Fix line numbers in case of commonJS file with no sourcemap

Previously if someone imports or runs a commonJS file (one that won't
need to go through babel) we still need to wrap it in some code to run
it. But we don't have a sourcemap to update, unless it already had
one(internal babel adds it). This leads to all lines being off by 1.

This is fixed by updating the sourcemap in the other case.

Unfortunately short of generating an "identity" sourcemap and then
shifting it by 1 with adding `;` to the first mapping, this can't be
done.

The sourcemap implementation specifically wants to find each mapping, so
unless it can do that it will not do anything.

The remaining hack (adjusting any available sourcemap) still stands as
it also fixes the columns on the *first* line of the file. As well as
actually being better.

js/bundle_test.go

@@ -91,7 +91,7 @@ func TestNewBundle(t *testing.T) {
 		_, err := getSimpleBundle(t, "/script.js", `throw new Error("aaaa");`)
 		exception := new(scriptExceptionError)
 		require.ErrorAs(t, err, &exception)
-		require.EqualError(t, err, "Error: aaaa\n\tat file:///script.js:2:7(3)\n")
+		require.EqualError(t, err, "Error: aaaa\n\tat file:///script.js:1:34(3)\n")
 	})
 	t.Run("InvalidExports", func(t *testing.T) {
 		t.Parallel()
@@ -164,13 +164,14 @@ func TestNewBundle(t *testing.T) {
 				// ES2015 modules are not supported
 				{
 					"Modules", "base", `export default function() {};`,
-					"file:///script.js: Line 2:1 Unexpected reserved word (and 2 more errors)",
+					"file:///script.js: Line 1:28 Unexpected reserved word (and 2 more errors)",
 				},
 				// BigInt is not supported
 				{
 					"BigInt", "base",
-					`module.exports.default = function() {}; BigInt(1231412444)`,
-					"ReferenceError: BigInt is not defined\n\tat file:///script.js:2:47(7)\n",
+					`module.exports.default = function() {};
+BigInt(1231412444)`,
+					"ReferenceError: BigInt is not defined\n\tat file:///script.js:2:7(7)\n",
 				},
 			}
 

js/compiler/compiler.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"os"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -207,8 +208,14 @@ func (c *Compiler) compileImpl(
 ) (*goja.Program, string, error) {
 	code := src
 	state := compilationState{srcMap: srcMap, compiler: c, wrapped: wrap}
-	if wrap { // the lines in the sourcemap (if available) will be fixed by increaseMappingsByOne
-		code = "(function(module, exports){\n" + code + "\n})\n"
+	if wrap {
+		conditionalNewLine := ""
+		if strings.Contains(code, "//# sourceMappingURL=") {
+			// the lines in the sourcemap (if available) will be fixed by increaseMappingsByOne
+			conditionalNewLine = "\n"
+			// if there is no sourcemap - bork only the first line of code, but leave the remaining ones.
+		}
+		code = "(function(module, exports){" + conditionalNewLine + code + "\n})\n"
 	}
 	opts := parser.WithDisableSourceMaps
 	if c.Options.SourceMapLoader != nil {

js/compiler/compiler_test.go

@@ -84,7 +84,7 @@ func TestCompile(t *testing.T) {
 		src := `exports.d=1+(function() { return 2; })()`
 		pgm, code, err := c.Compile(src, "script.js", false)
 		require.NoError(t, err)
-		assert.Equal(t, "(function(module, exports){\nexports.d=1+(function() { return 2; })()\n})\n", code)
+		assert.Equal(t, "(function(module, exports){exports.d=1+(function() { return 2; })()\n})\n", code)
 		rt := goja.New()
 		v, err := rt.RunProgram(pgm)
 		require.NoError(t, err)
@@ -131,8 +131,7 @@ func TestCompile(t *testing.T) {
 		c.Options.CompatibilityMode = lib.CompatibilityModeExtended
 		pgm, code, err := c.Compile(`import "something";`, "script.js", false)
 		require.NoError(t, err)
-		assert.Equal(t, `(function(module, exports){
-"use strict";require("something");
+		assert.Equal(t, `(function(module, exports){"use strict";require("something");
 })
 `, code)
 		var requireCalled bool

