Merge pull request #26904 from xedin/rdar-52774804-5.1

[5.1][Diagnostics] Don't crash trying to diagnose missing opaque result type

Author: AnnaZaks

lib/Sema/CSDiagnostics.cpp

@@ -2959,6 +2959,9 @@ bool MissingGenericArgumentsFailure::diagnoseForAnchor(
     return false;
 
   auto *DC = getDeclContext();
+  if (!DC)
+    return true;
+
   if (auto *SD = dyn_cast<SubscriptDecl>(DC)) {
     emitDiagnostic(SD, diag::note_call_to_subscript, SD->getFullName());
     return true;
@@ -3008,11 +3011,13 @@ bool MissingGenericArgumentsFailure::diagnoseParameter(
     emitDiagnostic(loc, diag::unbound_generic_parameter, GP);
   }
 
-  if (!hasLoc(GP))
-    return true;
-
   Type baseTyForNote;
   auto *DC = getDeclContext();
+  if (!DC)
+    return true;
+
+  if (!hasLoc(GP))
+    return true;
 
   if (auto *NTD =
           dyn_cast_or_null<NominalTypeDecl>(DC->getSelfNominalTypeDecl())) {
@@ -3034,6 +3039,9 @@ void MissingGenericArgumentsFailure::emitGenericSignatureNote(
   auto &TC = getTypeChecker();
   auto *paramDC = getDeclContext();
 
+  if (!paramDC)
+    return;
+
   auto *GTD = dyn_cast<GenericTypeDecl>(paramDC);
   if (!GTD || anchor.is<Expr *>())
     return;

lib/Sema/CSDiagnostics.h

@@ -1334,7 +1334,9 @@ class MissingGenericArgumentsFailure final : public FailureDiagnostic {
 
   DeclContext *getDeclContext() const {
     auto *GP = Parameters.front();
-    return GP->getDecl()->getDeclContext();
+    auto *decl = GP->getDecl();
+
+    return decl ? decl->getDeclContext() : nullptr;
   }
 
   bool diagnoseAsError() override;

validation-test/compiler_crashers_2_fixed/sr11236.swift

@@ -0,0 +1,12 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+public func trichotomy<T : Comparable>(x: T, y: T) -> some Comparable {
+  if x < y { return -1 } 
+  else if x == y { return 0 }
+  return 1
+}
+
+public func myTri<T: Comparable, U: Comparable> (retval: UnsafeMutablePointer<U>, x: UnsafeMutablePointer<T>, y: UnsafeMutablePointer<T>) {
+  retval.initialize(to: trichotomy(x: x, y: y))
+}
+