Fix #21914: Don't project nested wildcard patterns to nullable #21934
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Fix #21914
The wildcard patterns are projected to nullable #21850, which increases the running time exponentially for complex patterns, due to the way we simplify and minus spaces.
However, the current space analyse setup is only able to track nullable value at top level, so we should not project nested wildcard patterns (not at top level) to nullable.
The warnings in
tests/warn/i20121.scala,tests/warn/i20122.scala, andtests/warn/i20123.scalawill become wrong again, but there is no simple solution to fix them quickly.I couldn't create a minimised test for #21914, but I have verified locally the compile time becomes normal again with this fix.