Subject: Re: [PATCH v3 1/5] CodingGuidelines: add shell piping guidelines

From: SZEDER Gábor <[email-masked]>
Date: Thu, 27 Sep 2018 23:18:26 +0200

On Tue, Sep 25, 2018 at 02:58:08PM -0700, Matthew DeVore wrote:
> Here is the new commit with updated message (I will wait for a day or
> two before I send a reroll):
> 
>     Documentation: add shell guidelines
> 
>     Add the following guideline to Documentation/CodingGuidelines:
> 
>             &&, ||, and | should appear at the end of lines, not the
>             beginning, and the \ line continuation character should be
>             omitted
> 
>     And the following to t/README (since it is specific to writing tests):
> 
>             pipes and $(git ...) should be avoided when they swallow exit
>             codes of Git processes
> 
>     Signed-off-by: Matthew DeVore <[email-masked]>
> 
> diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
> index 48aa4edfb..3d2cfea9b 100644
> --- a/Documentation/CodingGuidelines
> +++ b/Documentation/CodingGuidelines
> @@ -118,6 +118,24 @@ For shell scripts specifically (not exhaustive):
>                  do this
>          fi
> 
> + - If a command sequence joined with && or || or | spans multiple
> +   lines, put each command on a separate line and put && and || and |
> +   operators at the end of each line, rather than the start. This
> +   means you don't need to use \ to join lines, since the above
> +   operators imply the sequence isn't finished.
> +
> +        (incorrect)
> +        grep blob verify_pack_result \
> +        | awk -f print_1.awk \
> +        | sort >actual &&
> +        ...
> +
> +        (correct)
> +        grep blob verify_pack_result |
> +        awk -f print_1.awk |
> +        sort >actual &&
> +        ...
> +
>   - We prefer "test" over "[ ... ]".
> 
>   - We do not write the noiseword "function" in front of shell
> @@ -163,7 +181,6 @@ For shell scripts specifically (not exhaustive):
> 
>     does not have such a problem.
> 
> -
>  For C programs:
> 
>   - We use tabs to indent, and interpret tabs as taking up to
> diff --git a/t/README b/t/README
> index 9028b47d9..3e28b72c4 100644
> --- a/t/README
> +++ b/t/README
> @@ -461,6 +461,32 @@ Don't:
>     platform commands; just use '! cmd'.  We are not in the business
>     of verifying that the world given to us sanely works.
> 
> + - Use Git upstream in the non-final position in a piped chain, as in:

Note the starting upper case 'U'.

> +
> +     git -C repo ls-files |
> +     xargs -n 1 basename |
> +     grep foo
> +
> +   which will discard git's exit code and may mask a crash. In the
> +   above example, all exit codes are ignored except grep's.
> +
> +   Instead, write the output of that command to a temporary
> +   file with ">" or assign it to a variable with "x=$(git ...)" rather
> +   than pipe it.
> +
> + - Use command substitution in a way that discards git's exit code.

'U' again.

> +   When assigning to a variable, the exit code is not discarded, e.g.:
> +
> +     x=$(git cat-file -p $sha) &&
> +     ...
> +
> +   is OK because a crash in "git cat-file" will cause the "&&" chain
> +   to fail, but:
> +
> +     test_cmp expect $(git cat-file -p $sha)
> +
> +   is not OK and a crash in git could go undetected.

Well, this is not OK indeed, because it doesn't make any sense in the
first place :)  'test_cmp' requires two paths as argumens, but the
output of 'git cat-file -p' is the whole _content_ of the given object.

>   - use perl without spelling it as "$PERL_PATH". This is to help our

Note the starting lower case 'u'.

This is because these are the continuation of the "Don't:" some lines
earlier, so your new points should start with a lower case 'u' as
well.

Sidenote: I think we should consider reformatting this whole section
as:

  - Don't do this.
  - Don't do that.

because it grew so much that when I look at the last points, then that
starting "Don't:" has already scrolled out of my screen.

>     friends on Windows where the platform Perl often adds CR before
>     the end of line, and they bundle Git with a version of Perl that
> 
> 
> >
> >
> > These last two points, however, are specific to test scripts,
> > therefore I think they would be better placed in 't/README', where the
> > rest of the test-specific guidelines are.
> >
> > >  For C programs:
> > >
> > > --
> > > 2.19.0.444.g18242da7ef-goog
> > >