Propagate sysroot to module loader subinvocation

include/swift/AST/ModuleLoader.h

@@ -209,6 +209,7 @@ struct InterfaceSubContextDelegate {
   virtual std::error_code runInSubContext(StringRef moduleName,
                                           StringRef interfacePath,
                                           StringRef sdkPath,
+                                          std::optional<StringRef> sysroot,
                                           StringRef outputPath,
                                           SourceLoc diagLoc,
     llvm::function_ref<std::error_code(ASTContext&, ModuleDecl*,
@@ -217,6 +218,7 @@ struct InterfaceSubContextDelegate {
   virtual std::error_code runInSubCompilerInstance(StringRef moduleName,
                                                    StringRef interfacePath,
                                                    StringRef sdkPath,
+                                                   std::optional<StringRef> sysroot,
                                                    StringRef outputPath,
                                                    SourceLoc diagLoc,
                                                    bool silenceErrors,

include/swift/Frontend/Frontend.h

@@ -222,6 +222,10 @@ class CompilerInvocation {
     SearchPathOpts.VFSOverlayFiles = Overlays;
   }
 
+  void setSysRoot(StringRef SysRoot) {
+    SearchPathOpts.setSysRoot(SysRoot);
+  }
+
   void setExtraClangArgs(const std::vector<std::string> &Args) {
     ClangImporterOpts.ExtraArgs = Args;
   }

include/swift/Frontend/ModuleInterfaceLoader.h

@@ -702,6 +702,7 @@ struct InterfaceSubContextDelegateImpl : InterfaceSubContextDelegate {
   std::error_code runInSubContext(StringRef moduleName,
                                   StringRef interfacePath,
                                   StringRef sdkPath,
+                                  std::optional<StringRef> sysroot,
                                   StringRef outputPath,
                                   SourceLoc diagLoc,
     llvm::function_ref<std::error_code(ASTContext&, ModuleDecl*,
@@ -710,6 +711,7 @@ struct InterfaceSubContextDelegateImpl : InterfaceSubContextDelegate {
   std::error_code runInSubCompilerInstance(StringRef moduleName,
                                            StringRef interfacePath,
                                            StringRef sdkPath,
+                                           std::optional<StringRef> sysroot,
                                            StringRef outputPath,
                                            SourceLoc diagLoc,
                                            bool silenceErrors,

lib/Frontend/ModuleInterfaceBuilder.cpp

@@ -356,7 +356,7 @@ bool ImplicitModuleInterfaceBuilder::buildSwiftModuleInternal(
     }
 
     SubError = (bool)subASTDelegate.runInSubCompilerInstance(
-        moduleName, interfacePath, sdkPath, OutPath, diagnosticLoc,
+        moduleName, interfacePath, sdkPath, sysroot, OutPath, diagnosticLoc,
         silenceInterfaceDiagnostics,
         [&](SubCompilerInstanceInfo &info) {
           auto EBuilder = ExplicitModuleInterfaceBuilder(

lib/Frontend/ModuleInterfaceBuilder.h

@@ -42,6 +42,7 @@ class ImplicitModuleInterfaceBuilder {
   InterfaceSubContextDelegate &subASTDelegate;
   const StringRef interfacePath;
   const StringRef sdkPath;
+  const std::optional<StringRef> sysroot;
   const StringRef moduleName;
   const StringRef moduleCachePath;
   const StringRef prebuiltCachePath;
@@ -87,15 +88,17 @@ class ImplicitModuleInterfaceBuilder {
       SourceManager &sourceMgr, DiagnosticEngine *diags,
       InterfaceSubContextDelegate &subASTDelegate,
       StringRef interfacePath, StringRef sdkPath,
-      StringRef moduleName, StringRef moduleCachePath,
-      StringRef backupInterfaceDir, StringRef prebuiltCachePath,
-      StringRef ABIDescriptorPath, bool disableInterfaceFileLock = false,
+      std::optional<StringRef> sysroot, StringRef moduleName,
+      StringRef moduleCachePath, StringRef backupInterfaceDir,
+      StringRef prebuiltCachePath, StringRef ABIDescriptorPath,
+      bool disableInterfaceFileLock = false,
       bool silenceInterfaceDiagnostics = false,
       SourceLoc diagnosticLoc = SourceLoc(),
       DependencyTracker *tracker = nullptr)
       : sourceMgr(sourceMgr), diags(diags), subASTDelegate(subASTDelegate),
-        interfacePath(interfacePath), sdkPath(sdkPath), moduleName(moduleName),
-        moduleCachePath(moduleCachePath), prebuiltCachePath(prebuiltCachePath),
+        interfacePath(interfacePath), sdkPath(sdkPath), sysroot(sysroot),
+        moduleName(moduleName), moduleCachePath(moduleCachePath),
+        prebuiltCachePath(prebuiltCachePath),
         backupInterfaceDir(backupInterfaceDir),
         ABIDescriptorPath(ABIDescriptorPath),
         disableInterfaceFileLock(disableInterfaceFileLock),

