diffcore-pickaxe: scope -G to the -L tracked range

git log -L scopes its diff output to the tracked range, but pickaxe
(-S, -G) still runs in diffcore over the whole-file change, so -L -G
selects a commit whenever the pattern appears in any added or removed
line of the file, even outside the tracked range.

Teach -G to honor the range.  diff_grep() already runs an xdiff pass
and greps the +/- lines; route that pass through the line-range filter
so only the tracked range's lines are grepped.  Expose the filter as
diff_emit_line_ranges(), a line-range-scoped xdi_diff_outf(), thread
the filepair's line_ranges through the pickaxe callback, and pass it
from pickaxe_match().  Skip scoping under textconv, whose output is not
in the original file's line coordinates.

-G needs only a hit/no-hit answer, so the line-number concerns the
filter handles for patch and check output do not apply here.

-S is left matching the whole file: it counts needle occurrences per
blob rather than grepping the diff, so scoping it needs a different
approach, left to a follow-up.  has_changes() takes the range parameter
but ignores it for now.

Document the resulting -L pickaxe scoping: -G is range-scoped, while -S
still matches the whole file.

Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>

Author: mmontalbo

Documentation/line-range-options.adoc

@@ -20,6 +20,9 @@
 +
 Patch formatting options such as `--word-diff`, `--color-moved`,
 `--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
-as are pickaxe options (`-S`, `-G`) and `--diff-filter`.
+as are pickaxe options (`-S`, `-G`) and `--diff-filter`.  `-G` is
+scoped to the tracked range; `-S` is still evaluated over the whole
+file, so an `-S` query may select a commit for a change outside the
+range.
 +
 include::line-range-format.adoc[]

diff.c

@@ -2812,6 +2812,27 @@ static int line_range_filter_diff(struct line_range_filter *filter,
 	return ret;
 }
 
+/*
+ * Public entry point: run an xdiff of (one, two) but forward only the lines
+ * inside the given (post-image) line ranges to line_fn, the way "git log -L"
+ * scopes its output.  Lets a diff-driven operation outside diff.c (e.g.
+ * pickaxe -G) restrict itself to a tracked range.  Returns the latched return
+ * value of line_fn (so a consumer that signals a hit via a non-zero return
+ * works), or non-zero on xdiff failure.
+ */
+int diff_emit_line_ranges(mmfile_t *one, mmfile_t *two,
+			  const struct range_set *ranges,
+			  xdiff_emit_line_fn line_fn, void *cb_data,
+			  xpparam_t *xpp, xdemitconf_t *xecfg)
+{
+	struct line_range_filter filter;
+
+	/* the filter tracks the post-image position from hunk headers */
+	xecfg->flags &= ~XDL_EMIT_NO_HUNK_HDR;
+	line_range_filter_init(&filter, ranges, line_fn, cb_data);
+	return line_range_filter_diff(&filter, one, two, xpp, xecfg);
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;

diffcore-pickaxe.c

@@ -16,7 +16,8 @@
 
 typedef int (*pickaxe_fn)(mmfile_t *one, mmfile_t *two,
 			  struct diff_options *o,
-			  regex_t *regexp, kwset_t kws);
+			  regex_t *regexp, kwset_t kws,
+			  const struct range_set *ranges);
 
 struct diffgrep_cb {
 	regex_t *regexp;
@@ -42,16 +43,18 @@ static int diffgrep_consume(void *priv, char *line, unsigned long len)
 
 static int diff_grep(mmfile_t *one, mmfile_t *two,
 		     struct diff_options *o,
-		     regex_t *regexp, kwset_t kws UNUSED)
+		     regex_t *regexp, kwset_t kws UNUSED,
+		     const struct range_set *ranges)
 {
 	struct diffgrep_cb ecbdata;
 	xpparam_t xpp;
 	xdemitconf_t xecfg;
 	int ret;
 
