[feature request] Enable typescript 3.8.3 support

[vladimiry]

• Webpack config is a TS file, not JS.
• ts-loader@6.2.1
• typescript 3.8.3
• webpack@4.42.0
• workaround: enabling skipLibCheck TS compilation flag (not for the entire code base but just for the code part that compiles/runs webpack using the config presented in TS code).

---

ERROR in node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost' and 'WatchFactory'.
Named property 'watchDirectory' of types 'SolutionBuilderWithWatchHost' and 'WatchFactory' are not identical.

57 export interface SolutionBuilderWithWatchHost extends typescript.SolutionBuilderWithWatchHost<typescript.EmitAndSemanticDiagnosticsBuilderProgram>, WatchFactory {
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost' and 'WatchFactory'.
Named property 'watchFile' of types 'SolutionBuilderWithWatchHost' and 'WatchFactory' are not identical.

57 export interface SolutionBuilderWithWatchHost extends typescript.SolutionBuilderWithWatchHost<typescript.EmitAndSemanticDiagnosticsBuilderProgram>, WatchFactory {

[johnnyreilly]

Is the problem presenting because your webpack config is TS and not JS?

I suspect this would be fixed by publishing a new version of ts-loader; we encountered this issue when upgrading from 3.7 to 3.8.

Can you do me a favour and compile the latest version of ts-loader and try it on your project. If that works then I'd feel justified publishing a new release.

[vladimiry]

Is the problem presenting because your webpack config is TS and not JS?

I think so, yes, since skipLibCheck enabled by default I got the issue of typings incompatibility noticed.

Can you do me a favour and compile the latest version of ts-loader and try it on your project. If that works then I'd feel justified publishing a new release.

Can confirm the issue is gone if I use compiled from the master branch ts-loader version.

But if I then downgrade typescript 3.8.3 => 3.7.5 I get not the exact but similar to original error:

ERROR in node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory'.
  Named property 'watchDirectory' of types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory' are not identical.

57 export interface SolutionBuilderWithWatchHost extends typescript.SolutionBuilderWithWatchHost<typescript.EmitAndSemanticDiagnosticsBuilderProgram>, WatchFactory {
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory'.
  Named property 'watchFile' of types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory' are not identical.

57 export interface SolutionBuilderWithWatchHost extends typescript.SolutionBuilderWithWatchHost<typescript.EmitAndSemanticDiagnosticsBuilderProgram>, WatchFactory {

Errors diff (original and typescript@3.7.5 + ts-loader from master branch):

@@ -1,9 +1,9 @@
-ERROR in node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost' and 'WatchFactory'.
-Named property 'watchDirectory' of types 'SolutionBuilderWithWatchHost' and 'WatchFactory' are not identical.
+ERROR in node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory'.
+  Named property 'watchDirectory' of types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory' are not identical.
 
 57 export interface SolutionBuilderWithWatchHost extends typescript.SolutionBuilderWithWatchHost<typescript.EmitAndSemanticDiagnosticsBuilderProgram>, WatchFactory {
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost' and 'WatchFactory'.
-Named property 'watchFile' of types 'SolutionBuilderWithWatchHost' and 'WatchFactory' are not identical.
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+node_modules/ts-loader/dist/interfaces.d.ts:57:18 - error TS2320: Interface 'SolutionBuilderWithWatchHost' cannot simultaneously extend types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory'.
+  Named property 'watchFile' of types 'SolutionBuilderWithWatchHost<EmitAndSemanticDiagnosticsBuilderProgram>' and 'WatchFactory' are not identical.
 
 57 export interface SolutionBuilderWithWatchHost extends typescript.SolutionBuilderWithWatchHost<typescript.EmitAndSemanticDiagnosticsBuilderProgram>, WatchFactory {

So technically, in terms of TS typings, it looks like a breaking change comes in next release and then "typescript": "*" peer dependency doesn't look accurate enough. But majority of users won't notice the issue due to the JS webpack config file use and skipLibCheck workaround is there for legacy/typescript@<3.8.x users. So not a big concern I think. Maybe it's worth to add some tests in this project with TS-based webpack config use that would run using several recent TS releases.

[johnnyreilly]

If you'd like to add one of those tests I'd be very grateful 😄

Yeah the issue will have been resolved by this change here: 87340f4#diff-a84f60e04d03dd963458bd8a12f9ac20R71

Technically this is a breaking change, but because it's a fairly niche use case I think I'm happy to just treat it as a bugfix. I've raised a release PR: #1073

I'll plan to ship it some time today unless you've any compelling reason not to?

[vladimiry]

If you'd like to add one of those tests I'd be very grateful smile

I'm not ready to do that at the moment 😄

I'll plan to ship it some time today unless you've any compelling reason not to?

I don't, would be happy to update to a new version.

Closing the issue since version in master branch is working well and is about to be released.