Implementing ts-mocha is throwing type errors in Inject

[Navos]

Description / Steps to reproduce / Feature proposal

I've been trying to implement ts-mocha instead of the built in lb-mocha for faster test running and while I have taken care of the main issues within my code, one problem remains related to when inject checks if a getter or setter is a function.

The issue stems from the following lines: https://github.com/strongloop/loopback-next/blob/master/packages/context/src/inject.ts#L551 and https://github.com/strongloop/loopback-next/blob/master/packages/context/src/inject.ts#L426

When modifying the code and trying to make working adjustments, typeof targetType === 'function' returns true, but the check against the interface Function does not.

Current Behavior

The type of AuthenticateActionProvider.constructor[1] (Object) is not Setter function

Expected Behavior

It understand the given object is a function.

[raymondfeng]

It seems that ts-node does not emit Function for the design type of Setter. ts-mocha probably sees Object instead. Please note typeof Object === 'function' returns true as Object itself is a class/constructor.

[raymondfeng]

Maybe there is a possibility to relax the check if the design type is Object, which pretty much hints that no design type is inferred.

[raymondfeng]

@Navos Please try #2765

[raymondfeng]

@Navos Can you make sure emitDecoratorMetadata is enabled for your ts-mocha setup? See https://www.typescriptlang.org/docs/handbook/compiler-options.html.

#2765 skips the assertions but @loopback/rest also relies on the design time metadata for type introspection.

[Navos]

@raymondfeng I tried the separate branch and the added the emitDecoratorMetadata and still having the same issue. Debugging through the new code, isDesignTypeSupported is returning true.

[raymondfeng]

If you have a github repo to reproduce the issue, I can take a look.

[Navos]

Hey Raymond, I cant show you the code I am currently working on due to it being work related, but I reproduced the error with the log-extension example here https://github.com/Navos/ts-mocha-implementation/blob/master/package.json

[raymondfeng]

Here is the transpiled result from ts-node:

__decorate([
    context_1.inject(keys_1.EXAMPLE_LOG_BINDINGS.LOGGER, { optional: true }),
    __metadata("design:type", typeof (_a = typeof types_1.LogWriterFn !== "undefined" && types_1.LogWriterFn) === "function" ? _a : Object)
], LogActionProvider.prototype, "writeLog", void 0);
__decorate([
    context_1.inject(keys_1.EXAMPLE_LOG_BINDINGS.APP_LOG_LEVEL, { optional: true }),
    __metadata("design:type", typeof (_b = typeof keys_1.LOG_LEVEL !== "undefined" && keys_1.LOG_LEVEL) === "function" ? _b : Object)
], LogActionProvider.prototype, "logLevel", void 0);
LogActionProvider = __decorate([
    __param(0, context_1.inject.getter(core_1.CoreBindings.CONTROLLER_CLASS)),
    __param(1, context_1.inject.getter(core_1.CoreBindings.CONTROLLER_METHOD_NAME)),
    __param(2, context_1.inject(keys_1.EXAMPLE_LOG_BINDINGS.TIMER)),
    __metadata("design:paramtypes", [typeof (_c = typeof context_1.Getter !== "undefined" && context_1.Getter) === "function" ? _c : Object, typeof (_d = typeof context_1.Getter !== "undefined" && context_1.Getter) === "function" ? _d : Object, typeof (_e = typeof types_1.TimerFn !== "undefined" && types_1.TimerFn) === "function" ? _e : Object])
], LogActionProvider);

[raymondfeng]

And here is what tsc produces:

__decorate([
    context_1.inject(keys_1.EXAMPLE_LOG_BINDINGS.LOGGER, { optional: true }),
    __metadata("design:type", Function)
], LogActionProvider.prototype, "writeLog", void 0);
__decorate([
    context_1.inject(keys_1.EXAMPLE_LOG_BINDINGS.APP_LOG_LEVEL, { optional: true }),
    __metadata("design:type", Number)
], LogActionProvider.prototype, "logLevel", void 0);
LogActionProvider = __decorate([
    __param(0, context_1.inject.getter(core_1.CoreBindings.CONTROLLER_CLASS)),
    __param(1, context_1.inject.getter(core_1.CoreBindings.CONTROLLER_METHOD_NAME)),
    __param(2, context_1.inject(keys_1.EXAMPLE_LOG_BINDINGS.TIMER)),
    __metadata("design:paramtypes", [Function, Function, Function])
], LogActionProvider);

[raymondfeng]

typeof context_1.Getter is undefined as Getter is just a TypeScript type definition and it's erased at runtime. As a result, ts-node only emits Object instead of Function.

[Navos]

@raymondfeng Hey Raymond, what will happen with this issue?

[bajtos]

Possibly related: #3160

@Navos is this issue still relevant? Have you managed to find any solution or any workaround?

I am looking into ways how to switch loopback-next from Mocha to Jest (see #3159). It seems to me that the solution for on-the-fly-compilation used by Jest is different from the solution used by ts-mocha (and ts-node) and the problem described in this issue is not triggered by Jest.

Would you like to try Jest instead of ts-mocha and let us know if it works any better?