This is a major refactor of Lake's build code. The key changes:
* **Job Registration**: Significant build jobs are now registered by
build functions. The DSL inserts this registration automatically into
user-defined targets and facets, so this change should require no
end-user adaption. Registered jobs are incrementally awaited by the main
build function and the progress counter now indicates how many of these
jobs are completed and left-to-await. On the positive side, this means
the counter is now always accurate. On the negative side, this means
that jobs are displayed even if they are no-ops (i.e., if the target is
already up-to-date).
* **Log Retention**: Logs are now part of a Lake monad's state instead
of being eagerly printed. As a result, build jobs retain their logs.
Using this change, logs are are now always printed after their
associated caption (e.g., `[X/Y] Building Foo`) and are not arbitrarily
interleaved with the output of other jobs.
* **Simplify the build monad stack**: Previously, there was a lot of
confused mixing between the various build monads in the codebase (i.e.,
`JobM`, `ScedulerM`, `BuildM`, `RecBuildM`, and `IndexBuildM` ). This
refactor attempts to make there use more consistent and straightforward:
* `FetchM` (formerly `IndexBuildM`) is the top-level build monad used by
targets and facets and is now uniformly used in the codebase for all
top-level build functions.
* `JobM` is the monad of asynchronous build jobs. It is more limited
than `FetchM` due to the fact that the build cache can not be modified
asynchronously.
* `SpawnM` (formerly `SchedulerM`) is the monad used to spawn build
jobs. It lifts into `FetchM`.
* `RecBuildM` and `CoreBuildM` (formerly `BuildM`) have been relegated
to internal details of how `FetchM` / `JobM` are implemented / run and
are no longer used outside of that context.
* **Pretty progress.** Build progress (e.g., `[X/Y] Building Foo`) is
now updated on a single line via ANSI escape sequences when Lake is
outputting to a terminal. Redirected Lake output still sees progress on
separate lines.
* **Warnings-as-error option.** Adds a `--wfail` option to Lake that
will cause a build to fail if Lake logs any warnings doing a build.
Unlike some systems, this does not convert warnings into errors and it
does not abort jobs which log warnings. Instead, only the top-level
build fails.
* **Build log cache.** Logs from builds are now cached to a file and
replayed when the build is revisited. For example, this means multiple
runs of a `--wfail` Lean build (without changes) will still produce the
same warnings even though there is now an up-to-date `.olean` for the
module.
Closes#2349. Closes#2764.
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