Restrict interpolation types based on format; Include typing for formatParams

[nicegamer7]

Currently, it's possible to pass any variable as an interpolation, which isn't great since it can be error prone. Take the following as an example:

// Poorly named variable
const username = { name: 'some_user', ... };

// ...

// Assuming key fallback
t("Hello {{username}}", { username });
// -> "Hello [object Object]"

The above is not completely addressed in this PR. Instead, I'm first fixing a subset of this problem, which is formatted interpolations. Since the built-in interpolations must conform to the Intl formatters that they are passed to, this PR makes it so that any interpolation that is being formatted is restriced to the type that the corresponding Intl formatter expects. This PR also adds typing for formatParams.

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included
• commit message and code follows the Developer's Certification of Origin

[coveralls]

coverage: 92.36%. remained the same when pulling 666d724 on nicegamer7:feature/formatparams-types into 815cd83 on i18next:master.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[adrai]

@pedrodurek and also here?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[adrai]

I'm not sure we should enforce the format typings... what if someone uses the old formatting or custom formats?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[adrai]

@marcalexiei what is your opinion on this?

[marcalexiei]

I tried to port the on master branch.
(This PR is very old: InterpolationMap is inside t.d.ts files, here is inside index.d.ts 😅)

Right now tests are failing:

test errors

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The possible breaking change is that someone could have already declared formatter with these names but with different parameters like @adrai pointed out.

Simple solution

This computation should be performed only when _JSONFormat is set to v4 like in PluralSuffix.

i18next/typescript/t.d.ts

Lines 35 to 37 in 2f3384b

	type PluralSuffix = _JSONFormat extends 'v4'
	? 'zero' | 'one' | 'two' | 'few' | 'many' | 'other'
	: number | 'plural';

However if someone is using a custom parser with JSONFormat set to v4 the issue will remain, so the only workaround I could think of is to add a new boolean flag under CustomTypeOptions to enable this kind of behaviour.

I personally don't find any of this two solutions quite appealing because I consider them a workaround.

Complex solution

The best, but more difficult, solution is to add a way to define formatters inside CustomTypeOptions so every user is able to customise them and they are inferred by the TFunction type when the key has them.
Basically something like what is already in place with Resources.

Unfortunately that is a lot of type gymnastic.

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Besides that I think that more tests should be added to test the behaviour of TFunction when providing a formatter using Intl API.

[adrai]

ok, will close this for now... if someone has time and motivation to take this over feel free to reopen or create a new PR