diff --git a/clang-tools-extra/clangd/Config.h b/clang-tools-extra/clangd/Config.h
--- a/clang-tools-extra/clangd/Config.h
+++ b/clang-tools-extra/clangd/Config.h
@@ -92,9 +92,6 @@
     /// Diagnose missing and unused includes.
     Strict,
     None,
-    /// The same as Strict, but using the include-cleaner library for
-    /// unused includes.
-    Experiment,
   };
   /// Controls warnings and errors when parsing code.
   struct {
diff --git a/clang-tools-extra/clangd/ConfigCompile.cpp b/clang-tools-extra/clangd/ConfigCompile.cpp
--- a/clang-tools-extra/clangd/ConfigCompile.cpp
+++ b/clang-tools-extra/clangd/ConfigCompile.cpp
@@ -430,16 +430,24 @@
               C.Diagnostics.Suppress.insert(N);
           });
 
-    if (F.UnusedIncludes)
-      if (auto Val = compileEnum<Config::IncludesPolicy>("UnusedIncludes",
-                                                         **F.UnusedIncludes)
-                         .map("Strict", Config::IncludesPolicy::Strict)
-                         .map("Experiment", Config::IncludesPolicy::Experiment)
-                         .map("None", Config::IncludesPolicy::None)
-                         .value())
+    if (F.UnusedIncludes) {
+      auto Val = compileEnum<Config::IncludesPolicy>("UnusedIncludes",
+                                                     **F.UnusedIncludes)
+                     .map("Strict", Config::IncludesPolicy::Strict)
+                     .map("None", Config::IncludesPolicy::None)
+                     .value();
+      if (!Val && **F.UnusedIncludes == "Experiment") {
+        diag(Warning,
+             "Experiment is deprecated for UnusedIncludes, use Strict instead.",
+             F.UnusedIncludes->Range);
+        Val = Config::IncludesPolicy::Strict;
+      }
+      if (Val) {
         Out.Apply.push_back([Val](const Params &, Config &C) {
           C.Diagnostics.UnusedIncludes = *Val;
         });
+      }
+    }
 
     if (F.AllowStalePreamble) {
       if (auto Val = F.AllowStalePreamble)
diff --git a/clang-tools-extra/clangd/ConfigFragment.h b/clang-tools-extra/clangd/ConfigFragment.h
--- a/clang-tools-extra/clangd/ConfigFragment.h
+++ b/clang-tools-extra/clangd/ConfigFragment.h
@@ -232,7 +232,6 @@
     ///
     /// Valid values are:
     /// - Strict
-    /// - Experiment
     /// - None
     std::optional<Located<std::string>> UnusedIncludes;
 
diff --git a/clang-tools-extra/clangd/IncludeCleaner.h b/clang-tools-extra/clangd/IncludeCleaner.h
--- a/clang-tools-extra/clangd/IncludeCleaner.h
+++ b/clang-tools-extra/clangd/IncludeCleaner.h
@@ -21,14 +21,9 @@
 #include "Headers.h"
 #include "ParsedAST.h"
 #include "clang-include-cleaner/Types.h"
-#include "index/CanonicalIncludes.h"
-#include "clang/Basic/SourceLocation.h"
-#include "clang/Tooling/Inclusions/StandardLibrary.h"
 #include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/DenseSet.h"
-#include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/StringSet.h"
-#include <optional>
 #include <tuple>
 #include <vector>
 
@@ -52,63 +47,6 @@
   std::vector<MissingIncludeDiagInfo> MissingIncludes;
 };
 
