C/C++ must be considered optional. More
optional than -Woverlength-strings, which is not in -Wall nor in -Wextra.
C/C++ allows creative use of whitespace to highlight the estructure of
the code in ways that -Wmisleading-indentation can't anticipate.
Including -Wmisleading-indentation in -Wall forces the developer to
surrender such freedom just to placate gcc:
"Don't make the program ugly just to placate static analysis tools such
as 'lint', 'clang', and GCC with extra warnings options such as
'-Wconversion' and '-Wundef'. These tools can help find bugs and unclear
code, but they can also generate so many false alarms that it hurts
readability to silence them with unnecessary casts, wrappers, and other
complications. For example, please don't insert casts to 'void' or calls
to do-nothing functions merely to pacify a lint checker".
I also think that -Wmisleading-indentation should not be enabled by
-Wall nor -Wextra because:
- -Wall is defined in the gcc manual as enabling all the warnings
about constructions that are easy to avoid (or modify to prevent the
warning), even in conjunction with macros. This is not true of
- It can't be portably disabled; older versions of gcc do not accept
'-Wno-misleading-indentation'. (At least 4.1.2 does not accept it).
- If there are no macros involved, it is independent of code
generation; once tested in the developer's machine there is no need
to test it again on every user's machine.
- It makes compilation a 0.5-1% slower for every user for no reason.
- -Wempty-body is much simpler to test for, and in general less
questionable than -Wmisleading-indentation, yet it is not enabled by
I think that keeping separated categories of warnings (instead of
warning about everything by default) is a valuable feature. Maybe both
-Wempty-body and -Wmisleading-indentation (and any future similar
options) could be put in a new category (-Wcoding-style or
-Wstatic-analysis, for example).
To summarize, I want 'gcc -Wall -Wextra' to:
- not warn about the use of whitespace beyond what the standard
- not warn about the format of one-liners.
- not being slowed down because of indentation parsing.
Please, take '-Wmisleading-indentation' out of -Wall (and don't move it
Thanks in advance,