PATCH: 3.1.6-test-1: strange cd behaviour

[Peter Stephenson <pws@ibmth.df.unipi.it>]

Peter Stephenson wrote:
> This is a story of horror.
>
> Without restoring the 3.0
> behaviour, the fix would be to do something clever when pwd is a prefix of
> the path --- i.e., $PWD/.. is automatically turned into $PWD:h, whether the
> directory exists or not, but $PWD/../dummy/.. becomes
> ${PWD:h}/dummy/.. which is weighed in the balance and found wanting.  This
> would get all the advantages and none of the disadvantages of the 3.0
> method (I hope).  The rule would be something like
> 
> - If $PWD is a prefix, rationalize away any immediately following ..'s
>   (and .'s, to be on the safe side) before doing any testing.
> - At that point, even if $PWD is a prefix, look at the path and see if it
>   contains any /../ or finishes with /.. . If so, stat() it and check
>   that it exists.  If not, return and let the chdir code handle errors.
> - If everything's OK so far (i.e. no ..'s, or the directory exists)
>   rationalize the rest of the path.

This does it:  as you see it's a significant chunk of extra code with no
other aim than making sure cd foo/.. doesn't work if foo doesn't exist
without preventing you from changing back up to directories that still
exist if yours doesn't.  But life is non-optimal.  If anybody has any
better suggestions...?

Please test this, since people tend to get cross if they can't change
directories properly.

Note that this has the effect that `cd $PWD/<relative>' is tested in
exactly the same way as `cd <relative>', where <relative> is any relative
path.  So `cd $PWD/..' will also always work if $PWD doesn't exist but its
parent does, regardless (obviously) of whether you use the variable $PWD or
the full directory name.  That's the effect of the code change between 3.0
and 3.1.  (Of course, if you're somewhere else in cdpath, none of this
matters.)

--- Src/builtin.c.cd	Tue Jul 13 14:31:03 1999
+++ Src/builtin.c	Wed Jul 14 14:26:38 1999
@@ -1045,11 +1045,41 @@
 static void
 fixdir(char *src)
 {
-    char *dest = src;
-    char *d0 = dest;
-#ifdef __CYGWIN__
+    char *dest = src, *d0 = dest, *chks = src, *ptrp;
+#ifdef __CYGWIN
     char *s0 = src;
 #endif
+    int donecheck = 0, len;
+
+    /*
+     * Normally, we should not rationalize away path segments foo/.. if
+     * the directory foo does not exist.  However, if foo was part of
+     * pwd then we should allow it, because we know the current
+     * directory was once valid, although may have been deleted, and `cd
+     * ..' should always work as long as the parent directory exists.
+     * Hence we find an initial portion of the path consisting of pwd
+     * followed by any number of .. or . segments, and don't check
+     * that the original path exists.  After this point (given by
+     * chks), if there are any remaining ..'s in the path we
+     * check that the directory with the remaining portion
+     * unrationalized really exists, and return if it doesn't.
+     *
+     * Bug:  this is ridiculously heavy handed.
+     */
+    len = strlen(pwd);
+    if (!strncmp(src, pwd, len) && src[len] == '/') {
+	chks = src + len;
+	while (*chks == '/')
+	    chks++;
+	while (*chks == '.' &&
+	       (!chks[1] || chks[1] == '/' ||
+		(chks[1] == '.' && (!chks[2] || chks[2] == '/')))) {
+	    while (*chks == '.')
+		chks++;
+	    while (*chks == '/')
+		chks++;
+	}
+    }
 
 /*** if have RFS superroot directory ***/
 #ifdef HAVE_SUPERROOT
@@ -1085,6 +1115,31 @@
 	}
 	if (src[0] == '.' && src[1] == '.' &&
 	  (src[2] == '\0' || src[2] == '/')) {
+	    if (!donecheck && src >= chks) {
+		/*
+		 * We need to check the original path exists, to catch
+		 * problems like 'cd nonexistent/..'.  We use dest
+		 * as far as we've got, plus the rest of src.
+		 * We only need to do this once, as any later ..'s
+		 * will automatically be tested here.
+		 */
+		struct stat st;
+		char *testdir;
+		if (dest == src)
+		    testdir = dupstring(d0);
+		else {
+		    *dest = '\0';
+		    testdir = dyncat(d0, src);
+		}
+		for (chks = src, ptrp = testdir + (dest - d0); *chks;
+		     chks++, ptrp++)
+		    *ptrp = (*chks == Meta) ? (*++chks ^ 32) : *chks;
+		if (stat(testdir, &st) < 0 || !S_ISDIR(st.st_mode)) {
+		    strcpy(d0, testdir);
+		    return;
+		}
+		donecheck = 1;
+	    }
 	    if (dest > d0 + 1) {
 		/* remove a foo/.. combination */
 		for (dest--; dest > d0 + 1 && dest[-1] != '/'; dest--);

-- 
Peter Stephenson <pws@ibmth.df.unipi.it>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy