Exclusive capabilities V2 #22338
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Exclusive capabilities V2 #22338
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The subsumes check mistakenly allowed any capability to subsume `cap`, since `cap` is expanded as `caps.cap`, and by the path subcapturing rule `caps.cap <: caps`, where the capture set of `caps` is empty. This allowed quite a few hidden errors to go through. This commit fixes the subcapturing issue and all downstream issues caused by that fix. In particular: - Don't use path comparison for `x subsumes caps.cap` - Don't allow an opened existential on the left of a comparison to leak into a capture set on the right. This would give a "leak" error later in healCaptures. - Print pre-cc annotated capturing types with @retains annotations with `^`. The annotation is already rendered as a set in this case, but the `^` was missing. - Don't recheck `_` right hand sides of uninitialized variables. These were handled in ways that broke freshness checking. The new `uninitialied` scheme does not have this problem.
This is necessary because the compiler is free in previous phases to dealias or not. Therefore, capture checking should not depend on aliasing. The main difference is that now arguments to type aliases are not necessarily boxed. They are boxed only if they need boxing in the dealiased type.
When printing a type `C^` where `C` extends `Capability`, don't show the `^`. This is overridden under -Yprint-debug.
- Add Mutable trait and mut modifier.
- Add dedicated tests `isMutableVar` and `isMutableVarOrAccessor`
so that update methods can share the same flag `Mutable` with mutable vars.
- Disallow update methods overriding normal methods
- Disallow update methods which are not members of classes extending Mutable
- Add design document from papers repo to docs/internals
- Add readOnly capabilities
- Implement raeadOnly access
- Check that update methods are only called on references with exclusive capture sets.
- Use cap.rd as default capture set of Capability subtypes
- Make Mutable a Capability, this means Mutable class references get {cap.rd} as
default capture set.
- Use {cap} as capture set for creation of types extending Mutable
- Narrow retained capture set if expected type is read-only.
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Trying to squash commits and arrange them in a more logical order