Re: "${*:offset:length}" and ksh93/bash compatibility

[Jun T <takimoto-j@xxxxxxxxxxxxxxxxx>]

> 2022/03/14 0:22, Mikael Magnusson <mikachu@xxxxxxxxx> wrote:
> 
> I realized that this is not limited to $*,
> 
> zsh% a=(one two three); echo "${a[@]:0:2}"
> one two
> zsh% a=(one two three); echo "${a[*]:0:2}"
> on

The following patch seems to work for
 "${*:1:2}"   "${@:1:2}"  "$a[@]:0:2}"  "${a[*]:0:2}"

For example (with or without KSH_ARRAYS):

zsh% printf '<%s>\n' "${a[@]:0:2}"
<one>
<two>

If KSH_ARRAYS is not set, "$a:0:2" behaves like "${a[*]:0:2}".

I don't know if there are better/simpler solutions.
'make check' passes, but please do some tests to see if there
are any bad side effects.



diff --git a/Src/subst.c b/Src/subst.c
index 465fe970f..0f98e6ea3 100644
--- a/Src/subst.c
+++ b/Src/subst.c
@@ -1854,6 +1854,12 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
      * nested (P) flags.
      */
     int fetch_needed;
+    /*
+     * If an array parameter is quoted but has :offset:length (as in
+     * "${array:off:len}"), we apply :off:len as array index before
+     * joining the array into a string (for compatibility with ksh/bash).
+     */
+    int quoted_array_with_offset = 0;
 
     *s++ = '\0';
     /*
@@ -3377,7 +3383,16 @@ colonsubscript:
 			    return NULL;
 		    }
 		}
-		if (isarr) {
+		/*
+		 * We've got :OFFSET (and :LENGTH).
+		 * If aval is non-NULL but isarr is 0, PARAM is (probably)
+		 * an array but quoted like "${PARAM:OFFSET}". We apply
+		 * :OFFSET as array index (as if it is not quoted). We will
+		 * join them later (search for quoted_array_with_offset).
+		 */
+		if (aval && !isarr)
+		    quoted_array_with_offset = 1;
+		if (isarr || quoted_array_with_offset) {
 		    int alen, count;
 		    char **srcptr, **dstptr, **newarr;
 
@@ -3622,9 +3637,9 @@ colonsubscript:
      * exception is that ${name:-word} and ${name:+word} will have already
      * done any requested splitting of the word value with quoting preserved.
      */
-    if (ssub || spbreak || spsep || sep) {
+    if (ssub || spbreak || spsep || sep || quoted_array_with_offset) {
 	int force_split = !ssub && (spbreak || spsep);
-	if (isarr) {
+	if (isarr || quoted_array_with_offset) {
 	    /* sep non-null here means F or j flag, force join */
 	    if (nojoin == 0 || sep) {
 		val = sepjoin(aval, sep, 1);