Remove improper stdlib overrides on macOS when running plugins

Author: owenv

Sources/SPMBuildCore/Plugins/DefaultPluginScriptRunner.swift

@@ -466,12 +466,19 @@ public struct DefaultPluginScriptRunner: PluginScriptRunner, Cancellable {
 
         var env = Environment.current
 
+        // FIXME: This is largely a workaround for improper rpath setup on Linux. It should be
+        // removed once the Swift Build backend switches to use swiftc as the linker driver
+        // for targets with Swift sources. For now, limit the scope to non-macOS, so that
+        // plugins do not inadvertently use the toolchain stdlib instead of the OS stdlib
+        // when built with a Swift.org toolchain.
+        #if !os(macOS)
         // Update the environment for any runtime library paths that tools compiled
         // for the command plugin might require after they have been built.
         let runtimeLibPaths = self.toolchain.runtimeLibraryPaths
         for libPath in runtimeLibPaths {
             env.appendPath(key: .libraryPath, value: libPath.pathString)
         }
+        #endif
 
 #if os(Windows)
         let pluginLibraryPath = self.toolchain.swiftPMLibrariesLocation.pluginLibraryPath.pathString

Sources/SwiftBuildSupport/PIFBuilder.swift

@@ -367,12 +367,18 @@ public final class PIFBuilder {
                             buildCommands: result.buildCommands.map( { buildCommand in
                                 var newEnv: Environment = buildCommand.configuration.environment
 
+                                // FIXME: This is largely a workaround for improper rpath setup on Linux. It should be
+                                // removed once the Swift Build backend switches to use swiftc as the linker driver
+                                // for targets with Swift sources. For now, limit the scope to non-macOS, so that
+                                // plugins do not inadvertently use the toolchain stdlib instead of the OS stdlib
+                                // when built with a Swift.org toolchain.
+                                #if !os(macOS)
                                 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)
                                 }
+                                #endif
 
                                 // Append the system path at the end so that necessary system tool paths can be found
                                 if let pathValue = Environment.current[EnvironmentKey.path] {

Tests/CommandsTests/BuildCommandTests.swift

@@ -1415,8 +1415,11 @@ struct BuildCommandTestCases {
         let hostArch: String
         #if arch(arm64)
         hostArch = "arm64"
-        #else
+        #elseif arch(x86_64)
         hostArch = "x86_64"
+        #else
+        Issue.record("test is not supported on host arch")
+        return
         #endif
 
         // Unversioned triple - build should pass
@@ -1439,9 +1442,9 @@ struct BuildCommandTestCases {
                 )
         }
 
-        if buildSystem == .swiftbuild {
-            // Versioned triple with unsupported deployment target - build should fail
-            try await fixture(name: "Miscellaneous/RequiresOlderDeploymentTarget") { path in
+        // Versioned triple with unsupported deployment target - build should fail
+        try await withKnownIssue {
+            _ = try await fixture(name: "Miscellaneous/RequiresOlderDeploymentTarget") { path in
                 await #expect(throws: Error.self) {
                     try await executeSwiftBuild(
                         path,
@@ -1451,6 +1454,9 @@ struct BuildCommandTestCases {
                     )
                 }
             }
+        } when: {
+            // The native build system does not correctly pass the elevated deployment target
+            buildSystem != .swiftbuild
         }
     }
 }