When a Keg is unlinked, brew-link gives a helpful message for how to proceed: adding the `--overwrite` flag.
For safety, it also recommends running in `--dry-run` mode first to see what would be deleted.
So a user's common flow would be:
1. run `brew link foo`
2. get error message with guidance
3. run `brew link --overwrite --dry-run foo`
4. inspect
5. run `brew link --overwrite foo`
In this flow, steps 3-5 are likely very common. Common enough that a user may use their shell history to re-populate their prompt with step 3's command, delete the `--dry-run` flag, and re-run. (The end goal, of course, is to link `foo`.)
The `--dry-run` flag needs to be removed from the command, of course. If it had been at the _end_ of the command, it would make the subsequent modification easier.
Instead of "up arrow, left-arrow a bunch, then backspace over --dry-run, hopefully not backspacing over the formula name", it would be easier for the user if the dry-run flag were already at the end of the command. Then the user can "up arrow, backspace a few times and hit enter".
What's more, if the last arg were `--dry-run`, a more advanced bash user could even use `!:-` to re-run the link command with all-but-the-last-arg.
We discussed the idea of adding a livecheck strategy to check crate
versions years ago but decided to put it off because it would have
only applied to one formula at the time (and it wasn't clear that a
crate was necessary in that case). We now have a few formulae that
use a crate in the `stable` URL (`cargo-llvm-cov`, `pngquant`,
`oakc`) and another formula with a crate resource (`deno`), so
there's some value to the idea now.
I established a standard approach for checking crate versions in a
somewhat recent `pngquant` `livecheck` block update and this commit
reworks it into a strategy, so we won't have to duplicate that
`livecheck` block in these cases. With this strategy, we usually
won't even need a `livecheck` block at all.
Under normal circumstances, a regex and/or strategy block shouldn't
be necessary but the strategy supports them when needed. The response
from the crates.io API is a JSON object, so this uses
`Json#versions_from_content` internally and a `strategy` block will
receive the parsed `json` object and a regex (the strategy default or
the regex from the `livecheck` block).
