1216630 - Print class source when calling toString on the constructor.

This is accomplished in the following ways.
LazyScripts and JSScripts now have 4 offsets:
- Source begin and end for the actual source. This is used for lazy parsing.

- toString begin and end for toString. Some kinds of functions, like async, only have a different begin offset. Class constructors have different offsets for both begin and end.

For syntactically present (i.e. non-default) constructors, the class source span is remembered directly on the LazyScript or JSScript. The toString implementation then splices out the substring directly. For default constructors, a new SRC_CLASS SrcNote type is added. It's binary and has as its arguments the begin and end offsets of the class expression or statement. MakeDefaultConstructor reads the note and overrides the cloned self-hosted function's source object. This is probably the least intrusive way to accomplish this.

js/src/jsscript.cpp

@@ -236,6 +236,7 @@ XDRRelazificationInfo(XDRState<mode>* xdr, HandleFunction fun, HandleScript scri
         uint32_t begin = script->sourceStart();
         uint32_t end = script->sourceEnd();
         uint32_t preludeStart = script->preludeStart();
+        uint32_t postludeEnd = script->postludeEnd();
         uint32_t lineno = script->lineno();
         uint32_t column = script->column();
 
@@ -244,6 +245,7 @@ XDRRelazificationInfo(XDRState<mode>* xdr, HandleFunction fun, HandleScript scri
             MOZ_ASSERT(begin == lazy->begin());
             MOZ_ASSERT(end == lazy->end());
             MOZ_ASSERT(preludeStart == lazy->preludeStart());
+            MOZ_ASSERT(postludeEnd == lazy->postludeEnd());
             MOZ_ASSERT(lineno == lazy->lineno());
             MOZ_ASSERT(column == lazy->column());
             // We can assert we have no inner functions because we don't
@@ -259,6 +261,11 @@ XDRRelazificationInfo(XDRState<mode>* xdr, HandleFunction fun, HandleScript scri
             lazy.set(LazyScript::Create(cx, fun, script, enclosingScope, script,
                                         packedFields, begin, end, preludeStart, lineno, column));
 
+            if (!lazy)
+                return false;
+
+            lazy->setPostludeEnd(postludeEnd);
+
             // As opposed to XDRLazyScript, we need to restore the runtime bits
             // of the script, as we are trying to match the fact this function
             // has already been parsed and that it would need to be re-lazified.
@@ -522,7 +529,7 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
             sourceObject = &enclosingScript->sourceObject()->as<ScriptSourceObject>();
         }
 
-        script = JSScript::Create(cx, options, sourceObject, 0, 0, 0);
+        script = JSScript::Create(cx, options, sourceObject, 0, 0, 0, 0);
         if (!script)
             return false;
 
@@ -609,6 +616,8 @@ js::XDRScript(XDRState<mode>* xdr, HandleScope scriptEnclosingScope, HandleScrip
         return false;
     if (!xdr->codeUint32(&script->preludeStart_))
         return false;
+    if (!xdr->codeUint32(&script->postludeEnd_))
+        return false;
 
     if (!xdr->codeUint32(&lineno) ||
         !xdr->codeUint32(&column) ||
@@ -940,6 +949,7 @@ js::XDRLazyScript(XDRState<mode>* xdr, HandleScope enclosingScope, HandleScript
         uint32_t begin;
         uint32_t end;
         uint32_t preludeStart;
+        uint32_t postludeEnd;
         uint32_t lineno;
         uint32_t column;
         uint64_t packedFields;
@@ -954,6 +964,7 @@ js::XDRLazyScript(XDRState<mode>* xdr, HandleScope enclosingScope, HandleScript
             begin = lazy->begin();
             end = lazy->end();
             preludeStart = lazy->preludeStart();
+            postludeEnd = lazy->postludeEnd();
             lineno = lazy->lineno();
             column = lazy->column();
             packedFields = lazy->packedFields();
@@ -961,6 +972,7 @@ js::XDRLazyScript(XDRState<mode>* xdr, HandleScope enclosingScope, HandleScript
 
         if (!xdr->codeUint32(&begin) || !xdr->codeUint32(&end) ||
             !xdr->codeUint32(&preludeStart) ||
+            !xdr->codeUint32(&postludeEnd) ||
             !xdr->codeUint32(&lineno) || !xdr->codeUint32(&column) ||
             !xdr->codeUint64(&packedFields))
         {
@@ -972,6 +984,7 @@ js::XDRLazyScript(XDRState<mode>* xdr, HandleScope enclosingScope, HandleScript
                                         packedFields, begin, end, preludeStart, lineno, column));
             if (!lazy)
                 return false;
+            lazy->setPostludeEnd(postludeEnd);
             fun->initLazyScript(lazy);
         }
     }
@@ -1015,6 +1028,15 @@ JSScript::setSourceObject(JSObject* object)
     sourceObject_ = object;
 }
 
+void
+JSScript::setDefaultClassConstructorSpan(JSObject* sourceObject, uint32_t start, uint32_t end)
+{
+    MOZ_ASSERT(isDefaultClassConstructor());
+    setSourceObject(sourceObject);
+    preludeStart_ = start;
+    postludeEnd_ = end;
+}
+
 js::ScriptSourceObject&
 JSScript::scriptSourceUnwrap() const {
     return UncheckedUnwrap(sourceObject())->as<ScriptSourceObject>();
@@ -1443,10 +1465,10 @@ JSScript::sourceData(JSContext* cx, HandleScript script)
 }
 
 /* static */ JSFlatString*
-JSScript::sourceDataWithPrelude(JSContext* cx, HandleScript script)
+JSScript::sourceDataForToString(JSContext* cx, HandleScript script)
 {
     MOZ_ASSERT(script->scriptSource()->hasSourceData());
-    return script->scriptSource()->substring(cx, script->preludeStart(), script->sourceEnd());
+    return script->scriptSource()->substring(cx, script->preludeStart(), script->postludeEnd());
 }
 
 UncompressedSourceCache::AutoHoldEntry::AutoHoldEntry()
@@ -2448,7 +2470,7 @@ JSScript::initCompartment(ExclusiveContext* cx)
 /* static */ JSScript*
 JSScript::Create(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
                  HandleObject sourceObject, uint32_t bufStart, uint32_t bufEnd,
-                 uint32_t preludeStart)
+                 uint32_t preludeStart, uint32_t postludeEnd)
 {
     MOZ_ASSERT(bufStart <= bufEnd);
 
@@ -2471,6 +2493,7 @@ JSScript::Create(ExclusiveContext* cx, const ReadOnlyCompileOptions& options,
     script->sourceStart_ = bufStart;
     script->sourceEnd_ = bufEnd;
     script->preludeStart_ = preludeStart;
+    script->postludeEnd_ = postludeEnd;
 
     return script;
 }
@@ -3407,7 +3430,7 @@ CreateEmptyScriptForClone(JSContext* cx, HandleScript src)
            .setVersion(src->getVersion());
 
     return JSScript::Create(cx, options, sourceObject, src->sourceStart(), src->sourceEnd(),
-                            src->preludeStart());
+                            src->preludeStart(), src->postludeEnd());
 }
 
 JSScript*
@@ -3968,6 +3991,7 @@ LazyScript::LazyScript(JSFunction* fun, void* table, uint64_t packedFields,
     begin_(begin),
     end_(end),
     preludeStart_(preludeStart),
+    postludeEnd_(end),
     lineno_(lineno),
     column_(column)
 {