More careful type variable instance improvements #19659
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The previous code tried to recursively apply the current instance of FullyDefinedAccumulator to the prospective instance type. This can have unforeseen side-effects, as i19637 shows. We now are more conservative: We check that the prospective instance type is already fully defined without the possibility to instantiate more type variables. This still passes the test cases that type variable improvement solves and avoids the problem with scala#19637. Fixes scala#19637
dwijnand
approved these changes
Feb 9, 2024
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The previous code tried to recursively apply the current instance of FullyDefinedAccumulator to the prospective instance type. This can have unforeseen side-effects, as i19637 shows. We now are more conservative: We check that the prospective instance type is already fully defined without the possibility to instantiate more type variables. This still passes the test cases that type variable improvement solves and avoids the problem with #19637.
Fixes #19637