@cypress/webpack-preprocessor: missing type dependencies and other type errors

Current behavior

Reduced test case: https://github.com/OliverJAsh/cypress-10-ts-errors

This is a brand new Cypress project using the latest version of all libraries.

Run yarn and then tsc.

Result:

$ tsc
node_modules/@cypress/webpack-preprocessor/dist/index.d.ts:1:23 - error TS2688: Cannot find type definition file for 'webpack-dev-server'.

1 /// <reference types="webpack-dev-server" />
                        ~~~~~~~~~~~~~~~~~~

node_modules/@cypress/webpack-preprocessor/dist/index.d.ts:2:23 - error TS2688: Cannot find type definition file for 'webpack-dev-server-3'.

2 /// <reference types="webpack-dev-server-3" />
                        ~~~~~~~~~~~~~~~~~~~~

node_modules/@cypress/webpack-preprocessor/dist/index.d.ts:4:26 - error TS7016: Could not find a declaration file for module 'bluebird'. '/Users/oliverash/Development/temp/cypress-10-ts-errors/node_modules/bluebird/js/release/bluebird.js' implicitly has an 'any' type.
  Try `npm i --save-dev @types/bluebird` if it exists or add a new declaration (.d.ts) file containing `declare module 'bluebird';`

4 import * as Promise from 'bluebird';
                           ~~~~~~~~~~


Found 3 errors in the same file, starting at: node_modules/@cypress/webpack-preprocessor/dist/index.d.ts:1

I attempted to workaround these errors by installing some of the missing type dependencies: https://github.com/OliverJAsh/cypress-10-ts-errors/commit/0e602ffe9a4d89372e68c06e849d12fa32af23ff

However, now I have a different error:

$ tsc
cypress.config.ts:7:16 - error TS2769: No overload matches this call.
  The last overload gave the following error.
    Argument of type '"file:preprocessor"' is not assignable to parameter of type '"task"'.

7             on("file:preprocessor", webpackPreprocessor({}));
                 ~~~~~~~~~~~~~~~~~~~

  node_modules/cypress/types/cypress.d.ts:5521:5
    5521     (action: 'task', tasks: Tasks): void
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The last overload is declared here.

node_modules/@cypress/webpack-preprocessor/dist/index.d.ts:2:23 - error TS2688: Cannot find type definition file for 'webpack-dev-server-3'.

2 /// <reference types="webpack-dev-server-3" />
                        ~~~~~~~~~~~~~~~~~~~~


Found 2 errors in 2 files.

Errors  Files
     1  cypress.config.ts:7
     1  node_modules/@cypress/webpack-preprocessor/dist/index.d.ts:2

Desired behavior

No type errors.

Test code to reproduce

See above.

Cypress Version

10.2.0

Other

Related: https://github.com/cypress-io/cypress/issues/9570

[OliverJAsh]

Also, if we don’t type check this file and we only rely on type checking inside our editors, the next time someone opens it in their editor they might be surprised to find a type error left by someone else. We type check all files in our CI build to ensure that all files remain free of type errors so there are no nasty surprises like this.

[lmiller1990]

Can you send me your test case so I can see how it compares to mine?

I copied pasted the tsconfig.json from here into cypress then ran yarn tsc --project cyperss. I just realized it was not compiling cypress.config.ts, though - so actually, it’s not type checking cypress.config.ts. 👎, so disregard my initial comment.

I wonder if webpack-preprocessor even needs the webpack-dev-server (and webpack-dev-server-3 types) at all. It doesn’t list those dependencies anywhere, so I think this is probably a bug in how we generate our types. Either way, this seems like a bug to me.