Ensure there are no optional syntax collection in the syntax tree

All syntax collections should be non-optional, which makes it easier to work with them. Also, the semantics of what an empty collection vs. a `nil` collection have not been clear.

CodeGeneration/Sources/SyntaxSupport/AvailabilityNodes.swift

@@ -180,8 +180,7 @@ public let AVAILABILITY_NODES: [Node] = [
       Child(
         name: "Components",
         kind: .collection(kind: .versionComponentList, collectionElementName: "VersionComponent"),
-        documentation: "Any version components that are not the major version . For example, for `1.2.0`, this will contain `.2.0`",
-        isOptional: true
+        documentation: "Any version components that are not the major version . For example, for `1.2.0`, this will contain `.2.0`"
       ),
     ]
   ),

CodeGeneration/Sources/SyntaxSupport/ExprNodes.swift

@@ -354,8 +354,7 @@ public let EXPR_NODES: [Node] = [
       ),
       Child(
         name: "Items",
-        kind: .collection(kind: .closureCaptureList, collectionElementName: "Item"),
-        isOptional: true
+        kind: .collection(kind: .closureCaptureList, collectionElementName: "Item")
       ),
       Child(
         name: "RightSquare",

CodeGeneration/Sources/SyntaxSupport/StmtNodes.swift

@@ -86,8 +86,7 @@ public let STMT_NODES: [Node] = [
       ),
       Child(
         name: "CatchItems",
-        kind: .collection(kind: .catchItemList, collectionElementName: "CatchItem"),
-        isOptional: true
+        kind: .collection(kind: .catchItemList, collectionElementName: "CatchItem", defaultsToEmpty: true)
       ),
       Child(
         name: "Body",
@@ -240,8 +239,7 @@ public let STMT_NODES: [Node] = [
       ),
       Child(
         name: "CatchClauses",
-        kind: .collection(kind: .catchClauseList, collectionElementName: "CatchClause"),
-        isOptional: true
+        kind: .collection(kind: .catchClauseList, collectionElementName: "CatchClause", defaultsToEmpty: true)
       ),
     ]
   ),

CodeGeneration/Tests/ValidateSyntaxNodes/ValidateSyntaxNodes.swift

@@ -760,4 +760,23 @@ class ValidateSyntaxNodes: XCTestCase {
 
     assertFailuresMatchXFails(failures, expectedFailures: [])
   }
+
+  func testNoOptionalSyntaxCollections() {
+    var failures: [ValidationFailure] = []
+
+    for node in SYNTAX_NODES.compactMap(\.layoutNode) {
+      for child in node.children {
+        if case .collection = child.kind, child.isOptional, !child.isUnexpectedNodes {
+          failures.append(
+            ValidationFailure(
+              node: node.kind,
+              message: "child '\(child.name)' is an optional syntax collection. All syntax collections should be non-optional."
+            )
+          )
+        }
+      }
+    }
+
+    assertFailuresMatchXFails(failures, expectedFailures: [])
+  }
 }

Sources/SwiftParser/Availability.swift

@@ -299,7 +299,7 @@ extension Parser {
       let unexpectedAfterComponents = self.parseUnexpectedVersionTokens()
       return RawVersionTupleSyntax(
         major: major,
-        components: nil,
+        components: RawVersionComponentListSyntax(elements: [], arena: self.arena),
         unexpectedAfterComponents,
         arena: self.arena
       )

Sources/SwiftParser/Expressions.swift

@@ -1733,7 +1733,7 @@ extension Parser {
 
       captures = RawClosureCaptureClauseSyntax(
         leftSquare: lsquare,
-        items: elements.isEmpty ? nil : RawClosureCaptureListSyntax(elements: elements, arena: self.arena),
+        items: RawClosureCaptureListSyntax(elements: elements, arena: self.arena),
         RawUnexpectedNodesSyntax(unexpectedNodes, arena: self.arena),
         rightSquare: rsquare,
         arena: self.arena

