Add ToolsVersion flag for experiementalMultiLang

Author: dschaefer2

Sources/PackageLoading/TargetSourcesBuilder.swift

@@ -220,6 +220,12 @@ public struct TargetSourcesBuilder {
         try diagnoseInfoPlistConflicts(in: resources)
         diagnoseInvalidResource(in: target.resources)
 
+        // It's an error to contain mixed language source files
+        // Unless experimental flag is turned on
+        if sources.containsMixedLanguage && !toolsVersion.experimentalMultiLang {
+            throw Module.Error.mixedSources(targetPath)
+        }
+
         return (sources, resources, headers, ignored, others)
     }
 

Sources/PackageLoading/ToolsVersionParser.swift

@@ -358,12 +358,12 @@ public struct ToolsVersionParser {
         /// - Note: For a misspelt Swift tools version specification `"// swift-too1s-version:5.3"`, the first `"1"` is considered as the first character of the version specifier, and so `"1s-version:5.3"` is taken as the version specifier.
         let versionSpecifier = specificationSnippetFromLabelToLineTerminator[startIndexOfVersionSpecifier..<indexOfVersionSpecifierTerminator]
 
-        /// Look for experimental features. They are space separated values contained in parenthases right after the ";", e.g. "// swift-tools-version: 6.3;(experimentalCGen)"
+        /// Look for experimental features. They are comma separated values contained in parenthases right after the ";", e.g. "// swift-tools-version: 6.4;(experimentalCGen,experimentalMultiLang)"
         var experimentalFeatures: Set<ToolsVersion.ExperimentalFeature> = []
         if indexOfVersionSpecifierTerminator < specificationWithIgnoredTrailingContents.endIndex, specificationWithIgnoredTrailingContents[indexOfVersionSpecifierTerminator...].hasPrefix(";(") {
             let startOfExperimentalFeatures = specificationWithIgnoredTrailingContents.index(indexOfVersionSpecifierTerminator, offsetBy: 2)
             if let endOfExperimentalFeatures = specificationWithIgnoredTrailingContents[startOfExperimentalFeatures...].firstIndex(where: { $0 == ")" }) {
-                for featureString in specificationWithIgnoredTrailingContents[startOfExperimentalFeatures..<endOfExperimentalFeatures].split(separator: " ", omittingEmptySubsequences: true) {
+                for featureString in specificationWithIgnoredTrailingContents[startOfExperimentalFeatures..<endOfExperimentalFeatures].split(separator: ",", omittingEmptySubsequences: true) {
                     if let feature = ToolsVersion.ExperimentalFeature(rawValue: String(featureString)) {
                         experimentalFeatures.insert(feature)
                     }

Sources/PackageModel/ToolsVersion.swift

@@ -90,6 +90,7 @@ public struct ToolsVersion: Equatable, Hashable, Codable, Sendable {
     /// Experimental features
     public enum ExperimentalFeature: String, Sendable, Codable {
         case experimentalCGen
+        case experimentalMultiLang
     }
     public let experimentalFeatures: Set<ExperimentalFeature>?
 
@@ -104,6 +105,10 @@ public struct ToolsVersion: Equatable, Hashable, Codable, Sendable {
         self >= .v6_3 && experimentalFeatures?.contains(.experimentalCGen) == true
     }
 
+    public var experimentalMultiLang: Bool {
+        self >= .v6_4 && experimentalFeatures?.contains(.experimentalMultiLang) == true
+    }
+
     /// Create an instance of tools version from a given string.
     public init?(string: String, experimentalFeatures: Set<ExperimentalFeature>) {
         guard let match = ToolsVersion.toolsVersionRegex.firstMatch(

Tests/PackageLoadingTests/PackageBuilderTests.swift

@@ -78,6 +78,7 @@ struct PackageBuilderTests {
         let manifest = Manifest.createRootManifest(
             displayName: "pkg",
             path: .root,
+            toolsVersion: try #require(ToolsVersion(string: "6.4.0", experimentalFeatures: [.experimentalMultiLang])),
             targets: [
                 try TargetDescription(name: "foo"),
             ]
@@ -97,6 +98,27 @@ struct PackageBuilderTests {
         }
     }
 
