Fix MacCatalyst minimum deployment fallback (#5620)

If a package does not specify a custom deployment target for MacCatalyst, we are supposed to fallback to the iOS one, if declared. This currently does not work for test targets, because we prefer the minimum XCTest deployment target, even if it may be lower than the customized iOS one.

Author: neonichu

Sources/PackageGraph/PackageGraph+Loading.swift

@@ -617,14 +617,19 @@ private func computePlatforms(
     for platformName in remainingPlatforms.sorted() {
         let platform = platformRegistry.platformByName[platformName]!
 
-        let oldestSupportedVersion: PlatformVersion
+        let minimumSupportedVersion: PlatformVersion
         if usingXCTest, let xcTestMinimumDeploymentTarget = xcTestMinimumDeploymentTargets[platform] {
-            oldestSupportedVersion = xcTestMinimumDeploymentTarget
-        } else if platform == .macCatalyst, let iOS = derivedPlatforms.first(where: { $0.platform == .iOS }) {
+            minimumSupportedVersion = xcTestMinimumDeploymentTarget
+        } else {
+            minimumSupportedVersion = platform.oldestSupportedVersion
+        }
+
+        let oldestSupportedVersion: PlatformVersion
+        if platform == .macCatalyst, let iOS = derivedPlatforms.first(where: { $0.platform == .iOS }) {
             // If there was no deployment target specified for Mac Catalyst, fall back to the iOS deployment target.
-            oldestSupportedVersion = max(platform.oldestSupportedVersion, iOS.version)
+            oldestSupportedVersion = max(minimumSupportedVersion, iOS.version)
         } else {
-            oldestSupportedVersion = platform.oldestSupportedVersion
+            oldestSupportedVersion = minimumSupportedVersion
         }
 
         let supportedPlatform = SupportedPlatform(

Tests/PackageGraphTests/PackageGraphTests.swift

@@ -1926,6 +1926,13 @@ class PackageGraphTests: XCTestCase {
             "openbsd": "0.0"
         ]
 
+        let customXCTestMinimumDeploymentTargets = [
+            PackageModel.Platform.macOS: PlatformVersion("10.15"),
+            PackageModel.Platform.iOS: PlatformVersion("11.0"),
+            PackageModel.Platform.tvOS: PlatformVersion("11.0"),
+            PackageModel.Platform.watchOS: PlatformVersion("4.0"),
+        ]
+
         do {
             // One platform with an override.
             let manifest = Manifest.createRootManifest(
@@ -1947,13 +1954,6 @@ class PackageGraphTests: XCTestCase {
                 ]
             )
 
-            let customXCTestMinimumDeploymentTargets = [
-                PackageModel.Platform.macOS: PlatformVersion("10.15"),
-                PackageModel.Platform.iOS: PlatformVersion("11.0"),
-                PackageModel.Platform.tvOS: PlatformVersion("11.0"),
-                PackageModel.Platform.watchOS: PlatformVersion("4.0"),
-            ]
-
             let observability = ObservabilitySystem.makeForTesting()
             let graph = try loadPackageGraph(
                 fileSystem: fs,
@@ -2093,6 +2093,59 @@ class PackageGraphTests: XCTestCase {
                 }
             }
         }
+
+        do {
+            // Test MacCatalyst overriding behavior.
+            let manifest = Manifest.createRootManifest(
+                name: "pkg",
+                platforms: [
+                    PlatformDescription(name: "ios", version: "15.0"),
+                ],
+                products: [
+                    try ProductDescription(name: "cbar", type: .library(.automatic), targets: ["cbar"]),
+                ],
+                targets: [
+                    try TargetDescription(name: "cbar"),
+                    try TargetDescription(name: "test", type: .test)
+                ]
+            )
+
+            let observability = ObservabilitySystem.makeForTesting()
+            let graph = try loadPackageGraph(
+                fileSystem: fs,
+                manifests: [manifest],
+                customXCTestMinimumDeploymentTargets: customXCTestMinimumDeploymentTargets,
+                observabilityScope: observability.topScope
+            )
+            XCTAssertNoDiagnostics(observability.diagnostics)
+
+            PackageGraphTester(graph) { result in
+                let expectedDeclaredPlatforms = [
+                    "ios": "15.0",
+                ]
+
+                var expectedDerivedPlatforms = defaultDerivedPlatforms.merging(expectedDeclaredPlatforms, uniquingKeysWith: { lhs, rhs in rhs })
+                var expectedDerivedPlatformsForTests = defaultDerivedPlatforms.merging(customXCTestMinimumDeploymentTargets.map { ($0.name, $1.versionString) }, uniquingKeysWith: { lhs, rhs in rhs })
+                expectedDerivedPlatformsForTests["ios"] = expectedDeclaredPlatforms["ios"]
+
+                // Gets derived to be the same as the declared iOS deployment target.
+                expectedDerivedPlatforms["maccatalyst"] = expectedDeclaredPlatforms["ios"]
+                expectedDerivedPlatformsForTests["maccatalyst"] = expectedDeclaredPlatforms["ios"]
+
+                result.checkTarget("test") { target in
+                    target.checkDeclaredPlatforms(expectedDeclaredPlatforms)
+                    target.checkDerivedPlatforms(expectedDerivedPlatformsForTests)
+                }
+                result.checkTarget("cbar") { target in
+                    target.checkDeclaredPlatforms(expectedDeclaredPlatforms)
+                    target.checkDerivedPlatforms(expectedDerivedPlatforms)
+                }
+                result.checkProduct("cbar") { product in
+                    product.checkDeclaredPlatforms(expectedDeclaredPlatforms)
+                    product.checkDerivedPlatforms(expectedDerivedPlatforms)
+                }
+            }
+        }
     }
 
     func testCustomPlatforms() throws {