Inherit current environment in build tool plugin custom tasks (#8880)

The native build system is extending the calling environment, such as
the PATH to the build tool invocations. Update the PIF Builder to do the
same. Enable testing of vendored binary build tools on macOS with the
swiftbuild build system.

Author: cmcgee1024

Sources/SwiftBuildSupport/PIFBuilder.swift

@@ -361,10 +361,16 @@ public final class PIFBuilder {
 
                                 let runtimeLibPaths = buildParameters.toolchain.runtimeLibraryPaths
 
+                                // Add paths to swift standard runtime libraries to the library path so that they can be found at runtime
                                 for libPath in runtimeLibPaths {
                                     newEnv.appendPath(key: .libraryPath, value: libPath.pathString)
                                 }
 
+                                // Append the system path at the end so that necessary system tool paths can be found
+                                if let pathValue = Environment.current[EnvironmentKey.path] {
+                                    newEnv.appendPath(key: .path, value: pathValue)
+                                }
+
                                 let writableDirectories: [AbsolutePath] = [pluginOutputDir]
 
                                 return PackagePIFBuilder.CustomBuildCommand(

Tests/FunctionalTests/PluginTests.swift

@@ -299,13 +299,20 @@ final class PluginTests {
 
     @Test(
         .enabled(if: (try? UserToolchain.default)!.supportsSwiftConcurrency(), "skipping because test environment doesn't support concurrency"),
-        .enabled(if: ProcessInfo.hostOperatingSystem == .macOS, "Test is only supported on macOS")
+        .enabled(if: ProcessInfo.hostOperatingSystem == .macOS, "Test is only supported on macOS"),
+        arguments: [BuildSystemProvider.Kind.native, .swiftbuild]
     )
-    func testUseOfVendedBinaryTool() async throws {
+    func testUseOfVendedBinaryTool(buildSystem: BuildSystemProvider.Kind) async throws {
         try await fixture(name: "Miscellaneous/Plugins") { fixturePath in
-            let (stdout, _) = try await executeSwiftBuild(fixturePath.appending("MyBinaryToolPlugin"), configuration: .debug, extraArgs: ["--product", "MyLocalTool"])
-            #expect(stdout.contains("Linking MyLocalTool"), "stdout:\n\(stdout)")
-            #expect(stdout.contains("Build of product 'MyLocalTool' complete!"), "stdout:\n\(stdout)")
+            let (stdout, _) = try await executeSwiftBuild(fixturePath.appending("MyBinaryToolPlugin"), configuration: .debug, extraArgs: ["--product", "MyLocalTool"], buildSystem: buildSystem)
+            if buildSystem == .native {
+                #expect(stdout.contains("Linking MyLocalTool"), "stdout:\n\(stdout)")
+                #expect(stdout.contains("Build of product 'MyLocalTool' complete!"), "stdout:\n(stdout)")
+            } else if buildSystem == .swiftbuild {
+                #expect(stdout.contains("Build complete!"), "stdout:\n\(stdout)")
+            } else {
+                Issue.record("Test has no expectation for \(buildSystem)")
+            }
         }
     }