[ASTGen] Make generate(decl:) return optional value

Author: rintaro

lib/ASTGen/Sources/ASTGen/ASTGen.swift

@@ -110,7 +110,9 @@ struct ASTGenVisitor {
       of: CodeBlockItemSyntax.self,
       split: Self.splitCodeBlockItemIfConfig
     ) { element in
-      let astNode = generate(codeBlockItem: element)
+      guard let astNode = generate(codeBlockItem: element) else {
+        return
+      }
       if !isTopLevel {
         out.append(astNode)
         return
@@ -463,7 +465,7 @@ public func buildTopLevelASTNodes(
 /// Generate an AST node at the given source location. Returns the generated
 /// ASTNode and mutate the pointee of `endLocPtr` to the end of the node.
 private func _build<Node: SyntaxProtocol, Result>(
-  generator: (ASTGenVisitor) -> (Node) -> Result,
+  generator: (ASTGenVisitor) -> (Node) -> Result?,
   diagEngine: BridgedDiagnosticEngine,
   sourceFilePtr: UnsafeMutableRawPointer,
   sourceLoc: BridgedSourceLoc,

lib/ASTGen/Sources/ASTGen/Decls.swift

@@ -18,7 +18,7 @@ import SwiftDiagnostics
 // MARK: - TypeDecl
 
 extension ASTGenVisitor {
-  func generate(decl node: DeclSyntax) -> BridgedDecl {
+  func generate(decl node: DeclSyntax) -> BridgedDecl? {
     switch node.as(DeclSyntaxEnum.self) {
     case .accessorDecl:
       fatalError("Should be generated as a part of another decl")
@@ -72,7 +72,7 @@ extension ASTGenVisitor {
     return self.generateWithLegacy(node)
   }
 
-  func generate(memberBlockItem node: MemberBlockItemSyntax) -> BridgedDecl {
+  func generate(memberBlockItem node: MemberBlockItemSyntax) -> BridgedDecl? {
     // TODO: Set semicolon loc.
     generate(decl: node.decl)
   }
@@ -852,19 +852,22 @@ extension ASTGenVisitor {
 extension ASTGenVisitor {
   @inline(__always)
   func generate(memberBlockItemList node: MemberBlockItemListSyntax) -> [BridgedDecl] {
-    var allBridged: [BridgedDecl] = []
+    var allMembers: [BridgedDecl] = []
     visitIfConfigElements(node, of: MemberBlockItemSyntax.self) { element in
       if let ifConfigDecl = element.decl.as(IfConfigDeclSyntax.self) {
         return .ifConfigDecl(ifConfigDecl)
       }
 
       return .underlying(element)
     } body: { member in
+      guard let member = self.generate(decl: member.decl) else {
+        return
+      }
       // TODO: Set semicolon loc.
-      allBridged.append(self.generate(decl: member.decl))
+      allMembers.append(member)
     }
 
-    return allBridged
+    return allMembers
   }
 
   @inline(__always)

lib/ASTGen/Sources/ASTGen/Stmts.swift

@@ -67,11 +67,11 @@ extension ASTGenVisitor {
     return self.generateWithLegacy(node)
   }
 
-  func generate(codeBlockItem node: CodeBlockItemSyntax) -> ASTNode {
+  func generate(codeBlockItem node: CodeBlockItemSyntax) -> ASTNode? {
     // TODO: Set semicolon loc.
     switch node.item {
     case .decl(let node):
-      return .decl(self.generate(decl: node))
+      return self.generate(decl: node).map { .decl($0) }
     case .stmt(let node):
       return .stmt(self.generate(stmt: node))
     case .expr(let node):
@@ -87,7 +87,10 @@ extension ASTGenVisitor {
       of: CodeBlockItemSyntax.self,
       split: Self.splitCodeBlockItemIfConfig
     ) { codeBlockItem in
-      allItems.append(self.generate(codeBlockItem: codeBlockItem).bridged)
+      guard let item = self.generate(codeBlockItem: codeBlockItem) else {
+        return
+      }
+      allItems.append(item.bridged)
     }
 
     return allItems.lazy.bridgedArray(in: self)