tweak message

src/ast/nodes/ThisExpression.js

@@ -1,6 +1,8 @@
 import Node from '../Node.js';
 import getLocation from '../../utils/getLocation.js';
 
+const warning = `The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten. See https://github.com/rollup/rollup/wiki/Troubleshooting#this-is-undefined for more information`;
+
 export default class ThisExpression extends Node {
 	initialise ( scope ) {
 		const lexicalBoundary = scope.findLexicalBoundary();
@@ -8,9 +10,9 @@ export default class ThisExpression extends Node {
 		if ( lexicalBoundary.isModuleScope ) {
 			this.alias = this.module.context;
 			if ( this.alias === 'undefined' ) {
-				const location = getLocation(this.module.code, this.module.ast.end);
-				const detail = `${this.module.id}, line: ${location.line}, column: ${location.column}`;
-				this.module.bundle.onwarn( `The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten (in ${detail})`);
+				const { line, column } = getLocation( this.module.code, this.start );
+				const detail = `${this.module.id} (${line}:${column + 1})`; // use one-based column number convention
+				this.module.bundle.onwarn( `${detail} ${warning}` );
 			}
 		}
 	}

test/function/warn-on-top-level-this/_config.js

@@ -1,13 +1,12 @@
 const assert = require( 'assert' );
 
 module.exports = {
+	solo: true,
 	description: 'warns on top-level this (#770)',
 	warnings: warnings => {
-		const message = `The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten`;
-		assert.equal(warnings.length, 1);
-		assert.equal(warnings[0].indexOf(message), 0);
-		assert(warnings[0].match(/\(in.*warn-on-top-level-this.*\)/));
-		assert(warnings[0].match(/line: 4, column: 0/));
+		assert.deepEqual( warnings, [
+			`main.js (3:1) The 'this' keyword is equivalent to 'undefined' at the top level of an ES module, and has been rewritten. See https://github.com/rollup/rollup/wiki/Troubleshooting#this-is-undefined for more information`
+		]);
 	},
 	runtimeError: err => {
 		assert.equal( err.message, `Cannot set property 'foo' of undefined` );