Skip "type" keyword during import declarations

[MaxGraey]

Support following declarations:

import type { Foo } from "./foo";
import type * as Foo from "./foo";

This will introduced in TS 4.5 so support this as well:

import { type Foo, Boo } from "./foo";
import { Boo, type Foo } from "./foo";

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[dcodeIO]

It may be worth to note that these behave differently in between TS and AS, in that TS will not include the respective source file, while AS always will. This can be unexpected, particularly since using the type keyword is typically done for this exact purpose. So there seems to be a tension here, and I am not sure that the desire to support the syntax outweighs the risks.

Perhaps, a compromise could be to display a warning to inform the developer that the syntax is supported, but has different semantics?

[MaxGraey]

In terms of TS, it's just speeding up type checking. Behaviour does not change much, just appear some restrictions. For AS, these restrictions do not make much sense. At least for now, but I wonder btw if we could also speedup / simplify / skip some checks with such notation? So I don't see much point in displaying a warning, as it's more of a constraint for TS, but not for AS.

[dcodeIO]

Hmm, so is my understanding wrong that this is mainly there to force elision, i.e., that code / top-level statements etc. of the other file doesn't matter / execute? I believe I got that from the relevant announcement. In more familiar terms, it seems that import preserves side effects, while import type is deliberately used so it does not.

[MaxGraey]

It not forces. It just hint which means imported name will uses only as type but not as object / class (for constructing, sub-classing or accessing to some static field / method).

[trusktr]

closes #2317

[mkoch-otto]

Any news? :)

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