Re: [PATCH/RFC][GSoC] make "git diff --no-index $directory $file" DWIM better.

[re-adding cc:git]

On Sun, Mar 15, 2015 at 2:45 PM, Yurii Shevtsov [off-list ref] wrote:

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On Sun, Mar 15, 2015 at 11:35 AM, Yurii Shevtsov [off-list ref] wrote:

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make "git diff --no-index $directory $file" DWIM better.

Specify the area affected by the change, followed by a colon, followed
by the change summary. Drop the period at the end. So, something like:

    diff: improve '--no-index <directory> <file>' DWIMing

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Changes 'git diff --no-index $directory $file' behaviour.
Now it is transformed to 'git diff --no-index $directory/&file $file'
instead of throwing an error.

Write in imperative mood, so "Change" rather than "Changes". By
itself, the first sentence isn't saying much; it would read better if
you combined the two sentences into one.

Got it! My commit message requires improvements

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---
-       if (mode1 && mode2 && S_ISDIR(mode1) != S_ISDIR(mode2))
-               return error("file/directory conflict: %s, %s", name1, name2);
+       if (mode1 && mode2 && S_ISDIR(mode1) != S_ISDIR(mode2)) {
+               struct strbuf dirnfile;

Is this name supposed to stand for "dir'n'file", a shorthand for
"dir-and-file"? Perhaps a simpler more idiomatic name such as "path"
would suffice. Also, you can initialize the strbuf here at point of
declaration:

    struct strbuf path = STRBUF_INIT;

Yes it is supposed to be "dir-and-file" I thought "path" isn't
descriptive enough because it could be path to dir. But if you insist,
no problems

The reason I asked was because it is not uncommon for variable names
with an 'n' suffix to mean "length" of something, so the 'n' in 'dirn'
was a bit confusing. I personally find the idiomatic name 'path'
easier to grok, however, Junio, of course, has final say-so. It's okay
to argue for your choice in naming if you feel strongly that it is
better.

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+               const char *dir, *file;
+               char *filename;
+               int ret = 0;
+
+               dir = S_ISDIR(mode1) ? name1 : name2;
+               file = (dir == name1) ? name2 : name1;
+               strbuf_init(&dirnfile, strlen(name1) + strlen(name2) + 2);

Unless this is a performance critical loop where you want to avoid
multiple re-allocations, it's customary to pass 0 for the second
argument. Doing so makes the code a bit easier to read and understand,
and avoids questions like this one: Why are you adding 2 to the
requested length? I presume that you're taking the "/" and NUL into
account, however, strbuf takes NUL into account on its own as part of
its contract, so you probably wanted to add only 1.

Yes I thought about performance. I thought it is reasonable since I
always know size of resulting string. Checked strbuf.c one more time,
yoг are right I should really add only 1

A few reasons I probably would just pass 0 in this case: (1) this
string construction is not performance critical; (2) a person reading
the code has to spend extra time double-checking the math; (3) the
math may become outdated if someone later alters the string
construction in some way, thus it's a potential maintenance burden;
(4) terser code tends to be easier to read and understand at a glance,
so the less verbose the code, the better.

However, as usual, it's entirely acceptable to argue for your version
if you feel strongly about it.

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+               strbuf_addstr(&dirnfile, dir);
+               if (dirnfile.buf[dirnfile.len - 1] != '/')

I don't know how others feel about it, but it makes me a bit
uncomfortable to see potential access of array item -1. I suppose, in
this case, neither name will be zero-length, however, I'd still feel
more comfortable seeing that documented formally, either via assert():

    assert(dirnfile.len > 0);
    if (dirnfile.buf[dirnfile.len - 1] != '/')

or:

    if (dirnfile.len > 0 && dirnfile.buf[dirnfile.len - 1] != '/')

My fault again