Index: clang-tools-extra/trunk/clangd/index/IndexAction.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/index/IndexAction.cpp
+++ clang-tools-extra/trunk/clangd/index/IndexAction.cpp
@@ -135,6 +135,11 @@
   bool BeginInvocation(CompilerInstance &CI) override {
     // We want all comments, not just the doxygen ones.
     CI.getLangOpts().CommentOpts.ParseAllComments = true;
+    // Index the whole file even if there are warnings and -Werror is set.
+    // Avoids some analyses too. Set in two places as we're late to the party.
+    CI.getDiagnosticOpts().IgnoreWarnings = true;
+    CI.getDiagnostics().setIgnoreAllWarnings(true);
+
     return WrapperFrontendAction::BeginInvocation(CI);
   }
 
Index: clang-tools-extra/trunk/unittests/clangd/IndexActionTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/IndexActionTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/IndexActionTests.cpp
@@ -29,6 +29,8 @@
 
 MATCHER_P(HasDigest, Digest, "") { return arg.Digest == Digest; }
 
+MATCHER_P(HasName, Name, "") { return arg.Name == Name; }
+
 MATCHER(HasSameURI, "") {
   llvm::StringRef URI = testing::get<0>(arg);
   const std::string &Path = testing::get<1>(arg);
@@ -43,6 +45,7 @@
 
 void checkNodesAreInitialized(const IndexFileIn &IndexFile,
                               const std::vector<std::string> &Paths) {
+  ASSERT_TRUE(IndexFile.Sources);
   EXPECT_THAT(Paths.size(), IndexFile.Sources->size());
   for (llvm::StringRef Path : Paths) {
     auto URI = toUri(Path);
@@ -224,6 +227,27 @@
                                         HasDigest(digest(HeaderCode))))));
 }
 
+TEST_F(IndexActionTest, NoWarnings) {
+  std::string MainFilePath = testPath("main.cpp");
+  std::string MainCode = R"cpp(
+      void foo(int x) {
+        if (x = 1) // -Wparentheses
+          return;
+        if (x = 1) // -Wparentheses
+          return;
+      }
+      void bar() {}
+  )cpp";
+  addFile(MainFilePath, MainCode);
+  // We set -ferror-limit so the warning-promoted-to-error would be fatal.
+  // This would cause indexing to stop (if warnings weren't disabled).
+  IndexFileIn IndexFile = runIndexingAction(
+      MainFilePath, {"-ferror-limit=1", "-Wparentheses", "-Werror"});
+  ASSERT_TRUE(IndexFile.Sources);
+  ASSERT_NE(0u, IndexFile.Sources->size());
+  EXPECT_THAT(*IndexFile.Symbols, ElementsAre(HasName("foo"), HasName("bar")));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang