build: introduce SWIFTPM_BUILD_ONLY_TESTS support

This adds support for an environment variable to exclude all
dependencies from being built. We can externally pass in the appropriate
include and library search paths allowing us to control the build and
share the artifacts from the previous build reducing overall cost in CI.

Author: compnerd

Package.swift

@@ -15,7 +15,91 @@
 import class Foundation.ProcessInfo
 import PackageDescription
 
-// When building the toolchain on the CI for ELF platforms, remove the CI's
+func defined(_ variable: String) -> Bool {
+    ProcessInfo.processInfo.environment[variable] != nil
+}
+
+var buildOnlyTests: Bool {
+    defined("SWIFTPM_BUILD_ONLY_TESTS")
+}
+
+var useLocalDependencies: Bool {
+    defined("SWIFTCI_USE_LOCAL_DEPS")
+}
+
+var useLLBuildFramework: Bool {
+    defined("SWIFTPM_LLBUILD_FWK")
+}
+
+var useSwiftBuildFramework: Bool {
+    defined("SWIFTPM_SWBUILD_FRAMEWORK")
+}
+
+@MainActor
+func LLBuildFrameworkDependency<T>(enabled: [T] = [], disabled: [T] = []) -> [T] {
+    if useLLBuildFramework { return enabled }
+    return disabled
+}
+
+@MainActor
+func SwiftBuildFrameworkDependency<T>(enabled: [T] = [], disabled: [T] = []) -> [T] {
+    if useSwiftBuildFramework { return enabled }
+    return disabled
+}
+
+var dependencies: [Package.Dependency] {
+    if buildOnlyTests { return [] }
+
+    if useLocalDependencies {
+        return [
+            .package(path: "../swift-argument-parser"),
+            .package(path: "../swift-crypto"),
+            .package(path: "../swift-syntax"),
+            .package(path: "../swift-system"),
+            .package(path: "../swift-collections"),
+            .package(path: "../swift-certificates"),
+            .package(path: "../swift-toolchain-sqlite"),
+        ] + LLBuildFrameworkDependency(disabled: [
+            .package(name: "swift-llbuild", path: "../llbuild"),
+        ]) + SwiftBuildFrameworkDependency(enabled: [
+            .package(path: "../swift-build"),
+        ], disabled: [
+            .package(path: "../swift-tools-support-core"),
+            .package(path: "../swift-driver"),
+        ])
+    }
+
+    /// When not using local dependencies, the branch to use for llbuild and TSC
+    /// repositories.
+    let relatedDependenciesBranch = "main"
+
+    return [
+        // The 'swift-argument-parser' version declared here must match that
+        // used by 'swift-driver' and 'sourcekit-lsp'. Please coordinate
+        // dependency version changes here with those projects.
+        .package(url: "https://github.com/apple/swift-argument-parser.git", .upToNextMinor(from: "1.5.1")),
+        .package(url: "https://github.com/apple/swift-crypto.git", .upToNextMinor(from: "3.0.0")),
+        .package(url: "https://github.com/swiftlang/swift-syntax.git", branch: relatedDependenciesBranch),
+        .package(url: "https://github.com/apple/swift-system.git", from: "1.1.1"),
+        .package(url: "https://github.com/apple/swift-collections.git", "1.0.1" ..< "1.2.0"),
+        .package(url: "https://github.com/apple/swift-certificates.git", "1.0.1" ..< "1.6.0"),
+        .package(url: "https://github.com/swiftlang/swift-toolchain-sqlite.git", from: "1.0.0"),
+
+        // For use in previewing documentation
+        .package(url: "https://github.com/swiftlang/swift-docc-plugin", from: "1.1.0"),
+    ] + LLBuildFrameworkDependency(disabled: [
+        .package(url: "https://github.com/swiftlang/swift-llbuild.git", branch: relatedDependenciesBranch),
+    ]) + SwiftBuildFrameworkDependency(enabled: [
+        .package(url: "https://github.com/swiftlang/swift-build.git", branch: relatedDependenciesBranch),
+    ], disabled: [
+        .package(url: "https://github.com/swiftlang/swift-tools-support-core.git", branch: relatedDependenciesBranch),
+        .package(url: "https://github.com/swiftlang/swift-driver.git", branch: relatedDependenciesBranch),
+    ])
+}
+
+
+// When building the toolchain on the CI for ELF platforms, remove the CI's !=
+// nil
 // stdlib absolute runpath and add ELF's $ORIGIN relative paths before installing.
 let swiftpmLinkSettings: [LinkerSetting]
 let packageLibraryLinkSettings: [LinkerSetting]
@@ -101,39 +185,14 @@ if ProcessInfo.processInfo.environment["SWIFTCI_INSTALL_RPATH_OS"] == "android"
  */
 let autoProducts = [swiftPMProduct, swiftPMDataModelProduct]
 
