ironhead reported in IRC that some Cygwin guys (not he, he’s just the

packager) complain that mksh collapses two leading slashes; IIRC POSIX
has a clause for UNC pathnames, so stop doing that, plus add a test

check.t

@@ -1,4 +1,4 @@
-# $MirOS: src/bin/mksh/check.t,v 1.431 2011/03/21 21:57:32 tg Exp $
+# $MirOS: src/bin/mksh/check.t,v 1.432 2011/03/23 18:47:04 tg Exp $
 # $OpenBSD: bksl-nl.t,v 1.2 2001/01/28 23:04:56 niklas Exp $
 # $OpenBSD: history.t,v 1.5 2001/01/28 23:04:56 niklas Exp $
 # $OpenBSD: read.t,v 1.3 2003/03/10 03:48:16 david Exp $
@@ -25,7 +25,7 @@
 # http://www.research.att.com/~gsf/public/ifs.sh
 
 expected-stdout:
-	@(#)MIRBSD KSH R39 2011/03/21
+	@(#)MIRBSD KSH R39 2011/03/23
 description:
 	Check version of shell.
 stdin:
@@ -8384,6 +8384,36 @@ expected-stdout:
 	24 ?lnnix/nix =lnnix/nix: No such file or directory !2
 	25 ?lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself =lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself/lnself: Too many levels of symbolic links !62
 ---
+name: realpath-2
+description:
+	Ensure that exactly two leading slashes are not collapsed
+	POSIX guarantees this exception, e.g. for UNC paths on Cygwin
+category: os:mirbsd
+stdin:
+	ln -s /bin t1
+	ln -s //bin t2
+	ln -s ///bin t3
+	realpath /bin
+	realpath //bin
+	realpath ///bin
+	realpath /usr/bin
+	realpath /usr//bin
+	realpath /usr///bin
+	realpath t1
+	realpath t2
+	realpath t3
+	rm -f t1 t2 t3
+expected-stdout:
+	/bin
+	//bin
+	/bin
+	/usr/bin
+	/usr/bin
+	/usr/bin
+	/bin
+	//bin
+	/bin
+---
 name: crash-1
 description:
 	Crashed during March 2011, fixed on vernal equinōx ☺

funcs.c

@@ -38,7 +38,7 @@
 #endif
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/funcs.c,v 1.177 2011/03/16 20:56:32 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/funcs.c,v 1.178 2011/03/23 18:47:06 tg Exp $");
 
 #if HAVE_KILLPG
 /*
@@ -242,6 +242,9 @@ do_realpath(const char *upath)
 	/* ipath and upath are in memory at the same time -> unchecked */
 	Xinit(xs, xp, strlen(ip = ipath) + 1, ATEMP);
 
+	/* now jump into the deep of the loop */
+	goto beginning_of_a_pathname;
+
 	while (*ip) {
 		/* skip slashes in input */
 		while (*ip == '/')
@@ -328,11 +331,25 @@ do_realpath(const char *upath)
 			 * restart if symlink target is an absolute path,
 			 * otherwise continue with currently resolved prefix
 			 */
-			xp = (ldest[0] == '/') ? Xstring(xs, xp) :
+			/* append rest of current input path to link target */
-			    Xrestpos(xs, xp, pos);
 			tp = shf_smprintf("%s%s%s", ldest, *ip ? "/" : "", ip);
 			afree(ipath, ATEMP);
 			ip = ipath = tp;
+			if (ldest[0] != '/') {
+				/* symlink target is a relative path */
+				xp = Xrestpos(xs, xp, pos);
+			} else {
+				/* symlink target is an absolute path */
+				xp = Xstring(xs, xp);
+ beginning_of_a_pathname:
+				/* assert: (ip == ipath)[0] == '/' */
+				/* assert: xp == xs.beg => start of path */
+
+				if (ip[1] == '/' && ip[2] != '/') {
+					/* keep UNC names, per POSIX */
+					Xput(xs, xp, '/');
+				}
+			}
 		}
 		/* otherwise (no symlink) merely go on */
 	}

sh.h

@@ -154,9 +154,9 @@
 #endif
 
 #ifdef EXTERN
-__RCSID("$MirOS: src/bin/mksh/sh.h,v 1.450 2011/03/21 21:57:33 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/sh.h,v 1.451 2011/03/23 18:47:07 tg Exp $");
 #endif
-#define MKSH_VERSION "R39 2011/03/21"
+#define MKSH_VERSION "R39 2011/03/23"
 
 #ifndef MKSH_INCLUDES_ONLY