[#4461] Change typescript declaration for .writeFile()

cli/types/index.d.ts

@@ -1776,13 +1776,21 @@ declare namespace Cypress {
       })
     ```
      */
-    writeFile<C extends FileContents>(filePath: string, contents: C, options?: Partial<Loggable>): Chainable<C>
+    writeFile<C extends FileContents>(filePath: string, contents: C, encoding: Encodings): Chainable<C>
     /**
      * Write to a file with the specified encoding and contents.
      *
      * @see https://on.cypress.io/writefile
+    ```
+    cy.writeFile('path/to/ascii.txt', 'Hello World', {
+      flag: 'a+',
+      encoding: 'ascii'
+    }).then((text) => {
+      expect(text).to.equal('Hello World') // true
+    })
+    ```
      */
-    writeFile<C extends FileContents>(filePath: string, contents: C, encoding: Encodings, options?: Partial<Loggable>): Chainable<C>
+    writeFile<C extends FileContents>(filePath: string, contents: C, options?: Partial<WriteFileOptions>): Chainable<C>
 
     /**
      * jQuery library bound to the AUT
@@ -2318,6 +2326,12 @@ declare namespace Cypress {
     cancelable: boolean
   }
 
+  /** Options to change the default behavior of .writeFile */
+  interface WriteFileOptions extends Loggable {
+    flag: string
+    encoding: Encodings
+  }
+
   // Kind of onerous, but has a nice auto-complete. Also fallbacks at the end for custom stuff
   /**
    * @see https://on.cypress.io/should

cli/types/tests/chainer-examples.ts

@@ -424,3 +424,9 @@ cy
   })
 
 cy.get('#result').should('have.text', 'John Doe')
+
+cy.writeFile('../file.path', '', 'utf-8')
+cy.writeFile('../file.path', '', {
+  flag: 'a+',
+  encoding: 'utf-8'
+})