prefix_path: support prefixes not ending in trailing slash

The prefix_path_gently() -- and its wrapper prefix_path() -- function
normalizes the provided path and optionally adds the provided prefix to
relative paths. If the prefix does not end in a trailing slash, the
function will combine the last component of the prefix with the first
component of the relative path. This is unlikely to produce a desirable
result.

Teach prefix_path_gently() to check if the prefix ends in a slash. If it
does not, then insert a slash between the prefix and the path. Take care
to avoid inserting a slash if the prefix is empty.

Add test cases to cover the relative path behavior, which was previously
untested.

Signed-off-by: Jacob Keller <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jacob-keller

setup.c

@@ -139,7 +139,9 @@ char *prefix_path_gently(const char *prefix, int len,
 			return NULL;
 		}
 	} else {
-		sanitized = xstrfmt("%.*s%s", len, len ? prefix : "", path);
+		sanitized = xstrfmt("%.*s%s%s", len, len ? prefix : "",
+				    !len || prefix[len - 1] == '/' ? "" : "/",
+				    path);
 		if (remaining_prefix)
 			*remaining_prefix = len;
 		if (normalize_path_copy_len(sanitized, sanitized, remaining_prefix)) {

t/t0060-path-utils.sh

@@ -307,6 +307,24 @@ test_expect_success SYMLINKS 'prefix_path works with absolute path to a symlink
 	test_cmp expect actual
 '
 
+test_expect_success 'prefix_path works with relative path' '
+	echo "prefix/a" >expect &&
+	test-tool path-utils prefix_path "prefix/" "a" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'prefix_path works with relative path and prefix not ending in /' '
+	echo "prefix/a" >expect &&
+	test-tool path-utils prefix_path "prefix" "a" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'prefix_path works with relative path and empty prefix' '
+	echo "a" >expect &&
+	test-tool path-utils prefix_path "" "a" >actual &&
+	test_cmp expect actual
+'
+
 relative_path /foo/a/b/c/	/foo/a/b/	c/
 relative_path /foo/a/b/c/	/foo/a/b	c/
 relative_path /foo/a//b//c/	///foo/a/b//	c/		POSIX