Split the switch for really large enums into chunks.

This works around the compiler issue by adding the default and having more than one switch with none being complete. Fixes #904
apple · Sep 27, 2019 · 5b56dfe · 5b56dfe
1 parent 155b9a9
commit 5b56dfe
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Showing 3 changed files with 65 additions and 8 deletions.
diff --git a/Reference/generated_swift_names_enum_cases.pb.swift b/Reference/generated_swift_names_enum_cases.pb.swift
@@ -2247,6 +2247,9 @@ enum ProtobufUnittestGenerated_GeneratedSwiftReservedEnum: SwiftProtobuf.Enum {
     case .m: return 497
     case .major: return 498
     case .makeIterator: return 499
+    default: break
+    }
+    switch self {
     case .mapEntry: return 500
     case .mapHash: return 501
     case .mapKeyType: return 502
@@ -2602,7 +2605,12 @@ enum ProtobufUnittestGenerated_GeneratedSwiftReservedEnum: SwiftProtobuf.Enum {
     case .written: return 852
     case .yday: return 853
     case .UNRECOGNIZED(let i): return i
+    default: break
     }
+
+    // Can't get here, all the cases are listed in the above switches.
+    // See https://github.com/apple/swift-protobuf/issues/904 for more details.
+    fatalError()
   }
 
 }

diff --git a/Sources/protoc-gen-swift/EnumGenerator.swift b/Sources/protoc-gen-swift/EnumGenerator.swift
@@ -199,17 +199,58 @@ class EnumGenerator {
   private func generateRawValueProperty(printer p: inout CodePrinter) {
     let visibility = generatorOptions.visibilitySourceSnippet
 
+    // See https://github.com/apple/swift-protobuf/issues/904 for the full
+    // details on why the default has to get added even though the switch
+    // is complete.
+
+    // This is a "magic" value, currently picked based on the Swift 5.1
+    // compiler, it will need ensure the warning doesn't trigger on all
+    // versions of the compiler, meaning if the error starts to show up
+    // again, all one can do is lower the limit.
+    let maxCasesInSwitch = 500
+
+    let neededCases = mainEnumValueDescriptorsSorted.count +
+      (enumDescriptor.hasUnknownPreservingSemantics ? 1 : 0)
+    let useMultipleSwitches = neededCases > maxCasesInSwitch
+
     p.print("\(visibility)var rawValue: Int {\n")
     p.indent()
-    p.print("switch self {\n")
-    for v in mainEnumValueDescriptorsSorted {
-      let dottedName = namer.dottedRelativeName(enumValue: v)
-      p.print("case \(dottedName): return \(v.number)\n")
-    }
-    if enumDescriptor.hasUnknownPreservingSemantics {
-      p.print("case .\(unrecognizedCaseName)(let i): return i\n")
+
+    if useMultipleSwitches {
+      for (i, v) in mainEnumValueDescriptorsSorted.enumerated() {
+        if (i % maxCasesInSwitch) == 0 {
+          if i > 0 {
+            p.print(
+              "default: break\n",
+              "}\n")
+          }
+          p.print("switch self {\n")
+        }
+        let dottedName = namer.dottedRelativeName(enumValue: v)
+        p.print("case \(dottedName): return \(v.number)\n")
+      }
+      if enumDescriptor.hasUnknownPreservingSemantics {
+        p.print("case .\(unrecognizedCaseName)(let i): return i\n")
+      }
+      p.print(
+        "default: break\n",
+        "}\n",
+        "\n",
+        "// Can't get here, all the cases are listed in the above switches.\n",
+        "// See https://github.com/apple/swift-protobuf/issues/904 for more details.\n",
+        "fatalError()\n")
+    } else {
+      p.print("switch self {\n")
+      for v in mainEnumValueDescriptorsSorted {
+        let dottedName = namer.dottedRelativeName(enumValue: v)
+        p.print("case \(dottedName): return \(v.number)\n")
+      }
+      if enumDescriptor.hasUnknownPreservingSemantics {
+        p.print("case .\(unrecognizedCaseName)(let i): return i\n")
+      }
+      p.print("}\n")
     }
-    p.print("}\n")
+
     p.outdent()
     p.print("}\n")
   }

diff --git a/Tests/SwiftProtobufTests/generated_swift_names_enum_cases.pb.swift b/Tests/SwiftProtobufTests/generated_swift_names_enum_cases.pb.swift
@@ -2247,6 +2247,9 @@ enum ProtobufUnittestGenerated_GeneratedSwiftReservedEnum: SwiftProtobuf.Enum {
     case .m: return 497
     case .major: return 498
     case .makeIterator: return 499
+    default: break
+    }
+    switch self {
     case .mapEntry: return 500
     case .mapHash: return 501
     case .mapKeyType: return 502
@@ -2602,7 +2605,12 @@ enum ProtobufUnittestGenerated_GeneratedSwiftReservedEnum: SwiftProtobuf.Enum {
     case .written: return 852
     case .yday: return 853
     case .UNRECOGNIZED(let i): return i
+    default: break
     }
+
+    // Can't get here, all the cases are listed in the above switches.
+    // See https://github.com/apple/swift-protobuf/issues/904 for more details.
+    fatalError()
   }
 
 }