merge-file: add --diff-algorithm option
Make it possible to use other diff algorithms than the 'myers'
default algorithm, when using the 'git merge-file' command, to help
avoid spurious conflicts by selecting a more recent algorithm such
as 'histogram', for instance when using 'git merge-file' as part of
a custom merge driver.
Signed-off-by: Antonin Delpeuch <antonin@delpeuch.eu>
Reviewed-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-merge-file.txt b/Documentation/git-merge-file.txt
index 6a081ea..71915a0 100644
--- a/Documentation/git-merge-file.txt
+++ b/Documentation/git-merge-file.txt
@@ -92,6 +92,12 @@
Instead of leaving conflicts in the file, resolve conflicts
favouring our (or their or both) side of the lines.
+--diff-algorithm={patience|minimal|histogram|myers}::
+ Use a different diff algorithm while merging. The current default is "myers",
+ but selecting more recent algorithm such as "histogram" can help
+ avoid mismerges that occur due to unimportant matching lines
+ (such as braces from distinct functions). See also
+ linkgit:git-diff[1] `--diff-algorithm`.
EXAMPLES
--------
diff --git a/builtin/merge-file.c b/builtin/merge-file.c
index 832c93d..1f98733 100644
--- a/builtin/merge-file.c
+++ b/builtin/merge-file.c
@@ -1,5 +1,6 @@
#include "builtin.h"
#include "abspath.h"
+#include "diff.h"
#include "hex.h"
#include "object-name.h"
#include "object-store.h"
@@ -28,6 +29,30 @@ static int label_cb(const struct option *opt, const char *arg, int unset)
return 0;
}
+static int set_diff_algorithm(xpparam_t *xpp,
+ const char *alg)
+{
+ long diff_algorithm = parse_algorithm_value(alg);
+ if (diff_algorithm < 0)
+ return -1;
+ xpp->flags = (xpp->flags & ~XDF_DIFF_ALGORITHM_MASK) | diff_algorithm;
+ return 0;
+}
+
+static int diff_algorithm_cb(const struct option *opt,
+ const char *arg, int unset)
+{
+ xpparam_t *xpp = opt->value;
+
+ BUG_ON_OPT_NEG(unset);
+
+ if (set_diff_algorithm(xpp, arg))
+ return error(_("option diff-algorithm accepts \"myers\", "
+ "\"minimal\", \"patience\" and \"histogram\""));
+
+ return 0;
+}
+
int cmd_merge_file(int argc, const char **argv, const char *prefix)
{
const char *names[3] = { 0 };
@@ -48,6 +73,9 @@ int cmd_merge_file(int argc, const char **argv, const char *prefix)
XDL_MERGE_FAVOR_THEIRS),
OPT_SET_INT(0, "union", &xmp.favor, N_("for conflicts, use a union version"),
XDL_MERGE_FAVOR_UNION),
+ OPT_CALLBACK_F(0, "diff-algorithm", &xmp.xpp, N_("<algorithm>"),
+ N_("choose a diff algorithm"),
+ PARSE_OPT_NONEG, diff_algorithm_cb),
OPT_INTEGER(0, "marker-size", &xmp.marker_size,
N_("for conflicts, use this marker size")),
OPT__QUIET(&quiet, N_("do not warn about conflicts")),
diff --git a/t/t6403-merge-file.sh b/t/t6403-merge-file.sh
index 2c92209..fb872c5 100755
--- a/t/t6403-merge-file.sh
+++ b/t/t6403-merge-file.sh
@@ -56,7 +56,67 @@
deduxit me super semitas jusitiae,
EOF
- printf "propter nomen suum." >>new4.txt
+ printf "propter nomen suum." >>new4.txt &&
+
+ cat >base.c <<-\EOF &&
+ int f(int x, int y)
+ {
+ if (x == 0)
+ {
+ return y;
+ }
+ return x;
+ }
+
+ int g(size_t u)
+ {
+ while (u < 30)
+ {
+ u++;
+ }
+ return u;
+ }
+ EOF
+
+ cat >ours.c <<-\EOF &&
+ int g(size_t u)
+ {
+ while (u < 30)
+ {
+ u++;
+ }
+ return u;
+ }
+
+ int h(int x, int y, int z)
+ {
+ if (z == 0)
+ {
+ return x;
+ }
+ return y;
+ }
+ EOF
+
+ cat >theirs.c <<-\EOF
+ int f(int x, int y)
+ {
+ if (x == 0)
+ {
+ return y;
+ }
+ return x;
+ }
+
+ int g(size_t u)
+ {
+ while (u > 34)
+ {
+ u--;
+ }
+ return u;
+ }
+ EOF
'
test_expect_success 'merge with no changes' '
@@ -447,4 +507,66 @@
grep "not a git repository" err
'
+test_expect_success 'merging C files with "myers" diff algorithm creates some spurious conflicts' '
+ cat >expect.c <<-\EOF &&
+ int g(size_t u)
+ {
+ while (u < 30)
+ {
+ u++;
+ }
+ return u;
+ }
+
+ int h(int x, int y, int z)
+ {
+ <<<<<<< ours.c
+ if (z == 0)
+ ||||||| base.c
+ while (u < 30)
+ =======
+ while (u > 34)
+ >>>>>>> theirs.c
+ {
+ <<<<<<< ours.c
+ return x;
+ ||||||| base.c
+ u++;
+ =======
+ u--;
+ >>>>>>> theirs.c
+ }
+ return y;
+ }
+ EOF
+
+ test_must_fail git merge-file -p --diff3 --diff-algorithm myers ours.c base.c theirs.c >myers_output.c &&
+ test_cmp expect.c myers_output.c
+'
+
+test_expect_success 'merging C files with "histogram" diff algorithm avoids some spurious conflicts' '
+ cat >expect.c <<-\EOF &&
+ int g(size_t u)
+ {
+ while (u > 34)
+ {
+ u--;
+ }
+ return u;
+ }
+
+ int h(int x, int y, int z)
+ {
+ if (z == 0)
+ {
+ return x;
+ }
+ return y;
+ }
+ EOF
+
+ git merge-file -p --diff3 --diff-algorithm histogram ours.c base.c theirs.c >histogram_output.c &&
+ test_cmp expect.c histogram_output.c
+'
+
test_done
