gv_magicalize: Refactor

This refactors to eliminate redundant code.  Some things are magical
only if we are using the main stash; others in any stash; one only in
PL_debstash.

Previously, the switches were structured thusly:
 1) if we aren't using the main stash, handle things not requiring the
        main stash
 2) if we are using the main stash, handle all len > 1 things that can
        be in the main stash.  This duplicates much of item 1)
 3) if we are using the main stash, handle all len == 1 things that can
        be in the main stash.  This duplicates some of item 1)

The new structure is
 if (len > 1) {
    1) handle len > 1 things not requiring main stash, regardless of the
       stash we are in
    2) handle len > 1 things requiring main stash
 } else {
    3) handle len == 1 things, regardless of the stash we are in.
 }

This removes the duplicated code.

The case for 'a' and 'b' are special.  When 'a' stands for "args" it is
len > 1 and that is handled in 1).

But 'a' can also mean a single character, as 'b' always does.  These
cases are handled in 3).  These are the only two len == 1 characters
that don't have to be in the main package, so there is an extra
conditional clause to allow that.

Author: khwilliamson

gv.c

@@ -2094,11 +2094,11 @@ S_gv_magicalize(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len,
         goto try_core;
     }
 
-    if (stash != PL_defstash) { /* not the main stash */
-        /* We only have to check for a few names here: a, b, EXPORT, ISA
-           and VERSION. All the others apply only to the main stash or to
-           CORE (which is checked right after this). */
+    if (len > 1) {
             switch (*name) {
+
+          /* The first set don't require this to be the main stash */
+
             case 'E':
                 if (
                     len >= 6 && name[1] == 'X' &&
@@ -2122,16 +2122,15 @@ S_gv_magicalize(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len,
                     GvMULTI_on(gv_AVadd(gv));
                     break;
                 }
-                /* FALLTHROUGH */
-            case 'b':
-                if (len == 1 && sv_type == SVt_PV)
-                    GvMULTI_on(gv);
-                /* FALLTHROUGH */
-            default:
+            goto try_core;
+
+          default:
+
+            /* The remainder apply only to the main stash */
+            if (stash != PL_defstash) {
                 goto try_core;
             }
-    }
-    else if (len > 1) {
+
             switch (*name) {
             case 'A':
                 if (memEQs(name, len, "ARGV")) {
@@ -2141,21 +2140,6 @@ S_gv_magicalize(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len,
                     GvMULTI_on(gv);
                 }
                 break;
-            case 'E':
-                if (
-                    len >= 6 && name[1] == 'X' &&
-                    (memEQs(name, len, "EXPORT")
-                    ||memEQs(name, len, "EXPORT_OK")
-                    ||memEQs(name, len, "EXPORT_FAIL")
-                    ||memEQs(name, len, "EXPORT_TAGS"))
-                )
-                    GvMULTI_on(gv);
-                break;
-            case 'I':
-                if (memEQs(name, len, "ISA")) {
-                    gv_magicalize_isa(gv);
-                }
-                break;
             case 'S':
                 if (memEQs(name, len, "SIG")) {
                     HV *hv;
@@ -2187,10 +2171,6 @@ S_gv_magicalize(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len,
                     }
                 }
                 break;
-            case 'V':
-                if (memEQs(name, len, "VERSION"))
-                    GvMULTI_on(gv);
-                break;
             case '\003':        /* $^CHILD_ERROR_NATIVE */
                 if (memEQs(name, len, "\003HILD_ERROR_NATIVE"))
                     goto magicalize;
@@ -2292,10 +2272,15 @@ S_gv_magicalize(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len,
                 paren = (SSize_t)(I32)uv;
                 goto storeparen;
             }
-            }
-    } else {
-        /* Names of length 1.  (Or 0. But name is NUL terminated, so that will
-           be case '\0' in this switch statement (ie a default case)  */
+        }
+        }
+    }
+    else if (   stash == PL_defstash         /* Names of length 1. */
+             || *name == 'a' || *name == 'b')
+    {
+        /* All but the above two length 1 names have to be in the main stash.
+         * */
+
         switch (*name) {
         case '&':		/* $& */
             paren = RX_BUFF_IDX_FULLMATCH;
@@ -2450,10 +2435,15 @@ S_gv_magicalize(pTHX_ GV *gv, HV *stash, const char *name, STRLEN len,
             SvREFCNT_dec(sv);
         }
         break;
-        case 'a':
+
+        case 'a':  /* The len > 1 case was handled above */
         case 'b':
             if (sv_type == SVt_PV)
                 GvMULTI_on(gv);
+            /* FALLTHROUGH */
+
+          default:
+            goto try_core;
         }
     }