-let shoudUseSwiftBuildFramework = (ProcessInfo.processInfo.environment["SWIFTPM_SWBUILD_FRAMEWORK"] != nil)
-
-let swiftDriverDeps: [Target.Dependency]
-let swiftTSCBasicsDeps: [Target.Dependency]
-let swiftToolsCoreSupportAutoDeps: [Target.Dependency]
-let swiftTSCTestSupportDeps: [Target.Dependency]
-
-if shoudUseSwiftBuildFramework {
-    swiftDriverDeps = []
-    swiftTSCBasicsDeps = []
-    swiftToolsCoreSupportAutoDeps = []
-    swiftTSCTestSupportDeps = []
-} else {
-    swiftDriverDeps = [
-        .product(name: "SwiftDriver", package: "swift-driver")
-    ]
-    swiftTSCBasicsDeps = [
-        .product(name: "TSCBasic", package: "swift-tools-support-core"),
-    ]
-    swiftToolsCoreSupportAutoDeps = [
-        .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core")
-    ]
-    swiftTSCTestSupportDeps = [
-        .product(name: "TSCTestSupport", package: "swift-tools-support-core"),
-    ]
-}
 let package = Package(
     name: "SwiftPM",
     platforms: [
         .macOS(.v13),
         .iOS(.v17),
         .macCatalyst(.v17),
     ],
+    dependencies: dependencies,
     products:
     autoProducts.flatMap {
         (includeDynamicLibrary ? [
@@ -272,7 +331,9 @@ let package = Package(
                 .product(name: "DequeModule", package: "swift-collections"),
                 .product(name: "OrderedCollections", package: "swift-collections"),
                 .product(name: "SystemPackage", package: "swift-system"),
-            ] + swiftToolsCoreSupportAutoDeps,
+            ] + SwiftBuildFrameworkDependency(disabled: [
+                .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core")
+            ]),
             exclude: ["CMakeLists.txt", "Vendor/README.md"],
             swiftSettings: swift6CompatibleExperimentalFeatures + [
                 .enableExperimentalFeature("StrictConcurrency"),
@@ -323,7 +384,9 @@ let package = Package(
         .target(
             /** Shim for llbuild library */
             name: "SPMLLBuild",
-            dependencies: ["Basics"],
+            dependencies: ["Basics"] + LLBuildFrameworkDependency(disabled: [
+                .product(name: "llbuildSwift", package: "swift-llbuild"),
+            ]),
             exclude: ["CMakeLists.txt"],
             swiftSettings: commonExperimentalFeatures + [
                 .unsafeFlags(["-static"]),
@@ -335,7 +398,9 @@ let package = Package(
             name: "SwiftFixIt",
             dependencies: [
                 "Basics",
-            ] + swiftTSCBasicsDeps + swiftSyntaxDependencies(
+            ] + SwiftBuildFrameworkDependency(disabled: [
+                .product(name: "TSCBasic", package: "swift-tools-support-core"),
+            ]) + swiftSyntaxDependencies(
                 ["SwiftDiagnostics", "SwiftIDEUtils", "SwiftParser", "SwiftSyntax"]
             ),
             exclude: ["CMakeLists.txt"],
@@ -349,7 +414,9 @@ let package = Package(
             name: "BinarySymbols",
             dependencies: [
                 "Basics",
-            ] + swiftTSCBasicsDeps,
+            ] + SwiftBuildFrameworkDependency(disabled: [
+                .product(name: "TSCBasic", package: "swift-tools-support-core"),
+            ]),
             exclude: ["CMakeLists.txt"],
             swiftSettings: commonExperimentalFeatures + [
                 .unsafeFlags(["-static"]),
@@ -514,7 +581,9 @@ let package = Package(
                 "SPMLLBuild",
                 .product(name: "OrderedCollections", package: "swift-collections"),
                 "DriverSupport",
-            ] + swiftDriverDeps,
+            ] + SwiftBuildFrameworkDependency(disabled: [
+                .product(name: "SwiftDriver", package: "swift-driver")
+            ]),
             exclude: ["CMakeLists.txt"],
             swiftSettings: commonExperimentalFeatures + [
                 .unsafeFlags(["-static"]),
@@ -525,7 +594,9 @@ let package = Package(
             dependencies: [
                 "Basics",
                 "PackageModel",
-            ] + swiftDriverDeps,
+            ] + SwiftBuildFrameworkDependency(disabled: [
+                .product(name: "SwiftDriver", package: "swift-driver")
+            ]),
             exclude: ["CMakeLists.txt"],
             swiftSettings: commonExperimentalFeatures + [
                 .unsafeFlags(["-static"]),
@@ -549,7 +620,11 @@ let package = Package(
             dependencies: [
                 "SPMBuildCore",
                 "PackageGraph",
-            ],
+            ] + SwiftBuildFrameworkDependency(enabled: [
+                .product(name: "SwiftBuild", package: "swift-build"),
+                // This is here to statically link the build service in the same executable as SwiftPM
+                .product(name: "SWBBuildService", package: "swift-build"),
+            ]),
             exclude: ["CMakeLists.txt", "README.md"],
             swiftSettings: commonExperimentalFeatures
         ),
@@ -825,7 +900,9 @@ let package = Package(
                 "SourceControl",
                 .product(name: "OrderedCollections", package: "swift-collections"),
                 "Workspace",
-            ] + swiftTSCTestSupportDeps,
+            ] + SwiftBuildFrameworkDependency(disabled: [
+                .product(name: "TSCTestSupport", package: "swift-tools-support-core"),
+            ]),
             swiftSettings: [
                 .unsafeFlags(["-static"]),
             ]
@@ -1012,7 +1089,7 @@ package.targets.append(contentsOf: [
 
