[Diagnostics] Add a tailored diagnostic for no accessible initializers

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -2899,6 +2899,27 @@ bool MissingMemberFailure::diagnoseAsError() {
       diagnostic.highlight(baseExpr->getSourceRange())
           .highlight(nameLoc.getSourceRange());
       correction->addFixits(diagnostic);
+    } else if (instanceTy->getAnyNominal() &&
+               getName().getBaseName() == DeclBaseName::createConstructor()) {
+      auto &cs = getConstraintSystem();
+
+      auto memberName = getName().getBaseName();
+      auto result = cs.performMemberLookup(
+          ConstraintKind::ValueMember, memberName, metatypeTy,
+          FunctionRefKind::DoubleApply, getLocator(),
+          /*includeInaccessibleMembers=*/true);
+
+      // If there are no `init` members at all produce a tailored
+      // diagnostic for that, otherwise fallback to generic
+      // "no such member" one.
+      if (result.ViableCandidates.empty() &&
+          result.UnviableCandidates.empty()) {
+        emitDiagnostic(anchor->getLoc(), diag::no_accessible_initializers,
+                       instanceTy)
+            .highlight(baseExpr->getSourceRange());
+      } else {
+        emitBasicError(baseType);
+      }
     } else {
       emitBasicError(baseType);
     }

test/decl/class/circular_inheritance.swift

@@ -59,6 +59,7 @@ class Outer3 // expected-error {{circular reference}}
 protocol Initable {
   init()
   // expected-note@-1 {{protocol requires initializer 'init()' with type '()'; do you want to add a stub?}}
+  // expected-note@-2 {{did you mean 'init'?}}
 }
 
 protocol Shape : Circle {}

test/decl/protocol/special/coding/class_codable_default_initializer.swift

@@ -7,7 +7,7 @@ class NoInitializers { // expected-error {{class 'NoInitializers' has no initial
 
   func foo() {
     // The class should not receive a default constructor.
-    let _ = NoInitializers.init() // expected-error {{type 'NoInitializers' has no member 'init'}}
+    let _ = NoInitializers.init() // expected-error {{'NoInitializers' cannot be constructed because it has no accessible initializers}}
   }
 }