On Sat, Dec 31, 2016 at 1:31 PM, Robert Widmann <devteam.codafi@gmail.com> wrote:
Whoops, should only look through one level of optionality. You get the
gist.
~Robert Widmann
On Dec 31, 2016, at 2:31 PM, Robert Widmann <devteam.codafi@gmail.com> > wrote:
I taught LinkedExprAnalyzer about ForceValueExpr
if (auto FVE = dyn_cast<ForceValueExpr>(expr)) {
LTI.collectedTypes.insert(CS.getType(FVE)->lookThroughAllAny
OptionalTypes().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 < > swift-dev@swift.org> wrote:
On Dec 30, 2016, at 2:07 PM, Jacob Bandes-Storch via swift-dev < > swift-dev@swift.org> wrote:
This is a pretty great bug: 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
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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