Support Deno 1.4.0 Strict Type Import / Export

[asos-craigmorten]

Describe the bug

Deno 1.4.0 introduced stricter checks on the import and export of types for all users using the --unstable flag. These (presumably) will be integrated with Deno stable in an upcoming release.

This request is to make the necessary changes to support these stricter checks, especially given eta requires the --unstable flag to run and thus is immediately broken by this latest release.

See relevant section in release blog post: https://deno.land/posts/v1.4#stricter-type-checks-in-code--unstablecode

To Reproduce

Create a file called repro.ts with the following contents:

import "https://deno.land/x/eta@v1.6.2/mod.ts";

And run deno run --unstable repro.ts.

Note there are several errors:

error: TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { TemplateFunction } from "./compile.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/containers.ts:5:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { TemplateFunction } from "./compile.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/config.ts:7:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { Cacher } from "./storage.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/config.ts:8:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/utils.ts:8:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/parse.ts:6:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/compile-string.ts:5:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { AstObject } from "./parse.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/compile-string.ts:6:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig, PartialConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/compile.ts:7:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { CallbackFn } from "./file-handlers.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/compile.ts:8:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/file-utils.ts:10:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig, PartialConfig, EtaConfigWithFilename } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/file-handlers.ts:12:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { TemplateFunction } from "./compile.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/file-handlers.ts:13:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/file-helpers.ts:5:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { EtaConfig, PartialConfig } from "./config.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/render.ts:8:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { TemplateFunction } from "./compile.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/render.ts:9:1

TS1371 [ERROR]: This import is never used as a value and must use 'import type' because the 'importsNotUsedAsValues' is set to 'error'.
import { CallbackFn } from "./file-handlers.ts";
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    at https://deno.land/x/eta@v1.6.2/render.ts:10:1

Found 16 errors.

Expected behavior

The import should work without throwing typescript errors relating to type imports and exports.

Screenshots

--

Package & Environment Details

• MacOS Mojave 10.14.6
• eta@v1.6.2

$ deno --version
deno 1.4.0
v8 8.7.75
typescript 4.0.2

Additional context

Encountered attempting to upgrade Opine to Deno 1.4.0