Prevent loop when babel can transpile but goja can't parse

.golangci.yml

@@ -60,4 +60,5 @@ linters:
   - wsl
   - gomnd
   - goerr113 # most of the errors here are meant for humans
+  - nlreturn
   fast: false

js/compiler/compiler.go

@@ -70,7 +70,7 @@ func (c *Compiler) Transform(src, filename string) (code string, srcmap *SourceM
 	return b.Transform(c.logger, src, filename)
 }
 
-// Compile the program in the given CompatibilityMode, optionally running pre and post code.
+// Compile the program in the given CompatibilityMode, wrapping it between pre and post code
 func (c *Compiler) Compile(src, filename, pre, post string,
 	strict bool, compatMode lib.CompatibilityMode) (*goja.Program, string, error) {
 	code := pre + src + post
@@ -81,7 +81,8 @@ func (c *Compiler) Compile(src, filename, pre, post string,
 			if err != nil {
 				return nil, code, err
 			}
-			return c.Compile(code, filename, pre, post, strict, compatMode)
+			// the compatibility mode "decreases" here as we shouldn't transform twice
+			return c.Compile(code, filename, pre, post, strict, lib.CompatibilityModeBase)
 		}
 		return nil, code, err
 	}

js/compiler/compiler_test.go

@@ -22,8 +22,10 @@ package compiler
 import (
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/dop251/goja"
+	"github.com/dop251/goja/parser"
 	"github.com/stretchr/testify/assert"
 
 	"github.com/loadimpact/k6/lib"
@@ -149,5 +151,26 @@ func TestCompile(t *testing.T) {
 			assert.Contains(t, err.Error(), `SyntaxError: script.js: Unexpected token (1:3)
 > 1 | 1+(=>2)()`)
 		})
+
+		t.Run("Invalid for goja but not babel", func(t *testing.T) {
+			ch := make(chan struct{})
+			go func() {
+				defer close(ch)
+				// This is a string with U+2029 Paragraph separator in it
+				// the important part is that goja won't parse it but babel will transform it but still
+				// goja won't be able to parse the result it is actually "\<U+2029>"
+				_, _, err := c.Compile(string([]byte{0x22, 0x5c, 0xe2, 0x80, 0xa9, 0x22}), "script.js", "", "", true, lib.CompatibilityModeExtended)
+				assert.IsType(t, parser.ErrorList{}, err)
+				assert.Contains(t, err.Error(), ` Unexpected token ILLEGAL`)
+			}()
+
+			select {
+			case <-ch:
+				// everything is fine
+			case <-time.After(time.Second):
+				// it took too long
+				t.Fatal("takes too long")
+			}
+		})
 	})
 }