Sources/SwiftParser/Statements.swift

@@ -384,7 +384,7 @@ extension Parser {
       unexpectedBeforeDoKeyword,
       doKeyword: doKeyword,
       body: body,
-      catchClauses: elements.isEmpty ? nil : RawCatchClauseListSyntax(elements: elements, arena: self.arena),
+      catchClauses: RawCatchClauseListSyntax(elements: elements, arena: self.arena),
       arena: self.arena
     )
   }
@@ -416,7 +416,7 @@ extension Parser {
     return RawCatchClauseSyntax(
       unexpectedBeforeCatchKeyword,
       catchKeyword: catchKeyword,
-      catchItems: catchItems.isEmpty ? nil : RawCatchItemListSyntax(elements: catchItems, arena: self.arena),
+      catchItems: RawCatchItemListSyntax(elements: catchItems, arena: self.arena),
       body: body,
       arena: self.arena
     )

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -1936,19 +1936,17 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     }
 
     if let unexpectedAfterComponents = node.unexpectedAfterComponents {
-      if let components = node.components,
-        unexpectedAfterComponents.allSatisfy({ $0.is(VersionComponentSyntax.self) })
-      {
+      if unexpectedAfterComponents.allSatisfy({ $0.is(VersionComponentSyntax.self) }) {
         addDiagnostic(
           unexpectedAfterComponents,
-          TrailingVersionAreIgnored(major: node.major, components: components),
+          TrailingVersionAreIgnored(major: node.major, components: node.components),
           handledNodes: [unexpectedAfterComponents.id]
         )
       } else {
         addDiagnostic(
           unexpectedAfterComponents,
           CannotParseVersionTuple(versionTuple: unexpectedAfterComponents),
-          handledNodes: [node.major.id, node.components?.id, unexpectedAfterComponents.id].compactMap { $0 }
+          handledNodes: [node.major.id, node.components.id, unexpectedAfterComponents.id]
         )
       }
     }

Sources/SwiftSyntax/generated/raw/RawSyntaxNodes.swift

@@ -2715,7 +2715,7 @@ public struct RawCatchClauseSyntax: RawSyntaxNodeProtocol {
       _ unexpectedBeforeCatchKeyword: RawUnexpectedNodesSyntax? = nil, 
       catchKeyword: RawTokenSyntax, 
       _ unexpectedBetweenCatchKeywordAndCatchItems: RawUnexpectedNodesSyntax? = nil, 
-      catchItems: RawCatchItemListSyntax?, 
+      catchItems: RawCatchItemListSyntax, 
       _ unexpectedBetweenCatchItemsAndBody: RawUnexpectedNodesSyntax? = nil, 
       body: RawCodeBlockSyntax, 
       _ unexpectedAfterBody: RawUnexpectedNodesSyntax? = nil, 
@@ -2727,7 +2727,7 @@ public struct RawCatchClauseSyntax: RawSyntaxNodeProtocol {
       layout[0] = unexpectedBeforeCatchKeyword?.raw
       layout[1] = catchKeyword.raw
       layout[2] = unexpectedBetweenCatchKeywordAndCatchItems?.raw
-      layout[3] = catchItems?.raw
+      layout[3] = catchItems.raw
       layout[4] = unexpectedBetweenCatchItemsAndBody?.raw
       layout[5] = body.raw
       layout[6] = unexpectedAfterBody?.raw
@@ -2747,8 +2747,8 @@ public struct RawCatchClauseSyntax: RawSyntaxNodeProtocol {
     layoutView.children[2].map(RawUnexpectedNodesSyntax.init(raw:))
   }
 
