diffcore: add a pickaxe option to find a specific blob

Sometimes users are given a hash of an object and they want to
identify it further (ex.: Use verify-pack to find the largest blobs,
but what are these? or [1])

One might be tempted to extend git-describe to also work with blobs,
such that `git describe <blob-id>` gives a description as
'<commit-ish>:<path>'.  This was implemented at [2]; as seen by the sheer
number of responses (>110), it turns out this is tricky to get right.
The hard part to get right is picking the correct 'commit-ish' as that
could be the commit that (re-)introduced the blob or the blob that
removed the blob; the blob could exist in different branches.

Junio hinted at a different approach of solving this problem, which this
patch implements. Teach the diff machinery another flag for restricting
the information to what is shown. For example:

    $ ./git log --oneline --find-object=v2.0.0:Makefile
    b2feb64309 Revert the whole "ask curl-config" topic for now
    47fbfded53 i18n: only extract comments marked with "TRANSLATORS:"

we observe that the Makefile as shipped with 2.0 was appeared in
v1.9.2-471-g47fbfded53 and in v2.0.0-rc1-5-gb2feb6430b.  The
reason why these commits both occur prior to v2.0.0 are evil
merges that are not found using this new mechanism.

[1] https://stackoverflow.com/questions/223678/which-commit-has-this-blob
[2] https://public-inbox.org/git/20171028004419.10139-1-sbeller@google.com/

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index dd0dba5..f9cf85d 100644 (file)
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -492,6 +492,15 @@ occurrences of that string did not change).
 See the 'pickaxe' entry in linkgit:gitdiffcore[7] for more
 information.
 
+--find-object=<object-id>::
+       Look for differences that change the number of occurrences of
+       the specified object. Similar to `-S`, just the argument is different
+       in that it doesn't search for a specific string but for a specific
+       object id.
++
+The object can be a blob or a submodule commit. It implies the `-t` option in
+`git-log` to also find trees.
+
 --pickaxe-all::
        When `-S` or `-G` finds a change, show all the changes in that
        changeset, not just the files that contain the change
@@ -500,6 +509,7 @@ information.
 --pickaxe-regex::
        Treat the <string> given to `-S` as an extended POSIX regular
        expression to match.
+
 endif::git-format-patch[]
 
 -O<orderfile>::

diff --git a/diff.c b/diff.c
index 5508745..a872bdc 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -4082,6 +4082,7 @@ void diff_setup(struct diff_options *options)
        options->interhunkcontext = diff_interhunk_context_default;
        options->ws_error_highlight = ws_error_highlight_default;
        options->flags.rename_empty = 1;
+       options->objfind = NULL;
 
        /* pathchange left =NULL by default */
        options->change = diff_change;
@@ -4487,6 +4488,23 @@ static int parse_ws_error_highlight_opt(struct diff_options *opt, const char *ar
        return 1;
 }
 
+static int parse_objfind_opt(struct diff_options *opt, const char *arg)
+{
+       struct object_id oid;
+
+       if (get_oid(arg, &oid))
+               return error("unable to resolve '%s'", arg);
+
+       if (!opt->objfind)
+               opt->objfind = xcalloc(1, sizeof(*opt->objfind));
+
+       opt->pickaxe_opts |= DIFF_PICKAXE_KIND_OBJFIND;
+       opt->flags.recursive = 1;
+       opt->flags.tree_in_recursive = 1;
+       oidset_insert(opt->objfind, &oid);
+       return 1;
+}
+
 int diff_opt_parse(struct diff_options *options,
                   const char **av, int ac, const char *prefix)
 {
@@ -4736,7 +4754,8 @@ int diff_opt_parse(struct diff_options *options,
        else if ((argcount = short_opt('O', av, &optarg))) {
                options->orderfile = prefix_filename(prefix, optarg);
                return argcount;
-       }
+       } else if (skip_prefix(arg, "--find-object=", &arg))
+               return parse_objfind_opt(options, arg);
        else if ((argcount = parse_long_opt("diff-filter", av, &optarg))) {
                int offending = parse_diff_filter_opt(optarg, options);
                if (offending)

diff --git a/diff.h b/diff.h
index 9ec4f82..8a56cac 100644 (file)
--- a/diff.h
+++ b/diff.h
@@ -7,6 +7,7 @@
 #include "tree-walk.h"
 #include "pathspec.h"
 #include "object.h"
+#include "oidset.h"
 
 struct rev_info;
 struct diff_options;
@@ -173,6 +174,8 @@ struct diff_options {
        enum diff_words_type word_diff;
        enum diff_submodule_format submodule_format;
 
+       struct oidset *objfind;
+
        /* this is set by diffcore for DIFF_FORMAT_PATCH */
        int found_changes;
 
@@ -325,8 +328,11 @@ extern void diff_setup_done(struct diff_options *);
 
 #define DIFF_PICKAXE_KIND_S    4 /* traditional plumbing counter */
 #define DIFF_PICKAXE_KIND_G    8 /* grep in the patch */
+#define DIFF_PICKAXE_KIND_OBJFIND      16 /* specific object IDs */
 
-#define DIFF_PICKAXE_KINDS_MASK (DIFF_PICKAXE_KIND_S | DIFF_PICKAXE_KIND_G)
+#define DIFF_PICKAXE_KINDS_MASK (DIFF_PICKAXE_KIND_S | \
+                                DIFF_PICKAXE_KIND_G | \
+                                DIFF_PICKAXE_KIND_OBJFIND)
 
