Re: [PATCH v3 6/6] diff: shortcut for diff'ing two binary SHA-1 objects
From: Junio C Hamano <hidden>
Date: 2016-06-15 23:02:16
Nguyễn Thái Ngọc Duy [off-list ref] writes:
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If we are given two SHA-1 and asked to determine if they are different (but not _what_ differences), we know right away by comparing SHA-1. A side effect of this patch is, because large files are marked binary, diff-tree will not need to unpack them. 'diff-index --cached' will not either. But 'diff-files' still does. Signed-off-by: Nguyễn Thái Ngọc Duy <redacted> --- diff.c | 13 +++++++++++++ t/t1050-large.sh | 8 ++++++++ 2 files changed, 21 insertions(+)diff --git a/diff.c b/diff.c index d381a6f..b85bcfb 100644 --- a/diff.c +++ b/diff.c@@ -2324,6 +2324,19 @@ static void builtin_diff(const char *name_a, } else if (!DIFF_OPT_TST(o, TEXT) && ( (!textconv_one && diff_filespec_is_binary(one)) || (!textconv_two && diff_filespec_is_binary(two)) )) { + if (!one->data && !two->data && + S_ISREG(one->mode) && S_ISREG(two->mode) && + !DIFF_OPT_TST(o, BINARY)) { + if (!hashcmp(one->sha1, two->sha1)) { + if (must_show_header) + fprintf(o->file, "%s", header.buf); + goto free_ab_and_return; + } + fprintf(o->file, "%s", header.buf); + fprintf(o->file, "%sBinary files %s and %s differ\n", + line_prefix, lbl[0], lbl[1]); + goto free_ab_and_return; + }
A tangent. I think one and two can point at the same object only when this filepair is involved in rename/copy. In other words, one and two with the same <mode,sha1,name> would not be given to this code. And must-show-header would be set to true long before we get here in fill-metainfo in such a case. I think this new code and the original below which you copied this one from can probably be simplified. It already felt wrong to see two copies of "fprintf(o->file "%s", header.buf)" and now we have four of them. Because this is a copy-and-paste of the identical logic from below, I do not want you to attempt fixing this tangent in this patch, though. Thanks.
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if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0) die("unable to read files to diff"); /* Quite common confusing case */diff --git a/t/t1050-large.sh b/t/t1050-large.sh index 711f22c..b294963 100755 --- a/t/t1050-large.sh +++ b/t/t1050-large.sh@@ -116,6 +116,14 @@ test_expect_success 'diff --stat' ' git diff --stat HEAD^ HEAD ' +test_expect_success 'diff' ' + git diff HEAD^ HEAD +' + +test_expect_success 'diff --cached' ' + git diff --cached HEAD^ +' + test_expect_success 'hash-object' ' git hash-object large1 '