Changes in CC around classes, constructors, this #23874
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These problems were discovered once we started recording uses of this references. The recording is not yet part of this commit because it requires downstream bugfixes in the compiler.
These fell through the cracks before since we only considered named outer refs. But inner classes can have outer this references check needd to be tracked in use sets.
Previously there was a boundary condition where this could be the case for outermost classes.
A constructor should never capture `this`, the object it constructs.
Was shockingly missing before.
- Charge the use set of the initializer to the class constructor - Charge the declared capture set to the class
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odersky
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- Propagate expected type into blocks
The level checking should do the proper avoidance so that local symbols
would not leak into type variables of the expected type.
- Don't automatically add a FreshCap owner to its hidden set
- Don't use span capture sets for function types as the underlying set
Based on #23874
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This PR started with a shocking discovery. We actually did not record this-references in use sets. Once this was fixed, some tests failed and the stdlib build broke with 20 errors. 18 of these were oversights that were not caught before and were easily fixed. 2 of them pointed to further capture checking problems. This caused a sequence of successive fixes until everything compiled again and all the tests made sense.
The order in the commits here is a bit different: We first apply the fixes to the stdlib and the compiler and then start recording uses of this. This is so that we don't have a failing build in intermediate steps.