Fix incorrect behavior of 'cd ../.foo' (#46)

The cd builtin was removing '.' from directory names when combined
with a preceding '../', which caused commands like 'cd ../.local'
to become 'cd ../local'. This patch fixes the problem by limiting
the extra handling to leading '..'. The bugfix comes from ksh93v-
2013-10-10-alpha, although this version is a shortened patch from
Solaris (as ksh93v- refactored a decent amount of the code for the
cd builtin).

src/cmd/ksh93/bltins/cd_pwd.c:
- cd should only check for leading '..', as trying to handle a lone
  '.' only causes problems.

src/cmd/ksh93/tests/builtins.sh:
- Add a regression test for this problem based on the test present in
  ksh93v- 2013-10-10-alpha.

Patch from Solaris:
https://github.com/oracle/solaris-userland/blob/860d27f/components/ksh93/patches/270-23319761.patch

NEWS

@@ -3,6 +3,11 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-06-26:
+
+- Changing to a directory that has a name starting with a '.' will no
+  longer fail if preceded by '../' (i.e. 'cd ../.local' will now work).
+
 2020-06-24:
 
 - Fixed buggy tab completion of tilde-expanded paths such as

src/cmd/ksh93/bltins/cd_pwd.c

@@ -109,34 +109,20 @@ int	b_cd(int argc, char *argv[],Shbltin_t *context)
 		if(!oldpwd)
 			oldpwd = path_pwd(shp,1);
 	}
-	if(*dir=='.')
+	if(*dir!='/')
 	{
-		/* test for pathname . ./ .. or ../ */
-		int	n=0;
-		char	*sp;
-		for(dp=dir; *dp=='.'; dp++)
+		/* check for leading .. */
+		char *cp;
+		sfprintf(shp->strbuf,"%s",dir);
+		cp = sfstruse(shp->strbuf);
+		pathcanon(cp, 0);
+		if(cp[0]=='.' && cp[1]=='.' && (cp[2]=='/' || cp[2]==0))
 		{
-			if(*++dp=='.' && (*++dp=='/' || *dp==0))
-				n++;
-			else if(*dp && *dp!='/')
-				break;
-			if(*dp==0)
-				break;
-		}
-		if(n)	
-		{
-			cdpath = 0;
-			sp = oldpwd + strlen(oldpwd);
-			while(n--)
-			{
-				while(--sp > oldpwd && *sp!='/');
-				if(sp==oldpwd)
-					break;
-
-			}
-			sfwrite(shp->strbuf,oldpwd,sp+1-oldpwd);
-			sfputr(shp->strbuf,dp,0);
-			dir = sfstruse(shp->strbuf);
+			if(!shp->strbuf2)
+				shp->strbuf2 = sfstropen();
+			sfprintf(shp->strbuf2,"%s/%s",oldpwd,cp);
+			dir = sfstruse(shp->strbuf2);
+			pathcanon(dir, 0);
 		}
 	}
 	rval = -1;

src/cmd/ksh93/include/version.h

@@ -17,4 +17,4 @@
 *                  David Korn <dgk@research.att.com>                   *
 *                                                                      *
 ***********************************************************************/
-#define SH_RELEASE	"93u+m 2020-06-24"
+#define SH_RELEASE	"93u+m 2020-06-26"

src/cmd/ksh93/tests/builtins.sh

@@ -717,5 +717,14 @@ chmod is $(whence -p chmod)
 chmod is a tracked alias for $(whence -p chmod)"
 [[ $actual == $expected ]] || err_exit '`whence -a` does not work correctly with tracked aliases'
 
+# ======
+# 'cd ../.foo' should not exclude the '.' in '.foo'
+(
+	cd "$tmp"
+	mkdir foo .bar
+	cd foo
+	cd ../.bar
+) || err_exit 'cd ../.bar when ../.bar exists should not fail'
+
 # ======
 exit $((Errors<125?Errors:125))