+    @Test
+    func testMixedSourcesDisabled() throws {
+        let foo: AbsolutePath = "/Sources/foo"
+
+        let fs = InMemoryFileSystem(emptyFiles:
+            foo.appending(components: "Foo.swift").pathString,
+            foo.appending(components: "CFoo.c").pathString
+        )
+
+        let manifest = Manifest.createRootManifest(
+            displayName: "pkg",
+            path: .root,
+            targets: [
+                try TargetDescription(name: "foo"),
+            ]
+        )
+        try PackageBuilderTester(manifest, in: fs) { package, diagnostics in
+            diagnostics.check(diagnostic: "target at '\(foo)' contains mixed language source files; feature not supported", severity: .error)
+        }
+    }
+
     @Test
     func testBrokenSymlink() throws {
         try testWithTemporaryDirectory { path in

Tests/PackageLoadingTests/ToolsVersionParserTests.swift

@@ -838,13 +838,24 @@ final class ToolsVersionParserTests: XCTestCase {
         XCTAssertEqual(version.description, "5.0.0")
     }
 
-    func testExperimentalFlag() throws {
-        let version = try ToolsVersionParser.parse(utf8String: "// swift-tools-version: 6.3;(experimentalCGen)")
-        XCTAssertEqual(version, ToolsVersion(version: .init(6, 3, 0)))
-        XCTAssertTrue(version.experimentalFeatures?.contains(.experimentalCGen) == true)
-
-        let version2 = try ToolsVersionParser.parse(utf8String: "// swift-tools-version: 6.3;(experimentalIgnored)")
-        XCTAssertEqual(version2, ToolsVersion(version: .init(6, 3, 0)))
-        XCTAssertNil(version2.experimentalFeatures)
+    func testExperimentalFlags() throws {
+        let cgen = try ToolsVersionParser.parse(utf8String: "// swift-tools-version: 6.3;(experimentalCGen)")
+        XCTAssertEqual(cgen, ToolsVersion(version: .init(6, 3, 0)))
+        XCTAssertTrue(cgen.experimentalFeatures?.contains(.experimentalCGen) == true)
+        XCTAssertTrue(cgen.experimentalFeatures?.contains(.experimentalMultiLang) ?? false == false)
+
+        let multiLang = try ToolsVersionParser.parse(utf8String: "// swift-tools-version: 6.4;(experimentalMultiLang)")
+        XCTAssertEqual(multiLang, ToolsVersion(version: .init(6, 4, 0)))
+        XCTAssertTrue(multiLang.experimentalFeatures?.contains(.experimentalMultiLang) == true)
+        XCTAssertTrue(multiLang.experimentalFeatures?.contains(.experimentalCGen) ?? false == false)
+
+        let both = try ToolsVersionParser.parse(utf8String: "// swift-tools-version: 6.4;(experimentalCGen,experimentalMultiLang)")
+        XCTAssertEqual(both, ToolsVersion(version: .init(6, 4, 0)))
+        XCTAssertTrue(both.experimentalFeatures?.contains(.experimentalMultiLang) == true)
+        XCTAssertTrue(both.experimentalFeatures?.contains(.experimentalCGen) == true)
+
+        let invalid = try ToolsVersionParser.parse(utf8String: "// swift-tools-version: 6.3;(experimentalIgnored)")
+        XCTAssertEqual(invalid, ToolsVersion(version: .init(6, 3, 0)))
+        XCTAssertNil(invalid.experimentalFeatures)
     }
 }

Tests/PackageModelTests/ToolsVersionTests.swift

@@ -9,7 +9,9 @@
 // See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
+
 import Foundation
+import PackageLoading
 import PackageModel
 import Testing
 

Tests/SwiftBuildSupportTests/PIFBuilderTests.swift

@@ -1039,6 +1039,7 @@ struct PIFBuilderTests {
                 Manifest.createRootManifest(
                     displayName: "Pkg",
                     path: "/Pkg",
+                    toolsVersion: try #require(ToolsVersion(string: "6.4.0", experimentalFeatures: [.experimentalMultiLang])),
                     targets: [
                         TargetDescription(name: "lib"),
                     ]