feat: infer argument types in command implementations (#17496)

Co-authored-by: Chris Breiding <chrisbreiding@users.noreply.github.com>
Co-authored-by: Chris Breiding <chrisbreiding@gmail.com>

cli/types/cypress.d.ts

@@ -262,7 +262,7 @@ declare namespace Cypress {
      * Currently executing test runnable instance.
      */
     currentTest: {
-      title: string,
+      title: string
       titlePath: string[]
     }
 
@@ -402,9 +402,9 @@ declare namespace Cypress {
      * @see https://on.cypress.io/api/commands
      */
     Commands: {
-      add(name: string, fn: (...args: any[]) => CanReturnChainable): void
-      add(name: string, options: CommandOptions, fn: (...args: any[]) => CanReturnChainable): void
-      overwrite(name: string, fn: (...args: any[]) => CanReturnChainable): void
+      add<T extends keyof Chainable>(name: T, fn: Chainable[T]): void
+      add<T extends keyof Chainable>(name: T, options: CommandOptions, fn: Chainable[T]): void
+      overwrite<T extends keyof Chainable>(name: T, fn: Chainable[T]): void
     }
 
     /**

cli/types/tests/cypress-tests.ts

@@ -62,17 +62,31 @@ namespace CypressIsCyTests {
   })
 }
 
+declare namespace Cypress {
+  interface Chainable {
+    newCommand: (arg: string) => void
+  }
+}
+
 namespace CypressCommandsTests {
-  Cypress.Commands.add('newCommand', () => {
+  Cypress.Commands.add('newCommand', (arg) => {
+    // $ExpectType string
+    arg
     return
   })
-  Cypress.Commands.add('newCommand', { prevSubject: true }, () => {
+  Cypress.Commands.add('newCommand', { prevSubject: true }, (arg) => {
+    // $ExpectType string
+    arg
     return
   })
-  Cypress.Commands.add('newCommand', () => {
+  Cypress.Commands.add('newCommand', (arg) => {
+    // $ExpectType string
+    arg
     return new Promise((resolve) => {})
   })
-  Cypress.Commands.overwrite('newCommand', () => {
+  Cypress.Commands.overwrite('newCommand', (arg) => {
+    // $ExpectType string
+    arg
     return
   })
 }