shared: add path_compare(), an ordering path comparison

... and make path_equal() a simple wrapper around it.

3 files changed, 53 insertions, 21 deletions

diff --git a/src/shared/path-util.c b/src/shared/path-util.c
index cdc61b1a79..53c0079760 100644
--- a/src/shared/path-util.c
+++ b/src/shared/path-util.c
@@ -400,12 +400,18 @@ char* path_startswith(const char *path, const char *prefix) {
         }
 }
 
-bool path_equal(const char *a, const char *b) {
+int path_compare(const char *a, const char *b) {
+        int d;
+
         assert(a);
         assert(b);
 
-        if ((a[0] == '/') != (b[0] == '/'))
-                return false;
+        /* A relative path and an abolute path must not compare as equal.
+         * Which one is sorted before the other does not really matter.
+         * Here a relative path is ordered before an absolute path. */
+        d = (a[0] == '/') - (b[0] == '/');
+        if (d)
+                return d;
 
         for (;;) {
                 size_t j, k;
@@ -414,25 +420,36 @@ bool path_equal(const char *a, const char *b) {
                 b += strspn(b, "/");
 
                 if (*a == 0 && *b == 0)
-                        return true;
+                        return 0;
 
-                if (*a == 0 || *b == 0)
-                        return false;
+                /* Order prefixes first: "/foo" before "/foo/bar" */
+                if (*a == 0)
+                        return -1;
+                if (*b == 0)
+                        return 1;
 
                 j = strcspn(a, "/");
                 k = strcspn(b, "/");
 
-                if (j != k)
-                        return false;
+                /* Alphabetical sort: "/foo/aaa" before "/foo/b" */
+                d = memcmp(a, b, MIN(j, k));
+                if (d)
+                        return (d > 0) - (d < 0); /* sign of d */
 
-                if (memcmp(a, b, j) != 0)
-                        return false;
+                /* Sort "/foo/a" before "/foo/aaa" */
+                d = (j > k) - (j < k);  /* sign of (j - k) */
+                if (d)
+                        return d;
 
                 a += j;
                 b += k;
         }
 }
 
+bool path_equal(const char *a, const char *b) {
+        return path_compare(a, b) == 0;
+}
+
 bool path_equal_or_files_same(const char *a, const char *b) {
         return path_equal(a, b) || files_same(a, b) > 0;
 }
diff --git a/src/shared/path-util.h b/src/shared/path-util.h
index bcf116ed3d..ca81b49cbf 100644
--- a/src/shared/path-util.h
+++ b/src/shared/path-util.h
@@ -44,6 +44,7 @@ char* path_make_absolute_cwd(const char *p);
 int path_make_relative(const char *from_dir, const char *to_path, char **_r);
 char* path_kill_slashes(char *path);
 char* path_startswith(const char *path, const char *prefix) _pure_;
+int path_compare(const char *a, const char *b) _pure_;
 bool path_equal(const char *a, const char *b) _pure_;
 bool path_equal_or_files_same(const char *a, const char *b);
 char* path_join(const char *root, const char *path, const char *rest);
diff --git a/src/test/test-path-util.c b/src/test/test-path-util.c
index 11aa52aaed..6396fcb398 100644
--- a/src/test/test-path-util.c
+++ b/src/test/test-path-util.c
@@ -27,23 +27,37 @@
 #include "macro.h"
 #include "strv.h"
 
+#define test_path_compare(a, b, result) {                 \
+                assert_se(path_compare(a, b) == result);  \
+                assert_se(path_compare(b, a) == -result); \
+                assert_se(path_equal(a, b) == !result);   \
+                assert_se(path_equal(b, a) == !result);   \
+        }
 
 static void test_path(void) {
-        assert_se(path_equal("/goo", "/goo"));
-        assert_se(path_equal("//goo", "/goo"));
-        assert_se(path_equal("//goo/////", "/goo"));
-        assert_se(path_equal("goo/////", "goo"));
+        test_path_compare("/goo", "/goo", 0);
+        test_path_compare("/goo", "/goo", 0);
+        test_path_compare("//goo", "/goo", 0);
+        test_path_compare("//goo/////", "/goo", 0);
+        test_path_compare("goo/////", "goo", 0);
+
+        test_path_compare("/goo/boo", "/goo//boo", 0);
+        test_path_compare("//goo/boo", "/goo/boo//", 0);
 
-        assert_se(path_equal("/goo/boo", "/goo//boo"));
-        assert_se(path_equal("//goo/boo", "/goo/boo//"));
+        test_path_compare("/", "///", 0);
 
-        assert_se(path_equal("/", "///"));
+        test_path_compare("/x", "x/", 1);
+        test_path_compare("x/", "/", -1);
 
-        assert_se(!path_equal("/x", "x/"));
-        assert_se(!path_equal("x/", "/"));
+        test_path_compare("/x/./y", "x/y", 1);
+        test_path_compare("x/.y", "x/y", -1);
 
-        assert_se(!path_equal("/x/./y", "x/y"));
-        assert_se(!path_equal("x/.y", "x/y"));
+        test_path_compare("foo", "/foo", -1);
+        test_path_compare("/foo", "/foo/bar", -1);
+        test_path_compare("/foo/aaa", "/foo/b", -1);
+        test_path_compare("/foo/aaa", "/foo/b/a", -1);
+        test_path_compare("/foo/a", "/foo/aaa", -1);
+        test_path_compare("/foo/a/b", "/foo/aaa", -1);
 
         assert_se(path_is_absolute("/"));
         assert_se(!path_is_absolute("./"));