assoc vs array append

[Grisha Levit]

If an indexed array is set via compound assignment, its values are
cleared at the start so any arithmetic expansions in the assignment
that reference the array and any [ind]+= assignments are evaluated
using the newly assigned values.  However, when assigning associative
arrays, any previously existing values are (re)used during assignment
instead.

declare -ai a=([0]=1); a=([0]=0 [0]+=10); echo $a
10
declare -Ai A=([0]=1); A=([0]=0 [0]+=10); echo $A
11

declare -ai a=([0]=1); a=([0]=0 [0]=a+10); echo $a
10
declare -Ai A=([0]=1); A=([0]=0 [0]=A+10); echo $A
11
declare -Ai A=([0]=1); A=( 0  0  0  A+10); echo $A
11

Seems like we can just swap in the new hash at the start of the
compound assignment process.  But I'm probably missing something
because there's a lot of code to handle pulling values out of a hash
table not associated with the new variable that seems like it would
not be necessary if we do so.
---
diff --git a/arrayfunc.c b/arrayfunc.c
index 1f70b9b5..a4166624 100644
--- a/arrayfunc.c
+++ b/arrayfunc.c
@@ -719,7 +719,11 @@ assign_compound_array_list (SHELL_VAR *var,
WORD_LIST *nlist, int flags)
       if (a && array_p (var))
        array_flush (a);
       else if (h && assoc_p (var))
-       nhash = assoc_create (h->nbuckets);
+       {
+         nhash = assoc_create (h->nbuckets);
+         var_setassoc (var, nhash);
+         assoc_dispose (h);
+       }
     }

 #if ASSOC_KVPAIR_ASSIGNMENT
@@ -727,12 +731,6 @@ assign_compound_array_list (SHELL_VAR *var,
WORD_LIST *nlist, int flags)
     {
       iflags = flags & ~ASS_APPEND;
       assign_assoc_from_kvlist (var, nlist, nhash, iflags);
-      if (nhash && nhash != h)
-       {
-         h = assoc_cell (var);
-         var_setassoc (var, nhash);
-         assoc_dispose (h);
-       }
       return 1;                /* XXX - check return value */
     }
 #endif
@@ -882,13 +880,6 @@ assign_compound_array_list (SHELL_VAR *var,
WORD_LIST *nlist, int flags)
        free (val);
     }

-  if (assoc_p (var) && nhash && nhash != h)
-    {
-      h = assoc_cell (var);
-      var_setassoc (var, nhash);
-      assoc_dispose (h);
-    }
-
   return (any_failed ? 0 : 1);
 }