Merge pull request #4422 from slavapestov/fix-try-expr-diagnostic-3.0

Sema: Look through TryExpr in FailureDiagnosis (3.0)

Author: slavapestov

lib/Sema/CSDiag.cpp

@@ -1982,6 +1982,7 @@ class FailureDiagnosis :public ASTVisitor<FailureDiagnosis, /*exprresult*/bool>{
 
   bool visitExpr(Expr *E);
   bool visitIdentityExpr(IdentityExpr *E);
+  bool visitTryExpr(TryExpr *E);
   bool visitTupleExpr(TupleExpr *E);
 
   bool visitUnresolvedMemberExpr(UnresolvedMemberExpr *E);
@@ -6257,6 +6258,12 @@ bool FailureDiagnosis::visitIdentityExpr(IdentityExpr *E) {
   return false;
 }
 
+/// A TryExpr doesn't change it's argument, nor does it change the contextual
+/// type.
+bool FailureDiagnosis::visitTryExpr(TryExpr *E) {
+  return visit(E->getSubExpr());
+}
+
 bool FailureDiagnosis::visitExpr(Expr *E) {
   // Check each of our immediate children to see if any of them are
   // independently invalid.
@@ -6311,7 +6318,7 @@ void ConstraintSystem::diagnoseFailureForExpr(Expr *expr) {
   // inconsistent state.
   simplify(/*ContinueAfterFailures*/true);
 
-  // Look through RebindSelfInConstructorExpr to avoid weird sema issues.
+  // Look through RebindSelfInConstructorExpr to avoid weird Sema issues.
   if (auto *RB = dyn_cast<RebindSelfInConstructorExpr>(expr))
     expr = RB->getSubExpr();
 

test/Constraints/diagnostics.swift

@@ -769,3 +769,14 @@ struct SR1752 {
 let sr1752: SR1752? = nil
 
 true ? nil : sr1752?.foo() // don't generate a warning about unused result since foo returns Void
+
+// <rdar://problem/27891805> QoI: FailureDiagnosis doesn't look through 'try'
+struct rdar27891805 {
+  init(contentsOf: String, encoding: String) throws {}
+  init(contentsOf: String, usedEncoding: inout String) throws {}
+  init<T>(_ t: T) {}
+}
+
+try rdar27891805(contentsOfURL: nil, usedEncoding: nil)
+// expected-error@-1 {{argument labels '(contentsOfURL:, usedEncoding:)' do not match any available overloads}}
+// expected-note@-2 {{overloads for 'rdar27891805' exist with these partially matching parameter lists: (contentsOf: String, encoding: String), (contentsOf: String, usedEncoding: inout String)}}