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Make incremental compilation aware of synthesized mirrors #18310

Merged
merged 3 commits into from
Jul 31, 2023
Merged

Make incremental compilation aware of synthesized mirrors #18310

merged 3 commits into from
Jul 31, 2023

Commits on Jul 29, 2023

  1. ExtractDependencies: Split dependency recording in separate class 

    This will be used later in this PR to perform dependency recording during
Typer.

The new API is slightly higher level:
- Dependencies are recorded using `addUsedName`, `addUsedRawName` and `addClassDependency`.
- `addUsedName` takes a Symbol instead of a Name and takes care of name
  mangling, `addUsedRawName` is still available when there is no
  symbol (currently this only happens when recording a dependency on a renamed import).
- These methods do not take a `from` argument, instead they take care of
  calling `resolveDependencySource` internally.
- Recorded dependencies are sent to Zinc using `sendToZinc`.
    @smarter
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  2. Properly support xsbti.compile.IncOptions#useOptimizedSealed 

    This option is meant to avoid overcompilation involving sealed classes. By
default, Zinc invalidates all usages of a sealed class when a child is added or
removed, even though `val x: Sealed = new Child1` will work the same if
`Sealed` gets an extra child. When this option is on, Zinc only takes children
into account if the name usage is reported with `UseScope.PatMatTarget`. Note
that currently this is only set when traversing the scrutinee of a pattern
match (just like in the Scala 2 implementation), but to safely turn this option
on by default we would need to kept track of all call to `children` and
`sealedDescendants` in the compiler.

There were two issues related to this option before this commit:
- ExtractAPI was unnecessarily extracting the `@Child`
  annotation, so the API hash of a sealed class changed even with
  `useOptimizedSealed` enabled.
- When registering a used name with `UseScope.PatMatTarget` we should also
  register it with `UseScope.Default` because (part of) the scrutinee type
  might not be a sealed class, in which case it won't have
  a name hash for PatMatTarget but should still lead to invalidations.

Since we only ever use two values for the `UseScope` parameter of the
`usedName` callback, we create two vals `DefaultScopes` and `PatMatScopes` that
we reuse for performance.
    @smarter
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  3. Make incremental compilation aware of synthesized mirrors 

    A product mirror needs to be resynthesized if any class parameter changes, and
a sum mirror needs to be resynthesized if any child of the sealed type changes,
but previously this did not reliably work because the dependency recording in
ExtractDependencies was unaware of mirrors.

Instead of making ExtractDependencies aware of mirrors, we solve this by
directly recording the dependencies when the mirror is synthesized, this way we
can be sure to always correctly invalidate users of mirrors, even if the
synthesized mirror type is not present in the AST at phase ExtractDependencies.

This is the first time that we record dependencies outside of the
ExtractDependencies phase, in the future we should see if we can extend this
mechanism to record more dependencies during typechecking to make incremental
compilation more robust (e.g. by keeping track of symbols looked up by macros).

Eventually, we might even want to completely get rid of the ExtractDependencies
phase and record all dependencies on the fly if it turns out to be faster.
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