Allow unit test targets to import and link executable targets (#3316)

* Add a fast way to look up the package in which a particular target or product is defined.

* Allow SwiftTargetDescription, ClangTargetDescription, and ProductDescription to know the tools version of the package in which they are defined.  This allows compiler flags and other semantically significant changes to be conditionalized on the tools version.

In the cases where tools versions are synthesized, they get the tools version of the package defining the product or target for which they are being synthesized.  The fallback for anything that cannot be determined at all is always `.vNext`, which is the same as has been the case until now.

* Allow unit tests to import and link any main modules of executables that are implemented in Swift.  This uses a new Swift compiler flag to set the name of the entry point when emitting object code, and then uses linker flags to rename the main executable module's entry point back to `_main` again when actually linking the executable.

This is guarded by a tools version check, since packages written this way won't be testable on older toolchains.

Also, this is currently only done on Darwin and Linux.  A supplemental PR will generate a small stub containing code that implements `main` to call the per-module `<module>_main` function, which will be linked into the executable.

CHANGELOG.md

@@ -11,6 +11,8 @@ Swift v.Next
    * Improvements
 
    Adding a dependency requirement can now be done with the convenience initializer `.package(url: String, branch: String)`.
+
+   Test targets can now link against executable targets as if they were libraries, so that they can test any data strutures or algorithms in them.  All the code in the executable except for the main entry point itself is available to the unit test.  Separate executables are still linked, and can be tested as a subprocess in the same way as before.  This feature is available to tests defined in packages that have a tools version of `vNext` or newer. 
 
 
 

Fixtures/Miscellaneous/ExeTest/Package.swift

@@ -1,10 +1,10 @@
-// swift-tools-version:5.3
+// swift-tools-version: 999.0
 import PackageDescription
 
 let package = Package(
     name: "ExeTest",
     targets: [
-        .target(
+        .executableTarget(
             name: "Exe",
             dependencies: []
         ),

Fixtures/Miscellaneous/TestableExe/Package.swift

@@ -0,0 +1,25 @@
+// swift-tools-version: 999.0
+import PackageDescription
+
+let package = Package(
+    name: "TestableExe",
+    targets: [
+        .target(
+            name: "TestableExe1"
+        ),
+        .target(
+            name: "TestableExe2"
+        ),
+        .target(
+            name: "TestableExe3"
+        ),
+        .testTarget(
+            name: "TestableExeTests",
+            dependencies: [
+                "TestableExe1",
+                "TestableExe2",
+                "TestableExe3",
+            ]
+        ),
+    ]
+)

Fixtures/Miscellaneous/TestableExe/Sources/TestableExe1/main.swift

@@ -0,0 +1,5 @@
+public func GetGreeting1() -> String {
+    return "Hello, world"
+}
+
+print("\(GetGreeting1())!")

Fixtures/Miscellaneous/TestableExe/Sources/TestableExe2/main.swift

@@ -0,0 +1,5 @@
+public func GetGreeting2() -> String {
+    return "Hello, planet"
+}
+
+print("\(GetGreeting2())!")

Fixtures/Miscellaneous/TestableExe/Sources/TestableExe3/include/TestableExe3.h

@@ -0,0 +1 @@
+const char * GetGreeting3();

Fixtures/Miscellaneous/TestableExe/Sources/TestableExe3/main.c

@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include "include/TestableExe3.h"
+
+const char * GetGreeting3() {
+    return "Hello, universe";
+}
+
+int main() {
+    printf("%s!\n", GetGreeting3());
+}

