Bug 1547824 - Change JS::Value from union to class. r=jwalden

Now that all the bad type-punning is gone, JS::Value has a single
asBits_ field and we should use a class aggregate type instead.

Differential Revision: https://phabricator.services.mozilla.com/D46325

--HG--
extra : moz-landing-system : lando

js/public/JSON.h

@@ -15,15 +15,12 @@
 #include "jstypes.h"  // JS_PUBLIC_API
 
 #include "js/RootingAPI.h"  // JS::Handle, JS::MutableHandle
+#include "js/Value.h"       // JS::Value
 
 struct JSContext;
 class JSObject;
 class JSString;
 
-namespace JS {
-union Value;
-}
-
 using JSONWriteCallback = bool (*)(const char16_t* buf, uint32_t len,
                                    void* data);
 

js/public/LocaleSensitive.h

@@ -15,15 +15,12 @@
 
 #include "js/RootingAPI.h"  // JS::Handle, JS::MutableHandle
 #include "js/Utility.h"     // JS::UniqueChars
+#include "js/Value.h"       // JS::Value
 
 struct JSContext;
 struct JSRuntime;
 class JSString;
 
-namespace JS {
-union Value;
-}
-
 /**
  * Set the default locale for the ECMAScript Internationalization API
  * (Intl.Collator, Intl.NumberFormat, Intl.DateTimeFormat, and others that will

js/public/TypeDecls.h

@@ -46,7 +46,7 @@ typedef unsigned char Latin1Char;
 
 class Symbol;
 class BigInt;
-union Value;
+class Value;
 
 class Compartment;
 class Realm;

js/public/Value.h

@@ -27,7 +27,7 @@
 #include "js/Utility.h"
 
 namespace JS {
-union Value;
+class Value;
 }
 
 /* JS::Value can store a full int32_t. */
@@ -340,7 +340,7 @@ static inline double CanonicalizeNaN(double d) {
  *   conditional move (not speculated) to zero the payload register if the type
  *   doesn't match.
  */
-union alignas(8) Value {
+class alignas(8) Value {
  private:
   uint64_t asBits_;
 

js/src/builtin/Object.h

@@ -9,12 +9,9 @@
 
 #include "jsapi.h"
 
+#include "js/Value.h"
 #include "vm/NativeObject.h"
 
-namespace JS {
-union Value;
-}  // namespace JS
-
 namespace js {
 
 // Object constructor native. Exposed only so the JIT can know its address.

js/src/builtin/streams/QueueingStrategies.h

@@ -10,14 +10,10 @@
 #define builtin_stream_QueueingStrategies_h
 
 #include "js/Class.h"         // JSClass, js::ClassSpec
+#include "js/Value.h"         // JS::Value
+#include "vm/JSContext.h"     // JSContext
 #include "vm/NativeObject.h"  // js::NativeObject
 
-struct JSContext;
-
-namespace JS {
-union Value;
-}
-
 namespace js {
 
 class ByteLengthQueuingStrategy : public NativeObject {

js/src/wasm/AsmJS.h

@@ -31,7 +31,7 @@ class JSFunction;
 
 namespace JS {
 
-union Value;
+class Value;
 
 template <typename T>
 class Handle;