snippets: correctly escape backslashes in generated expressions

features/step_definition_snippets.feature

@@ -70,3 +70,20 @@ Feature: step definition snippets
         return 'pending';
       });
       """
+
+  Scenario: a step resulting in special characters in the expression
+    Given a file named "features/number.feature" with:
+      """
+      Feature: a feature
+        Scenario: a scenario
+          Given a person's (secret) desires
+      """
+    When I run cucumber-js
+    Then it fails
+    And the output contains the text:
+      """
+      Given('a person\'s \\(secret) desires', function () {
+        // Write code here that turns the phrase above into concrete actions
+        return 'pending';
+      });
+      """

src/formatter/step_definition_snippet_builder/javascript_snippet_syntax.ts

@@ -1,3 +1,4 @@
+import { GeneratedExpression } from '@cucumber/cucumber-expressions'
 import {
   ISnippetSnytax,
   ISnippetSyntaxBuildOptions,
@@ -43,9 +44,8 @@ export default class JavaScriptSnippetSyntax implements ISnippetSnytax {
         if (this.snippetInterface === SnippetInterface.Callback) {
           allParameterNames.push(CALLBACK_NAME)
         }
-        return `${prefix + functionName}('${generatedExpression.source.replace(
-          /'/g,
-          "\\'"
+        return `${prefix + functionName}('${this.escapeSpecialCharacters(
+          generatedExpression
         )}', ${functionKeyword}(${allParameterNames.join(', ')}) {\n`
       }
     )
@@ -56,4 +56,13 @@ export default class JavaScriptSnippetSyntax implements ISnippetSnytax {
       '});'
     )
   }
+
+  private escapeSpecialCharacters(generatedExpression: GeneratedExpression) {
+    let source = generatedExpression.source
+    // double up any backslashes because we're in a javascript string
+    source = source.replace(/\\/g, '\\\\')
+    // escape any single quotes because that's our quote delimiter
+    source = source.replace(/'/g, "\\'")
+    return source
+  }
 }

src/formatter/step_definition_snippet_builder/javascript_snippet_syntax_spec.ts

@@ -145,6 +145,33 @@ describe('JavascriptSnippetSyntax', () => {
       })
     })
 
+    describe('pattern contains escapes', () => {
+      it('returns the proper snippet', () => {
+        // Arrange
+        const syntax = new JavascriptSnippetSyntax(SnippetInterface.Synchronous)
+        const buildOptions: ISnippetSyntaxBuildOptions = {
+          comment: 'comment',
+          functionName: 'functionName',
+          generatedExpressions: generateExpressions(
+            'the user (with permissions) executes the action'
+          ),
+          stepParameterNames: [],
+        }
+
+        // Act
+        const result = syntax.build(buildOptions)
+
+        // Assert
+        expect(result).to.eql(
+          reindent(`
+            functionName('the user \\\\(with permissions) executes the action', function () {
+              // comment
+              return 'pending';
+            });`)
+        )
+      })
+    })
+
     describe('multiple patterns', () => {
       it('returns the snippet with the other choices commented out', function () {
         // Arrange