-struct ReferencedLocations {
-  llvm::DenseSet<SourceLocation> User;
-  llvm::DenseSet<tooling::stdlib::Symbol> Stdlib;
-};
-
-/// Finds locations of all symbols used in the main file.
-///
-/// - RecursiveASTVisitor finds references to symbols and records their
-///   associated locations. These may be macro expansions, and are not resolved
-///   to their spelling or expansion location. These locations are later used to
-///   determine which headers should be marked as "used" and "directly used".
-/// - If \p Tokens is not nullptr, we also examine all identifier tokens in the
-///   file in case they reference macros macros.
-/// We use this to compute unused headers, so we:
-///
-/// - cover the whole file in a single traversal for efficiency
-/// - don't attempt to describe where symbols were referenced from in
-///   ambiguous cases (e.g. implicitly used symbols, multiple declarations)
-/// - err on the side of reporting all possible locations
-ReferencedLocations findReferencedLocations(ASTContext &Ctx, Preprocessor &PP,
-                                            const syntax::TokenBuffer *Tokens);
-ReferencedLocations findReferencedLocations(ParsedAST &AST);
-
-struct ReferencedFiles {
-  llvm::DenseSet<FileID> User;
-  llvm::DenseSet<tooling::stdlib::Header> Stdlib;
-  /// Files responsible for the symbols referenced in the main file and defined
-  /// in private headers (private headers have IWYU pragma: private, include
-  /// "public.h"). We store spelling of the public header (with quotes or angle
-  /// brackets) files here to avoid dealing with full filenames and visibility.
-  llvm::StringSet<> SpelledUmbrellas;
-};
-
-/// Retrieves IDs of all files containing SourceLocations from \p Locs.
-/// The output only includes things SourceManager sees as files (not macro IDs).
-/// This can include <built-in>, <scratch space> etc that are not true files.
-/// \p HeaderResponsible returns the public header that should be included given
-/// symbols from a file with the given FileID (example: public headers should be
-/// preferred to non self-contained and private headers).
-/// \p UmbrellaHeader returns the public public header is responsible for
-/// providing symbols from a file with the given FileID (example: MyType.h
-/// should be included instead of MyType_impl.h).
-ReferencedFiles findReferencedFiles(
-    const ReferencedLocations &Locs, const SourceManager &SM,
-    llvm::function_ref<FileID(FileID)> HeaderResponsible,
-    llvm::function_ref<std::optional<StringRef>(FileID)> UmbrellaHeader);
-ReferencedFiles findReferencedFiles(const ReferencedLocations &Locs,
-                                    const IncludeStructure &Includes,
-                                    const CanonicalIncludes &CanonIncludes,
-                                    const SourceManager &SM);
-
-/// Maps FileIDs to the internal IncludeStructure representation (HeaderIDs).
-/// FileIDs that are not true files (<built-in> etc) are dropped.
-llvm::DenseSet<IncludeStructure::HeaderID>
-translateToHeaderIDs(const ReferencedFiles &Files,
-                     const IncludeStructure &Includes, const SourceManager &SM);
-
 /// Retrieves headers that are referenced from the main file but not used.
 /// In unclear cases, headers are not marked as unused.
 std::vector<const Inclusion *>
@@ -117,7 +55,6 @@
           const llvm::StringSet<> &ReferencedPublicHeaders);
 
 IncludeCleanerFindings computeIncludeCleanerFindings(ParsedAST &AST);
-std::vector<const Inclusion *> computeUnusedIncludes(ParsedAST &AST);
 
 std::vector<Diag> issueIncludeCleanerDiagnostics(ParsedAST &AST,
                                                  llvm::StringRef Code);
diff --git a/clang-tools-extra/clangd/IncludeCleaner.cpp b/clang-tools-extra/clangd/IncludeCleaner.cpp
--- a/clang-tools-extra/clangd/IncludeCleaner.cpp
+++ b/clang-tools-extra/clangd/IncludeCleaner.cpp
@@ -16,7 +16,6 @@
 #include "URI.h"
 #include "clang-include-cleaner/Analysis.h"
 #include "clang-include-cleaner/Types.h"
-#include "index/CanonicalIncludes.h"
 #include "support/Logger.h"
 #include "support/Path.h"
 #include "support/Trace.h"
@@ -24,7 +23,6 @@
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
-#include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/TemplateName.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/Diagnostic.h"
@@ -36,7 +34,6 @@
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/Core/Replacement.h"
 #include "clang/Tooling/Inclusions/HeaderIncludes.h"
-#include "clang/Tooling/Inclusions/IncludeStyle.h"
 #include "clang/Tooling/Inclusions/StandardLibrary.h"
 #include "clang/Tooling/Syntax/Tokens.h"
 #include "llvm/ADT/ArrayRef.h"
@@ -66,181 +63,6 @@
 
