On Upgrade to Angular 7, get a tslint error for truthiness check

[navneetkarnani]

Check these issues for a trail:
microsoft/TypeScript#26262
microsoft/TypeScript@14d3c69

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Description of the PR

The Typescript 3.1 compiler (one that is used with Angular 7 onwards), has a check for void functions being checked for Truthiness. This change fixes the service function to have multiple return types if the HttpClient is being used, which is where the code gets generated.

[jcollard]

👍 Resolve my issue.

[navneetkarnani]

Addresses: #8836

[navneetkarnani]

@roni-frantchi , since you are the creator of typescript-angular, please review. I don't see a reviewer for typescript on the technical committee

[cbetrifork]

Will the PR not create error when formParams is FormData type, for 'multipart/form-data'?

Since it forces the formParams to be HttpParams or void.

[roni-frantchi]

@navneetkarnani to @cbetrifork 's point, it seems like your solution holds up because TypeScript isn't smart enough (yet?) to warn you of truthiness checks in void union types.
As in:

interface Foo {
    yo(): number;
    append(): void;
    voidi(): void;
}

interface Bar {
    yo(): string;
    append(): boolean;
}

let union: Foo | Bar;
let foo: Foo;

const unionAsExpected = union.yo() / 10; // Error: you can't divide something that might be a string
const voidAsExpected = foo.voidi() || true; // Error: Void can't be tested for truthiness

const bummer = union.append() || true; // No error... Should have been caught? append() returns a type that's a union of void, can it be checked for truthiness?

[navneetkarnani]

Will the PR not create error when formParams is FormData type, for 'multipart/form-data'?

Since it forces the formParams to be HttpParams or void.

Changing recommendation to "any" instead of specific type to avoid having to specify all possible combinations ( and that I may not be aware of ).

[roni-frantchi]

@navneetkarnani using any would solve it, but as you've mention, we lose type safety.
Here's another way to go at it, which I think will solve it: #9012 .
What do you think?.