Fixtures/Miscellaneous/TestableExe/Tests/TestableExeTests/TestableExeTests.swift

@@ -0,0 +1,73 @@
+import XCTest
+import TestableExe1
+import TestableExe2
+// import TestableExe3
+import class Foundation.Bundle
+
+final class TestableExeTests: XCTestCase {
+    func testExample() throws {
+        // This is an example of a functional test case.
+        // Use XCTAssert and related functions to verify your tests produce the correct
+        // results.
+
+        print(GetGreeting1())
+        XCTAssertEqual(GetGreeting1(), "Hello, world")
+        print(GetGreeting2())
+        XCTAssertEqual(GetGreeting2(), "Hello, planet")
+        // XCTAssertEqual(String(cString: GetGreeting3()), "Hello, universe")
+
+        // Some of the APIs that we use below are available in macOS 10.13 and above.
+        guard #available(macOS 10.13, *) else {
+            return
+        }
+
+        var execPath = productsDirectory.appendingPathComponent("TestableExe1")
+        var process = Process()
+        process.executableURL = execPath
+        var pipe = Pipe()
+        process.standardOutput = pipe
+        try process.run()
+        process.waitUntilExit()
+        var data = pipe.fileHandleForReading.readDataToEndOfFile()
+        var output = String(data: data, encoding: .utf8)
+        XCTAssertEqual(output, "Hello, world!\n")
+
+        execPath = productsDirectory.appendingPathComponent("TestableExe2")
+        process = Process()
+        process.executableURL = execPath
+        pipe = Pipe()
+        process.standardOutput = pipe
+        try process.run()
+        process.waitUntilExit()
+        data = pipe.fileHandleForReading.readDataToEndOfFile()
+        output = String(data: data, encoding: .utf8)
+        XCTAssertEqual(output, "Hello, planet!\n")
+
+        execPath = productsDirectory.appendingPathComponent("TestableExe3")
+        process = Process()
+        process.executableURL = execPath
+        pipe = Pipe()
+        process.standardOutput = pipe
+        try process.run()
+        process.waitUntilExit()
+        data = pipe.fileHandleForReading.readDataToEndOfFile()
+        output = String(data: data, encoding: .utf8)
+        XCTAssertEqual(output, "Hello, universe!\n")
+    }
+
+    /// Returns path to the built products directory.
+    var productsDirectory: URL {
+      #if os(macOS)
+        for bundle in Bundle.allBundles where bundle.bundlePath.hasSuffix(".xctest") {
+            return bundle.bundleURL.deletingLastPathComponent()
+        }
+        fatalError("couldn't find the products directory")
+      #else
+        return Bundle.main.bundleURL
+      #endif
+    }
+
+    static var allTests = [
+        ("testExample", testExample),
+    ]
+}

Sources/Build/BuildPlan.swift

@@ -121,6 +121,18 @@ extension BuildParameters {
         return args
     }
 
+    /// Computes the linker flags to use in order to rename a module-named main function to 'main' for the target platform, or nil if the linker doesn't support it for the platform.
+    fileprivate func linkerFlagsForRenamingMainFunction(of target: ResolvedTarget) -> [String]? {
+        var args: [String] = []
+        if self.triple.isDarwin() {
+            args = ["-alias", "_\(target.c99name)_main", "_main"]
+        }
+        else if self.triple.isLinux() {
+            args = ["--defsym", "main=\(target.c99name)_main"]
+        }
+        return args.flatMap { ["-Xlinker", $0] }
+    }
+
     /// Returns the scoped view of build settings for a given target.
     fileprivate func createScope(for target: ResolvedTarget) -> BuildSettings.Scope {
         return BuildSettings.Scope(target.underlyingTarget.buildSettings, environment: buildEnvironment)
@@ -195,6 +207,11 @@ public final class ClangTargetBuildDescription {
     public var clangTarget: ClangTarget {
         return target.underlyingTarget as! ClangTarget
     }
+
+    /// The tools version of the package that declared the target.  This can
+    /// can be used to conditionalize semantically significant changes in how
+    /// a target is built.
+    public let toolsVersion: ToolsVersion
 
     /// The build parameters.
     let buildParameters: BuildParameters
@@ -249,11 +266,12 @@ public final class ClangTargetBuildDescription {
     }
 
     /// Create a new target description with target and build parameters.
-    init(target: ResolvedTarget, buildParameters: BuildParameters, fileSystem: FileSystem = localFileSystem, diagnostics: DiagnosticsEngine) throws {
+    init(target: ResolvedTarget, toolsVersion: ToolsVersion, buildParameters: BuildParameters, fileSystem: FileSystem = localFileSystem, diagnostics: DiagnosticsEngine) throws {
         assert(target.underlyingTarget is ClangTarget, "underlying target type mismatch \(target)")
         self.fileSystem = fileSystem
         self.diagnostics = diagnostics
         self.target = target
+        self.toolsVersion = toolsVersion
         self.buildParameters = buildParameters
         self.tempsPath = buildParameters.buildPath.appending(component: target.c99name + ".build")
         self.derivedSources = Sources(paths: [], root: tempsPath.appending(component: "DerivedSources"))
@@ -472,6 +490,11 @@ public final class SwiftTargetBuildDescription {
     /// The target described by this target.
     public let target: ResolvedTarget
 
+    /// The tools version of the package that declared the target.  This can
+    /// can be used to conditionalize semantically significant changes in how
+    /// a target is built.
+    public let toolsVersion: ToolsVersion
+
     /// The build parameters.
     let buildParameters: BuildParameters
 
