feat(prettier): output to stdout instead of write file by default unless specified --write flag

[axetroy]

Why?

1. In order to stay consistent with prettier cli
2. for deno fmt example.ts to print formatted code in stdout
3. better integrated with IDE(eg. vscode/webstorm/atom...)

before: without --write

deno run prettier/main.ts script1.ts --allow-read --allow-write

after: with --write

deno run prettier/main.ts script1.ts --allow-read --allow-write --write

This PR bring BREAKING CHANGE: Prettier now output to stdout instead of overwriting the file by default. unless specified --write flag

When should be output to stdout?

1. without --write/--check flag
2. when source content not equal to formatted content

[kt3k]

I think this feature is nice to have.

We need to be careful with the timing of merging of this PR because this will break deno fmt temporarily.

[axetroy]

@ry it's ready for review.

[ry]

@axetroy It LGTM. I'm a bit concerned that this will break "deno fmt" (we should be using a tagged link to std/prettier and not master link).

[axetroy]

@ry yes. it will break the demo fmt

And I think about again that when should be output to stdout?

When should be output to stdout?

1. without --write/--check flag
2. when source content not equal to formatted content

formatted code should always be printed to stdout even source content equal to formatted content. How about it?

[kt3k]

@ry I think it's now safe to merge this PR. I checked deno fmt now maps to run prettier/main.ts <files> --write.

$ deno version
deno: 0.6.0
v8: 7.6.53
typescript: 3.4.1
$ deno fmt -D . | grep prettier/main | grep JS
DEBUG JS - args [ "https://deno.land/std/prettier/main.ts", ".", "--write" ]

[kt3k]

@axetroy Thank you for updating! LGTM

[axetroy]

waiting for #424

[ry]

LGTM

[ry]

Thanks @axetroy, @kt3k!