refspec: support asterisks in the middle of a pattern

We used to assume a refspec would only have an asterisk in the middle of
their respective pattern. This has not been a valid assumption for some
time now with git.

Instead of assuming where the asterisk is going to be, change the logic
to treat each pattern as having two halves with a replacement bit in the
middle, where the asterisk is.

src/refspec.c

@@ -181,30 +181,44 @@ int git_refspec_dst_matches(const git_refspec *refspec, const char *refname)
 static int refspec_transform(
 	git_buf *out, const char *from, const char *to, const char *name)
 {
-	size_t to_len   = to   ? strlen(to)   : 0;
-	size_t from_len = from ? strlen(from) : 0;
-	size_t name_len = name ? strlen(name) : 0;
+	const char *from_star, *to_star;
+	const char *name_slash, *from_slash;
+	size_t replacement_len, star_offset;
 
 	git_buf_sanitize(out);
+	git_buf_clear(out);
 
-	if (git_buf_set(out, to, to_len) < 0)
-		return -1;
-
-	if (to_len > 0) {
-		/* No '*' at the end of 'to' means that refspec is mapped to one
-		 * specific branch, so no actual transformation is needed.
+	/*
+	 * There are two parts to each side of a refspec, the bit
+	 * before the star and the bit after it. The star can be in
+	 * the middle of the pattern, so we need to look at each bit
+	 * individually.
 	 */
-		if (out->ptr[to_len - 1] != '*')
-			return 0;
-		git_buf_shorten(out, 1); /* remove trailing '*' copied from 'to' */
-	}
+	from_star = strchr(from, '*');
+	to_star = strchr(to, '*');
+
+	assert(from_star && to_star);
+
+	/* star offset, both in 'from' and in 'name' */
+	star_offset = from_star - from;
+
+	/* the first half is copied over */
+	git_buf_put(out, to, to_star - to);
+
+	/* then we copy over the replacement, from the star's offset to the next slash in 'name' */
+	name_slash = strchr(name + star_offset, '/');
+	if (!name_slash)
+		name_slash = strrchr(name, '\0');
+
+	/* if there is no slash after the star in 'from', we want to copy everything over */
+	from_slash = strchr(from + star_offset, '/');
+	if (!from_slash)
+		name_slash = strrchr(name, '\0');
 
-	if (from_len > 0) /* ignore trailing '*' from 'from' */
-		from_len--;
-	if (from_len > name_len)
-		from_len = name_len;
+	replacement_len = (name_slash - name) - star_offset;
+	git_buf_put(out, name + star_offset, replacement_len);
 
-	return git_buf_put(out, name + from_len, name_len - from_len);
+	return git_buf_puts(out, to_star + 1);
 }
 
 int git_refspec_transform(git_buf *out, const git_refspec *spec, const char *name)

tests/network/refspecs.c

@@ -84,4 +84,27 @@ void test_network_refspecs__parsing(void)
 
 	assert_refspec(GIT_DIRECTION_FETCH, "master", true);
 	assert_refspec(GIT_DIRECTION_PUSH, "master", true);
+
+	assert_refspec(GIT_DIRECTION_FETCH, "refs/pull/*/head:refs/remotes/origin/pr/*", true);
+}
+
+void assert_transform(const char *refspec, const char *name, const char *result)
+{
+	git_refspec spec;
+	git_buf buf = GIT_BUF_INIT;
+
+	git_refspec__parse(&spec, refspec, true);
+	cl_git_pass(git_refspec_transform(&buf, &spec, name));
+	cl_assert_equal_s(result, buf.ptr);
+
+	git_buf_free(&buf);
+	git_refspec__free(&spec);
+}
+
+void test_network_refspecs__transform_mid_star(void)
+{
+	assert_transform("refs/pull/*/head:refs/remotes/origin/pr/*", "refs/pull/23/head", "refs/remotes/origin/pr/23");
+	assert_transform("refs/heads/*:refs/remotes/origin/*", "refs/heads/master", "refs/remotes/origin/master");
+	assert_transform("refs/heads/*:refs/heads/*", "refs/heads/master", "refs/heads/master");
+	assert_transform("refs/*:refs/*", "refs/heads/master", "refs/heads/master");
 }