Re: [PATCH v2 1/2] git-prompt: make __git_eread intended use explicit

From: Junio C Hamano <gitster@pobox.com>
Date: Dec 5, 2017, 00:27 UTC
Message-ID: <xmqqd13ukohs.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <e8d35c35-ffd5-ef10-bc6a-0834c1703995@robertabel.eu>

Robert Abel <rabel@robertabel.eu> writes:

Show 18 quoted lines

> Hi Junio,
>
> On 04 Dec 2017 18:58, Junio C Hamano wrote:
>> Robert Abel <rabel@robertabel.eu> writes:
>>> __git_eread is used to read a single line of a given file (if it exists)
>>> into a variable without the EOL. All six current users of __git_eread
>>> use it that way and don't expect multi-line content.
>> 
>> Changing $@ to $2 does not change whether this is about "multi-line"
>> or not. 
>
> I'm aware of that. I was documenting current usage. The function is used
> to read file contents (which are expected to be a single line) into
> _a_ (i.e. single) variable.
>
> None of the current users of the function expect tokens to be split,
> which is why I removed it in preparation of patch 2/2, which would
> break tokenizing file contents.

I know all of the above, but I think you misunderstood the point I wanted to raise, so let me try again. The thing is, none of what you just wrote changes the fact that lack of callers that want to do "multi-line" is IRRELEVANT. True, there is no caller that wants to read multiple lines---it is a true statement, but it is irrelevant statement. On the other hand, it is true and relevant that no caller expects to split a line into multiple variables.

By changing "$@" to "$2" there, you would have broken callers that wanted the helper function to read into multiple variables (if there were such callers). Explaining the current usage that nobody does so *IS* a valid justification for the change. It is relevant.

With or without that change, a caller that wanted to read multiple lines from the file would never have worked. It was just doing a single "read" built-in, so the only thing that would have been worked on is the first line of the file. Your change wouldn't have changed that---if a caller wanted to peek into the second line, your change wouldn't have helped such a caller. And it is not like your change would have broken such a caller that were happily reading the second and subsequent line. The original wouldn't allowed it to read the second line anyway.

Contrasting this with the above obsesrvation about possible breakage for multi-variable callers (if there were such callers---luckily there wasn't any), I hope that you can see why the lack of "multi-line" caller in the existing usage is totally irrelevant when analyzing this change and explaining why this is a good change.

HTH.