[Macros] Add option to disable sandbox for exectuable plugins

`-disable-sandbox` to disable sandboxing when invoking subprocess from
from the frontend. Since `sandbox(7)` in macOS doesn't support nested
sandbox, complation used to fail when the parent build process is sandboxed.

include/swift/AST/PluginLoader.h

@@ -44,6 +44,7 @@ private:
 
   ASTContext &Ctx;
   DependencyTracker *DepTracker;
+  const bool disableSandbox;
 
   /// Map a module name to an plugin entry that provides the module.
   llvm::Optional<llvm::DenseMap<swift::Identifier, PluginEntry>> PluginMap;
@@ -52,8 +53,9 @@ private:
   llvm::DenseMap<swift::Identifier, PluginEntry> &getPluginMap();
 
 public:
-  PluginLoader(ASTContext &Ctx, DependencyTracker *DepTracker)
-      : Ctx(Ctx), DepTracker(DepTracker) {}
+  PluginLoader(ASTContext &Ctx, DependencyTracker *DepTracker,
+               bool disableSandbox = false)
+      : Ctx(Ctx), DepTracker(DepTracker), disableSandbox(disableSandbox) {}
 
   void setRegistry(PluginRegistry *newValue);
   PluginRegistry *getRegistry();

include/swift/AST/PluginRegistry.h

@@ -89,6 +89,9 @@ class LoadedExecutablePlugin {
   /// Callbacks to be called when the connection is restored.
   llvm::SmallVector<std::function<void(void)> *, 0> onReconnect;
 
+  /// Disable sandbox.
+  bool disableSandbox = false;
+
   /// Flag to dump plugin messagings.
   bool dumpMessaging = false;
 
@@ -99,9 +102,11 @@ class LoadedExecutablePlugin {
 
 public:
   LoadedExecutablePlugin(llvm::StringRef ExecutablePath,
-                         llvm::sys::TimePoint<> LastModificationTime)
+                         llvm::sys::TimePoint<> LastModificationTime,
+                         bool disableSandbox)
       : ExecutablePath(ExecutablePath),
-        LastModificationTime(LastModificationTime){};
+        LastModificationTime(LastModificationTime),
+        disableSandbox(disableSandbox){};
   ~LoadedExecutablePlugin();
 
   /// The last modification time of 'ExecutablePath' when this object is
@@ -181,7 +186,7 @@ public:
   /// Load an executable plugin specified by \p path .
   /// If \p path plugin is already loaded, this returns the cached object.
   llvm::Expected<LoadedExecutablePlugin *>
-  loadExecutablePlugin(llvm::StringRef path);
+  loadExecutablePlugin(llvm::StringRef path, bool disableSandbox);
 };
 
 } // namespace swift

include/swift/Frontend/FrontendOptions.h

@@ -415,6 +415,9 @@ public:
   /// are present at LTO time.
   bool HermeticSealAtLink = false;
 
+  /// Disable using the sandbox when executing subprocesses.
+  bool DisableSandbox = false;
+
   /// The different modes for validating TBD against the LLVM IR.
   enum class TBDValidationMode {
     Default,        ///< Do the default validation for the current platform.

include/swift/Option/Options.td

@@ -1948,4 +1948,9 @@ def load_plugin_executable:
            "of module names where the macro types are declared">,
   MetaVarName<"<path>#<module-names>">;
 
+def disable_sandbox:
+  Flag<["-"], "disable-sandbox">,
+  Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>,
+  HelpText<"Disable using the sandbox when executing subprocesses">;
+
 include "FrontendOptions.td"

lib/AST/PluginLoader.cpp

@@ -199,7 +199,8 @@ PluginLoader::loadExecutablePlugin(StringRef path) {
     DepTracker->addDependency(resolvedPath, /*IsSystem=*/false);
 
   // Load the plugin.
-  auto plugin = getRegistry()->loadExecutablePlugin(resolvedPath);
+  auto plugin =
+      getRegistry()->loadExecutablePlugin(resolvedPath, disableSandbox);
   if (!plugin) {
     resolvedPath.push_back(0);
     return llvm::handleErrors(

lib/AST/PluginRegistry.cpp

@@ -84,7 +84,7 @@ void *LoadedLibraryPlugin::getAddressOfSymbol(const char *symbolName) {
 }
 
 llvm::Expected<LoadedExecutablePlugin *>
-PluginRegistry::loadExecutablePlugin(StringRef path) {
+PluginRegistry::loadExecutablePlugin(StringRef path, bool disableSandbox) {
   llvm::sys::fs::file_status stat;
   if (auto err = llvm::sys::fs::status(path, stat)) {
     return llvm::errorCodeToError(err);
@@ -114,7 +114,7 @@ PluginRegistry::loadExecutablePlugin(StringRef path) {
   }
 
   auto plugin = std::make_unique<LoadedExecutablePlugin>(
-      path, stat.getLastModificationTime());
+      path, stat.getLastModificationTime(), disableSandbox);
 
   plugin->setDumpMessaging(dumpMessaging);
 