-  public var catchItems: RawCatchItemListSyntax? {
-    layoutView.children[3].map(RawCatchItemListSyntax.init(raw:))
+  public var catchItems: RawCatchItemListSyntax {
+    layoutView.children[3].map(RawCatchItemListSyntax.init(raw:))!
   }
 
   public var unexpectedBetweenCatchItemsAndBody: RawUnexpectedNodesSyntax? {
@@ -3129,7 +3129,7 @@ public struct RawClosureCaptureClauseSyntax: RawSyntaxNodeProtocol {
       _ unexpectedBeforeLeftSquare: RawUnexpectedNodesSyntax? = nil, 
       leftSquare: RawTokenSyntax, 
       _ unexpectedBetweenLeftSquareAndItems: RawUnexpectedNodesSyntax? = nil, 
-      items: RawClosureCaptureListSyntax?, 
+      items: RawClosureCaptureListSyntax, 
       _ unexpectedBetweenItemsAndRightSquare: RawUnexpectedNodesSyntax? = nil, 
       rightSquare: RawTokenSyntax, 
       _ unexpectedAfterRightSquare: RawUnexpectedNodesSyntax? = nil, 
@@ -3141,7 +3141,7 @@ public struct RawClosureCaptureClauseSyntax: RawSyntaxNodeProtocol {
       layout[0] = unexpectedBeforeLeftSquare?.raw
       layout[1] = leftSquare.raw
       layout[2] = unexpectedBetweenLeftSquareAndItems?.raw
-      layout[3] = items?.raw
+      layout[3] = items.raw
       layout[4] = unexpectedBetweenItemsAndRightSquare?.raw
       layout[5] = rightSquare.raw
       layout[6] = unexpectedAfterRightSquare?.raw
@@ -3161,8 +3161,8 @@ public struct RawClosureCaptureClauseSyntax: RawSyntaxNodeProtocol {
     layoutView.children[2].map(RawUnexpectedNodesSyntax.init(raw:))
   }
 
-  public var items: RawClosureCaptureListSyntax? {
-    layoutView.children[3].map(RawClosureCaptureListSyntax.init(raw:))
+  public var items: RawClosureCaptureListSyntax {
+    layoutView.children[3].map(RawClosureCaptureListSyntax.init(raw:))!
   }
 
   public var unexpectedBetweenItemsAndRightSquare: RawUnexpectedNodesSyntax? {
@@ -7067,7 +7067,7 @@ public struct RawDoStmtSyntax: RawStmtSyntaxNodeProtocol {
       _ unexpectedBetweenDoKeywordAndBody: RawUnexpectedNodesSyntax? = nil, 
       body: RawCodeBlockSyntax, 
       _ unexpectedBetweenBodyAndCatchClauses: RawUnexpectedNodesSyntax? = nil, 
-      catchClauses: RawCatchClauseListSyntax?, 
+      catchClauses: RawCatchClauseListSyntax, 
       _ unexpectedAfterCatchClauses: RawUnexpectedNodesSyntax? = nil, 
       arena: __shared SyntaxArena
     ) {
@@ -7079,7 +7079,7 @@ public struct RawDoStmtSyntax: RawStmtSyntaxNodeProtocol {
       layout[2] = unexpectedBetweenDoKeywordAndBody?.raw
       layout[3] = body.raw
       layout[4] = unexpectedBetweenBodyAndCatchClauses?.raw
-      layout[5] = catchClauses?.raw
+      layout[5] = catchClauses.raw
       layout[6] = unexpectedAfterCatchClauses?.raw
     }
     self.init(unchecked: raw)
@@ -7105,8 +7105,8 @@ public struct RawDoStmtSyntax: RawStmtSyntaxNodeProtocol {
     layoutView.children[4].map(RawUnexpectedNodesSyntax.init(raw:))
   }
 