 	/*
-	 * We have both sides; need to run textual diff and see if
-	 * the pattern appears on added/deleted lines.
+	 * We have both sides; need to run textual diff and see if the
+	 * pattern appears on added/deleted lines.  Under -L (ranges set),
+	 * forward only the tracked range's lines so the match is scoped.
 	 */
 	memset(&xpp, 0, sizeof(xpp));
 	memset(&xecfg, 0, sizeof(xecfg));
@@ -65,8 +68,12 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	 * An xdiff error might be our "data->hit" from above. See the
 	 * comment for xdiff_emit_line_fn in xdiff-interface.h
 	 */
-	ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
-			    &ecbdata, &xpp, &xecfg);
+	if (ranges)
+		ret = diff_emit_line_ranges(one, two, ranges, diffgrep_consume,
+					    &ecbdata, &xpp, &xecfg);
+	else
+		ret = xdi_diff_outf(one, two, NULL, diffgrep_consume,
+				    &ecbdata, &xpp, &xecfg);
 	if (ecbdata.hit)
 		return 1;
 	if (ret)
@@ -119,8 +126,13 @@ static unsigned int contains(mmfile_t *mf, regex_t *regexp, kwset_t kws,
 
 static int has_changes(mmfile_t *one, mmfile_t *two,
 		       struct diff_options *o UNUSED,
-		       regex_t *regexp, kwset_t kws)
+		       regex_t *regexp, kwset_t kws,
+		       const struct range_set *ranges UNUSED)
 {
+	/*
+	 * -S counts needle occurrences in each whole blob.  Scoping this to
+	 * a -L range is left to a follow-up; for now -S ignores the range.
+	 */
 	unsigned int c1 = one ? contains(one, regexp, kws, 0) : 0;
 	unsigned int c2 = two ? contains(two, regexp, kws, c1 + 1) : 0;
 	return c1 != c2;
@@ -169,7 +181,13 @@ static int pickaxe_match(struct diff_filepair *p, struct diff_options *o,
 	mf1.size = fill_textconv(o->repo, textconv_one, p->one, &mf1.ptr);
 	mf2.size = fill_textconv(o->repo, textconv_two, p->two, &mf2.ptr);
 
-	ret = fn(&mf1, &mf2, o, regexp, kws);
+	/*
+	 * -L scopes the search to the tracked range.  Skip that under
+	 * textconv: the range is in original-file line coordinates, which do
+	 * not map onto textconv output, so fall back to the whole file.
+	 */
+	ret = fn(&mf1, &mf2, o, regexp, kws,
+		 (textconv_one || textconv_two) ? NULL : p->line_ranges);
 
 	if (textconv_one)
 		free(mf1.ptr);

t/t4211-line-log.sh

@@ -1078,4 +1078,33 @@ test_expect_success '--check does not report blank-at-eof outside the range' '
 	test_grep ! "blank line at EOF" actual
 '
 
+test_expect_success '-L -G is scoped to the tracked range' '
+	git checkout --orphan grep-scope &&
+	git reset --hard &&
+	cat >gp.c <<-\EOF &&
+	int func1()
+	{
+	    return ALPHA;
+	}
+
+	int func2()
+	{
+	    return BETA;
+	}
+	EOF
+	git add gp.c &&
+	test_tick &&
+	git commit -m "add gp.c" &&
+	sed -e "s/ALPHA/ALPHA2/" -e "s/BETA/BETA2/" gp.c >tmp &&
+	mv tmp gp.c &&
+	git commit -a -m "touch both functions" &&
+	# The commit changes ALPHA (func1) and BETA (func2).  Tracking func2,
+	# -G BETA matches its in-range change; -G ALPHA must not, since ALPHA
+	# changes only outside the tracked range.
+	git log -L:func2:gp.c -G BETA --format=%s >actual &&
+	test_grep "touch both functions" actual &&
+	git log -L:func2:gp.c -G ALPHA --format=%s >actual &&
+	test_grep ! "touch both functions" actual
+'
+
 test_done