Added comment, inlined function.

Author: DanielRosenwasser

src/compiler/checker.ts

@@ -4548,7 +4548,7 @@ namespace ts {
          * @param target The right-hand-side of the relation.
          * @param relation The relation considered. One of 'identityRelation', 'assignableRelation', or 'subTypeRelation'.
          * Used as both to determine which checks are performed and as a cache of previously computed results.
-         * @param errorNode The node upon which all errors will be reported, if defined.
+         * @param errorNode The suggested node upon which all errors will be reported, if defined. This may or may not be the actual node used.
          * @param headMessage If the error chain should be prepended by a head message, then headMessage will be used.
          * @param containingMessageChain A chain of errors to prepend any new errors found.
          */
@@ -4593,16 +4593,6 @@ namespace ts {
             }
             return result !== Ternary.False;
 
-            function reportErrorAndTryImproveErrorNode(
-                    newErrorNode: Node,
-                    message: DiagnosticMessage,
-                    arg0?: string,
-                    arg1?: string,
-                    arg2?: string) {
-                errorNode = newErrorNode || errorNode;
-                reportError(message, arg0, arg1, arg2);
-            }
-
             function reportError(message: DiagnosticMessage, arg0?: string, arg1?: string, arg2?: string): void {
                 errorInfo = chainDiagnosticMessages(errorInfo, message, arg0, arg1, arg2);
             }
@@ -4777,11 +4767,13 @@ namespace ts {
                 for (let prop of getPropertiesOfObjectType(source)) {
                     if (!isKnownProperty(target, prop.name)) {
                         if (reportErrors) {
-                            reportErrorAndTryImproveErrorNode(
-                                prop.valueDeclaration,
-                                Diagnostics.Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1,
-                                symbolToString(prop),
-                                typeToString(target));
+                            // We know *exactly* where things went wrong when comparing the types.
+                            // Use this property as the error node as this will be more helpful in
+                            // reasoning about what went wrong.
+                            errorNode = prop.valueDeclaration
+                            reportError(Diagnostics.Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1,
+                                        symbolToString(prop),
+                                        typeToString(target));
                         }
                         return true;
                     }