Merge pull request #16374 from davidungar/rdar-39947138-better-diag-for-unverifyable-switch

Rdar 39947138 Different diagnostics for proveably vs unproveably non-exhaustive switch.

Author: David Ungar

include/swift/AST/DiagnosticsSema.def

@@ -3954,6 +3954,10 @@ ERROR(empty_switch_stmt,none,
       "'switch' statement body must have at least one 'case' or 'default' "
       "block; do you want to add a default case?",())
 ERROR(non_exhaustive_switch,none, "switch must be exhaustive", ())
+ERROR(possibly_non_exhaustive_switch,none,
+      "the compiler is unable to check that this switch is exhaustive in reasonable time",
+      ())
+
 NOTE(missing_several_cases,none,
      "do you want to add "
      "%select{missing cases|a default clause}0"

lib/Sema/TypeCheckSwitchStmt.cpp

@@ -1351,7 +1351,8 @@ namespace {
       SpaceTooLarge,
     };
 
-    void diagnoseMissingCases(RequiresDefault defaultReason, Space uncovered,
+    void diagnoseMissingCases(const RequiresDefault defaultReason,
+                              Space uncovered,
                               const CaseStmt *unknownCase = nullptr,
                               bool sawDowngradablePattern = false) {
       SourceLoc startLoc = Switch->getStartLoc();
@@ -1377,14 +1378,18 @@ namespace {
             mainDiagType = diag::non_exhaustive_switch_warn;
           break;
         case RequiresDefault::UncoveredSwitch:
-        case RequiresDefault::SpaceTooLarge:
-          TC.diagnose(startLoc, diag::non_exhaustive_switch);
+        case RequiresDefault::SpaceTooLarge: {
+          auto diagnostic = defaultReason == RequiresDefault::UncoveredSwitch
+                                ? diag::non_exhaustive_switch
+                                : diag::possibly_non_exhaustive_switch;
+          TC.diagnose(startLoc, diagnostic);
           TC.diagnose(unknownCase->getLoc(),
                       diag::non_exhaustive_switch_drop_unknown)
             .fixItRemoveChars(unknownCase->getStartLoc(),
                               unknownCase->getLoc());
           return;
         }
+        }
       }
 
       switch (uncovered.checkDowngradeToWarning()) {
@@ -1427,7 +1432,7 @@ namespace {
         return;
       case RequiresDefault::SpaceTooLarge: {
         OS << tok::kw_default << ":\n" << "<#fatalError()#>" << "\n";
-        TC.diagnose(startLoc, diag::non_exhaustive_switch);
+        TC.diagnose(startLoc, diag::possibly_non_exhaustive_switch);
         TC.diagnose(startLoc, diag::missing_several_cases, /*default*/true)
           .fixItInsert(insertLoc, buffer.str());
       }

test/Compatibility/exhaustive_switch.swift

@@ -442,7 +442,7 @@ enum ContainsOverlyLargeEnum {
 }
 
 func quiteBigEnough() -> Bool {
-  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{switch must be exhaustive}}
+  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{the compiler is unable to check that this switch is exhaustive in reasonable time}}
   // expected-note@-1 {{do you want to add a default clause?}}
   case (.case0, .case0): return true
   case (.case1, .case1): return true
@@ -458,7 +458,7 @@ func quiteBigEnough() -> Bool {
   case (.case11, .case11): return true
   }
 
-  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{switch must be exhaustive}}
+  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{the compiler is unable to check that this switch is exhaustive in reasonable time}}
   // expected-note@-1 {{do you want to add a default clause?}}
   case (.case0, _): return true
   case (.case1, _): return true
@@ -473,7 +473,7 @@ func quiteBigEnough() -> Bool {
   case (.case10, _): return true
   }
 
-  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{switch must be exhaustive}}
+  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{the compiler is unable to check that this switch is exhaustive in reasonable time}}
   case (.case0, _): return true
   case (.case1, _): return true
   case (.case2, _): return true

test/Sema/exhaustive_switch.swift

@@ -465,7 +465,7 @@ enum ContainsOverlyLargeEnum {
 }
 
 func quiteBigEnough() -> Bool {
-  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{switch must be exhaustive}}
+  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{the compiler is unable to check that this switch is exhaustive in reasonable time}}
   // expected-note@-1 {{do you want to add a default clause?}}
   case (.case0, .case0): return true
   case (.case1, .case1): return true
@@ -481,7 +481,7 @@ func quiteBigEnough() -> Bool {
   case (.case11, .case11): return true
   }
 
-  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{switch must be exhaustive}}
+  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{the compiler is unable to check that this switch is exhaustive in reasonable time}}
   // expected-note@-1 {{do you want to add a default clause?}}
   case (.case0, _): return true
   case (.case1, _): return true
@@ -496,7 +496,7 @@ func quiteBigEnough() -> Bool {
   case (.case10, _): return true
   }
 
-  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{switch must be exhaustive}}
+  switch (OverlyLargeSpaceEnum.case1, OverlyLargeSpaceEnum.case2) { // expected-error {{the compiler is unable to check that this switch is exhaustive in reasonable time}}
   case (.case0, _): return true
   case (.case1, _): return true
   case (.case2, _): return true