-  public var catchClauses: RawCatchClauseListSyntax? {
-    layoutView.children[5].map(RawCatchClauseListSyntax.init(raw:))
+  public var catchClauses: RawCatchClauseListSyntax {
+    layoutView.children[5].map(RawCatchClauseListSyntax.init(raw:))!
   }
 
   public var unexpectedAfterCatchClauses: RawUnexpectedNodesSyntax? {
@@ -22129,7 +22129,7 @@ public struct RawVersionTupleSyntax: RawSyntaxNodeProtocol {
       _ unexpectedBeforeMajor: RawUnexpectedNodesSyntax? = nil, 
       major: RawTokenSyntax, 
       _ unexpectedBetweenMajorAndComponents: RawUnexpectedNodesSyntax? = nil, 
-      components: RawVersionComponentListSyntax?, 
+      components: RawVersionComponentListSyntax, 
       _ unexpectedAfterComponents: RawUnexpectedNodesSyntax? = nil, 
       arena: __shared SyntaxArena
     ) {
@@ -22139,7 +22139,7 @@ public struct RawVersionTupleSyntax: RawSyntaxNodeProtocol {
       layout[0] = unexpectedBeforeMajor?.raw
       layout[1] = major.raw
       layout[2] = unexpectedBetweenMajorAndComponents?.raw
-      layout[3] = components?.raw
+      layout[3] = components.raw
       layout[4] = unexpectedAfterComponents?.raw
     }
     self.init(unchecked: raw)
@@ -22157,8 +22157,8 @@ public struct RawVersionTupleSyntax: RawSyntaxNodeProtocol {
     layoutView.children[2].map(RawUnexpectedNodesSyntax.init(raw:))
   }
 
-  public var components: RawVersionComponentListSyntax? {
-    layoutView.children[3].map(RawVersionComponentListSyntax.init(raw:))
+  public var components: RawVersionComponentListSyntax {
+    layoutView.children[3].map(RawVersionComponentListSyntax.init(raw:))!
   }
 
   public var unexpectedAfterComponents: RawUnexpectedNodesSyntax? {

Sources/SwiftSyntax/generated/raw/RawSyntaxValidation.swift

@@ -501,7 +501,7 @@ func validateLayout(layout: RawSyntaxBuffer, as kind: SyntaxKind) {
     assertNoError(kind, 0, verify(layout[0], as: RawUnexpectedNodesSyntax?.self))
     assertNoError(kind, 1, verify(layout[1], as: RawTokenSyntax.self, tokenChoices: [.keyword("catch")]))
     assertNoError(kind, 2, verify(layout[2], as: RawUnexpectedNodesSyntax?.self))
-    assertNoError(kind, 3, verify(layout[3], as: RawCatchItemListSyntax?.self))
+    assertNoError(kind, 3, verify(layout[3], as: RawCatchItemListSyntax.self))
     assertNoError(kind, 4, verify(layout[4], as: RawUnexpectedNodesSyntax?.self))
     assertNoError(kind, 5, verify(layout[5], as: RawCodeBlockSyntax.self))
     assertNoError(kind, 6, verify(layout[6], as: RawUnexpectedNodesSyntax?.self))
@@ -547,7 +547,7 @@ func validateLayout(layout: RawSyntaxBuffer, as kind: SyntaxKind) {
     assertNoError(kind, 0, verify(layout[0], as: RawUnexpectedNodesSyntax?.self))
     assertNoError(kind, 1, verify(layout[1], as: RawTokenSyntax.self, tokenChoices: [.tokenKind(.leftSquare)]))
     assertNoError(kind, 2, verify(layout[2], as: RawUnexpectedNodesSyntax?.self))
-    assertNoError(kind, 3, verify(layout[3], as: RawClosureCaptureListSyntax?.self))
+    assertNoError(kind, 3, verify(layout[3], as: RawClosureCaptureListSyntax.self))
     assertNoError(kind, 4, verify(layout[4], as: RawUnexpectedNodesSyntax?.self))
     assertNoError(kind, 5, verify(layout[5], as: RawTokenSyntax.self, tokenChoices: [.tokenKind(.rightSquare)]))
     assertNoError(kind, 6, verify(layout[6], as: RawUnexpectedNodesSyntax?.self))
@@ -994,7 +994,7 @@ func validateLayout(layout: RawSyntaxBuffer, as kind: SyntaxKind) {
     assertNoError(kind, 2, verify(layout[2], as: RawUnexpectedNodesSyntax?.self))
     assertNoError(kind, 3, verify(layout[3], as: RawCodeBlockSyntax.self))
     assertNoError(kind, 4, verify(layout[4], as: RawUnexpectedNodesSyntax?.self))
-    assertNoError(kind, 5, verify(layout[5], as: RawCatchClauseListSyntax?.self))
+    assertNoError(kind, 5, verify(layout[5], as: RawCatchClauseListSyntax.self))
     assertNoError(kind, 6, verify(layout[6], as: RawUnexpectedNodesSyntax?.self))
   case .documentationAttributeArgumentList:
     for (index, element) in layout.enumerated() {
@@ -2638,7 +2638,7 @@ func validateLayout(layout: RawSyntaxBuffer, as kind: SyntaxKind) {
     assertNoError(kind, 0, verify(layout[0], as: RawUnexpectedNodesSyntax?.self))
     assertNoError(kind, 1, verify(layout[1], as: RawTokenSyntax.self, tokenChoices: [.tokenKind(.integerLiteral)]))
     assertNoError(kind, 2, verify(layout[2], as: RawUnexpectedNodesSyntax?.self))
-    assertNoError(kind, 3, verify(layout[3], as: RawVersionComponentListSyntax?.self))
+    assertNoError(kind, 3, verify(layout[3], as: RawVersionComponentListSyntax.self))
     assertNoError(kind, 4, verify(layout[4], as: RawUnexpectedNodesSyntax?.self))
   case .whereClause:
     assert(layout.count == 5)

