Move diagnostics collector logic into prepare function

Sources/_OpenAPIGeneratorCore/Diagnostics.swift

@@ -175,7 +175,7 @@ public protocol DiagnosticCollector {
 ///
 /// If a diagnostic with a severity of `.error` is emitted, this collector will throw the diagnostic as an error.
 public struct ErrorThrowingDiagnosticCollector: DiagnosticCollector {
-    private let upstream: any DiagnosticCollector
+    let upstream: any DiagnosticCollector
 
     /// Initializes a new `ErrorThrowingDiagnosticCollector` with an upstream `DiagnosticCollector`.
     ///

Sources/_OpenAPIGeneratorCore/DiagnosticsCollectorProvider.swift

@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftOpenAPIGenerator open source project
+//
+// Copyright (c) 2023 Apple Inc. and the SwiftOpenAPIGenerator project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+/// A feature that can be explicitly enabled before being released.
+///
+/// Commonly used to get early feedback on breaking changes, before
+/// they are enabled by default, which can only be done in a major version.
+///
+/// Once a feature is enabled unconditionally in the next major version,
+/// the corresponding feature flag should be removed at the same time.
+///
+/// For example: a breaking feature is being built while version 0.1 is out,
+/// and is hidden behind a feature flag. Once ready, the feature is
+/// enabled unconditionally on main and the feature flag removed, and version
+/// 0.2 is tagged. (This is for pre-1.0 versioning, would be 1.0 and 2.0 after
+/// 1.0 is released.)
+import Foundation
+
+/// Prepares a diagnostics collector.
+/// - Parameter outputPath: A file path where to persist the YAML file. If `nil`, diagnostics will be printed to stderr.
+/// - Returns: A tuple containing:
+///   - An instance of `DiagnosticCollector` conforming to `Sendable`.
+///   - A closure to finalize the diagnostics collection
+public func preparedDiagnosticsCollector(outputPath: URL?) -> (any DiagnosticCollector & Sendable, () throws -> Void) {
+    let innerDiagnostics: any DiagnosticCollector & Sendable
+    let finalizeDiagnostics: () throws -> Void
+
+    if let outputPath {
+        let _diagnostics = _YamlFileDiagnosticsCollector(url: outputPath)
+        finalizeDiagnostics = _diagnostics.finalize
+        innerDiagnostics = _diagnostics
+    } else {
+        innerDiagnostics = StdErrPrintingDiagnosticCollector()
+        finalizeDiagnostics = {}
+    }
+    let diagnostics = ErrorThrowingDiagnosticCollector(upstream: innerDiagnostics)
+    return (diagnostics, finalizeDiagnostics)
+}

Sources/_OpenAPIGeneratorCore/YamlFileDiagnosticsCollector.swift

@@ -20,7 +20,7 @@ struct _DiagnosticsYamlFileContent: Encodable {
 }
 
 /// A collector that writes diagnostics to a YAML file.
-final public class _YamlFileDiagnosticsCollector: DiagnosticCollector, @unchecked Sendable {
+final class _YamlFileDiagnosticsCollector: DiagnosticCollector, @unchecked Sendable {
     /// Protects `diagnostics`.
     private let lock = NSLock()
 
@@ -32,19 +32,17 @@ final public class _YamlFileDiagnosticsCollector: DiagnosticCollector, @unchecke
 
     /// Creates a new collector.
     /// - Parameter url: A file path where to persist the YAML file.
-    public init(url: URL) { self.url = url }
+    init(url: URL) { self.url = url }
 
-    /// Emits a diagnostic message to the collector.
-    /// - Parameter diagnostic: The diagnostic message to be collected.
-    public func emit(_ diagnostic: Diagnostic) {
+    func emit(_ diagnostic: Diagnostic) {
         lock.lock()
         defer { lock.unlock() }
         diagnostics.append(diagnostic)
     }
 
     /// Finishes writing to the collector by persisting the accumulated
     /// diagnostics to a YAML file.
-    public func finalize() throws {
+    func finalize() throws {
         lock.lock()
         defer { lock.unlock() }
         let sortedDiagnostics = diagnostics.sorted(by: { a, b in a.description < b.description })
@@ -55,10 +53,3 @@ final public class _YamlFileDiagnosticsCollector: DiagnosticCollector, @unchecke
         try encoder.encode(container).write(to: url, atomically: true, encoding: .utf8)
     }
 }
-
-/// Prepares a diagnostics collector.
-/// - Parameter url: A file path where to persist the YAML file.
-/// - Returns: An instance of `DiagnosticCollector` conforming to `Sendable`.
-public func preparedDiagnosticsCollector(url: URL) -> any DiagnosticCollector & Sendable {
-    _YamlFileDiagnosticsCollector(url: url)
-}

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

@@ -42,21 +42,7 @@ extension _GenerateOptions {
                 featureFlags: resolvedFeatureFlags
             )
         }
-        let innerDiagnostics: any DiagnosticCollector & Sendable
-        let finalizeDiagnostics: () throws -> Void
-        if let diagnosticsOutputPath {
-            let _diagnostics = preparedDiagnosticsCollector(url: diagnosticsOutputPath)
-            if let yamlCollector = _diagnostics as? _YamlFileDiagnosticsCollector {
-                finalizeDiagnostics = { try yamlCollector.finalize() }
-            } else {
-                finalizeDiagnostics = {}
-            }
-            innerDiagnostics = _diagnostics
-        } else {
-            innerDiagnostics = StdErrPrintingDiagnosticCollector()
-            finalizeDiagnostics = {}
-        }
-        let diagnostics = ErrorThrowingDiagnosticCollector(upstream: innerDiagnostics)
+        let (diagnostics, finalizeDiagnostics) = preparedDiagnosticsCollector(outputPath: diagnosticsOutputPath)
         let doc = self.docPath
         print(
             """

Tests/OpenAPIGeneratorCoreTests/Test_DiagnosticsCollectorProvider.swift

@@ -0,0 +1,42 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftOpenAPIGenerator open source project
+//
+// Copyright (c) 2023 Apple Inc. and the SwiftOpenAPIGenerator project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+@testable import _OpenAPIGeneratorCore
+
+final class Test_DiagnosticsCollectorProvider: XCTestCase {
+
+    func testPreparedDiagnosticsCollectorWithOutputPath() throws {
+        let outputPath = URL(fileURLWithPath: "/path/to/diagnostics.yaml")
+        let (diagnostics, _) = preparedDiagnosticsCollector(outputPath: outputPath)
+        XCTAssertTrue(diagnostics is ErrorThrowingDiagnosticCollector)
+
+        if let errorThrowingCollector = diagnostics as? ErrorThrowingDiagnosticCollector {
+            XCTAssertTrue(errorThrowingCollector.upstream is _YamlFileDiagnosticsCollector)
+        } else {
+            XCTFail("Expected diagnostics to be `ErrorThrowingDiagnosticCollector`")
+        }
+    }
+
+    func testPreparedDiagnosticsCollectorWithoutOutputPath() throws {
+        let outputPath: URL? = nil
+        let (diagnostics, _) = preparedDiagnosticsCollector(outputPath: outputPath)
+        XCTAssertTrue(diagnostics is ErrorThrowingDiagnosticCollector)
+        if let errorThrowingCollector = diagnostics as? ErrorThrowingDiagnosticCollector {
+            XCTAssertTrue(errorThrowingCollector.upstream is StdErrPrintingDiagnosticCollector)
+        } else {
+            XCTFail("Expected diagnostics to be `ErrorThrowingDiagnosticCollector`")
+        }
+    }
+}