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From: Jeff King <peff@peff.net>
To: "Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>
Cc: git@vger.kernel.org, Stefan Beller <sbeller@google.com>,
	Brandon Williams <bmwill@google.com>,
	Junio C Hamano <gitster@pobox.com>, Johannes Sixt <j6t@kdbg.org>
Subject: Re: [PATCH v3 4/4] trace.c: be smart about what env to print in trace_run_command()
Date: Fri, 12 Jan 2018 08:33:55 -0500	[thread overview]
Message-ID: <20180112133355.GE27499@sigill.intra.peff.net> (raw)
In-Reply-To: <20180112095607.18293-5-pclouds@gmail.com>

On Fri, Jan 12, 2018 at 04:56:07PM +0700, Nguyễn Thái Ngọc Duy wrote:

> The previous concatenate_env() is kinda dumb. It receives a env delta
> in child_process and blindly follows it. If the run_command() user
> "adds" more vars of the same value, or deletes vars that do not exist
> in parent env in the first place (*), then why bother to print them?
> 
> This patch checks child_process.env against parent environment and
> only print the actual differences. The unset syntax (and later on cwd)
> follows closely shell syntax for easy reading/guessing and copy/paste.

I like it.

> There is an interesting thing with this change. In the previous patch,
> we unconditionally print new vars. With submodule code we may have
> something like this
> 
>     trace: ... GIT_DIR='.git' git 'status' '--porcelain=2'
> 
> but since parent's GIT_DIR usually has the same value '.git' too, this
> change suppress that, now we can't see that the above command runs in
> a separate repo. This is the run for printing cwd. Now we have
> 
>     trace: ... cd foo; git 'status' '--porcelain=2'

Makes sense (though s/run/reason/ in the last paragraph?).

> Another equally interesting thing is, some caller can do "unset GIT_DIR;
> set GIT_DIR=.git". Since parent env can have the same value '.git', we
> don't re-print GIT_DIR=.git. In that case must NOT print "unset GIT_DIR"
> or the user will be misled to think the new command has no GIT_DIR.

Interesting. I wonder if any callers actually do that. It seems like
kind of an odd thing, but maybe a caller sets GIT_DIR on top of the
clearing of local_repo_env.

> A note about performance. Yes we're burning a lot more cycles for
> displaying something this nice. But because it's protected by
> $GIT_TRACE, and run_command() should not happen often anyway, it should
> not feel any slower than before.

I'd agree that performance probably doesn't matter much here.

> +		/*
> +		 * Do we have a sequence of "unset GIT_DIR; GIT_DIR=foo"?
> +		 * Then don't bother with the unset thing.
> +		 */
> +		if (i + 1 < envs.nr &&
> +		    !strcmp(env, envs.items[i + 1].string))
>  			continue;

Are we guaranteed that "FOO" and "FOO=bar" appear next to each other in the
sorted list? I think "FOO123=bar" could come between.

I also think this is a special case of a more general problem. FOO could
appear any number of times in the "env" array, as a deletion or with
multiple values. Our prep_childenv() would treat that as "last one
wins", I think. Could we just do the same here?

