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[Sema] NFC: Simplify type coercion of ClosureExprs #12468

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Oct 16, 2017
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[Sema] NFC: Simplify type coercion of ClosureExprs #12468

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24 changes: 8 additions & 16 deletions lib/Sema/CSApply.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6317,24 +6317,16 @@ Expr *ExprRewriter::coerceToType(Expr *expr, Type toType,
// Coercion from one function type to another, this produces a
// FunctionConversionExpr in its full generality.
if (auto fromFunc = fromType->getAs<FunctionType>()) {
// If toType is a NoEscape or NoReturn function type and the expression is
// a ClosureExpr, propagate these bits onto the ClosureExpr. Do not
// *remove* any bits that are already on the closure though.
// Note that in this case, we do not want to propagate the 'throws' bit
// to the closure type, as the closure has already been analyzed for
// throwing subexpressions. We also don't want to change the convention
// of the original closure.
// If we have a ClosureExpr, then we can safely propagate the 'no escape'
// bit to the closure without invalidating prior analysis.
auto fromEI = fromFunc->getExtInfo(), toEI = toFunc->getExtInfo();
if (toEI.isNoEscape() && !fromEI.isNoEscape()) {
swift::AnyFunctionType::ExtInfo newEI(fromEI.getRepresentation(),
toEI.isAutoClosure(),
toEI.isNoEscape() | fromEI.isNoEscape(),
toEI.throws() & fromEI.throws());
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This is such a weird computation. We take the "autoclosure" bit from the "to" type, "noescape" from either type (even though it's only on the "to" type based on the "if" statement above) and "throws" from both types (which makes no sense).

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Indeed. Don't forget that this goofiness only happened when the no escape bit and only the no escape bit needed propagating. Thanks for the review!

auto newToType = FunctionType::get(fromFunc->getInput(),
fromFunc->getResult(), newEI);
if (applyTypeToClosureExpr(cs, expr, newToType)) {
fromFunc = newToType;
// Propagating the bits in might have satisfied the entire
auto newFromFunc = FunctionType::get(fromFunc->getInput(),
fromFunc->getResult(),
fromEI.withNoEscape());
if (applyTypeToClosureExpr(cs, expr, newFromFunc)) {
fromFunc = newFromFunc;
// Propagating the 'no escape' bit might have satisfied the entire
// conversion. If so, we're done, otherwise keep converting.
if (fromFunc->isEqual(toType))
return expr;
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