Make URL argument for SwiftFormatter optional.

Author: allevato

Sources/SwiftFormat/SwiftFormatter.swift

@@ -65,12 +65,14 @@ public final class SwiftFormatter {
   ///
   /// - Parameters:
   ///   - source: The Swift source code to be formatted.
-  ///   - url: A file URL denoting the filename/path that should be assumed for this source code.
+  ///   - url: A file URL denoting the filename/path that should be assumed for this syntax tree,
+  ///     which is associated with any diagnostics emitted during formatting. If this is nil, a
+  ///     dummy value will be used.
   ///   - outputStream: A value conforming to `TextOutputStream` to which the formatted output will
   ///     be written.
   /// - Throws: If an unrecoverable error occurs when formatting the code.
   public func format<Output: TextOutputStream>(
-    source: String, assumingFileURL url: URL, to outputStream: inout Output
+    source: String, assumingFileURL url: URL?, to outputStream: inout Output
   ) throws {
     let sourceFile = try SyntaxParser.parse(source: source)
     try format(syntax: sourceFile, assumingFileURL: url, to: &outputStream)
@@ -80,15 +82,19 @@ public final class SwiftFormatter {
   ///
   /// - Parameters:
   ///   - syntax: The Swift syntax tree to be converted to source code and formatted.
-  ///   - url: A file URL denoting the filename/path that should be assumed for this syntax tree.
+  ///   - url: A file URL denoting the filename/path that should be assumed for this syntax tree,
+  ///     which is associated with any diagnostics emitted during formatting. If this is nil, a
+  ///     dummy value will be used.
   ///   - outputStream: A value conforming to `TextOutputStream` to which the formatted output will
   ///     be written.
   /// - Throws: If an unrecoverable error occurs when formatting the code.
   public func format<Output: TextOutputStream>(
-    syntax: SourceFileSyntax, assumingFileURL url: URL, to outputStream: inout Output
+    syntax: SourceFileSyntax, assumingFileURL url: URL?, to outputStream: inout Output
   ) throws {
+    let assumedURL = url ?? URL(fileURLWithPath: "source")
+
     let context = Context(
-      configuration: configuration, diagnosticEngine: diagnosticEngine, fileURL: url,
+      configuration: configuration, diagnosticEngine: diagnosticEngine, fileURL: assumedURL,
       sourceFileSyntax: syntax)
     let pipeline = FormatPipeline(context: context)
     let transformedSyntax = pipeline.visit(syntax)