Stabilize the "approximate suggestion" flag, use for the epoch

[Manishearth]

We're going to be using rustfix for epoch upgrades, and we need a way to signal to the tool that a suggestion may not apply (and instead to prompt with it).

We have an unstable "approximate suggestion" flag. I propose stabilizing this. We should also start using it everywhere.

cc @rust-lang/dev-tools

[nrc]

I'm mostly in favour. I wonder if the flag is future proof enough - should we upgrade it to an enum?

[oli-obk]

Like a suggestion kind field that currently only allows "approximate" and "automatic"?

[killercup]

Interesting, I’m kinda in favor of using an enum. Even if it probably doesn’t matter much for now and we can always add other fields and either deprecate this or specialize it’s meaning with new fields if we care about backward compat even though it’s not as nice. What are other options besides approx and auto? Something like “template” with placeholders for editors to put cursors in (like classical textmate snippets)? Oliver Schneider <notifications@github.com> schrieb am Mo. 23. Apr. 2018 um 11:17:

…

Like a suggestion kind field that currently only allows "approximate" and "automatic"? — You are receiving this because you are on a team that was mentioned. Reply to this email directly, view it on GitHub <#50168 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AABOX8fi3tRMz3Of-Chx7aKUSIED7Judks5trZwXgaJpZM4TfAO4> .

[Manishearth]

There's also a difference between those which _may_ work and those which _definitrly won't work_. Macros fall within the former, but placeholders fall within the latter.

…

On Mon, Apr 23, 2018, 2:24 AM Pascal Hertleif ***@***.***> wrote: Interesting, I’m kinda in favor of using an enum. It probably doesn’t matter much for now and we can always add other fields and either deprecate this or specialize it’s meaning with new fields if we care about backward compat even though it’s not as nice. What are other options besides approx and auto? Something like “template” with placeholders for editors to put cursors in (like classical textmate snippets)? Oliver Schneider ***@***.***> schrieb am Mo. 23. Apr. 2018 um 11:17: > Like a suggestion kind field that currently only allows "approximate" and > "automatic"? > > — > You are receiving this because you are on a team that was mentioned. > Reply to this email directly, view it on GitHub > <#50168 (comment)>, > or mute the thread > < https://github.com/notifications/unsubscribe-auth/AABOX8fi3tRMz3Of-Chx7aKUSIED7Judks5trZwXgaJpZM4TfAO4 > > . > — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#50168 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABivSFkDrg9OLKyoBspOGevOGUHUojU7ks5trZ3BgaJpZM4TfAO4> .

[killercup]

Dev tools meeting: Let's use an enum with these variants at first (represented as string in JSON output):

1. unspecified (all lints will use this by default)
2. machine-applicable
3. approximate (we might want to subdivide this further in the future, e.g. "appox because macros", "placeholder used", …)

Will implement, then do a FCP on this issue

[killercup]

impl in #50486

[killercup]

This landed.