@@ -147,7 +147,9 @@ llvm::Error LoadedExecutablePlugin::spawnIfNeeded() {
 
   // Apply sandboxing.
   llvm::BumpPtrAllocator Allocator;
-  Sandbox::apply(command, Allocator);
+  if (!disableSandbox) {
+    Sandbox::apply(command, Allocator);
+  }
 
   // Launch.
   auto childInfo = ExecuteWithPipe(command[0], command);

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -395,6 +395,8 @@ bool ArgsToFrontendOptionsConverter::convert(
   Opts.UseCASBackend = Args.hasArg(OPT_cas_backend);
   Opts.EmitCASIDFile = Args.hasArg(OPT_cas_emit_casid_file);
 
+  Opts.DisableSandbox = Args.hasArg(OPT_disable_sandbox);
+
   return false;
 }
 

lib/Frontend/Frontend.cpp

@@ -812,8 +812,9 @@ bool CompilerInstance::setUpModuleLoaders() {
 
 bool CompilerInstance::setUpPluginLoader() {
   /// FIXME: If Invocation has 'PluginRegistry', we can set it. But should we?
-  auto loader =
-      std::make_unique<PluginLoader>(*Context, getDependencyTracker());
+  auto loader = std::make_unique<PluginLoader>(
+      *Context, getDependencyTracker(),
+      Invocation.getFrontendOptions().DisableSandbox);
   Context->setPluginLoader(std::move(loader));
   return false;
 }

test/Macros/macro_plugin_disable_sandbox.swift

@@ -0,0 +1,84 @@
+// REQUIRES: swift_swift_parser
+
+// sandbox-exec is only avaiable in Darwin
+// REQUIRES: OS=macosx
+
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/plugins)
+
+// RUN: split-file %s %t
+
+//== Build the plugins
+// RUN: %host-build-swift \
+// RUN:   -swift-version 5 \
+// RUN:   -emit-library \
+// RUN:   -o %t/plugins/%target-library-name(MacroDefinition) \
+// RUN:   -module-name=MacroDefinition \
+// RUN:   %t/MacroDefinition.swift \
+// RUN:   -g -no-toolchain-stdlib-rpath
+
+// RUN: %swift-build-cxx-plugin -o %t/mock-plugin %t/TestPlugin.c
+
+//== Nested sandbox. Expected to fail because sandbox-exec doesn't support nested sandboxing.
+// RUN: not sandbox-exec -p '(version 1)(allow default)' \
+// RUN:   %swift-target-frontend \
+// RUN:   -typecheck -verify \
+// RUN:   -swift-version 5 \
+// RUN:   -external-plugin-path %t/plugins#%swift-plugin-server \
+// RUN:   -load-plugin-executable %t/mock-plugin#TestPlugin \
+// RUN:   -module-name MyApp \
+// RUN:   %t/test.swift
+
+//== Avoid nested sandbox by -disable-sandbox
+// RUN: sandbox-exec -p '(version 1)(allow default)' \
+// RUN:   %swift-target-frontend \
+// RUN:   -disable-sandbox \
+// RUN:   -typecheck -verify \
+// RUN:   -swift-version 5 \
+// RUN:   -external-plugin-path %t/plugins#%swift-plugin-server \
+// RUN:   -load-plugin-executable %t/mock-plugin#TestPlugin \
+// RUN:   -module-name MyApp \
+// RUN:   %t/test.swift
+
+
+//--- MacroDefinition.swift
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+
+public struct StringifyMacro: ExpressionMacro {
+  public static func expansion(
+    of macro: some FreestandingMacroExpansionSyntax,
+    in context: some MacroExpansionContext
+  ) -> ExprSyntax {
+    guard let argument = macro.arguments.first?.expression else {
+      fatalError("boom")
+    }
+
+    return "(\(argument), \(StringLiteralExprSyntax(content: argument.description)))"
+  }
+}
+
+//--- TestPlugin.c
+#include "swift-c/MockPlugin/MockPlugin.h"
+
+MOCK_PLUGIN([
+  {
+    "expect": {"getCapability": {}},
+    "response": {"getCapabilityResult": {"capability": {"protocolVersion": 1}}}
+  },
+  {
+    "expect": {"expandFreestandingMacro": {
+                "macro": {"moduleName": "TestPlugin", "typeName": "TestStringMacro"}}},
+    "response": {"expandMacroResult": {"expandedSource": "\"test string\"", "diagnostics": []}}
+  }
+])
+
+//--- test.swift
+@freestanding(expression) macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroDefinition", type: "StringifyMacro")
+@freestanding(expression) macro testString() -> String = #externalMacro(module: "TestPlugin", type: "TestStringMacro")
+
+func test() {
+  let _: String = #stringify(42).1
+  let _: String = #testString
+}