Merge pull request #8995 from bradcray/localize-default-hash

Use on-clause to compute defaultHash on locale owning string

[reviewed by @mppf and @ronawho ]

This simple change seems to address the problem in issue #8990
by using an on-clause to ensure that defaultHash is computed on
the same locale where a string is allocated.

This leads me to wonder what we could do to guard against such
accidental "remote meddling in string buffer data" mistakes
in the future (e.g., use a getter/setter for the internal data
that contains locality assertions when --checks are on?)

Fixes #8990.

modules/internal/String.chpl

@@ -1870,10 +1870,15 @@ module String {
 
   pragma "no doc"
   inline proc chpl__defaultHash(x : string): uint {
-    // Use djb2 (Dan Bernstein in comp.lang.c), XOR version
-    var hash: int(64) = 5381;
-    for c in 0..#(x.length) {
-      hash = ((hash << 5) + hash) ^ x.buff[c];
+    var hash: int(64);
+    on __primitive("chpl_on_locale_num",
+                   chpl_buildLocaleID(x.locale_id, c_sublocid_any)) {
+      // Use djb2 (Dan Bernstein in comp.lang.c), XOR version
+      var locHash: int(64) = 5381;
+      for c in 0..#(x.length) {
+        locHash = ((locHash << 5) + locHash) ^ x.buff[c];
+      }
+      hash = locHash;
     }
     return hash;
   }