[clangd] Fix clang tidy provider when multiple config files exist in directory tree

Currently Clang tidy provider searches from the root directory up to the target directory, this is the opposite of how clang-tidy searches for config files.
The result of this is .clang-tidy files are ignored in any subdirectory of a directory containing a .clang-tidy file.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D96204

Author: njames93

clang-tools-extra/clangd/TidyProvider.cpp

@@ -106,7 +106,7 @@ class DotClangTidyTree {
     llvm::SmallVector<DotClangTidyCache *> Caches;
     {
       std::lock_guard<std::mutex> Lock(Mu);
-      for (auto I = path::begin(Parent), E = path::end(Parent); I != E; ++I) {
+      for (auto I = path::rbegin(Parent), E = path::rend(Parent); I != E; ++I) {
         assert(I->end() >= Parent.begin() && I->end() <= Parent.end() &&
                "Canonical path components should be substrings");
         llvm::StringRef Ancestor(Parent.begin(), I->end() - Parent.begin());

clang-tools-extra/clangd/unittests/CMakeLists.txt

@@ -93,6 +93,7 @@ add_unittest(ClangdUnitTests ClangdTests
   TestIndex.cpp
   TestTU.cpp
   TestWorkspace.cpp
+  TidyProviderTests.cpp
   TypeHierarchyTests.cpp
   URITests.cpp
   XRefsTests.cpp

clang-tools-extra/clangd/unittests/TidyProviderTests.cpp

@@ -0,0 +1,60 @@
+//===-- TidyProviderTests.cpp - Clang tidy configuration provider tests ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "TestFS.h"
+#include "TidyProvider.h"
+#include "gtest/gtest.h"
+
+namespace clang {
+namespace clangd {
+
+namespace {
+
+TEST(TidyProvider, NestedDirectories) {
+  MockFS FS;
+  FS.Files[testPath(".clang-tidy")] = R"yaml(
+  Checks: 'llvm-*'
+  CheckOptions:
+    - key: TestKey
+      value: 1
+)yaml";
+  FS.Files[testPath("sub1/.clang-tidy")] = R"yaml(
+  Checks: 'misc-*'
+  CheckOptions:
+    - key: TestKey
+      value: 2
+)yaml";
+  FS.Files[testPath("sub1/sub2/.clang-tidy")] = R"yaml(
+  Checks: 'bugprone-*'
+  CheckOptions:
+    - key: TestKey
+      value: 3
+  InheritParentConfig: true
+)yaml";
+
+  TidyProvider Provider = provideClangTidyFiles(FS);
+
+  auto BaseOptions = getTidyOptionsForFile(Provider, testPath("File.cpp"));
+  ASSERT_TRUE(BaseOptions.Checks.hasValue());
+  EXPECT_EQ(*BaseOptions.Checks, "llvm-*");
+  EXPECT_EQ(BaseOptions.CheckOptions.lookup("TestKey").Value, "1");
+
+  auto Sub1Options = getTidyOptionsForFile(Provider, testPath("sub1/File.cpp"));
+  ASSERT_TRUE(Sub1Options.Checks.hasValue());
+  EXPECT_EQ(*Sub1Options.Checks, "misc-*");
+  EXPECT_EQ(Sub1Options.CheckOptions.lookup("TestKey").Value, "2");
+
+  auto Sub2Options =
+      getTidyOptionsForFile(Provider, testPath("sub1/sub2/File.cpp"));
+  ASSERT_TRUE(Sub2Options.Checks.hasValue());
+  EXPECT_EQ(*Sub2Options.Checks, "misc-*,bugprone-*");
+  EXPECT_EQ(Sub2Options.CheckOptions.lookup("TestKey").Value, "3");
+}
+} // namespace
+} // namespace clangd
+} // namespace clang