@@ -504,7 +527,9 @@ public final class SwiftTargetBuildDescription {
 
     /// The path to the swiftmodule file after compilation.
     var moduleOutputPath: AbsolutePath {
-        let dirPath = (target.type == .executable) ? tempsPath : buildParameters.buildPath
+        // If we're an executable and we're not allowing test targets to link against us, we hide the module.
+        let allowLinkingAgainstExecutables = (buildParameters.triple.isDarwin() || buildParameters.triple.isLinux()) && toolsVersion >= .vNext
+        let dirPath = (target.type == .executable && !allowLinkingAgainstExecutables) ? tempsPath : buildParameters.buildPath
         return dirPath.appending(component: target.c99name + ".swiftmodule")
     }
 
@@ -555,6 +580,7 @@ public final class SwiftTargetBuildDescription {
     /// Create a new target description with target and build parameters.
     init(
         target: ResolvedTarget,
+        toolsVersion: ToolsVersion,
         buildParameters: BuildParameters,
         pluginInvocationResults: [PluginInvocationResult] = [],
         prebuildCommandResults: [PrebuildCommandResult] = [],
@@ -564,6 +590,7 @@ public final class SwiftTargetBuildDescription {
     ) throws {
         assert(target.underlyingTarget is SwiftTarget, "underlying target type mismatch \(target)")
         self.target = target
+        self.toolsVersion = toolsVersion
         self.buildParameters = buildParameters
         // Unless mentioned explicitly, use the target type to determine if this is a test target.
         self.isTestTarget = isTestTarget ?? (target.type == .test)
@@ -677,6 +704,24 @@ public final class SwiftTargetBuildDescription {
         args += buildParameters.sanitizers.compileSwiftFlags()
         args += ["-parseable-output"]
 
+        // If we're compiling the main module of an executable other than the one that
+        // implements a test suite, and if the package tools version indicates that we
+        // should, we rename the `_main` entry point to `_<modulename>_main`.
+        //
+        // This will allow tests to link against the module without any conflicts. And
+        // when we link the executable, we will ask the linker to rename the entry point
+        // symbol to just `_main` again (or if the linker doesn't support it, we'll
+        // generate a source containing a redirect).
+        if target.type == .executable && !isTestTarget && toolsVersion >= .vNext {
+            // We only do this if the linker supports it, as indicated by whether we
+            // can construct the linker flags. In the future we will use a generated
+            // code stub for the cases in which the linker doesn't support it, so that
+            // we can rename the symbol unconditionally.
+            if buildParameters.linkerFlagsForRenamingMainFunction(of: target) != nil {
+                args += ["-Xfrontend", "-entry-point-function-name", "-Xfrontend", "\(target.c99name)_main"]
+            }
+        }
+
         // Only add the build path to the framework search path if there are binary frameworks to link against.
         if !libraryBinaryPaths.isEmpty {
             args += ["-F", buildParameters.buildPath.pathString]
@@ -1018,6 +1063,11 @@ public final class ProductBuildDescription {
     /// The reference to the product.
     public let product: ResolvedProduct
 
+    /// The tools version of the package that declared the product.  This can
+    /// can be used to conditionalize semantically significant changes in how
+    /// a target is built.
+    public let toolsVersion: ToolsVersion
+
     /// The build parameters.
     let buildParameters: BuildParameters
 
@@ -1029,7 +1079,7 @@ public final class ProductBuildDescription {
         return buildParameters.binaryPath(for: product)
     }
 
-    /// The objects in this product.
+    /// All object files to link into this product.
     ///
     // Computed during build planning.
     public fileprivate(set) var objects = SortedArray<AbsolutePath>()
@@ -1067,9 +1117,10 @@ public final class ProductBuildDescription {
     let diagnostics: DiagnosticsEngine
 
