In insertNodeAfter, handle file with no trailing newline (#23814)

src/harness/fourslash.ts

@@ -2662,10 +2662,10 @@ Actual: ${stringify(fullActual)}`);
         public verifyImportFixAtPosition(expectedTextArray: string[], errorCode: number | undefined, preferences: ts.UserPreferences | undefined) {
             const { fileName } = this.activeFile;
             const ranges = this.getRanges().filter(r => r.fileName === fileName);
-            if (ranges.length !== 1) {
+            if (ranges.length > 1) {
                 this.raiseError("Exactly one range should be specified in the testfile.");
             }
-            const range = ts.first(ranges);
+            const range = ts.firstOrUndefined(ranges);
 
             const codeFixes = this.getCodeFixes(fileName, errorCode, preferences).filter(f => f.fixId === undefined); // TODO: GH#20315 filter out those that use the import fix ID;
 
@@ -2684,7 +2684,7 @@ Actual: ${stringify(fullActual)}`);
                 const change = ts.first(codeFix.changes);
                 ts.Debug.assert(change.fileName === fileName);
                 this.applyEdits(change.fileName, change.textChanges, /*isFormattingEdit*/ false);
-                const text = this.rangeText(range);
+                const text = range ? this.rangeText(range) : this.getFileContent(this.activeFile.fileName);
                 actualTextArray.push(text);
                 scriptInfo.updateContent(originalContent);
             }

src/services/textChanges.ts

@@ -177,10 +177,10 @@ namespace ts.textChanges {
     }
 
     function getAdjustedEndPosition(sourceFile: SourceFile, node: Node, options: ConfigurableEnd) {
+        const { end } = node;
         if (options.useNonAdjustedEndPosition || isExpression(node)) {
-            return node.getEnd();
+            return end;
         }
-        const end = node.getEnd();
         const newEnd = skipTrivia(sourceFile.text, end, /*stopAfterLineBreak*/ true);
         return newEnd !== end && isLineBreak(sourceFile.text.charCodeAt(newEnd - 1))
             ? newEnd
@@ -466,7 +466,11 @@ namespace ts.textChanges {
                 }
             }
             const endPosition = getAdjustedEndPosition(sourceFile, after, {});
-            return this.replaceRange(sourceFile, createTextRange(endPosition), newNode, this.getInsertNodeAfterOptions(after));
+            const options = this.getInsertNodeAfterOptions(after);
+            return this.replaceRange(sourceFile, createTextRange(endPosition), newNode, {
+                ...options,
+                prefix: after.end === sourceFile.end && isStatement(after) ? (options.prefix ? `\n${options.prefix}` : "\n") : options.prefix,
+            });
         }
 
         private getInsertNodeAfterOptions(node: Node): InsertNodeOptions {