Add source file builder

Author: akkyie

Sources/SwiftSyntaxBuilder/Syntax/Buildables/SourceFile.swift

@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftSyntax
+
+public struct SourceFile: SyntaxBuildable {
+  let builder: SyntaxListBuildable
+
+  public init(@SyntaxListBuilder makeBuilder: () -> SyntaxListBuildable) {
+    self.builder = makeBuilder()
+  }
+
+  public func buildSyntax(format: Format, leadingTrivia: Trivia) -> Syntax {
+    let syntaxList = builder.buildSyntaxList(format: format, leadingTrivia: leadingTrivia)
+
+    return SourceFileSyntax {
+      for syntax in syntaxList {
+        $0.addStatement(CodeBlockItemSyntax {
+            $0.useItem(syntax)
+        })
+      }
+    }
+  }
+}

Tests/SwiftSyntaxBuilderTest/Declarations/SourceFileTests.swift

@@ -0,0 +1,29 @@
+import XCTest
+import SwiftSyntax
+
+@testable import SwiftSyntaxBuilder
+
+final class SourceFileTests: XCTestCase {
+  let format = Format(indentWidth: 2).indented()
+
+  func testSourceFile() {
+    let sourceFile = SourceFile {
+      Import("SwiftSyntax")
+
+      Struct("ExampleStruct") {
+        Let("syntax", of: "Syntax")
+      }
+    }
+
+    let syntax = sourceFile.buildSyntax(format: format, leadingTrivia: .zero)
+
+    var text = ""
+    syntax.write(to: &text)
+    XCTAssertEqual(text, """
+      import SwiftSyntax
+      struct ExampleStruct {
+        let syntax: Syntax
+      }
+    """)
+  }
+}