Forbid extraction of empty spans

Author: amcasey

src/harness/unittests/extractMethods.ts

@@ -404,6 +404,12 @@ function test(x: number) {
             "Cannot extract range containing conditional break or continue statements."
         ]);
 
+        testExtractRangeFailed("extractRangeFailed9",
+        `var x = ([#||]1 + 2);`,
+        [
+            "Statement or expression expected."
+        ]);
+
         testExtractMethod("extractMethod1",
             `namespace A {
     let x = 1;

src/services/refactors/extractMethod.ts

@@ -162,6 +162,11 @@ namespace ts.refactor.extractMethod {
      */
     export function getRangeToExtract(sourceFile: SourceFile, span: TextSpan): RangeToExtract {
         const length = span.length || 0;
+
+        if (length === 0) {
+            return { errors: [createFileDiagnostic(sourceFile, span.start, length, Messages.StatementOrExpressionExpected)] };
+        }
+
         // Walk up starting from the the start position until we find a non-SourceFile node that subsumes the selected span.
         // This may fail (e.g. you select two statements in the root of a source file)
         let start = getParentNodeInSpan(getTokenAtPosition(sourceFile, span.start, /*includeJsDocComment*/ false), sourceFile, span);