-Peff

  reply	other threads:[~2018-01-12 13:34 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-10 10:48 [PATCH] run-command.c: print env vars when GIT_TRACE is set Nguyễn Thái Ngọc Duy
2018-01-10 18:09 ` Brandon Williams
2018-01-10 19:14   ` Stefan Beller
2018-01-10 19:26     ` Brandon Williams
2018-01-10 19:35       ` Stefan Beller
2018-01-11  9:47 ` [PATCH v2] " Nguyễn Thái Ngọc Duy
2018-01-11 11:25   ` Duy Nguyen
2018-01-11 17:53   ` Brandon Williams
2018-01-11 18:20     ` Stefan Beller
2018-01-11 19:27   ` Junio C Hamano
2018-01-12  9:23     ` Duy Nguyen
2018-01-12  9:56   ` [PATCH v3 0/4] " Nguyễn Thái Ngọc Duy
2018-01-12  9:56     ` [PATCH v3 1/4] trace.c: introduce trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-12 13:05       ` Jeff King
2018-01-12 13:11         ` Jeff King
2018-01-12  9:56     ` [PATCH v3 2/4] trace.c: print program 'git' when child_process.git_cmd is set Nguyễn Thái Ngọc Duy
2018-01-12 13:05       ` Jeff King
2018-01-12  9:56     ` [PATCH v3 3/4] trace.c: print env vars in trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-12 13:13       ` Jeff King
2018-01-12  9:56     ` [PATCH v3 4/4] trace.c: be smart about what env to print " Nguyễn Thái Ngọc Duy
2018-01-12 13:33       ` Jeff King [this message]
2018-01-12 18:24         ` Junio C Hamano
2018-01-12 18:45           ` Jeff King
2018-01-12 19:19             ` Junio C Hamano
2018-01-12 19:23               ` Jeff King
2018-01-12 20:28                 ` Brandon Williams
2018-01-12 22:54         ` Junio C Hamano
2018-01-13  4:54           ` Duy Nguyen
2018-01-13  6:47             ` Duy Nguyen
2018-01-12 13:36     ` [PATCH v3 0/4] run-command.c: print env vars when GIT_TRACE is set Jeff King
2018-01-12 13:38       ` [PATCH 5/4] sq_quote_argv: drop maxlen parameter Jeff King
2018-01-12 23:20         ` Junio C Hamano
2018-01-12 13:39       ` [PATCH 6/4] trace: avoid unnecessary quoting Jeff King
2018-01-12 18:06       ` [PATCH v3 0/4] run-command.c: print env vars when GIT_TRACE is set Stefan Beller
2018-01-12 17:19     ` Stefan Beller
2018-01-13  6:54       ` Duy Nguyen
2018-01-13  6:49     ` [PATCH v4 0/7] Trace env variables in run_command() Nguyễn Thái Ngọc Duy
2018-01-13  6:49       ` [PATCH v4 1/7] sq_quote_argv: drop maxlen parameter Nguyễn Thái Ngọc Duy
2018-01-13  6:49       ` [PATCH v4 2/7] trace: avoid unnecessary quoting Nguyễn Thái Ngọc Duy
2018-01-13  6:49       ` [PATCH v4 3/7] trace.c: move strbuf_release() out of print_trace_line() Nguyễn Thái Ngọc Duy
2018-01-13  7:14         ` Jeff King
2018-01-13  6:49       ` [PATCH v4 4/7] trace.c: introduce trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-13  6:49       ` [PATCH v4 5/7] trace.c: print program 'git' when child_process.git_cmd is set Nguyễn Thái Ngọc Duy
2018-01-13  6:49       ` [PATCH v4 6/7] trace.c: print env vars in trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-13  7:25         ` Jeff King
2018-01-16 22:13         ` Junio C Hamano
2018-01-16 22:20           ` Stefan Beller
2018-01-17  1:32             ` Junio C Hamano
2018-01-13  6:49       ` [PATCH v4 7/7] trace.c: print new cwd " Nguyễn Thái Ngọc Duy
2018-01-13  7:26       ` [PATCH v4 0/7] Trace env variables in run_command() Jeff King
2018-01-15 10:59       ` [PATCH v5 " Nguyễn Thái Ngọc Duy
2018-01-15 10:59         ` [PATCH v5 1/7] sq_quote_argv: drop maxlen parameter Nguyễn Thái Ngọc Duy
2018-01-15 10:59         ` [PATCH v5 2/7] trace: avoid unnecessary quoting Nguyễn Thái Ngọc Duy
2018-01-15 10:59         ` [PATCH v5 3/7] trace.c: move strbuf_release() out of print_trace_line() Nguyễn Thái Ngọc Duy
2018-01-16 18:24           ` Brandon Williams
2018-01-15 10:59         ` [PATCH v5 4/7] trace.c: introduce trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-17 22:21           ` Jeff King
2018-01-17 22:41             ` Junio C Hamano
2018-01-15 10:59         ` [PATCH v5 5/7] trace.c: print program 'git' when child_process.git_cmd is set Nguyễn Thái Ngọc Duy
2018-01-15 10:59         ` [PATCH v5 6/7] trace.c: print env vars in trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-16 18:32           ` Brandon Williams
2018-01-15 10:59         ` [PATCH v5 7/7] trace.c: print new cwd " Nguyễn Thái Ngọc Duy
2018-01-18  9:45         ` [PATCH v6 0/7] Trace env variables in run_command() Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 1/7] sq_quote_argv: drop maxlen parameter Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 2/7] trace: avoid unnecessary quoting Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 3/7] trace.c: move strbuf_release() out of print_trace_line() Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 4/7] run-command.c: introduce trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 5/7] run-command.c: print program 'git' when tracing git_cmd mode Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 6/7] run-command.c: print env vars in trace_run_command() Nguyễn Thái Ngọc Duy
2018-01-18  9:45           ` [PATCH v6 7/7] run-command.c: print new cwd " Nguyễn Thái Ngọc Duy
2018-01-19 21:39           ` [PATCH v6 0/7] Trace env variables in run_command() Jeff King
2018-01-11 10:07 ` [PATCH] run-command.c: print env vars when GIT_TRACE is set Jeff King
2018-01-11 11:13   ` Duy Nguyen
2018-01-11 18:21   ` Johannes Sixt

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