Sources/SwiftSyntax/generated/syntaxNodes/SyntaxNodes.swift

@@ -1925,7 +1925,7 @@ public struct CatchClauseSyntax: SyntaxProtocol, SyntaxHashable {
       _ unexpectedBeforeCatchKeyword: UnexpectedNodesSyntax? = nil,
       catchKeyword: TokenSyntax = .keyword(.catch),
       _ unexpectedBetweenCatchKeywordAndCatchItems: UnexpectedNodesSyntax? = nil,
-      catchItems: CatchItemListSyntax? = nil,
+      catchItems: CatchItemListSyntax = [],
       _ unexpectedBetweenCatchItemsAndBody: UnexpectedNodesSyntax? = nil,
       body: CodeBlockSyntax,
       _ unexpectedAfterBody: UnexpectedNodesSyntax? = nil,
@@ -1947,7 +1947,7 @@ public struct CatchClauseSyntax: SyntaxProtocol, SyntaxHashable {
           unexpectedBeforeCatchKeyword?.raw, 
           catchKeyword.raw, 
           unexpectedBetweenCatchKeywordAndCatchItems?.raw, 
-          catchItems?.raw, 
+          catchItems.raw, 
           unexpectedBetweenCatchItemsAndBody?.raw, 
           body.raw, 
           unexpectedAfterBody?.raw
@@ -1992,12 +1992,12 @@ public struct CatchClauseSyntax: SyntaxProtocol, SyntaxHashable {
     }
   }
 
-  public var catchItems: CatchItemListSyntax? {
+  public var catchItems: CatchItemListSyntax {
     get {
-      return data.child(at: 3, parent: Syntax(self)).map(CatchItemListSyntax.init)
+      return CatchItemListSyntax(data.child(at: 3, parent: Syntax(self))!)
     }
     set(value) {
-      self = CatchClauseSyntax(data.replacingChild(at: 3, with: value?.data, arena: SyntaxArena()))
+      self = CatchClauseSyntax(data.replacingChild(at: 3, with: value.data, arena: SyntaxArena()))
     }
   }
 
