Fix #2578: (part 2) Make for-generators filter only if prefixed with case.
#6448
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| isIrrefutable(gen.pat, gen.expr) | ||
| def needsNoFilter(gen: GenFrom): Boolean = | ||
| if (gen.checkMode == GenCheckMode.FilterAlways) // pattern was prefixed by `case` | ||
| isIrrefutable(gen.pat, gen.expr) |
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As a matter of principle, I think that if the user explicitly requested a "filtering binding" by writing case, then it is less surprising if we always emit a withFilter call. With zipped, we've already seen that emitting or not emitting the call can have unobvious consequences on typechecking. I think it'd be for the best if we just let the user decide whether the call is emitted or not.
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Good point. I'll change it.
| @@ -925,6 +936,22 @@ object desugar { | |||
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| } | |||
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| /** The selector of a match, which depends of the given `checkMode`. | |||
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The fact that @unchecked is also added to irrefutable patterns really confused me until I understood that annotating the selector only affects exhaustivity checks and not irrefutability checks. Perhaps we could note this in the doc?
| /** The selector of a match, which depends of the given `checkMode`. | |
| /** The selector of a match, which depends of the given `checkMode`. | |
| * | |
| * The @unchecked annotation is added whenever `checkMode` is not `Exhaustive` to silence | |
| * unnecessary inexhaustive match warnings. |
Non-matching members are already removed by the filter.
But wait with this for now, since we can't cross-compile easily otherwise. So currently this is enabled only under -strict.
Add a third mode, Ignore, for generators where the pattern is refutable, but we know it has already been used as a filter in an earlier step.
This was not classified as a pattern binding before, so no filtering was applied.
This is a complement to #6389. Together, they address all aspects of #2578.
The checking part of this is currently only enabled under -strict to allow cross-compilation with Scala 2. As things currently stand, this means it will be made standard in Scala 3.1.