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[CSDiagnostics] Diagnose ambiguous empty closures #41226

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Merged
merged 1 commit into from
Feb 5, 2022
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[CSDiagnostics] Diagnose ambiguous empty closures #41226

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2 changes: 2 additions & 0 deletions include/swift/AST/DiagnosticsSema.def
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Original file line number Diff line number Diff line change
Expand Up @@ -274,6 +274,8 @@ ERROR(cannot_infer_closure_parameter_type,none,
(StringRef))
ERROR(cannot_infer_closure_type,none,
"unable to infer closure type in the current context", ())
ERROR(cannot_infer_empty_closure_result_type,none,
"cannot infer return type of empty closure", ())
ERROR(cannot_infer_closure_result_type,none,
"cannot infer return type for closure with multiple statements; "
"add explicit type to disambiguate", ())
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4 changes: 4 additions & 0 deletions include/swift/Sema/CSFix.h
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Expand Up @@ -2335,6 +2335,10 @@ class SpecifyClosureReturnType final : public ConstraintFix {

bool diagnose(const Solution &solution, bool asNote = false) const override;

bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
return diagnose(*commonFixes.front().first);
}

static SpecifyClosureReturnType *create(ConstraintSystem &cs,
ConstraintLocator *locator);

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16 changes: 15 additions & 1 deletion lib/Sema/CSDiagnostics.cpp
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Expand Up @@ -7054,6 +7054,20 @@ bool UnableToInferClosureParameterType::diagnoseAsError() {
bool UnableToInferClosureReturnType::diagnoseAsError() {
auto *closure = castToExpr<ClosureExpr>(getRawAnchor());

auto *body = closure->getBody();
// For empty closures, let's produce a tailored message and suggest
// adding an expression to the body.
if (body->empty()) {
auto diagnostic =
emitDiagnostic(diag::cannot_infer_empty_closure_result_type);

diagnostic.fixItInsertAfter(closure->getInLoc().isValid()
? closure->getInLoc()
: body->getLBraceLoc(),
"<#result#>");
return true;
}

auto diagnostic = emitDiagnostic(diag::cannot_infer_closure_result_type);

// If there is a location for an 'in' token, then the argument list was
Expand All @@ -7068,7 +7082,7 @@ bool UnableToInferClosureReturnType::diagnoseAsError() {
//
// As such, we insert " () -> ReturnType in " right after the '{' that
// starts the closure body.
diagnostic.fixItInsertAfter(closure->getBody()->getLBraceLoc(),
diagnostic.fixItInsertAfter(body->getLBraceLoc(),
diag::insert_closure_return_type_placeholder,
/*argListSpecified=*/true);
}
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