 #define DIFF_PICKAXE_IGNORE_CASE       32
 

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 4b5d88e..72bb5a9 100644 (file)
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -124,13 +124,20 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
        mmfile_t mf1, mf2;
        int ret;
 
-       if (!o->pickaxe[0])
-               return 0;
-
        /* ignore unmerged */
        if (!DIFF_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two))
                return 0;
 
+       if (o->objfind) {
+               return  (DIFF_FILE_VALID(p->one) &&
+                        oidset_contains(o->objfind, &p->one->oid)) ||
+                       (DIFF_FILE_VALID(p->two) &&
+                        oidset_contains(o->objfind, &p->two->oid));
+       }
+
+       if (!o->pickaxe[0])
+               return 0;
+
        if (o->flags.allow_textconv) {
                textconv_one = get_textconv(p->one);
                textconv_two = get_textconv(p->two);
@@ -226,20 +233,22 @@ void diffcore_pickaxe(struct diff_options *o)
                        cflags |= REG_ICASE;
                regcomp_or_die(&regex, needle, cflags);
                regexp = &regex;
-       } else if (o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE &&
-                  has_non_ascii(needle)) {
-               struct strbuf sb = STRBUF_INIT;
-               int cflags = REG_NEWLINE | REG_ICASE;
-
-               basic_regex_quote_buf(&sb, needle);
-               regcomp_or_die(&regex, sb.buf, cflags);
-               strbuf_release(&sb);
-               regexp = &regex;
-       } else {
-               kws = kwsalloc(o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE
-                              ? tolower_trans_tbl : NULL);
-               kwsincr(kws, needle, strlen(needle));
-               kwsprep(kws);
+       } else if (opts & DIFF_PICKAXE_KIND_S) {
+               if (o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE &&
+                   has_non_ascii(needle)) {
+                       struct strbuf sb = STRBUF_INIT;
+                       int cflags = REG_NEWLINE | REG_ICASE;
+
+                       basic_regex_quote_buf(&sb, needle);
+                       regcomp_or_die(&regex, sb.buf, cflags);
+                       strbuf_release(&sb);
+                       regexp = &regex;
+               } else {
+                       kws = kwsalloc(o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE
+                                      ? tolower_trans_tbl : NULL);
+                       kwsincr(kws, needle, strlen(needle));
+                       kwsprep(kws);
+               }
        }
 
        /* Might want to warn when both S and G are on; I don't care... */
@@ -248,7 +257,7 @@ void diffcore_pickaxe(struct diff_options *o)
 
        if (regexp)
                regfree(regexp);
-       else
+       if (kws)
                kwsfree(kws);
        return;
 }

diff --git a/revision.c b/revision.c
index 5d11eca..30f65b3 100644 (file)
--- a/revision.c
+++ b/revision.c
@@ -2412,6 +2412,9 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
            revs->diffopt.flags.follow_renames)
                revs->diff = 1;
 
+       if (revs->diffopt.objfind)
+               revs->simplify_history = 0;
+
        if (revs->topo_order)
                revs->limited = 1;
 

diff --git a/t/t4064-diff-oidfind.sh b/t/t4064-diff-oidfind.sh
new file mode 100755 (executable)
index 0000000..3bdf317
--- /dev/null
+++ b/t/t4064-diff-oidfind.sh
@@ -0,0 +1,68 @@
+#!/bin/sh
+
+test_description='test finding specific blobs in the revision walking'
+. ./test-lib.sh
+
+test_expect_success 'setup ' '
+       git commit --allow-empty -m "empty initial commit" &&
+
+       echo "Hello, world!" >greeting &&
+       git add greeting &&
+       git commit -m "add the greeting blob" && # borrowed from Git from the Bottom Up
+       git tag -m "the blob" greeting $(git rev-parse HEAD:greeting) &&
+
+       echo asdf >unrelated &&
+       git add unrelated &&
+       git commit -m "unrelated history" &&
+
+       git revert HEAD^ &&
+
+       git commit --allow-empty -m "another unrelated commit"
+'
+
+test_expect_success 'find the greeting blob' '
+       cat >expect <<-EOF &&
+       Revert "add the greeting blob"
+       add the greeting blob
+       EOF
+
+       git log --format=%s --find-object=greeting^{blob} >actual &&
+
+       test_cmp expect actual
+'
+
+test_expect_success 'setup a tree' '
+       mkdir a &&
+       echo asdf >a/file &&
+       git add a/file &&
+       git commit -m "add a file in a subdirectory"
+'
+
+test_expect_success 'find a tree' '
+       cat >expect <<-EOF &&
+       add a file in a subdirectory
+       EOF
+
+       git log --format=%s -t --find-object=HEAD:a >actual &&
+
+       test_cmp expect actual
+'
+
+test_expect_success 'setup a submodule' '
+       test_create_repo sub &&
+       test_commit -C sub sub &&
+       git submodule add ./sub sub &&
+       git commit -a -m "add sub"
+'
+
+test_expect_success 'find a submodule' '
+       cat >expect <<-EOF &&
+       add sub
+       EOF
+
+       git log --format=%s --find-object=HEAD:sub >actual &&
+
+       test_cmp expect actual
+'
+
+test_done