[Diagnostics] Don't include @unknown default in the empty switch fix-it (#28476)

Author: owenv

lib/Sema/TypeCheckSwitchStmt.cpp

@@ -1207,6 +1207,12 @@ namespace {
             }
             if (!Context.LangOpts.EnableNonFrozenEnumExhaustivityDiagnostics)
               continue;
+
+            // This can occur if the switch is empty and the subject type is an
+            // enum. If decomposing the enum type yields an unknown space that
+            // is not required, don't suggest adding it in the fix-it.
+            if (flat.isAllowedButNotRequired())
+              continue;
           }
 
           process(flat, flats.size() == 1);

test/Sema/exhaustive_switch.swift

@@ -1,5 +1,9 @@
-// RUN: %target-typecheck-verify-swift -swift-version 5 -enable-library-evolution
-// RUN: %target-typecheck-verify-swift -swift-version 4 -enable-library-evolution -enable-nonfrozen-enum-exhaustivity-diagnostics
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -swift-version 5 -enable-library-evolution %S/Inputs/exhaustive_switch_testable_helper.swift -emit-module -o %t
+// RUN: %target-typecheck-verify-swift -swift-version 5 -enable-library-evolution -I %t
+// RUN: %target-typecheck-verify-swift -swift-version 4 -enable-library-evolution -enable-nonfrozen-enum-exhaustivity-diagnostics -I %t
+
+import exhaustive_switch_testable_helper
 
 func foo(a: Int?, b: Int?) -> Int {
   switch (a, b) {
@@ -1214,6 +1218,54 @@ func sr11160_extra() {
   }
 }
 
+public enum SR11672Tests {
+  
+  @frozen public enum FrozenSameModule {
+    case a, b
+  }
+  
+  func testNotRequired(_ value: NonExhaustive, _ value2: FrozenEnum, _ value3: FrozenSameModule) {
+    switch value {
+      // expected-error@-1 {{switch must be exhaustive}}
+      // expected-note@-2 {{add missing case: '.a'}}
+      // expected-note@-3 {{add missing case: '.b'}}
+      // Do not suggest adding '@unknown default'
+    }
+    
+    switch value2 {
+      // expected-error@-1 {{switch must be exhaustive}}
+      // expected-note@-2 {{add missing case: '.a'}}
+      // expected-note@-3 {{add missing case: '.b'}}
+      // expected-note@-4 {{add missing case: '.c'}}
+    }
+    
+    switch value3 {
+      // expected-error@-1 {{switch must be exhaustive}}
+      // expected-note@-2 {{add missing case: '.a'}}
+      // expected-note@-3 {{add missing case: '.b'}}
+    }
+  }
+  
+  @inlinable public func testNotRequired2(_ value: FrozenSameModule) {
+    switch value {
+      // expected-error@-1 {{switch must be exhaustive}}
+      // expected-note@-2 {{add missing case: '.a'}}
+      // expected-note@-3 {{add missing case: '.b'}}
+    }
+  }
+  
+  // Inlinable code is considered "outside" the module and must include a default
+  // case.
+  @inlinable public func testRequired(_ value: NonExhaustive) {
+    switch value {
+      // expected-error@-1 {{switch must be exhaustive}}
+      // expected-note@-2 {{add missing case: '.a'}}
+      // expected-note@-3 {{add missing case: '.b'}}
+      // expected-note@-4 {{handle unknown values using "@unknown default"}}
+    }
+  }
+}
+
 // SR-11212 tests: Some of the tests here rely on compiler bugs related to
 // implicit (un)tupling in patterns.
 //

test/stmt/nonexhaustive_switch_stmt_editor.swift

@@ -19,6 +19,10 @@ public func testNonExhaustive(_ value: NonExhaustive) {
   case .b: break
   }
 
+  switch value { // expected-error {{switch must be exhaustive}}
+  // expected-note@-1 {{do you want to add missing cases?}} {{3-3=case .a:\n<#code#>\ncase .b:\n<#code#>\n@unknown default:\n<#code#>\n}}
+  }
+
   switch value {
   case .a: break
   case .b: break