Gradually deprecate running swift-format without input paths; require '-' for stdin in the future

Author: TTOzzi

Sources/swift-format/Frontend/Frontend.swift

@@ -97,7 +97,12 @@ class Frontend {
 
   /// Runs the linter or formatter over the inputs.
   final func run() {
-    if lintFormatOptions.paths.isEmpty {
+    if lintFormatOptions.paths == ["-"] {
+      processStandardInput()
+    } else if lintFormatOptions.paths.isEmpty {
+      diagnosticsEngine.emitWarning(
+        "running swift-format with no input paths is deprecated and will be removed in the future; specify '-' to use stdin"
+      )
       processStandardInput()
     } else {
       processURLs(