Make SyntaxCollection conform to ExpressibleByArrayLiteral

This hoists the ability to create syntax collections from `SwiftSyntaxBuilder` to the `SwiftSyntax` module.

Impact on API compatibility: Initializing an `ExprListSyntax` or `UnexpectedNodesSyntax` now requires the nodes to be `ExprSyntax` and `Syntax` opposed to `ExprSyntaxProtocol` or `SyntaxProtocol`, respectively. `ExprListSyntax` is used as the child of a `SequenceExprSyntax`. I think this is OK because
- Users don’t genrally construct `UnexpectedNodesSyntax`
- To construct a `SequenceExprSyntax`, you can use the result builder on `SequenceExprSyntax`, which takes `ExprSyntaxProtocol`

Author: ahoppen

CodeGeneration/Sources/generate-swiftsyntax/GenerateSwiftSyntax.swift

@@ -120,7 +120,6 @@ struct GenerateSwiftSyntax: ParsableCommand {
         GeneratedFileSpec(swiftSyntaxGeneratedDir + ["TriviaPieces.swift"], triviaPiecesFile),
 
         // SwiftSyntaxBuilder
-        GeneratedFileSpec(swiftSyntaxBuilderGeneratedDir + ["BuildableCollectionNodes.swift"], buildableCollectionNodesFile),
         GeneratedFileSpec(swiftSyntaxBuilderGeneratedDir + ["BuildableNodes.swift"], buildableNodesFile),
         GeneratedFileSpec(swiftSyntaxBuilderGeneratedDir + ["ResultBuilders.swift"], resultBuildersFile),
         GeneratedFileSpec(

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntaxbuilder/BuildableCollectionNodesFile.swift

@@ -10,7 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-public protocol SyntaxCollection: SyntaxProtocol, BidirectionalCollection where Element: SyntaxProtocol, Index == SyntaxChildrenIndex {
+public protocol SyntaxCollection: SyntaxProtocol, BidirectionalCollection, ExpressibleByArrayLiteral
+where Element: SyntaxProtocol, Index == SyntaxChildrenIndex {
   associatedtype Iterator = SyntaxCollectionIterator<Element>
 
   /// The ``SyntaxKind`` of the syntax node that conforms to ``SyntaxCollection``.
@@ -58,6 +59,10 @@ extension SyntaxCollection {
     self.init(SyntaxData.forRoot(raw, rawNodeArena: arena))
   }
 
+  public init(arrayLiteral elements: Element...) {
+    self.init(elements)
+  }
+
   /// The number of elements, `present` or `missing`, in this collection.
   public var count: Int {
     return layoutView.children.count

Sources/SwiftSyntax/SyntaxCollection.swift

@@ -19,7 +19,6 @@ add_swift_host_library(SwiftSyntaxBuilder
   WithTrailingCommaSyntax+EnsuringTrailingComma.swift
 
 
-  generated/BuildableCollectionNodes.swift
   generated/BuildableNodes.swift
   generated/ResultBuilders.swift
   generated/RenamedChildrenBuilderCompatibility.swift

Sources/SwiftSyntaxBuilder/CMakeLists.txt

@@ -49,3 +49,21 @@ extension MemberBlockItemListBuilder {
     return buildExpression(MemberBlockItemSyntax(decl: expression))
   }
 }
+
+// MARK: Initializing collections from protocols
+// These initializers allow the creation of syntax collections that have a base
+// node as their element from the corresponding protocol type.
+// These are used by the result builders.
+// Since we only have two of these, it doesn’t make sense to generate them.
+
+extension ExprListSyntax {
+  init(_ elements: [ExprSyntaxProtocol]) {
+    self = ExprListSyntax(elements.map { ExprSyntax(fromProtocol: $0) } as [ExprSyntax])
+  }
+}
+
+extension UnexpectedNodesSyntax {
+  public init(_ elements: [SyntaxProtocol]) {
+    self = UnexpectedNodesSyntax(elements.map { Syntax(fromProtocol: $0) } as [Syntax])
+  }
+}