I taught LinkedExprAnalyzer about ForceValueExpr
if (auto FVE = dyn_cast<ForceValueExpr>(expr)) {
LTI.collectedTypes.insert(CS.getType(FVE)->lookThroughAllAnyOptionalTypes().getPointer());
return { false, expr };
}
This seems to get it - didn’t check whether this regresses things, but this
seems to be the right fix at a high level.
~Robert Widmann
> On Dec 31, 2016, at 11:22 AM, Mark Lacey via swift-dev <[email protected]>
> wrote:
>
>>
>> On Dec 30, 2016, at 2:07 PM, Jacob Bandes-Storch via swift-dev
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> This is a pretty great bug: https://bugs.swift.org/browse/SR-3483
>> <https://bugs.swift.org/browse/SR-3483>
>>
>> let x: Double? = 1
>>
>> // error: ambiguous reference to member '+'
>> let sum = x! + x! + x!
>>
>> // error: value of optional type 'Double?' not unwrapped; did you mean
>> to use '!' or '?'?
>> let sum: Double = x! + x! + x!
>>
>> I've been poking around and I think the problem might be in
>> LinkedExprAnalyzer.
>
> Yeah I think you’re onto something there. Just looking at the output of the
> constraint solver and where bindings are happening in matchTypes(), it looks
> like the constraint optimizer is trying to force the result type of both adds
> to ‘Double?’ rather than ‘Double’, so we only ever try to solve for that type.
>
> I haven’t looked at the constraint optimizer code in a while, so I don’t have
> a lot of insight into the best fix, but it’s clearly the problematic piece
> here.
>
> Mark
>
>
>> This class collects type info about elements in a chain of binary operators
>> to speed up constraint solving. It does so in this case by grabbing the
>> DeclRefExpr's type:
>> https://github.com/apple/swift/tree/474096b9cbd6ff7ac998d7cea41d629512e25570#L230-L239
>>
>> <https://github.com/apple/swift/tree/474096b9cbd6ff7ac998d7cea41d629512e25570#L230-L239>
>>
>> However, since this is an ASTWalker, (I think) it automatically traverses
>> into the ForceValueExpr without remembering that the type it finds inside
>> (from the DeclRefExpr) should have one level of optionality removed when
>> added to the constraint system.
>>
>> This theory sort of makes sense to me, but it doesn't explain why the
>> simpler "let sum = x! + x!" typechecks correctly, because that goes through
>> the same code path.
>>
>> Am I correct that the LinkedExprAnalyzer probably needs to make sure it
>> doesn't keep the Optional when adding the type of a ForceValueExpr? Why
>> wouldn't this also cause problems for a single binop application?
>>
>> Would it be more appropriate for LinkedExprAnalyzer to be an ASTVisitor
>> (ExprVisitor) so that instead of just saying "yes, continue traversing
>> downwards" (by returning {true, expr}), its ForceValueExpr case could
>> recursively call visit() and then getAnyOptionalObjectType on the result?
>>
>>
>> Semi-eptly,
>> Jacob
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