Remove some unnecessary undefined checks in extractSymbol (#19256)

Author: Andy

Diff for: src/services/refactors/extractSymbol.ts

@@ -470,7 +470,7 @@ namespace ts.refactor.extractSymbol {
      * you may be able to extract into a class method *or* local closure *or* namespace function,
      * depending on what's in the extracted body.
      */
-    function collectEnclosingScopes(range: TargetRange): Scope[] | undefined {
+    function collectEnclosingScopes(range: TargetRange): Scope[] {
         let current: Node = isReadonlyArray(range.range) ? first(range.range) : range.range;
         if (range.facts & RangeFacts.UsesThis) {
             // if range uses this as keyword or as type inside the class then it can only be extracted to a method of the containing class
@@ -483,30 +483,27 @@ namespace ts.refactor.extractSymbol {
             }
         }
 
-        const start = current;
+        const scopes: Scope[] = [];
+        while (true) {
+            current = current.parent;
+            // A function parameter's initializer is actually in the outer scope, not the function declaration
+            if (current.kind === SyntaxKind.Parameter) {
+                // Skip all the way to the outer scope of the function that declared this parameter
+                current = findAncestor(current, parent => isFunctionLikeDeclaration(parent)).parent;
+            }
 
-        let scopes: Scope[] | undefined = undefined;
-        while (current) {
             // We want to find the nearest parent where we can place an "equivalent" sibling to the node we're extracting out of.
             // Walk up to the closest parent of a place where we can logically put a sibling:
             //  * Function declaration
             //  * Class declaration or expression
             //  * Module/namespace or source file
-            if (current !== start && isScope(current)) {
-                (scopes = scopes || []).push(current);
-            }
-
-            // A function parameter's initializer is actually in the outer scope, not the function declaration
-            if (current && current.parent && current.parent.kind === SyntaxKind.Parameter) {
-                // Skip all the way to the outer scope of the function that declared this parameter
-                current = findAncestor(current, parent => isFunctionLikeDeclaration(parent)).parent;
-            }
-            else {
-                current = current.parent;
+            if (isScope(current)) {
+                scopes.push(current);
+                if (current.kind === SyntaxKind.SourceFile) {
+                    return scopes;
+                }
             }
-
         }
-        return scopes;
     }
 
     function getFunctionExtractionAtIndex(targetRange: TargetRange, context: RefactorContext, requestedChangesIndex: number): RefactorEditInfo {
@@ -592,15 +589,7 @@ namespace ts.refactor.extractSymbol {
     function getPossibleExtractionsWorker(targetRange: TargetRange, context: RefactorContext): { readonly scopes: Scope[], readonly readsAndWrites: ReadsAndWrites } {
         const { file: sourceFile } = context;
 
-        if (targetRange === undefined) {
-            return undefined;
-        }
-
         const scopes = collectEnclosingScopes(targetRange);
-        if (scopes === undefined) {
-            return undefined;
-        }
-
         const enclosingTextRange = getEnclosingTextRange(targetRange, sourceFile);
         const readsAndWrites = collectReadsAndWrites(
             targetRange,