unit-tests: do show relative file paths on non-Windows, too

There are compilers other than Visual C that want to show absolute
paths.  Generalize the helper introduced by a2c5e294 (unit-tests: do
show relative file paths, 2023-09-25) so that it can also work with
a path that uses slash as the directory separator, and becomes
almost no-op once one-time preparation finds out that we are using a
compiler that already gives relative paths.  Incidentally, this also
should do the right thing on Windows with a compiler that shows
relative paths but with backslash as the directory separator (if
such a thing exists and is used to build git).

Reported-by: Randall S. Becker <rsbecker@nexbridge.com>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/t/unit-tests/test-lib.c b/t/unit-tests/test-lib.c
index 7bf9dfdb9595512f42357639c0eda40ad608bb34..66d6980ffbefd83ed350c323bf946b29cb54dbf2 100644 (file)
--- a/t/unit-tests/test-lib.c
+++ b/t/unit-tests/test-lib.c
@@ -21,12 +21,11 @@ static struct {
        .result = RESULT_NONE,
 };
 
-#ifndef _MSC_VER
-#define make_relative(location) location
-#else
 /*
  * Visual C interpolates the absolute Windows path for `__FILE__`,
  * but we want to see relative paths, as verified by t0080.
+ * There are other compilers that do the same, and are not for
+ * Windows.
  */
 #include "dir.h"
 
@@ -34,32 +33,66 @@ static const char *make_relative(const char *location)
 {
        static char prefix[] = __FILE__, buf[PATH_MAX], *p;
        static size_t prefix_len;
+       static int need_bs_to_fs = -1;
 
-       if (!prefix_len) {
+       /* one-time preparation */
+       if (need_bs_to_fs < 0) {
                size_t len = strlen(prefix);
-               const char *needle = "\\t\\unit-tests\\test-lib.c";
+               char needle[] = "t\\unit-tests\\test-lib.c";
                size_t needle_len = strlen(needle);
 
-               if (len < needle_len || strcmp(needle, prefix + len - needle_len))
-                       die("unexpected suffix of '%s'", prefix);
+               if (len < needle_len)
+                       die("unexpected prefix '%s'", prefix);
+
+               /*
+                * The path could be relative (t/unit-tests/test-lib.c)
+                * or full (/home/user/git/t/unit-tests/test-lib.c).
+                * Check the slash between "t" and "unit-tests".
+                */
+               prefix_len = len - needle_len;
+               if (prefix[prefix_len + 1] == '/') {
+                       /* Oh, we're not Windows */
+                       for (size_t i = 0; i < needle_len; i++)
+                               if (needle[i] == '\\')
+                                       needle[i] = '/';
+                       need_bs_to_fs = 0;
+               } else {
+                       need_bs_to_fs = 1;
+               }
 
-               /* let it end in a directory separator */
-               prefix_len = len - needle_len + 1;
+               /*
+                * prefix_len == 0 if the compiler gives paths relative
+                * to the root of the working tree.  Otherwise, we want
+                * to see that we did find the needle[] at a directory
+                * boundary.  Again we rely on that needle[] begins with
+                * "t" followed by the directory separator.
+                */
+               if (fspathcmp(needle, prefix + prefix_len) ||
+                   (prefix_len && prefix[prefix_len - 1] != needle[1]))
+                       die("unexpected suffix of '%s'", prefix);
        }
 
-       /* Does it not start with the expected prefix? */
-       if (fspathncmp(location, prefix, prefix_len))
+       /*
+        * Does it not start with the expected prefix?
+        * Return it as-is without making it worse.
+        */
+       if (prefix_len && fspathncmp(location, prefix, prefix_len))
                return location;
 
-       strlcpy(buf, location + prefix_len, sizeof(buf));
+       /*
+        * If we do not need to munge directory separator, we can return
+        * the substring at the tail of the location.
+        */
+       if (!need_bs_to_fs)
+               return location + prefix_len;
+
        /* convert backslashes to forward slashes */
+       strlcpy(buf, location + prefix_len, sizeof(buf));
        for (p = buf; *p; p++)
                if (*p == '\\')
                        *p = '/';
-
        return buf;
 }
-#endif
 
 static void msg_with_prefix(const char *prefix, const char *format, va_list ap)
 {