format-patch: add format.noprefix option

The previous commit dropped support for diff.noprefix in format-patch.
While this will do the right thing in most cases (where sending patches
without a prefix was an accidental side effect of the sender preferring
to see their local patches without prefixes), it left no good option for
a project or workflow where you really do want to send patches without
prefixes. You'd be stuck using "--no-prefix" for every invocation.

So let's add a config option specific to format-patch that enables this
behavior. That gives people who have such a workflow a way to get what
they want, but makes it hard to accidentally trigger it.

A more backwards-compatible way of doing the transition would be to have
format.noprefix default to diff.noprefix when it's not set. But that
doesn't really help the "accidental" problem; people would have to
manually set format.noprefix=false. And it's unlikely that anybody
really wants format.noprefix=true in the first place. I'm adding it here
mostly as an escape hatch, not because anybody has expressed any
interest in it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/format.txt

@@ -144,3 +144,10 @@ will only show notes from `refs/notes/bar`.
 format.mboxrd::
 	A boolean value which enables the robust "mboxrd" format when
 	`--stdout` is in use to escape "^>+From " lines.
+
+format.noprefix::
+	If set, do not show any source or destination prefix in patches.
+	This is equivalent to the `diff.noprefix` option used by `git
+	diff` (but which is not respected by `format-patch`). Note that
+	by setting this, the receiver of any patches you generate will
+	have to apply them using the `-p0` option.

builtin/log.c

@@ -56,6 +56,7 @@ static int stdout_mboxrd;
 static const char *fmt_patch_subject_prefix = "PATCH";
 static int fmt_patch_name_max = FORMAT_PATCH_NAME_MAX_DEFAULT;
 static const char *fmt_pretty;
+static int format_no_prefix;
 
 static const char * const builtin_log_usage[] = {
 	N_("git log [<options>] [<revision-range>] [[--] <path>...]"),
@@ -1084,6 +1085,10 @@ static int git_format_config(const char *var, const char *value, void *cb)
 		stdout_mboxrd = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "format.noprefix")) {
+		format_no_prefix = 1;
+		return 0;
+	}
 
 	/*
 	 * ignore some porcelain config which would otherwise be parsed by
@@ -2002,6 +2007,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	s_r_opt.def = "HEAD";
 	s_r_opt.revarg_opt = REVARG_COMMITTISH;
 
+	if (format_no_prefix)
+		diff_set_noprefix(&rev.diffopt);
+
 	if (default_attach) {
 		rev.mime_boundary = default_attach;
 		rev.no_inline = 1;

t/t4014-format-patch.sh

@@ -2391,4 +2391,15 @@ test_expect_success 'format-patch does not respect diff.noprefix' '
 	grep "^--- a/blorp" actual
 '
 
+test_expect_success 'format-patch respects format.noprefix' '
+	git -c format.noprefix format-patch -1 --stdout >actual &&
+	grep "^--- blorp" actual
+'
+
+test_expect_success 'format-patch --default-prefix overrides format.noprefix' '
+	git -c format.noprefix \
+		format-patch -1 --default-prefix --stdout >actual &&
+	grep "^--- a/blorp" actual
+'
+
 test_done