 namespace {
 
-/// Crawler traverses the AST and feeds in the locations of (sometimes
-/// implicitly) used symbols into \p Result.
-class ReferencedLocationCrawler
-    : public RecursiveASTVisitor<ReferencedLocationCrawler> {
-public:
-  ReferencedLocationCrawler(ReferencedLocations &Result,
-                            const SourceManager &SM)
-      : Result(Result), SM(SM) {}
-
-  bool VisitDeclRefExpr(DeclRefExpr *DRE) {
-    add(DRE->getDecl());
-    add(DRE->getFoundDecl());
-    return true;
-  }
-
-  bool VisitMemberExpr(MemberExpr *ME) {
-    add(ME->getMemberDecl());
-    add(ME->getFoundDecl().getDecl());
-    return true;
-  }
-
-  bool VisitTagType(TagType *TT) {
-    add(TT->getDecl());
-    return true;
-  }
-
-  bool VisitFunctionDecl(FunctionDecl *FD) {
-    // Function definition will require redeclarations to be included.
-    if (FD->isThisDeclarationADefinition())
-      add(FD);
-    return true;
-  }
-
-  bool VisitCXXConstructExpr(CXXConstructExpr *CCE) {
-    add(CCE->getConstructor());
-    return true;
-  }
-
-  bool VisitTemplateSpecializationType(TemplateSpecializationType *TST) {
-    // Using templateName case is handled by the override TraverseTemplateName.
-    if (TST->getTemplateName().getKind() == TemplateName::UsingTemplate)
-      return true;
-    add(TST->getAsCXXRecordDecl()); // Specialization
-    return true;
-  }
-
-  // There is no VisitTemplateName in RAV, thus we override the Traverse version
-  // to handle the Using TemplateName case.
-  bool TraverseTemplateName(TemplateName TN) {
-    VisitTemplateName(TN);
-    return Base::TraverseTemplateName(TN);
-  }
-  // A pseudo VisitTemplateName, dispatched by the above TraverseTemplateName!
-  bool VisitTemplateName(TemplateName TN) {
-    if (const auto *USD = TN.getAsUsingShadowDecl()) {
-      add(USD);
-      return true;
-    }
-    add(TN.getAsTemplateDecl()); // Primary template.
-    return true;
-  }
-
-  bool VisitUsingType(UsingType *UT) {
-    add(UT->getFoundDecl());
-    return true;
-  }
-
-  bool VisitTypedefType(TypedefType *TT) {
-    add(TT->getDecl());
-    return true;
-  }
-
-  // Consider types of any subexpression used, even if the type is not named.
-  // This is helpful in getFoo().bar(), where Foo must be complete.
-  // FIXME(kirillbobyrev): Should we tweak this? It may not be desirable to
-  // consider types "used" when they are not directly spelled in code.
-  bool VisitExpr(Expr *E) {
-    TraverseType(E->getType());
-    return true;
-  }
-
-  bool TraverseType(QualType T) {
-    if (isNew(T.getTypePtrOrNull())) // don't care about quals
-      Base::TraverseType(T);
-    return true;
-  }
-
-  bool VisitUsingDecl(UsingDecl *D) {
-    for (const auto *Shadow : D->shadows())
-      add(Shadow->getTargetDecl());
-    return true;
-  }
-
-  // Enums may be usefully forward-declared as *complete* types by specifying
-  // an underlying type. In this case, the definition should see the declaration
-  // so they can be checked for compatibility.
-  bool VisitEnumDecl(EnumDecl *D) {
-    if (D->isThisDeclarationADefinition() && D->getIntegerTypeSourceInfo())
-      add(D);
-    return true;
-  }
-
-  // When the overload is not resolved yet, mark all candidates as used.
-  bool VisitOverloadExpr(OverloadExpr *E) {
-    for (const auto *ResolutionDecl : E->decls())
-      add(ResolutionDecl);
-    return true;
-  }
-
-private:
-  using Base = RecursiveASTVisitor<ReferencedLocationCrawler>;
-
-  void add(const Decl *D) {
-    if (!D || !isNew(D->getCanonicalDecl()))
-      return;
-    if (auto SS = StdRecognizer(D)) {
-      Result.Stdlib.insert(*SS);
-      return;
-    }
-    // Special case RecordDecls, as it is common for them to be forward
-    // declared multiple times. The most common cases are:
-    // - Definition available in TU, only mark that one as usage. The rest is
-    //   likely to be unnecessary. This might result in false positives when an
-    //   internal definition is visible.
-    // - There's a forward declaration in the main file, no need for other
-    //   redecls.
-    if (const auto *RD = llvm::dyn_cast<RecordDecl>(D)) {
-      if (const auto *Definition = RD->getDefinition()) {
-        Result.User.insert(Definition->getLocation());
-        return;
-      }
-      if (SM.isInMainFile(RD->getMostRecentDecl()->getLocation()))
-        return;
-    }
-    for (const Decl *Redecl : D->redecls())
-      Result.User.insert(Redecl->getLocation());
-  }
-
-  bool isNew(const void *P) { return P && Visited.insert(P).second; }
-
-  ReferencedLocations &Result;
-  llvm::DenseSet<const void *> Visited;
-  const SourceManager &SM;
-  tooling::stdlib::Recognizer StdRecognizer;
-};
-
-// Given a set of referenced FileIDs, determines all the potentially-referenced
-// files and macros by traversing expansion/spelling locations of macro IDs.
-// This is used to map the referenced SourceLocations onto real files.
-struct ReferencedFilesBuilder {
-  ReferencedFilesBuilder(const SourceManager &SM) : SM(SM) {}
-  llvm::DenseSet<FileID> Files;
-  llvm::DenseSet<FileID> Macros;
-  const SourceManager &SM;
-
-  void add(SourceLocation Loc) { add(SM.getFileID(Loc), Loc); }
-
-  void add(FileID FID, SourceLocation Loc) {
-    if (FID.isInvalid())
-      return;
-    assert(SM.isInFileID(Loc, FID));
-    if (Loc.isFileID()) {
-      Files.insert(FID);
-      return;
-    }
-    // Don't process the same macro FID twice.
-    if (!Macros.insert(FID).second)
-      return;
-    const auto &Exp = SM.getSLocEntry(FID).getExpansion();
-    add(Exp.getSpellingLoc());
-    add(Exp.getExpansionLocStart());
-    add(Exp.getExpansionLocEnd());
-  }
-};
-
 // Returns the range starting at '#' and ending at EOL. Escaped newlines are not
 // handled.
 clangd::Range getDiagnosticRange(llvm::StringRef Code, unsigned HashOffset) {
@@ -255,31 +77,6 @@
   return Result;
 }
 
