Degrade missing VFS overlays in serialized Swift options to warnings.

The VFS options turn into fatal errors when the referenced file
is not found. Since the Xcode build system tends to create a
lot of VFS overlays by default, stat them emit a warning if the
yaml file couldn't be found.

rdar://112939483

Author: adrian-prantl

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.cpp

@@ -1508,8 +1508,8 @@ bool ShouldUnique(StringRef arg) {
 } // namespace
 
 // static
-void SwiftASTContext::AddExtraClangArgs(const std::vector<std::string>& source,
-                                        std::vector<std::string>& dest) {
+void SwiftASTContext::AddExtraClangArgs(const std::vector<std::string> &source,
+                                        std::vector<std::string> &dest) {
   llvm::StringSet<> unique_flags;
   for (auto &arg : dest)
     unique_flags.insert(arg);
@@ -1653,6 +1653,41 @@ void SwiftASTContext::RemapClangImporterOptions(
   }
 }
 
+void SwiftASTContext::FilterClangImporterOptions(
+    std::vector<std::string> &extra_args, SwiftASTContext *ctx) {
+  std::string ivfs_arg;
+  // Copy back a filtered version of ExtraArgs.
+  std::vector<std::string> orig_args(std::move(extra_args));
+  for (auto &arg : orig_args) {
+    // The VFS options turn into fatal errors when the referenced file
+    // is not found. Since the Xcode build system tends to create a
+    // lot of VFS overlays by default, stat them and emit a warning if
+    // the yaml file couldn't be found.
+    if (StringRef(arg).startswith("-ivfs")) {
+      // Stash the argument.
+      ivfs_arg = arg;
+      continue;
+    }
+    if (!ivfs_arg.empty()) {
+      auto clear_ivfs_arg = llvm::make_scope_exit([&] { ivfs_arg.clear(); });
+      if (!FileSystem::Instance().Exists(arg)) {
+        if (ctx) {
+          std::string error;
+          llvm::raw_string_ostream(error)
+              << "Ignoring missing VFS file: " << arg
+              << "\nThis is the likely root cause for any subsequent compiler "
+                 "errors.";
+          ctx->AddDiagnostic(eDiagnosticSeverityWarning, error);
+        }
+        continue;
+      }
+      // Keep it.
+      extra_args.push_back(ivfs_arg);
+    }
+    extra_args.push_back(std::move(arg));
+  }
+}
+
 /// Retrieve the .dSYM bundle for \p module.
 static llvm::Optional<StringRef> GetDSYMBundle(Module &module) {
   auto sym_file = module.GetSymbolFile();
@@ -1909,6 +1944,8 @@ SwiftASTContext::CreateInstance(lldb::LanguageType language, Module &module,
 
   // Apply source path remappings found in the module's dSYM.
   swift_ast_sp->RemapClangImporterOptions(module.GetSourceMappingList());
+  swift_ast_sp->FilterClangImporterOptions(
+      swift_ast_sp->GetClangImporterOptions().ExtraArgs, swift_ast_sp.get());
 
   // Add Swift interfaces in the .dSYM at the end of the search paths.
   // .swiftmodules win over .swiftinterfaces, when they are loaded
@@ -2401,6 +2438,8 @@ lldb::TypeSystemSP SwiftASTContext::CreateInstance(
 
   // Apply source path remappings found in the target settings.
   swift_ast_sp->RemapClangImporterOptions(target.GetSourcePathMap());
+  swift_ast_sp->FilterClangImporterOptions(
+      swift_ast_sp->GetClangImporterOptions().ExtraArgs, swift_ast_sp.get());
 
   // This needs to happen once all the import paths are set, or
   // otherwise no modules will be found.

