fast-export: deal with tag objects that do not have a tagger

When no tagger was found (old Git produced tags like this),
no "tagger" line is printed (but this is incompatible with the current
git fast-import).

Alternatively, you can pass the option --fake-missing-tagger, forcing
fast-export to fake a tagger

	Unspecified Tagger <no-tagger>

with a tag date of the beginning of (Unix) time in the case of a missing
tagger, so that fast-import is still able to import the result.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-fast-export.txt

@@ -65,6 +65,12 @@ If the backend uses a similar \--import-marks file, this allows for
 incremental bidirectional exporting of the repository by keeping the
 marks the same across runs.
 
+--fake-missing-tagger::
+	Some old repositories have tags without a tagger.  The
+	fast-import protocol was pretty strict about that, and did not
+	allow that.  So fake a tagger to be able to fast-import the
+	output.
+
 
 EXAMPLES
 --------

builtin-fast-export.c

@@ -24,6 +24,7 @@ static const char *fast_export_usage[] = {
 
 static int progress;
 static enum { VERBATIM, WARN, STRIP, ABORT } signed_tag_mode = ABORT;
+static int fake_missing_tagger;
 
 static int parse_opt_signed_tag_mode(const struct option *opt,
 				     const char *arg, int unset)
@@ -297,10 +298,17 @@ static void handle_tag(const char *name, struct tag *tag)
 		message_size = strlen(message);
 	}
 	tagger = memmem(buf, message ? message - buf : size, "\ntagger ", 8);
-	if (!tagger)
-		die ("No tagger for tag %s", sha1_to_hex(tag->object.sha1));
-	tagger++;
-	tagger_end = strchrnul(tagger, '\n');
+	if (!tagger) {
+		if (fake_missing_tagger)
+			tagger = "tagger Unspecified Tagger "
+				"<unspecified-tagger> 0 +0000";
+		else
+			tagger = "";
+		tagger_end = tagger + strlen(tagger);
+	} else {
+		tagger++;
+		tagger_end = strchrnul(tagger, '\n');
+	}
 
 	/* handle signed tags */
 	if (message) {
@@ -326,9 +334,10 @@ static void handle_tag(const char *name, struct tag *tag)
 
 	if (!prefixcmp(name, "refs/tags/"))
 		name += 10;
-	printf("tag %s\nfrom :%d\n%.*s\ndata %d\n%.*s\n",
+	printf("tag %s\nfrom :%d\n%.*s%sdata %d\n%.*s\n",
 	       name, get_object_mark(tag->tagged),
 	       (int)(tagger_end - tagger), tagger,
+	       tagger == tagger_end ? "" : "\n",
 	       (int)message_size, (int)message_size, message ? message : "");
 }
 
@@ -483,6 +492,8 @@ int cmd_fast_export(int argc, const char **argv, const char *prefix)
 			     "Dump marks to this file"),
 		OPT_STRING(0, "import-marks", &import_filename, "FILE",
 			     "Import marks from this file"),
+		OPT_BOOLEAN(0, "fake-missing-tagger", &fake_missing_tagger,
+			     "Fake a tagger when tags lack one"),
 		OPT_END()
 	};
 

t/t9301-fast-export.sh

@@ -239,4 +239,24 @@ test_expect_success 'fast-export | fast-import when master is tagged' '
 
 '
 
+cat > tag-content << EOF
+object $(git rev-parse HEAD)
+type commit
+tag rosten
+EOF
+
+test_expect_success 'cope with tagger-less tags' '
+
+	TAG=$(git hash-object -t tag -w tag-content) &&
+	git update-ref refs/tags/sonnenschein $TAG &&
+	git fast-export -C -C --signed-tags=strip --all > output &&
+	test $(grep -c "^tag " output) = 4 &&
+	! grep "Unspecified Tagger" output &&
+	git fast-export -C -C --signed-tags=strip --all \
+		--fake-missing-tagger > output &&
+	test $(grep -c "^tag " output) = 4 &&
+	grep "Unspecified Tagger" output
+
+'
+
 test_done