fix comment parsing at start of file

* skip shebang if present (fixes: #28477)
* don't parse trailing comments as they are also treated like leading comments

Author: ajafff

src/compiler/scanner.ts

@@ -642,8 +642,18 @@ namespace ts {
         let pendingKind!: CommentKind;
         let pendingHasTrailingNewLine!: boolean;
         let hasPendingCommentRange = false;
-        let collecting = trailing || pos === 0;
+        let collecting = trailing;
         let accumulator = initial;
+        if (pos === 0) {
+            if (collecting) {
+                return accumulator;
+            }
+            collecting = true;
+            const shebang = getShebang(text);
+            if (shebang) {
+                pos = shebang.length;
+            }
+        }
         scan: while (pos >= 0 && pos < text.length) {
             const ch = text.charCodeAt(pos);
             switch (ch) {

src/testRunner/tsconfig.json

@@ -45,6 +45,7 @@
         "unittests/builder.ts",
         "unittests/cancellableLanguageServiceOperations.ts",
         "unittests/commandLineParsing.ts",
+        "unittests/comments.ts",
         "unittests/compileOnSave.ts",
         "unittests/compilerCore.ts",
         "unittests/configurationExtension.ts",

src/testRunner/unittests/comments.ts

@@ -0,0 +1,49 @@
+namespace ts {
+    describe("comment parsing", () => {
+        const withShebang = `#! node
+/** comment */
+// another one
+;`;
+        const noShebang = `/** comment */
+// another one
+;`;
+        const withTrailing = `;/* comment */
+// another one
+`
+        it("skips shebang", () => {
+            const result = getLeadingCommentRanges(withShebang, 0);
+            assert.isDefined(result);
+            assert.strictEqual(result!.length, 2);
+        });
+
+        it("treats all comments at start of file as leading comments", () => {
+            const result = getLeadingCommentRanges(noShebang, 0);
+            assert.isDefined(result);
+            assert.strictEqual(result!.length, 2);
+        });
+
+        it("returns leading comments if position is not 0", () => {
+            const result = getLeadingCommentRanges(withTrailing, 1);
+            assert.isDefined(result);
+            assert.strictEqual(result!.length, 1);
+            assert.strictEqual(result![0].kind, SyntaxKind.SingleLineCommentTrivia);
+        });
+
+        it("returns no trailing comments at start of file", () => {
+            const result = getTrailingCommentRanges(noShebang, 0);
+            assert.isUndefined(result);
+        });
+
+        it("returns no trailing comments at start of file if shebang is present", () => {
+            const result = getTrailingCommentRanges(withShebang, 0);
+            assert.isUndefined(result);
+        });
+
+        it("returns trailing comments if position is not 0", () => {
+            const result = getTrailingCommentRanges(withTrailing, 1);
+            assert.isDefined(result);
+            assert.strictEqual(result!.length, 1);
+            assert.strictEqual(result![0].kind, SyntaxKind.MultiLineCommentTrivia);
+        });
+    });
+}

tests/baselines/reference/exponentiationOperatorSyntaxError1.js

@@ -40,8 +40,7 @@ var temp = 10;
 
 //// [exponentiationOperatorSyntaxError1.js]
 // Error: early syntax error using ES7 SimpleUnaryExpression on left-hand side without ()
-Math.pow(// Error: early syntax error using ES7 SimpleUnaryExpression on left-hand side without ()
--1, 2);
+Math.pow(-1, 2);
 Math.pow(+1, 2);
 Math.pow(1, Math.pow(-2, 3));
 Math.pow(1, Math.pow(-2, -3));

tests/baselines/reference/shebangBeforeReferences.js

@@ -17,6 +17,7 @@ use(x);
 //// [f.js]
 #!/usr/bin/env node
 "use strict";
+/// <reference path="f.d.ts"/>
 exports.__esModule = true;
 var test_1 = require("test");
 use(test_1.x);