path: add mp_path_is_absolute()

Just move it from mp_path_join_bstr() to this new function.

options/path.c

@@ -254,6 +254,23 @@ char *mp_splitext(const char *path, bstr *root)
     return (char *)split + 1;
 }
 
+bool mp_path_is_absolute(struct bstr path)
+{
+    if (path.len && strchr(mp_path_separators, path.start[0]))
+        return true;
+
+#if HAVE_DOS_PATHS
+    // Note: "X:filename" is a path relative to the current working directory
+    //       of drive X, and thus is not an absolute path. It needs to be
+    //       followed by \ or /.
+    if (path.len >= 3 && path.start[1] == ':' &&
+        strchr(mp_path_separators, path.start[2]))
+        return true;
+#endif
+
+    return false;
+}
+
 char *mp_path_join_bstr(void *talloc_ctx, struct bstr p1, struct bstr p2)
 {
     if (p1.len == 0)
@@ -261,16 +278,7 @@ char *mp_path_join_bstr(void *talloc_ctx, struct bstr p1, struct bstr p2)
     if (p2.len == 0)
         return bstrdup0(talloc_ctx, p1);
 
-    bool is_absolute = strchr(mp_path_separators, p2.start[0]);
-#if HAVE_DOS_PATHS
-    // Note: "X:filename" is a path relative to the current working directory
-    //       of drive X, and thus is not an absolute path. It needs to be
-    //       followed by \ or /.
-    if (p2.len >= 3 && p2.start[1] == ':' &&
-        strchr(mp_path_separators, p2.start[2]))
-        is_absolute = true;
-#endif
-    if (is_absolute)
+    if (mp_path_is_absolute(p2))
         return bstrdup0(talloc_ctx, p2);
 
     bool have_separator = strchr(mp_path_separators, p1.start[p1.len - 1]);

options/path.h

@@ -77,6 +77,9 @@ void mp_path_strip_trailing_separator(char *path);
 char *mp_path_join(void *talloc_ctx, const char *p1, const char *p2);
 char *mp_path_join_bstr(void *talloc_ctx, struct bstr p1, struct bstr p2);
 
+// Return whether the path is absolute.
+bool mp_path_is_absolute(struct bstr path);
+
 char *mp_getcwd(void *talloc_ctx);
 
 bool mp_path_exists(const char *path);

test/paths.c

@@ -14,11 +14,25 @@ static void test_join(char *file, int line, char *a, char *b, char *c)
     talloc_free(res);
 }
 
+static void test_abs(char *file, int line, bool abs, char *a)
+{
+    if (mp_path_is_absolute(bstr0(a)) != abs) {
+        printf("%s:%d: mp_path_is_absolute('%s') => %d, expected %d\n",
+               file, line, a, !abs, abs);
+        abort();
+    }
+}
+
 #define TEST_JOIN(a, b, c) \
     test_join(__FILE__, __LINE__, a, b, c);
 
+#define TEST_ABS(abs, a) \
+    test_abs(__FILE__, __LINE__, abs, a)
+
 static void run(struct test_ctx *ctx)
 {
+    TEST_ABS(true, "/ab");
+    TEST_ABS(false, "ab");
     TEST_JOIN("",           "",             "");
     TEST_JOIN("a",          "",             "a");
     TEST_JOIN("/a",         "",             "/a");
@@ -29,6 +43,12 @@ static void run(struct test_ctx *ctx)
     TEST_JOIN("ab/",        "/cd",          "/cd");
     // Note: we prefer "/" on win32, but tolerate "\".
 #if HAVE_DOS_PATHS
+    TEST_ABS(true, "\\ab");
+    TEST_ABS(true, "c:\\");
+    TEST_ABS(true, "c:/");
+    TEST_ABS(false, "c:");
+    TEST_ABS(false, "c:a");
+    TEST_ABS(false, "c:a\\");
     TEST_JOIN("ab\\",       "cd",           "ab\\cd");
     TEST_JOIN("ab\\",       "\\cd",         "\\cd");
     TEST_JOIN("c:/",        "de",           "c:/de");