[PATCH v6 6/9] diff: bypass diff process with --no-ext-diff and in format-patch
From: Michael Montalbo via GitGitGadget <hidden>
Date: 2026-07-26 18:51:41
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
From: Michael Montalbo <redacted> Make --no-ext-diff disable diff.<driver>.process in addition to diff.<driver>.command. Although the two mechanisms work differently (command replaces Git's output, process feeds hunks back into the pipeline), both invoke external tools and --no-ext-diff means "no external tools." Replace the OPT_BOOL for --ext-diff with an OPT_CALLBACK that sets both allow_external and no_diff_process, so a single option controls both. Passing --ext-diff explicitly clears no_diff_process, so a later --ext-diff overrides an earlier --no-ext-diff. Disable the diff process unconditionally in format-patch so that generated patches are always based on the builtin diff algorithm and can be applied reliably by recipients who do not have the external tool. Document that --diff-algorithm also bypasses the diff process, since it forces the builtin algorithm. Signed-off-by: Michael Montalbo <redacted> --- Documentation/diff-algorithm-option.adoc | 3 +++ Documentation/diff-options.adoc | 4 +++- Documentation/gitattributes.adoc | 6 +++--- builtin/log.c | 7 +++++++ diff.c | 16 ++++++++++++++-- diff.h | 5 ++++- t/t4080-diff-process.sh | 16 ++++++++++++++++ 7 files changed, 50 insertions(+), 7 deletions(-)
diff --git a/Documentation/diff-algorithm-option.adoc b/Documentation/diff-algorithm-option.adoc
index 8e3a0b63d7..4d7e2ec35f 100644
--- a/Documentation/diff-algorithm-option.adoc
+++ b/Documentation/diff-algorithm-option.adoc@@ -18,3 +18,6 @@ For instance, if you configured the `diff.algorithm` variable to a non-default value and want to use the default one, then you have to use `--diff-algorithm=default` option. ++ +If you explicitly choose a diff algorithm, it also bypasses +`diff.<driver>.process` (see linkgit:gitattributes[5]).
diff --git a/Documentation/diff-options.adoc b/Documentation/diff-options.adoc
index 8a63b5e164..18b8b0ed24 100644
--- a/Documentation/diff-options.adoc
+++ b/Documentation/diff-options.adoc@@ -825,7 +825,9 @@ endif::git-format-patch[] to use this option with linkgit:git-log[1] and friends. `--no-ext-diff`:: - Disallow external diff drivers. + Disallow external diff helpers, including + `diff.<driver>.command` and `diff.<driver>.process` + (see linkgit:gitattributes[5]). `--textconv`:: `--no-textconv`::
diff --git a/Documentation/gitattributes.adoc b/Documentation/gitattributes.adoc
index f4ca4a8c7e..a03fb9deb1 100644
--- a/Documentation/gitattributes.adoc
+++ b/Documentation/gitattributes.adoc@@ -1073,9 +1073,9 @@ display, which is covered above); and combined diffs (`--cc` and merge diffs), whose protocol would have to be extended from a single old/new pair to one comparison per merge parent. -`--diff-algorithm` bypasses the process entirely, for every feature -listed above. The whitespace-ignoring options (`-w`, -`--ignore-space-change`, `--ignore-blank-lines`, and the like), +`--no-ext-diff` and `--diff-algorithm` bypass the process entirely, +for every feature listed above. The whitespace-ignoring options +(`-w`, `--ignore-space-change`, `--ignore-blank-lines`, and the like), `-I<regex>`, and `--anchored` also bypass it for the affected files: the tool is never told about these options, so it could not honor them, and Git falls back to the builtin diff, which does.
diff --git a/builtin/log.c b/builtin/log.c
index e464b30af4..363052f468 100644
--- a/builtin/log.c
+++ b/builtin/log.c@@ -2217,6 +2217,13 @@ int cmd_format_patch(int argc, if (argc > 1) die(_("unrecognized argument: %s"), argv[1]); + /* + * Disable diff.<driver>.process so that patches generated by + * format-patch are always based on the builtin diff algorithm + * and can be applied reliably. + */ + rev.diffopt.flags.no_diff_process = 1; + if (rev.diffopt.output_format & DIFF_FORMAT_NAME) die(_("--name-only does not make sense")); if (rev.diffopt.output_format & DIFF_FORMAT_NAME_STATUS)
diff --git a/diff.c b/diff.c
index aab012f922..1a487bb353 100644
--- a/diff.c
+++ b/diff.c@@ -6071,6 +6071,17 @@ static int diff_opt_submodule(const struct option *opt, return 0; } +static int diff_opt_ext_diff(const struct option *opt, + const char *arg, int unset) +{ + struct diff_options *options = opt->value; + + BUG_ON_OPT_ARG(arg); + options->flags.allow_external = !unset; + options->flags.no_diff_process = unset; + return 0; +} + static int diff_opt_textconv(const struct option *opt, const char *arg, int unset) {
@@ -6401,8 +6412,9 @@ struct option *add_diff_options(const struct option *opts, N_("exit with 1 if there were differences, 0 otherwise")), OPT_BOOL(0, "quiet", &options->flags.quick, N_("disable all output of the program")), - OPT_BOOL(0, "ext-diff", &options->flags.allow_external, - N_("allow an external diff helper to be executed")), + OPT_CALLBACK_F(0, "ext-diff", options, NULL, + N_("allow an external diff helper to be executed"), + PARSE_OPT_NOARG, diff_opt_ext_diff), OPT_CALLBACK_F(0, "textconv", options, NULL, N_("run external text conversion filters when comparing binary files"), PARSE_OPT_NOARG, diff_opt_textconv),
diff --git a/diff.h b/diff.h
index 7dc157968d..ee034d240d 100644
--- a/diff.h
+++ b/diff.h@@ -173,7 +173,10 @@ struct diff_flags { */ unsigned allow_external; - /** Disables diff.<driver>.process. */ + /** + * Disables diff.<driver>.process. Set by --no-ext-diff and by + * format-patch. + */ unsigned no_diff_process; /**
diff --git a/t/t4080-diff-process.sh b/t/t4080-diff-process.sh
index 3b75df082e..7e71b70ab9 100755
--- a/t/t4080-diff-process.sh
+++ b/t/t4080-diff-process.sh@@ -398,6 +398,22 @@ test_expect_success 'diff process bypassed by --diff-algorithm' ' test_path_is_missing backend.log ' +test_expect_success 'diff process bypassed by --no-ext-diff' ' + test_when_finished "rm -f backend.log" && + git -c diff.cdiff.process="$BACKEND --log=backend.log" \ + diff --no-ext-diff worddiff.c >actual && + test_grep "return 999" actual && + test_path_is_missing backend.log +' + +test_expect_success 'diff process not used by format-patch' ' + test_when_finished "rm -f backend.log" && + git -c diff.cdiff.process="$BACKEND --log=backend.log" \ + format-patch -1 --stdout -- logtest.c >actual && + test_grep "return 2" actual && + test_path_is_missing backend.log +' + test_expect_success 'diff process bypassed under whitespace-ignoring flags' ' test_when_finished "rm -f backend.log" && printf "a\nb\nc\n" >wsbypass.c &&
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