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.h

@@ -262,6 +262,9 @@ class SwiftASTContext : public TypeSystemSwift {
   static void AddExtraClangArgs(const std::vector<std::string>& source,
                                 std::vector<std::string>& dest);
   static std::string GetPluginServer(llvm::StringRef plugin_library_path);
+  /// Removes nonexisting VFS overlay options.
+  static void FilterClangImporterOptions(std::vector<std::string> &extra_args,
+                                         SwiftASTContext *ctx = nullptr);
 
   /// Add the target's swift-extra-clang-flags to the ClangImporter options.
   void AddUserClangArgs(TargetProperties &props);

lldb/test/API/lang/swift/clangimporter/missing_vfsoverlay/TestSwiftMissingVFSOverlay.py

@@ -4,7 +4,6 @@
 import lldbsuite.test.lldbutil as lldbutil
 import unittest2
 
-
 class TestSwiftMissingVFSOverlay(TestBase):
     mydir = TestBase.compute_mydir(__file__)
 
@@ -18,11 +17,11 @@ def setUp(self):
     @skipUnlessDarwin
     @swiftTest
     def test(self):
-        """Test that a broken Clang command line option is diagnosed
-        in the expression evaluator"""
+        """This used to be a test for a diagnostic, however,
+        this is no longer an unrecoverable error"""
         self.build()
         lldbutil.run_to_source_breakpoint(
             self, "break here", lldb.SBFileSpec("main.swift"),
             extra_images=["Foo"]
         )
-        self.expect("expr y", error=True, substrs=["IRGen", "overlay.yaml"])
+        self.expect("expr y", substrs=["42"])

lldb/test/Shell/Swift/MissingVFSOverlay.test

@@ -15,7 +15,8 @@ run
 expression 1
 
 # The {{ }} avoids accidentally matching the input script!
-# CHECK: a.out:{{ }}
-# CHECK-SAME: error:
+# CHECK: warning:
+# CHECK-SAME: a.out
+# CHECK: warning:
+# CHECK-SAME: Ignoring missing VFS
 # CHECK-SAME: overlay.yaml
-# CHECK-SAME: not found

lldb/unittests/Symbol/TestSwiftASTContext.cpp

@@ -12,9 +12,10 @@
 
 #include "gtest/gtest.h"
 
+#include "Plugins/TypeSystem/Swift/SwiftASTContext.h"
 #include "lldb/Host/FileSystem.h"
 #include "lldb/Host/HostInfo.h"
-#include "Plugins/TypeSystem/Swift/SwiftASTContext.h"
+#include "llvm/Support/FileUtilities.h"
 
 using namespace lldb;
 using namespace lldb_private;
@@ -255,3 +256,40 @@ TEST(ClangArgs, DoubleDash) {
   // Check that all ignored arguments got removed.
   EXPECT_EQ(dest, std::vector<std::string>({"-v"}));
 }
+
+TEST_F(TestSwiftASTContext, IVFS) {
+  const auto *Info = testing::UnitTest::GetInstance()->current_test_info();
+  llvm::SmallString<128> name;
+  auto ec = llvm::sys::fs::createTemporaryFile(
+      llvm::Twine(Info->test_case_name()) + "-" + Info->name(), "overlay.yaml",
+      name);
+  ASSERT_FALSE((bool)ec);
+  llvm::FileRemover remover(name);
+
+  std::string valid = name.str().str();
+  std::string invalid = name.str().drop_back(1).str() +"XXX";
+  std::vector<std::string> args;
+  args.push_back("-ivfsoverlay");
+  args.push_back(valid);
+
+  args.push_back("-ivfsoverlay");
+  args.push_back(invalid);
+
+  args.push_back("-ivfsstatcache");
+  args.push_back(valid);
+
+  args.push_back("-ivfsstatcache");
+  args.push_back(invalid);
+
+  std::vector<std::string> expected;
+  expected.push_back("-ivfsoverlay");
+  expected.push_back(valid);
+
+  expected.push_back("-ivfsstatcache");
+  expected.push_back(valid);
+
+  SwiftASTContext::FilterClangImporterOptions(args);
+
+  // Check that all ignored arguments got removed.
+  EXPECT_EQ(args, expected);
+}