Combine getLastChild helpers (microsoft#22418)

Author: Andy

src/compiler/parser.ts

@@ -7243,17 +7243,17 @@ namespace ts {
             forEachChild(sourceFile, visit);
 
             if (lastNodeEntirelyBeforePosition) {
-                const lastChildOfLastEntireNodeBeforePosition = getLastChild(lastNodeEntirelyBeforePosition);
+                const lastChildOfLastEntireNodeBeforePosition = getLastDescendant(lastNodeEntirelyBeforePosition);
                 if (lastChildOfLastEntireNodeBeforePosition.pos > bestResult.pos) {
                     bestResult = lastChildOfLastEntireNodeBeforePosition;
                 }
             }
 
             return bestResult;
 
-            function getLastChild(node: Node): Node {
+            function getLastDescendant(node: Node): Node {
                 while (true) {
-                    const lastChild = getLastChildWorker(node);
+                    const lastChild = getLastChild(node);
                     if (lastChild) {
                         node = lastChild;
                     }
@@ -7263,16 +7263,6 @@ namespace ts {
                 }
             }
 
-            function getLastChildWorker(node: Node): Node | undefined {
-                let last: Node;
-                forEachChild(node, child => {
-                    if (nodeIsPresent(child)) {
-                        last = child;
-                    }
-                });
-                return last;
-            }
-
             function visit(child: Node) {
                 if (nodeIsMissing(child)) {
                     // Missing nodes are effectively invisible to us.  We never even consider them

src/compiler/utilities.ts

@@ -3883,6 +3883,24 @@ namespace ts {
         return isStringLiteral(moduleSpecifier) ? moduleSpecifier.text : getTextOfNode(moduleSpecifier);
     }
 
+    export function getLastChild(node: Node): Node | undefined {
+        let lastChild: Node | undefined;
+        forEachChild(node,
+            child => {
+                if (nodeIsPresent(child)) lastChild = child;
+            },
+            children => {
+                // As an optimization, jump straight to the end of the list.
+                for (let i = children.length - 1; i >= 0; i--) {
+                    if (nodeIsPresent(children[i])) {
+                        lastChild = children[i];
+                        break;
+                    }
+                }
+            });
+        return lastChild;
+    }
+
     /** Add a value to a set, and return true if it wasn't already present. */
     export function addToSeen(seen: Map<true>, key: string | number): boolean {
         key = String(key);

src/services/utilities.ts

@@ -1499,17 +1499,4 @@ namespace ts {
     function getFirstChild(node: Node): Node | undefined {
         return node.forEachChild(child => child);
     }
-
-    function getLastChild(node: Node): Node | undefined {
-        let lastChild: Node | undefined;
-        node.forEachChild(
-            child => { lastChild = child; },
-            children => {
-                // As an optimization, jump straight to the end of the list.
-                if (children.length) {
-                    lastChild = last(children);
-                }
-            });
-        return lastChild;
-    }
 }