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1215,6 +1215,7 @@ class ModuleInterfaceLoaderImpl {
         ctx.SourceMgr, diagsToUse,
         astDelegate, interfacePath,
         ctx.SearchPathOpts.getSDKPath(),
+        ctx.SearchPathOpts.getSysRoot(),
         realName.str(), cacheDir,
         prebuiltCacheDir, backupInterfaceDir, StringRef(),
         Opts.disableInterfaceLock,
@@ -1250,6 +1251,7 @@ class ModuleInterfaceLoaderImpl {
       ImplicitModuleInterfaceBuilder fallbackBuilder(
         ctx.SourceMgr, &ctx.Diags, astDelegate, backupPath,
         ctx.SearchPathOpts.getSDKPath(),
+        ctx.SearchPathOpts.getSysRoot(),
         moduleName, cacheDir,
         prebuiltCacheDir, backupInterfaceDir, StringRef(),
         Opts.disableInterfaceLock,
@@ -1475,6 +1477,7 @@ bool ModuleInterfaceLoader::buildSwiftModuleFromSwiftInterface(
       RequireOSSAModules);
   ImplicitModuleInterfaceBuilder builder(SourceMgr, &Diags, astDelegate, InPath,
                                          SearchPathOpts.getSDKPath(),
+                                         SearchPathOpts.getSysRoot(),
                                          ModuleName, CacheDir, PrebuiltCacheDir,
                                          BackupInterfaceDir, ABIOutputPath,
                                          LoaderOpts.disableInterfaceLock,
@@ -1495,6 +1498,7 @@ bool ModuleInterfaceLoader::buildSwiftModuleFromSwiftInterface(
   assert(!backInPath.empty());
   ImplicitModuleInterfaceBuilder backupBuilder(SourceMgr, &Diags, astDelegate, backInPath,
                                                SearchPathOpts.getSDKPath(),
+                                               SearchPathOpts.getSysRoot(),
                                                ModuleName, CacheDir, PrebuiltCacheDir,
                                                BackupInterfaceDir, ABIOutputPath,
                                                LoaderOpts.disableInterfaceLock,
@@ -2049,12 +2053,13 @@ std::error_code
 InterfaceSubContextDelegateImpl::runInSubContext(StringRef moduleName,
                                                  StringRef interfacePath,
                                                  StringRef sdkPath,
+                                                 std::optional<StringRef> sysroot,
                                                  StringRef outputPath,
                                                  SourceLoc diagLoc,
     llvm::function_ref<std::error_code(ASTContext&, ModuleDecl*, ArrayRef<StringRef>,
                           StringRef, StringRef)> action) {
-  return runInSubCompilerInstance(moduleName, interfacePath, sdkPath, outputPath,
-                                  diagLoc, /*silenceErrors=*/false,
+  return runInSubCompilerInstance(moduleName, interfacePath, sdkPath, sysroot,
+                                  outputPath, diagLoc, /*silenceErrors=*/false,
                                   [&](SubCompilerInstanceInfo &info){
     std::string UserModuleVer = info.Instance->getInvocation().getFrontendOptions()
       .UserModuleVersion.getAsString();
@@ -2070,6 +2075,7 @@ std::error_code
 InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
                                                           StringRef interfacePath,
                                                           StringRef sdkPath,
+                                                          std::optional<StringRef> sysroot,
                                                           StringRef outputPath,
                                                           SourceLoc diagLoc,
                                                           bool silenceErrors,
@@ -2101,6 +2107,9 @@ InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
   subInvocation.setModuleName(moduleName);
   BuildArgs.push_back("-module-name");
   BuildArgs.push_back(moduleName);
+  if (sysroot) {
+    subInvocation.setSysRoot(sysroot.value());
+  }
 
   // FIXME: Hack for Darwin.swiftmodule, which cannot be rebuilt with C++
   // interop enabled by the Swift CI because it uses an old host SDK.

lib/Serialization/ScanningLoaders.cpp

@@ -155,7 +155,7 @@ SwiftModuleScanner::scanInterfaceFile(Twine moduleInterfacePath,
   std::optional<ModuleDependencyInfo> Result;
   std::error_code code = astDelegate.runInSubContext(
       realModuleName.str(), moduleInterfacePath.str(), sdkPath,
-      StringRef(), SourceLoc(),
+      Ctx.SearchPathOpts.getSysRoot(), StringRef(), SourceLoc(),
       [&](ASTContext &Ctx, ModuleDecl *mainMod, ArrayRef<StringRef> BaseArgs,
           StringRef Hash, StringRef UserModVer) {
         assert(mainMod);