@@ -2259,7 +2259,7 @@ public struct ClosureCaptureClauseSyntax: SyntaxProtocol, SyntaxHashable {
       _ unexpectedBeforeLeftSquare: UnexpectedNodesSyntax? = nil,
       leftSquare: TokenSyntax = .leftSquareToken(),
       _ unexpectedBetweenLeftSquareAndItems: UnexpectedNodesSyntax? = nil,
-      items: ClosureCaptureListSyntax? = nil,
+      items: ClosureCaptureListSyntax,
       _ unexpectedBetweenItemsAndRightSquare: UnexpectedNodesSyntax? = nil,
       rightSquare: TokenSyntax = .rightSquareToken(),
       _ unexpectedAfterRightSquare: UnexpectedNodesSyntax? = nil,
@@ -2281,7 +2281,7 @@ public struct ClosureCaptureClauseSyntax: SyntaxProtocol, SyntaxHashable {
           unexpectedBeforeLeftSquare?.raw, 
           leftSquare.raw, 
           unexpectedBetweenLeftSquareAndItems?.raw, 
-          items?.raw, 
+          items.raw, 
           unexpectedBetweenItemsAndRightSquare?.raw, 
           rightSquare.raw, 
           unexpectedAfterRightSquare?.raw
@@ -2326,12 +2326,12 @@ public struct ClosureCaptureClauseSyntax: SyntaxProtocol, SyntaxHashable {
     }
   }
 
-  public var items: ClosureCaptureListSyntax? {
+  public var items: ClosureCaptureListSyntax {
     get {
-      return data.child(at: 3, parent: Syntax(self)).map(ClosureCaptureListSyntax.init)
+      return ClosureCaptureListSyntax(data.child(at: 3, parent: Syntax(self))!)
     }
     set(value) {
-      self = ClosureCaptureClauseSyntax(data.replacingChild(at: 3, with: value?.data, arena: SyntaxArena()))
+      self = ClosureCaptureClauseSyntax(data.replacingChild(at: 3, with: value.data, arena: SyntaxArena()))
     }
   }
 
@@ -19002,7 +19002,7 @@ public struct VersionTupleSyntax: SyntaxProtocol, SyntaxHashable {
       _ unexpectedBeforeMajor: UnexpectedNodesSyntax? = nil,
       major: TokenSyntax,
       _ unexpectedBetweenMajorAndComponents: UnexpectedNodesSyntax? = nil,
-      components: VersionComponentListSyntax? = nil,
+      components: VersionComponentListSyntax,
       _ unexpectedAfterComponents: UnexpectedNodesSyntax? = nil,
       trailingTrivia: Trivia? = nil
 
@@ -19020,7 +19020,7 @@ public struct VersionTupleSyntax: SyntaxProtocol, SyntaxHashable {
           unexpectedBeforeMajor?.raw, 
           major.raw, 
           unexpectedBetweenMajorAndComponents?.raw, 
-          components?.raw, 
+          components.raw, 
           unexpectedAfterComponents?.raw
         ]
       let raw = RawSyntax.makeLayout(
@@ -19065,12 +19065,12 @@ public struct VersionTupleSyntax: SyntaxProtocol, SyntaxHashable {
   }
 
   /// Any version components that are not the major version . For example, for `1.2.0`, this will contain `.2.0`
-  public var components: VersionComponentListSyntax? {
+  public var components: VersionComponentListSyntax {
     get {
-      return data.child(at: 3, parent: Syntax(self)).map(VersionComponentListSyntax.init)
+      return VersionComponentListSyntax(data.child(at: 3, parent: Syntax(self))!)
     }
     set(value) {
-      self = VersionTupleSyntax(data.replacingChild(at: 3, with: value?.data, arena: SyntaxArena()))
+      self = VersionTupleSyntax(data.replacingChild(at: 3, with: value.data, arena: SyntaxArena()))
     }
   }