 // rdar://101868275 "error: cannot find 'XCTAssertEqual' in scope" can affect almost any functional test, so we flat out
 // disable them all until we know what is going on
-if ProcessInfo.processInfo.environment["SWIFTCI_DISABLE_SDK_DEPENDENT_TESTS"] == nil {
+if !defined("SWIFTCI_DISABLE_SDK_DEPENDENT_TESTS") {
     package.targets.append(contentsOf: [
         .testTarget(
             name: "FunctionalTests",
@@ -1060,109 +1137,17 @@ func swiftSyntaxDependencies(_ names: [String]) -> [Target.Dependency] {
   /// This means that the swift-syntax symbols don't need to be statically linked, which allows us to stay below the
   /// maximum number of exported symbols on Windows, in turn allowing us to build sourcekit-lsp using SwiftPM on Windows
   /// and run its tests.
-  let buildDynamicSwiftSyntaxLibrary = ProcessInfo.processInfo.environment["SWIFTSYNTAX_BUILD_DYNAMIC_LIBRARY"] != nil
+  let buildDynamicSwiftSyntaxLibrary = defined("SWIFTSYNTAX_BUILD_DYNAMIC_LIBRARY")
   if buildDynamicSwiftSyntaxLibrary {
     return [.product(name: "_SwiftSyntaxDynamic", package: "swift-syntax")]
   } else {
     return names.map { .product(name: $0, package: "swift-syntax") }
   }
 }
 
