Cache getSourceFileOfNode within the checker

Author: weswigham

src/compiler/checker.ts

@@ -1075,6 +1075,17 @@ namespace ts {
 
         return checker;
 
+        function getSourceFileOfNode(node: Node): SourceFile;
+        function getSourceFileOfNode(node: Node | undefined): SourceFile | undefined;
+        function getSourceFileOfNode(node: Node | undefined) {
+            if (!node) return node;
+            const links = getNodeLinks(node);
+            if (!hasProperty(links, "sourceFile")) {
+                links.sourceFile = ts.getSourceFileOfNode(node);
+            }
+            return links.sourceFile;
+        }
+
         function getCachedType(key: string | undefined) {
             return key ? cachedTypes.get(key) : undefined;
         }

src/compiler/types.ts

@@ -5337,6 +5337,7 @@ namespace ts {
         skipDirectInference?: true;         // Flag set by the API `getContextualType` call on a node when `Completions` is passed to force the checker to skip making inferences to a node's type
         declarationRequiresScopeChange?: boolean; // Set by `useOuterVariableScopeInParameter` in checker when downlevel emit would change the name resolution scope inside of a parameter.
         serializedTypes?: ESMap<string, TypeNode & {truncating?: boolean, addedLength: number}>; // Collection of types serialized at this location
+        sourceFile?: SourceFile | undefined; // Cached lookup result of `getSourceFileOfNode`
     }
 
     export const enum TypeFlags {