js/initcontext_test.go

@@ -102,7 +102,7 @@ func TestRequire(t *testing.T) {
 			require.NoError(t, fsext.WriteFile(fs, "/file.js", []byte(`throw new Error("aaaa")`), 0o755))
 			_, err := getSimpleBundle(t, "/script.js", `import "/file.js"; export default function() {}`, fs)
 			assert.EqualError(t, err,
-				"Error: aaaa\n\tat file:///file.js:2:7(3)\n\tat go.k6.io/k6/js.(*requireImpl).require-fm (native)\n\tat file:///script.js:1:0(15)\n")
+				"Error: aaaa\n\tat file:///file.js:1:34(3)\n\tat go.k6.io/k6/js.(*requireImpl).require-fm (native)\n\tat file:///script.js:1:0(15)\n")
 		})
 
 		imports := map[string]struct {
@@ -576,6 +576,40 @@ export default function(){
 	require.Equal(t, exception.String(), "exception in line 2\n\tat f2 (file:///module1.js:2:4(2))\n\tat file:///script.js:5:4(3)\n")
 }
 
+func TestSourceMapsCJS(t *testing.T) {
+	t.Parallel()
+	fs := fsext.NewMemMapFs()
+	require.NoError(t, fsext.WriteFile(fs, "/module1.js", []byte(`
+exports.f2 = function(){
+    throw "exception in line 2"
+    console.log("in f2")
+}
+exports.f1 = function(){
+    throw "exception in line 6"
+    console.log("in f1")
+}
+`[1:]), 0o644))
+	data := `
+import * as module1 from "./module1.js"
+
+export default function(){
+//    throw "exception in line 4"
+    module1.f2()
+    console.log("in default")
+}
+`[1:]
+	b, err := getSimpleBundle(t, "/script.js", data, fs)
+	require.NoError(t, err)
+
+	bi, err := b.Instantiate(context.Background(), 0)
+	require.NoError(t, err)
+	_, err = bi.getCallableExport(consts.DefaultFn)(goja.Undefined())
+	require.Error(t, err)
+	exception := new(goja.Exception)
+	require.ErrorAs(t, err, &exception)
+	require.Equal(t, exception.String(), "exception in line 2\n\tat file:///module1.js:2:5(2)\n\tat file:///script.js:5:4(3)\n")
+}
+
 func TestSourceMapsExternal(t *testing.T) {
 	t.Parallel()
 	fs := fsext.NewMemMapFs()

js/runner_test.go

@@ -85,7 +85,7 @@ func TestRunnerNew(t *testing.T) {
 	t.Run("Invalid", func(t *testing.T) {
 		t.Parallel()
 		_, err := getSimpleRunner(t, "/script.js", `blarg`)
-		assert.EqualError(t, err, "ReferenceError: blarg is not defined\n\tat file:///script.js:2:1(1)\n")
+		assert.EqualError(t, err, "ReferenceError: blarg is not defined\n\tat file:///script.js:1:28(1)\n")
 	})
 }
 

js/summary_test.go

@@ -698,6 +698,6 @@ func TestExceptionInHandleSummaryFallsBackToTextSummary(t *testing.T) {
 	assert.Equal(t, 1, len(logErrors))
 	errMsg, err := logErrors[0].String()
 	require.NoError(t, err)
-	assert.Contains(t, errMsg, "\"Error: intentional error\\n\\tat file:///script.js:5:11(3)\\n")
+	assert.Contains(t, errMsg, "\"Error: intentional error\\n\\tat file:///script.js:4:11(3)\\n")
 	assert.Equal(t, logErrors[0].Data, logrus.Fields{"hint": "script exception"})
 }