     /// Create a build description for a product.
-    init(product: ResolvedProduct, buildParameters: BuildParameters, fs: FileSystem, diagnostics: DiagnosticsEngine) {
+    init(product: ResolvedProduct, toolsVersion: ToolsVersion, buildParameters: BuildParameters, fs: FileSystem, diagnostics: DiagnosticsEngine) {
         assert(product.type != .library(.automatic), "Automatic type libraries should not be described.")
         self.product = product
+        self.toolsVersion = toolsVersion
         self.buildParameters = buildParameters
         self.fs = fs
         self.diagnostics = diagnostics
@@ -1148,6 +1199,20 @@ public final class ProductBuildDescription {
                 }
             }
             args += ["-emit-executable"]
+
+            // If we're linking an executable whose main module is implemented in Swift,
+            // we rename the `_<modulename>_main` entry point symbol to `_main` again.
+            // This is because executable modules implemented in Swift are compiled with
+            // a main symbol named that way to allow tests to link against it without
+            // conflicts. If we're using a linker that doesn't support symbol renaming,
+            // we will instead have generated a source file containing the redirect.
+            // Support for linking tests againsts executables is conditional on the tools
+            // version of the package that defines the executable product.
+            if product.executableModule.underlyingTarget is SwiftTarget, toolsVersion >= .vNext {
+                if let flags = buildParameters.linkerFlagsForRenamingMainFunction(of: product.executableModule) {
+                    args += flags
+                }
+            }
         case .plugin:
             throw InternalError("unexpectedly asked to generate linker arguments for a plugin product")
         }
@@ -1327,9 +1392,11 @@ public class BuildPlan {
             // if test manifest exists, prefer that over test detection,
             // this is designed as an escape hatch when test discovery is not appropriate
             // and for backwards compatibility for projects that have existing test manifests (LinuxMain.swift)
+            let toolsVersion = graph.package(for: testProduct)?.manifest.toolsVersion ?? .vNext
             if let testManifestTarget = testProduct.testManifestTarget, !generate {
                 let desc = try SwiftTargetBuildDescription(
                     target: testManifestTarget,
+                    toolsVersion: toolsVersion,
                     buildParameters: buildParameters,
                     isTestTarget: true
                 )
@@ -1361,6 +1428,7 @@ public class BuildPlan {
 
                 let target = try SwiftTargetBuildDescription(
                     target: testManifestTarget,
+                    toolsVersion: toolsVersion,
                     buildParameters: buildParameters,
                     isTestTarget: true,
                     testDiscoveryTarget: true
@@ -1403,18 +1471,24 @@ public class BuildPlan {
                     }
                 }
             }
+
+            // Determine the appropriate tools version to use for the target.
+            // This can affect what flags to pass and other semantics.
+            let toolsVersion = graph.package(for: target)?.manifest.toolsVersion ?? .vNext
 
             switch target.underlyingTarget {
             case is SwiftTarget:
                 targetMap[target] = try .swift(SwiftTargetBuildDescription(
                     target: target,
+                    toolsVersion: toolsVersion,
                     buildParameters: buildParameters,
                     pluginInvocationResults: pluginInvocationResults[target] ?? [],
                     prebuildCommandResults: prebuildCommandResults[target] ?? [],
                     fs: fileSystem))
             case is ClangTarget:
                 targetMap[target] = try .clang(ClangTargetBuildDescription(
                     target: target,
+                    toolsVersion: toolsVersion,
                     buildParameters: buildParameters,
                     fileSystem: fileSystem,
                     diagnostics: diagnostics))
@@ -1448,8 +1522,14 @@ public class BuildPlan {
         // Create product description for each product we have in the package graph except
         // for automatic libraries and plugins, because they don't produce any output.
         for product in graph.allProducts where product.type != .library(.automatic) && product.type != .plugin {
+
+            // Determine the appropriate tools version to use for the product.
+            // This can affect what flags to pass and other semantics.
+            let toolsVersion = graph.package(for: product)?.manifest.toolsVersion ?? .vNext
             productMap[product] = ProductBuildDescription(
-                product: product, buildParameters: buildParameters,
+                product: product,
+                toolsVersion: toolsVersion,
+                buildParameters: buildParameters,
                 fs: fileSystem,
                 diagnostics: diagnostics
             )
@@ -1635,9 +1715,21 @@ public class BuildPlan {
             switch dependency {
             case .target(let target, _):
                 switch target.type {
-                // Include executable and tests only if they're top level contents
-                // of the product. Otherwise they are just build time dependency.
-                case .executable, .test:
+                // Executable target have historically only been included if they are directly in the product's
+                // target list.  Otherwise they have always been just build-time dependencies.
+                // In tool version .vNext or greater, we also include executable modules implemented in Swift in
+                // any test products... this is to allow testing of executables.  Note that they are also still
+                // built as separate products that the test can invoke as subprocesses.
+                case .executable:
+                    if product.targets.contains(target) {
+                        staticTargets.append(target)
+                    } else if product.type == .test && target.underlyingTarget is SwiftTarget {
+                        if let toolsVersion = graph.package(for: product)?.manifest.toolsVersion, toolsVersion >= .vNext {
+                            staticTargets.append(target)
+                        }
+                    }
+                // Test targets should be included only if they are directly in the product's target list.
+                case .test:
                     if product.targets.contains(target) {
                         staticTargets.append(target)
                     }