Use == for instance tests against string constants
#12799
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We used `eq` before, as for other objetc singletons. But this means we are subject to the vagaries of string hashing. Fixes scala#12796
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| /** `tree.isInstanceOf[tp]`, with special treatment of singleton types */ | ||
| def isInstance(tp: Type)(using Context): Tree = tp.dealias match { | ||
| case ConstantType(c) if c.tag == StringTag => |
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Shouldn't we do it for other constants?
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The only constant types supporting the alternative comparison with eq are classes and strings. Class literals are hash consed, so == and eq are the same. So I believe String is the only type in need of a fix.
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To add, I didn't find this issue with integer constants.
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Null might also take advantage of this unless some other optimization is already handling it.
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We used
eqbefore, as for other objetc singletons. But this meanswe are subject to the vagaries of string hashing.
Fixes #12796
Fixes #6996