Change global const handling to silently ignore redeclarations

test/mjsunit/const-redecl.js

Index: test/mjsunit/const-redecl.js
diff --git a/test/mjsunit/const-redecl.js b/test/mjsunit/const-redecl.js
index 945970891b3ead90834c7fbba035beda7e6ff298..c0b97e6ced14c90b57b5226e87a8e35352bf621f 100644
--- a/test/mjsunit/const-redecl.js
+++ b/test/mjsunit/const-redecl.js
@@ -98,7 +98,8 @@ function TestAll(expected,s,opt_e) {
   var msg = s;
   if (opt_e) { e = opt_e; msg += "; " + opt_e; }
   assertEquals(expected, TestLocal(s,e), "local:'" + msg + "'");
-  assertEquals(expected, TestGlobal(s,e), "global:'" + msg + "'");
+  // Redeclarations of global consts do not throw, they are silently ignored.
+  assertEquals(42, TestGlobal(s, 42), "global:'" + msg + "'");
   assertEquals(expected, TestContext(s,e), "context:'" + msg + "'");
 }
 
@@ -218,3 +219,62 @@ TestAll(0, "var a,b,c,d,e,f,g,h; " + loop, "x");
 // Test that const inside with behaves correctly.
 TestAll(87, "with ({x:42}) { const x = 87; }", "x");
 TestAll(undefined, "with ({x:42}) { const x; }", "x");
+
+
+// Additional tests for how various combinations of re-declarations affect
+// the values of the var/const in question.
+try {
+  eval("var undefined;");
+} catch (ex) {
+  assertUnreachable("undefined (1) has thrown");
+}
+
+var original_undef = undefined;
+var undefined = 1;  // Should be silently ignored.
+assertEquals(original_undef, undefined, "undefined got overwritten");
+undefined = original_undef;
+
+var a; const a; const a = 1;
+assertEquals(1, a, "a has wrong value");
+a = 2;
+assertEquals(2, a, "a should be writable");
+
+var b = 1; const b = 2;
+assertEquals(2, b, "b has wrong value");
+
+var c = 1; const c = 2; const c = 3;
+assertEquals(3, c, "c has wrong value");
+
+const d = 1; const d = 2;
+assertEquals(1, d, "d has wrong value");
+
+const e = 1; var e = 2;
+assertEquals(1, e, "e has wrong value");
+
+const f = 1; const f;
+assertEquals(1, f, "f has wrong value");
+
+var g; const g = 1;
+assertEquals(1, g, "g has wrong value");
+g = 2;
+assertEquals(2, g, "g should be writable");
+
+const h; var h = 1;
+assertEquals(undefined,h,  "h has wrong value");
+
+eval("Object.defineProperty(this, 'i', { writable: true });"
+   + "const i = 7;"
+   + "assertEquals(7, i, \"i has wrong value\");");
+
+var global = this;
+assertThrows(function() {
+  Object.defineProperty(global, 'j', { writable: true })
+}, TypeError);
+const j = 2;  // This is what makes the function above throw, because the
+// const declaration gets hoisted and makes the property non-configurable.
+assertEquals(2, j, "j has wrong value");
+
+var k = 1; const k;
+// You could argue about the expected result here. For now, the winning
+// argument is that "const k;" is equivalent to "const k = undefined;".
+assertEquals(undefined, k, "k has wrong value");