Add dry run option to CLI

Sources/swift-openapi-generator/GenerateCommand.swift

@@ -48,10 +48,17 @@ struct _GenerateCommand: AsyncParsableCommand {
     )
     var pluginSource: PluginSource?
 
+    @Flag(
+        name: .customLong("dry-run"),
+        help: "Simulate the command and print the operations, without actually affecting the file system."
+    )
+    var isDryRun: Bool = false
+
     func run() async throws {
         try generate.runGenerator(
             outputDirectory: outputDirectory,
-            pluginSource: pluginSource
+            pluginSource: pluginSource,
+            isDryRun: isDryRun
         )
     }
 }

Sources/swift-openapi-generator/GenerateOptions+runGenerator.swift

@@ -22,9 +22,13 @@ extension _GenerateOptions {
     ///   - outputDirectory: The directory path to which the generator writes
     ///   the generated Swift files.
     ///   - pluginSource: The source of the generator invocation if from a plugin.
+    ///   - isDryRun: A Boolean value that indicates whether this invocation should
+    ///   be run in a testing mode to preview all the operations being carried out without
+    ///   making any actual changes.
     func runGenerator(
         outputDirectory: URL,
-        pluginSource: PluginSource?
+        pluginSource: PluginSource?,
+        isDryRun: Bool
     ) throws {
         let config = try loadedConfig()
         let sortedModes = try resolvedModes(config)
@@ -58,6 +62,7 @@ extension _GenerateOptions {
             - Diagnostics output path: \(diagnosticsOutputPath?.path ?? "<none - logs to stderr>")
             - Current directory: \(FileManager.default.currentDirectoryPath)
             - Plugin source: \(pluginSource?.rawValue ?? "<none>")
+            - Is dry run: \(isDryRun)
             - Additional imports: \(resolvedAdditionalImports.isEmpty ? "<none>" : resolvedAdditionalImports.joined(separator: ", "))
             """
         )
@@ -67,6 +72,7 @@ extension _GenerateOptions {
                 configs: configs,
                 pluginSource: pluginSource,
                 outputDirectory: outputDirectory,
+                isDryRun: isDryRun,
                 diagnostics: diagnostics
             )
         } catch let error as Diagnostic {

Sources/swift-openapi-generator/runGenerator.swift

@@ -16,20 +16,22 @@ import ArgumentParser
 import _OpenAPIGeneratorCore
 
 extension _Tool {
-
     /// Runs the generator with the specified configuration values.
     /// - Parameters:
     ///   - doc: A path to the OpenAPI document.
     ///   - configs: A list of generator configurations.
     ///   - pluginSource: The source of the generator invocation.
     ///   - outputDirectory: The directory to which the generator writes
     ///   the generated Swift files.
+    ///   - isDryRun: A Boolean value that indicates whether this invocation should
+    ///   be a dry run.
     ///   - diagnostics: A collector for diagnostics emitted by the generator.
     static func runGenerator(
         doc: URL,
         configs: [Config],
         pluginSource: PluginSource?,
         outputDirectory: URL,
+        isDryRun: Bool,
         diagnostics: any DiagnosticCollector
     ) throws {
         let docData: Data
@@ -45,6 +47,7 @@ extension _Tool {
                 config: config,
                 outputDirectory: outputDirectory,
                 outputFileName: config.mode.outputFileName,
+                isDryRun: isDryRun,
                 diagnostics: diagnostics
             )
         }
@@ -59,7 +62,8 @@ extension _Tool {
                 try replaceFileContents(
                     inDirectory: outputDirectory,
                     fileName: mode.outputFileName,
-                    with: { Data() }
+                    with: { Data() },
+                    isDryRun: isDryRun
                 )
             }
         }
@@ -74,62 +78,63 @@ extension _Tool {
     ///   the generated Swift file.
     ///   - outputFileName: The file name to which the generator writes
     ///   the generated Swift file.
+    ///   - isDryRun: A Boolean value that indicates whether this invocation should
+    ///   be a dry run.
     ///   - diagnostics: A collector for diagnostics emitted by the generator.
     static func runGenerator(
         doc: URL,
         docData: Data,
         config: Config,
         outputDirectory: URL,
         outputFileName: String,
+        isDryRun: Bool,
         diagnostics: any DiagnosticCollector
     ) throws {
-        let didChange = try replaceFileContents(
+        try replaceFileContents(
             inDirectory: outputDirectory,
-            fileName: outputFileName
-        ) {
-            let output = try _OpenAPIGeneratorCore.runGenerator(
-                input: .init(absolutePath: doc, contents: docData),
-                config: config,
-                diagnostics: diagnostics
-            )
-            return output.contents
-        }
-        print("File \(outputFileName): \(didChange ? "changed" : "unchanged")")
+            fileName: outputFileName,
+            with: {
+                let output = try _OpenAPIGeneratorCore.runGenerator(
+                    input: .init(absolutePath: doc, contents: docData),
+                    config: config,
+                    diagnostics: diagnostics
+                )
+                return output.contents
+            },
+            isDryRun: isDryRun
+        )
     }
 
     /// Evaluates a closure to generate file data and writes the data to disk
-    /// if the data is different than the current file contents.
+    /// if the data is different than the current file contents. Will write to disk
+    /// only if `isDryRun` is set as `false`.
     /// - Parameters:
     ///   - path: A path to the file.
     ///   - contents: A closure evaluated to produce the file contents data.
+    ///   - isDryRun: A Boolean value that indicates whether this invocation should
+    ///   be a dry run. File system changes will not be written to disk in this mode.
     /// - Throws: When writing to disk fails.
-    /// - Returns: `true` if the generated contents changed, otherwise `false`.
-    @discardableResult
     static func replaceFileContents(
         inDirectory outputDirectory: URL,
         fileName: String,
-        with contents: () throws -> Data
-    ) throws -> Bool {
+        with contents: () throws -> Data,
+        isDryRun: Bool
+    ) throws {
         let fileManager = FileManager.default
+        let path = outputDirectory.appendingPathComponent(fileName)
+        let data = try contents()
 
-        // Create directory if it doesn't exist.
-        if !fileManager.fileExists(atPath: outputDirectory.path) {
+        if let existingData = try? Data(contentsOf: path), existingData == data {
+            print("File \(path.lastPathComponent) already up to date.")
+            return
+        }
+        print("Writing data to file \(path.lastPathComponent)...")
+        if !isDryRun {
             try fileManager.createDirectory(
                 at: outputDirectory,
                 withIntermediateDirectories: true
             )
-        }
-
-        let path = outputDirectory.appendingPathComponent(fileName)
-        let data = try contents()
-        guard fileManager.fileExists(atPath: path.path) else {
-            return fileManager.createFile(atPath: path.path, contents: data)
-        }
-        let existingData = try? Data(contentsOf: path)
-        guard existingData == data else {
             try data.write(to: path)
-            return true
         }
-        return false
     }
 }