PATCH: Enable extendedglob in pattern with ${(*)name/pattern/replacement}

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

In retrospect I'm surprised this wasn't thought of before.  With this
you can for example enable backreferences without having to turn on
extendedglob for the whole surrounding context.

A different character could be chosen if (*) seems unwise for some
reason.  It should also be fairly straightforward to make (**) toggle
the option if there's a reason to force extendedglob off.

Patch includes (very brief) doc, and a test case.

diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo
index cbdae4d58..b3396721f 100644
--- a/Doc/Zsh/expn.yo
+++ b/Doc/Zsh/expn.yo
@@ -1422,7 +1422,7 @@ error, and the flag itself has no effect.
 enditem()
 
 The following flags are meaningful with the tt(${)...tt(#)...tt(}) or
-tt(${)...tt(%)...tt(}) forms.  The tt(S) and tt(I) flags may also be
+tt(${)...tt(%)...tt(}) forms.  The tt(S), tt(I), and tt(*) flags may also be
 used with the tt(${)...tt(/)...tt(}) forms.
 
 startitem()
@@ -1488,6 +1488,10 @@ will remove the same matches as for `tt(#)', but in reverse order, and the
 form using `tt(%%)' will remove the same matches as for `tt(##)' in reverse
 order.
 )
+item(tt(*))(
+Enable tt(EXTENDED_GLOB) for substitution via tt(${)...tt(/)...tt(}) or
+tt(${)...tt(//)...tt(}).
+)
 item(tt(B))(
 Include the index of the beginning of the match in the result.
 )
diff --git a/Src/subst.c b/Src/subst.c
index b98ddaf02..2af61653a 100644
--- a/Src/subst.c
+++ b/Src/subst.c
@@ -1708,7 +1708,7 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
     /*
      * This expressive name refers to the set of flags which
      * is applied to matching for #, %, / and their doubled variants:
-     * (M), (R), (B), (E), (N), (S).
+     * (M), (R), (B), (E), (N), (S), (*).
      */
     int flags = 0;
     /* Value from (I) flag, used for ditto. */
@@ -1930,6 +1930,10 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 		case '@':
 		    nojoin = 2;	/* nojoin = 2 means force */
 		    break;
+		case '*':
+		case Star:
+		    flags |= SUB_EGLOB;
+		    break;
 		case 'M':
 		    flags |= SUB_MATCH;
 		    break;
@@ -2810,7 +2814,7 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 		    c == '#' || c == Pound ||
 		    c == '?' || c == Quest ||
 		    c == '/')) {
-
+	int eglob = isset(EXTENDEDGLOB);
 	/*
 	 * Default index is 1 if no (I) or (I) gave zero.   But
 	 * why don't we set the default explicitly at the start
@@ -2832,9 +2836,10 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 	    char *ptr;
 	    /*
 	     * previous flags are irrelevant, except for (S) which
-	     * indicates shortest substring; else look for longest.
+	     * indicates shortest substring; else look for longest,
+	     # and (*) which temporarily enables extended globbing.
 	     */
-	    flags = (flags & SUB_SUBSTR) ? 0 : SUB_LONG;
+	    flags = ((flags & SUB_SUBSTR) ? 0 : SUB_LONG)|(flags & SUB_EGLOB);
 	    if ((c = *s) == '/') {
 		/* doubled, so replace all occurrences */
 		flags |= SUB_GLOBAL;
@@ -3136,7 +3141,10 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 		for (ap = aval; *ap; ap++) {
 		    untokenize(*ap);
 		}
+		if (flags & SUB_EGLOB)
+		    opts[EXTENDEDGLOB] = 1;
 		getmatcharr(&aval, s, flags, flnum, replstr);
+		opts[EXTENDEDGLOB] = eglob;
 	    } else {
 		if (vunset) {
 		    if (vunset > 0 && unset(UNSET)) {
@@ -3151,7 +3159,10 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 		    copied = 1;
 		    untokenize(val);
 		}
+		if (flags & SUB_EGLOB)
+		    opts[EXTENDEDGLOB] = 1;
 		getmatch(&val, s, flags, flnum, replstr);
+		opts[EXTENDEDGLOB] = eglob;
 	    }
 	    break;
 	}
diff --git a/Src/zsh.h b/Src/zsh.h
index 94f5099c6..6cf1b4186 100644
--- a/Src/zsh.h
+++ b/Src/zsh.h
@@ -1991,6 +1991,7 @@ struct tieddata {
 #define SUB_START	0x1000  /* force match at start with SUB_END
 				 * and no SUB_SUBSTR */
 #define SUB_LIST	0x2000  /* no substitution, return list of matches */
+#define SUB_EGLOB	0x4000	/* use extended globbing in patterns */
 
 /*
  * Structure recording multiple matches inside a test string.
diff --git a/Test/D02glob.ztst b/Test/D02glob.ztst
index f250244e7..176846d46 100644
--- a/Test/D02glob.ztst
+++ b/Test/D02glob.ztst
@@ -792,6 +792,11 @@
 *>*/glob.tmp/(flip|flop)
 *>*/glob.tmp/(flip|flop)/trailing/components
 
+  unsetopt extendedglob
+  print -r -- ${(*)=${(@s.+.):-A+B}/(#b)(?)/-${(L)match[1]} ${match[1]}}
+0:the '*' qualfier enables extended_glob for pattern matching
+>-a A -b B
+
 %clean
 
  # Fix unreadable-directory permissions so ztst can clean up properly