In watch builds, the compiler attempts to reuse as much information from
a prior compilation as possible. To accomplish this, it keeps a
reference to the most recently succeeded `TraitCompiler`, which contains
all analysis data for the program. However, `TraitCompiler` has an
internal reference to an `IncrementalBuild`, which is itself built on
top of its prior state. Consequently, all prior compilations continued
to be referenced, preventing garbage collection from cleaning up these
instances.
This commit changes the `AnalyzedIncrementalState` to no longer retain
a `TraitCompiler` instance, but only the analysis data it contains. This
breaks the retainer path to the prior incremental state, allowing it to
be garbage collected.
PR Close#42537
22bda2226b