[TypeScript] Possible breakage of LegacyElementMixin type definition with the release of 3.4.0 (No problem on 3.3.1)

[petersaints]

Steps to Reproduce

1. Import a Polymer component in TypeScript with an interface that extends both LegacyElementMixin and HTMLElement (e.g., https://www.webcomponents.org/element/@polymer/paper-dialog).
   import { PaperDialogElement } from '@polymer/paper-dialog/paper-dialog.js';
2. Try to compile your project.

#### Expected Results
No error during compilation.

#### Actual Results
The following errors occur:
node_modules/@polymer/paper-dialog/paper-dialog.d.ts:78:11 - error TS2320: Interface 'PaperDialogElement' cannot simultaneously extend types 'LegacyElementMixin' and 'HTMLElement'.
  Named property 'removeAttribute' of types 'LegacyElementMixin' and 'HTMLElement' are not identical.

78 interface PaperDialogElement extends PaperDialogBehavior, NeonAnimationRunnerBehavior, LegacyElementMixin, HTMLElement {
             ~~~~~~~~~~~~~~~~~~

node_modules/@polymer/paper-dialog/paper-dialog.d.ts:78:11 - error TS2320: Interface 'PaperDialogElement' cannot simultaneously extend types 'LegacyElementMixin' and 'HTMLElement'.
  Named property 'setAttribute' of types 'LegacyElementMixin' and 'HTMLElement' are not identical.

78 interface PaperDialogElement extends PaperDialogBehavior, NeonAnimationRunnerBehavior, LegacyElementMixin, HTMLElement {
             ~~~~~~~~~~~~~~~~~~


Found 2 errors.

I looked a bit into it and it seems that on Polymer v3.3.1 there were no removeAttribute and setAttribute methods on the LegacyElementMixin interface, whereas they are present in v3.4.0.

That wouldn't be a problem, but the method signature doesn't match the one found on HTMLElement so when an interface tries to extend both of those at the same they will clash.

On HTMLElement you have the following signatures:

removeAttribute(qualifiedName: string): void;
setAttribute(qualifiedName: string, value: string): void;

On version 3.4.0's LegacyElementMixin you have these signatures:
setAttribute(name: any, value: any): void;
removeAttribute(name: any): void;

As you can see, they are not pefect matches. string should be used instead of any.

I don't know exactly how do you generate your type definitions, since the library is not written in TypeScript. But you are probably doing it by extracting type information from JSDoc.

So could you please fix this small issue and make a quick v3.4.1 release?

Thanks in advance.

Browsers Affected

• Not applicable, this is a build time issue.

Versions

• @polymer/lit-element: v2.3.1
• @polymer/paper-dialog: v3.0.1
• @polymer/polymer: v3.4.0

[robrez]

Came to report the same thing, one of our CI pipelines broke today. Confirmed that pinning polymer ~3.3.0 fixes the issues

../../node_modules/@polymer/paper-icon-button/paper-icon-button.d.ts(75,11): error TS2320: Interface 'PaperIconButtonElement' cannot simultaneously extend types 'LegacyElementMixin' and 'HTMLElement'.
  Named property 'removeAttribute' of types 'LegacyElementMixin' and 'HTMLElement' are not identical.
../../node_modules/@polymer/paper-ripple/paper-ripple.d.ts(86,11): error TS2320: Interface 'PaperRippleElement' cannot simultaneously extend types 'LegacyElementMixin' and 'HTMLElement'.
  Named property 'setAttribute' of types 'LegacyElementMixin' and 'HTMLElement' are not identical.
../../node_modules/@polymer/paper-spinner/paper-spinner.d.ts(52,11): error TS2320: Interface 'PaperSpinnerElement' cannot simultaneously extend types 'LegacyElementMixin' and 'HTMLElement'.
  Named property 'removeAttribute' of types 'LegacyElementMixin' and 'HTMLElement' are not identical.

[robrez]

Looks like this PR maybe the intended fix: #5650

It came not long after v3.4.0 was released

[bicknellr]

Thanks for reporting! Yes, #5650 should fix this but I'm currently working some issues importing it internally since it goes through a different type checker there. Once that's fixed, I'll make a v3.4.1 release.

[bicknellr]

Sorry about the wait, turnaround time for those tests is kind of long and we had to do a few cycles. v3.4.1 is now released and should resolve this issue; let me know here if you're still experiencing this issue after upgrading. Again, thanks for reporting!