tools/check: `pigeon` runs old/cached version of Pigeon after Pigeon dependency is upgraded

[chrisbobbe]

Part of #621 was to upgrade Pigeon, from 17.2.0 to 18.0.0. After I did that, tools/check pigeon --all-files on my machine was running the old Pigeon, while in CI the newer Pigeon was running, as we want it to, and flagging the need to update generated files. I found a workaround: #621 (comment) but it would be nice not to require a manual step.

Can we make it so when we change the version of the Pigeon dependency, the next run of tools/check pigeon --all-files uses the updated version?

[gnprice]

To make the workaround explicit in this thread: it's that after an upgrade affecting package:pigeon, and before running tools/check pigeon, one runs dart run pigeon.

That just prints the pigeon CLI's help message… but first it causes the pigeon CLI binary itself to get rebuilt with the new package.

[gnprice]

Ran into this again just now (and had forgotten the workaround):
#1568 (comment)

Fixing this is probably just a couple of lines in tools/check, in the implementation of run_pigeon.