ASTGen: Suppress warnings about handling unknown enum cases.

When built as part of the compiler toolchain SwiftSyntax is built with library
evolution enabled. This means that switches over enums from SwiftSyntax must
include a default case to be considered exhaustive, or a warning will be
emitted. This change suppresses those warnings by adding `@unknown default`
cases wherever they are expected. As a compromise, these `@unknown default`
cases are wrapped with a `#if` to ensure they are only included in the CMake
build of ASTGen, but continue to be omitted from the SPM build which compiler
engineers use to iterate on ASTGen's implementation. This is needed to avoid
generating the opposite warning during the SPM build, since the compiler thinks
the `@unknown default` case is superfluous when SwiftSyntax is built
non-resiliently. As an aside, this catch-22 is a bummer and I think we should
change the compiler to suppress the unreachable default warning when the
default is annotated `@unknown`.

Author: tshortli

lib/ASTGen/CMakeLists.txt

@@ -103,6 +103,7 @@ endif()
 
 set(compile_options
   ${c_include_paths_args}
+  "SHELL: -DRESILIENT_SWIFT_SYNTAX"
   "SHELL: ${cxx_interop_flag}"
   "SHELL: -Xcc -std=c++17 -Xcc -DCOMPILED_WITH_SWIFT -Xcc -DSWIFT_TARGET"
 

lib/ASTGen/Sources/ASTGen/DeclAttrs.swift

@@ -58,6 +58,10 @@ extension ASTGenVisitor {
         addAttribute(self.generateDeclAttribute(attribute: node))
       case .ifConfigDecl:
         fatalError("unimplemented")
+#if RESILIENT_SWIFT_SYNTAX
+      @unknown default:
+        fatalError()
+#endif
       }
     }
 

lib/ASTGen/Sources/ASTGen/Decls.swift

@@ -68,6 +68,10 @@ extension ASTGenVisitor {
       return self.generate(typeAliasDecl: node).asDecl
     case .variableDecl(let node):
       return self.generate(variableDecl: node).asDecl
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
     return self.generateWithLegacy(node)
   }
@@ -421,6 +425,10 @@ extension ASTGenVisitor {
         accessors: CollectionOfOne(accessor).bridgedArray(in: self),
         rBraceLoc: rightBrace
       )
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
   }
 
@@ -726,6 +734,10 @@ extension ASTGenVisitor {
         } else {
           body.associativity = associativity
         }
+#if RESILIENT_SWIFT_SYNTAX
+      @unknown default:
+        fatalError()
+#endif
       }
     }
 

lib/ASTGen/Sources/ASTGen/DiagnosticsBridge.swift

@@ -73,6 +73,11 @@ fileprivate func emitDiagnosticParts(
       replaceStartLoc = bridgedSourceLoc(at: oldToken.endPositionBeforeTrailingTrivia)
       replaceEndLoc = bridgedSourceLoc(at: oldToken.endPosition)
       newText = newTrivia.description
+
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
 
     newText.withBridgedString { bridgedMessage in
@@ -208,6 +213,11 @@ extension SourceManager {
           at: oldToken.endPosition
         )
         newText = newTrivia.description
+
+#if RESILIENT_SWIFT_SYNTAX
+      @unknown default:
+        fatalError()
+#endif
       }
 
       newText.withBridgedString { bridgedMessage in

lib/ASTGen/Sources/ASTGen/Exprs.swift

@@ -197,6 +197,10 @@ extension ASTGenVisitor {
       preconditionFailure("should be handled in generate(sequenceExpr:)")
     case .unresolvedTernaryExpr:
       preconditionFailure("should be handled in generate(sequenceExpr:)")
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
     preconditionFailure("isExprMigrated() mismatch")
   }

lib/ASTGen/Sources/ASTGen/Generics.swift

@@ -69,6 +69,10 @@ extension ASTGenVisitor {
       case .layoutRequirement(_):
         // FIXME: Implement layout requirement translation.
         fatalError("Translation of layout requirements not implemented!")
+#if RESILIENT_SWIFT_SYNTAX
+      @unknown default:
+        fatalError()
+#endif
       }
     }
 

lib/ASTGen/Sources/ASTGen/Literals.swift

@@ -88,6 +88,10 @@ extension ASTGenVisitor {
       colonLocs = elementNodes.lazy
         .map({ self.generateSourceLoc($0.colon) })
         .bridgedArray(in: self)
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
     return .createParsed(
       self.ctx,

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -359,6 +359,10 @@ func checkMacroDefinition(
       replacementsPtr.pointee = replacementBuffer.baseAddress
       numReplacementsPtr.pointee = replacements.count
       return Int(BridgedMacroDefinitionKind.expandedMacro.rawValue)
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
   } catch let errDiags as DiagnosticsError {
     let srcMgr = SourceManager(cxxDiagnosticEngine: diagEnginePtr)
@@ -501,6 +505,9 @@ func expandFreestandingMacroIPC(
   case .expression: pluginMacroRole = .expression
   case .declaration: pluginMacroRole = .declaration
   case .codeItem: pluginMacroRole = .codeItem
+#if RESILIENT_SWIFT_SYNTAX
+  @unknown default: fatalError()
+#endif
   }
 
   // Send the message.
@@ -790,6 +797,11 @@ func expandAttachedMacroIPC(
     .declaration,
     .codeItem:
     preconditionFailure("unhandled macro role for attached macro")
+
+#if RESILIENT_SWIFT_SYNTAX
+  @unknown default:
+    fatalError()
+#endif
   }
 
   // Prepare syntax nodes to transfer.
@@ -990,6 +1002,10 @@ fileprivate extension SyntaxProtocol {
       formatted = self.formatted()
     case .disabled:
       formatted = Syntax(self)
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
     return formatted.trimmedDescription(matching: { $0.isWhitespace })
   }

lib/ASTGen/Sources/ASTGen/Patterns.swift

@@ -45,6 +45,10 @@ extension ASTGenVisitor {
       return self.generate(valueBindingPattern: node).asPattern
     case .wildcardPattern(let node):
       return self.generate(wildcardPattern: node).asPattern
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
   }
 

lib/ASTGen/Sources/ASTGen/SourceManager+MacroExpansionContext.swift

@@ -131,6 +131,11 @@ extension SourceManager.MacroExpansionContext: MacroExpansionContext {
 
     case .afterTrailingTrivia:
       rawPosition = node.endPosition
+
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
 
     let offsetWithinSyntaxNode =
@@ -164,6 +169,11 @@ extension SourceManager.MacroExpansionContext: MacroExpansionContext {
 
     case .filePath:
       break
+
+#if RESILIENT_SWIFT_SYNTAX
+    @unknown default:
+      fatalError()
+#endif
     }
 
     // Do the location lookup.