-// Add package dependency on llbuild when not bootstrapping.
-//
-// When bootstrapping SwiftPM, we can't use llbuild as a package dependency it
-// will provided by whatever build system (SwiftCI, bootstrap script) is driving
-// the build process. So, we only add these dependencies if SwiftPM is being
-// built directly using SwiftPM. It is a bit unfortunate that we've add the
-// package dependency like this but there is no other good way of expressing
-// this right now.
-
-/// When not using local dependencies, the branch to use for llbuild and TSC repositories.
-let relatedDependenciesBranch = "main"
-
-if ProcessInfo.processInfo.environment["SWIFTPM_LLBUILD_FWK"] == nil {
-    if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
-        package.dependencies += [
-            .package(url: "https://github.com/swiftlang/swift-llbuild.git", branch: relatedDependenciesBranch),
-        ]
-    } else {
-        // In Swift CI, use a local path to llbuild to interoperate with tools
-        // like `update-checkout`, which control the sources externally.
-        package.dependencies += [
-            .package(name: "swift-llbuild", path: "../llbuild"),
-        ]
-    }
-    package.targets.first(where: { $0.name == "SPMLLBuild" })!.dependencies += [
-        .product(name: "llbuildSwift", package: "swift-llbuild"),
-    ]
-}
-
-if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
-    package.dependencies += [
-        // The 'swift-argument-parser' version declared here must match that
-        // used by 'swift-driver' and 'sourcekit-lsp'. Please coordinate
-        // dependency version changes here with those projects.
-        .package(url: "https://github.com/apple/swift-argument-parser.git", .upToNextMinor(from: "1.5.1")),
-        .package(url: "https://github.com/apple/swift-crypto.git", .upToNextMinor(from: "3.0.0")),
-        .package(url: "https://github.com/swiftlang/swift-syntax.git", branch: relatedDependenciesBranch),
-        .package(url: "https://github.com/apple/swift-system.git", from: "1.1.1"),
-        .package(url: "https://github.com/apple/swift-collections.git", "1.0.1" ..< "1.2.0"),
-        .package(url: "https://github.com/apple/swift-certificates.git", "1.0.1" ..< "1.6.0"),
-        .package(url: "https://github.com/swiftlang/swift-toolchain-sqlite.git", from: "1.0.0"),
-        // For use in previewing documentation
-        .package(url: "https://github.com/swiftlang/swift-docc-plugin", from: "1.1.0"),
-    ]
-    if !swiftDriverDeps.isEmpty {
-        package.dependencies += [
-            .package(url: "https://github.com/swiftlang/swift-tools-support-core.git", branch: relatedDependenciesBranch),
-            .package(url: "https://github.com/swiftlang/swift-driver.git", branch: relatedDependenciesBranch),
-        ]
-    }
-} else {
-    package.dependencies += [
-        .package(path: "../swift-argument-parser"),
-        .package(path: "../swift-crypto"),
-        .package(path: "../swift-syntax"),
-        .package(path: "../swift-system"),
-        .package(path: "../swift-collections"),
-        .package(path: "../swift-certificates"),
-        .package(path: "../swift-toolchain-sqlite"),
-    ]
-    if !swiftDriverDeps.isEmpty {
-        package.dependencies += [
-            .package(path: "../swift-tools-support-core"),
-            .package(path: "../swift-driver"),
-        ]
-    }
-
-}
-
 /// If ENABLE_APPLE_PRODUCT_TYPES is set in the environment, then also define ENABLE_APPLE_PRODUCT_TYPES in each of the regular targets and test targets.
 if ProcessInfo.processInfo.environment["ENABLE_APPLE_PRODUCT_TYPES"] == "1" {
     for target in package.targets.filter({ $0.type == .regular || $0.type == .test }) {
         target.swiftSettings = (target.swiftSettings ?? []) + [ .define("ENABLE_APPLE_PRODUCT_TYPES") ]
     }
 }
-
-if !shoudUseSwiftBuildFramework {
-
-    let swiftbuildsupport: Target = package.targets.first(where: { $0.name == "SwiftBuildSupport" } )!
-    swiftbuildsupport.dependencies += [
-        .product(name: "SwiftBuild", package: "swift-build"),
-    ]
-
-    swiftbuildsupport.dependencies += [
-        // This is here to statically link the build service in the same executable as SwiftPM
-        .product(name: "SWBBuildService", package: "swift-build"),
-    ]
-
-    if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
-        package.dependencies += [
-            .package(url: "https://github.com/swiftlang/swift-build.git", branch: relatedDependenciesBranch),
-        ]
-    } else {
-        package.dependencies += [
-            .package(path: "../swift-build"),
-        ]
-    }
-}