[TypeChecker] Produce a tailored diagnostic for for-in sequence fai…
#27834
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| @@ -15,7 +15,7 @@ struct BadContainer2 : Sequence { // expected-error{{type 'BadContainer2' does n | |||
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| func bad_containers_2(bc: BadContainer2) { | |||
| for e in bc { } | |||
| // expected-error@-1{{variable 'e' is not bound by any pattern}} | |||
| // expected-warning@-1 {{immutable value 'e' was never used; consider replacing with '_' or removing it}} | |||
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Why did this and a few others below suddenly become valid?
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This is because BadContainer2 is declared to be conforming to Sequence, although it's invalid conformance constraint succeeds. It used to fail on the dependent member type associated with sequence element but I made it so that is handled as a hole.
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Everywhere variable 'e' is not bound by any pattern exists on a non-recursive decl is a sign that we are either not invalidating the AST properly, or we aren't constructing constraint systems with sufficient information to invalidate an associated pattern binding specifically. It's good to see movement here.
| // expected-error@-1 {{operator function '..<' requires that 'Lens<Int>' conform to 'Strideable'}} | ||
| // expected-error@-2 {{operator function '..<' requires that 'Lens<Int>.Stride' conform to 'SignedInteger'}} | ||
| // expected-error@-1 {{protocol 'Sequence' requires that 'Lens<Int>' conform to 'Strideable'}} | ||
| // expected-error@-2 {{protocol 'Sequence' requires that 'Lens<Int>.Stride' conform to 'SignedInteger'}} |
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This is technically not accurate, the requirement is not coming from the Sequence protocol itself.
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Diagnostics here aren't great because we still don't have a full coverage, but that's something on my radar.
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…lures `for-in` "sequence" expression is required to conform to `Sequence`.
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…lures
for-in"sequence" expression is required to conform toSequence.Resolves: rdar://problem/56559847