Isolate ModuleCache for SwiftPM tests

To workaround the ModuleCache issues that we've been seeing on Swift CI
<rdar://problem/51596389>

Author: aciidgh

Sources/Build/BuildPlan.swift

@@ -26,22 +26,14 @@ public struct BuildParameters {
         case auto
     }
 
-    // FIXME: Error handling.
-    //
-    /// Path to the module cache directory to use for SwiftPM's own tests.
-    public static let swiftpmTestCache = resolveSymlinks(try! determineTempDirectory()).appending(component: "org.swift.swiftpm.tests-3")
-
     /// Returns the directory to be used for module cache.
     fileprivate var moduleCache: AbsolutePath {
-        let base: AbsolutePath
         // FIXME: We use this hack to let swiftpm's functional test use shared
         // cache so it doesn't become painfully slow.
-        if Process.env["IS_SWIFTPM_TEST"] != nil {
-            base = BuildParameters.swiftpmTestCache
-        } else {
-            base = buildPath
+        if let path = Process.env["SWIFTPM_TESTS_MODULECACHE"] {
+            return AbsolutePath(path)
         }
-        return base.appending(component: "ModuleCache")
+        return buildPath.appending(component: "ModuleCache")
     }
 
     /// The path to the data directory.

Sources/Commands/SwiftTool.swift

@@ -675,7 +675,6 @@ public class SwiftTool<Options: ToolOptions> {
             let allowedDirectories = [
                 tempDir,
                 buildPath,
-                BuildParameters.swiftpmTestCache
             ].map(resolveSymlinks)
             args += ["sandbox-exec", "-p", sandboxProfile(allowedDirectories: allowedDirectories)]
         }
@@ -842,7 +841,7 @@ private func findPackageRoot() -> AbsolutePath? {
 /// Returns the build path from the environment, if present.
 private func getEnvBuildPath(workingDir: AbsolutePath) -> AbsolutePath? {
     // Don't rely on build path from env for SwiftPM's own tests.
-    guard Process.env["IS_SWIFTPM_TEST"] == nil else { return nil }
+    guard Process.env["SWIFTPM_TESTS_MODULECACHE"] == nil else { return nil }
     guard let env = Process.env["SWIFTPM_BUILD_DIR"] else { return nil }
     return AbsolutePath(env, relativeTo: workingDir)
 }

Sources/PackageLoading/ManifestLoader.swift

@@ -384,13 +384,21 @@ public final class ManifestLoader: ManifestLoaderProtocol {
             let runtimePath = self.runtimePath(for: manifestVersion).pathString
             let interpreterFlags = self.interpreterFlags(for: manifestVersion)
 
+            // FIXME: Workaround for the module cache bug that's been haunting Swift CI
+            // <rdar://problem/48443680>
+            let moduleCachePath = Process.env["SWIFTPM_TESTS_MODULECACHE"]
+
             var cmd = [String]()
           #if os(macOS)
             // If enabled, use sandbox-exec on macOS. This provides some safety against
             // arbitrary code execution when parsing manifest files. We only allow
             // the permissions which are absolutely necessary for manifest parsing.
             if isManifestSandboxEnabled {
-                cmd += ["sandbox-exec", "-p", sandboxProfile(cacheDir)]
+                let cacheDirs = [
+                    cacheDir,
+                    moduleCachePath.map{ AbsolutePath($0) }
+                ].compactMap{$0}
+                cmd += ["sandbox-exec", "-p", sandboxProfile(cacheDirs)]
             }
           #endif
             cmd += [resources.swiftCompiler.pathString]
@@ -399,6 +407,9 @@ public final class ManifestLoader: ManifestLoaderProtocol {
             cmd += verbosity.ccArgs
             cmd += ["-L", runtimePath, "-lPackageDescription"]
             cmd += interpreterFlags
+            if let moduleCachePath = moduleCachePath {
+                cmd += ["-module-cache-path", moduleCachePath]
+            }
 
             // Add the arguments for emitting serialized diagnostics, if requested.
             if serializedDiagnostics, cacheDir != nil {
@@ -542,7 +553,7 @@ public final class ManifestLoader: ManifestLoaderProtocol {
 }
 
 /// Returns the sandbox profile to be used when parsing manifest on macOS.
-private func sandboxProfile(_ cacheDir: AbsolutePath? = nil) -> String {
+private func sandboxProfile(_ cacheDirs: [AbsolutePath] = []) -> String {
     let stream = BufferedOutputByteStream()
     stream <<< "(version 1)" <<< "\n"
     // Deny everything by default.
@@ -559,7 +570,7 @@ private func sandboxProfile(_ cacheDir: AbsolutePath? = nil) -> String {
     for directory in Platform.darwinCacheDirectories() {
         stream <<< "    (regex #\"^\(directory.pathString)/org\\.llvm\\.clang.*\")" <<< "\n"
     }
-    if let cacheDir = cacheDir {
+    for cacheDir in cacheDirs {
         stream <<< "    (subpath \"\(cacheDir.pathString)\")" <<< "\n"
     }
     stream <<< ")" <<< "\n"

Sources/TestSupport/SwiftPMProduct.swift

@@ -115,7 +115,7 @@ public enum SwiftPMProduct {
       #endif
         // FIXME: We use this private environment variable hack to be able to
         // create special conditions in swift-build for swiftpm tests.
-        environment["IS_SWIFTPM_TEST"] = "1"
+        environment["SWIFTPM_TESTS_MODULECACHE"] = self.path.parentDirectory.pathString
         environment["SDKROOT"] = nil
 
         var completeArgs = [path.pathString]