Print a usage description when the user enters the swift-format command without arguments

Author: TTOzzi

Diff for: Sources/swift-format/Subcommands/Format.swift

@@ -36,8 +36,15 @@ extension SwiftFormatCommand {
     var performanceMeasurementOptions: PerformanceMeasurementsOptions
 
     func validate() throws {
-      if inPlace && formatOptions.paths.isEmpty {
-        throw ValidationError("'--in-place' is only valid when formatting files")
+      if formatOptions.paths.isEmpty, formatOptions.assumeFilename == nil {
+        throw ValidationError(
+          """
+          No input files specified. Use one of the following:
+            - Provide the path to a directory along with the '--recursive' option to format all Swift files within it.
+            - Provide the path to a specific Swift source code file.
+          Additionally, if you want to overwrite files in-place, use '--in-place'.
+          """
+        )
       }
     }
 

Diff for: Sources/swift-format/Subcommands/Lint.swift

@@ -32,6 +32,18 @@ extension SwiftFormatCommand {
     @OptionGroup(visibility: .hidden)
     var performanceMeasurementOptions: PerformanceMeasurementsOptions
 
+    func validate() throws {
+      if lintOptions.paths.isEmpty, lintOptions.assumeFilename == nil {
+        throw ValidationError(
+          """
+          No input files specified. Use one of the following:
+            - Provide the path to a directory along with the '--recursive' option to lint all Swift files within it.
+            - Provide the path to a specific Swift source code file.
+          """
+        )
+      }
+    }
+
     func run() throws {
       try performanceMeasurementOptions.printingInstructionCountIfRequested {
         let frontend = LintFrontend(lintFormatOptions: lintOptions)