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An unused @discardableResult should not throw an error #6785

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Merged
merged 1 commit into from
Jan 13, 2017
Merged

An unused @discardableResult should not throw an error #6785

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19 changes: 16 additions & 3 deletions lib/Sema/TypeCheckStmt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1082,9 +1082,22 @@ void TypeChecker::checkIgnoredExpr(Expr *E) {
// TODO: What about tuples which contain functions by-value that are
// dead?
if (E->getType()->is<AnyFunctionType>()) {
diagnose(E->getLoc(), diag::expression_unused_function)
.highlight(E->getSourceRange());
return;
bool isDiscardable = false;
if (auto *Fn = dyn_cast<ApplyExpr>(E)) {
if (auto *declRef = dyn_cast<DeclRefExpr>(Fn->getFn())) {
if (auto *funcDecl = dyn_cast<AbstractFunctionDecl>(declRef->getDecl())) {
if (funcDecl->getAttrs().hasAttribute<DiscardableResultAttr>()) {
isDiscardable = true;
}
}
}
}

if (!isDiscardable) {
diagnose(E->getLoc(), diag::expression_unused_function)
.highlight(E->getSourceRange());
return;
}
}

// If the result of this expression is of type "Never" or "()"
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6 changes: 6 additions & 0 deletions test/attr/attr_discardableResult.swift
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Expand Up @@ -176,3 +176,9 @@ func testOptionalChaining(c1: C1?, s1: S1?) {
s1?.f2Optional() // expected-warning {{result of call to 'f2Optional()' is unused}}
s1!.f2Optional() // expected-warning {{result of call to 'f2Optional()' is unused}}
}

@discardableResult func SR2948 (_ closure: @escaping ()->()) -> (()->()) {
closure()
return closure
}
SR2948({}) // okay