-// Finds locations of macros referenced from within the main file. That includes
-// references that were not yet expanded, e.g `BAR` in `#define FOO BAR`.
-void findReferencedMacros(const SourceManager &SM, Preprocessor &PP,
-                          const syntax::TokenBuffer *Tokens,
-                          ReferencedLocations &Result) {
-  trace::Span Tracer("IncludeCleaner::findReferencedMacros");
-  // FIXME(kirillbobyrev): The macros from the main file are collected in
-  // ParsedAST's MainFileMacros. However, we can't use it here because it
-  // doesn't handle macro references that were not expanded, e.g. in macro
-  // definitions or preprocessor-disabled sections.
-  //
-  // Extending MainFileMacros to collect missing references and switching to
-  // this mechanism (as opposed to iterating through all tokens) will improve
-  // the performance of findReferencedMacros and also improve other features
-  // relying on MainFileMacros.
-  for (const syntax::Token &Tok : Tokens->spelledTokens(SM.getMainFileID())) {
-    auto Macro = locateMacroAt(Tok, PP);
-    if (!Macro)
-      continue;
-    auto Loc = Macro->Info->getDefinitionLoc();
-    if (Loc.isValid())
-      Result.User.insert(Loc);
-    // FIXME: support stdlib macros
-  }
-}
 
 bool isFilteredByConfig(const Config &Cfg, llvm::StringRef HeaderPath) {
   // Convert the path to Unix slashes and try to match against the filter.
@@ -330,31 +127,6 @@
   return true;
 }
 
-// In case symbols are coming from non self-contained header, we need to find
-// its first includer that is self-contained. This is the header users can
-// include, so it will be responsible for bringing the symbols from given
-// header into the scope.
-FileID headerResponsible(FileID ID, const SourceManager &SM,
-                         const IncludeStructure &Includes) {
-  // Unroll the chain of non self-contained headers until we find the one that
-  // can be included.
-  for (const FileEntry *FE = SM.getFileEntryForID(ID); ID != SM.getMainFileID();
-       FE = SM.getFileEntryForID(ID)) {
-    // If FE is nullptr, we consider it to be the responsible header.
-    if (!FE)
-      break;
-    auto HID = Includes.getID(FE);
-    assert(HID && "We're iterating over headers already existing in "
-                  "IncludeStructure");
-    if (Includes.isSelfContained(*HID))
-      break;
-    // The header is not self-contained: put the responsibility for its symbols
-    // on its includer.
-    ID = SM.getFileID(SM.getIncludeLoc(ID));
-  }
-  return ID;
-}
-
 include_cleaner::Includes
 convertIncludes(const SourceManager &SM,
                 const llvm::ArrayRef<Inclusion> MainFileIncludes) {
@@ -546,81 +318,6 @@
 }
 } // namespace
 
-ReferencedLocations findReferencedLocations(ASTContext &Ctx, Preprocessor &PP,
-                                            const syntax::TokenBuffer *Tokens) {
-  trace::Span Tracer("IncludeCleaner::findReferencedLocations");
-  ReferencedLocations Result;
-  const auto &SM = Ctx.getSourceManager();
-  ReferencedLocationCrawler Crawler(Result, SM);
-  Crawler.TraverseAST(Ctx);
-  if (Tokens)
-    findReferencedMacros(SM, PP, Tokens, Result);
-  return Result;
-}
-
-ReferencedLocations findReferencedLocations(ParsedAST &AST) {
-  return findReferencedLocations(AST.getASTContext(), AST.getPreprocessor(),
-                                 &AST.getTokens());
-}
-
-ReferencedFiles findReferencedFiles(
-    const ReferencedLocations &Locs, const SourceManager &SM,
-    llvm::function_ref<FileID(FileID)> HeaderResponsible,
-    llvm::function_ref<std::optional<StringRef>(FileID)> UmbrellaHeader) {
-  std::vector<SourceLocation> Sorted{Locs.User.begin(), Locs.User.end()};
-  llvm::sort(Sorted); // Group by FileID.
-  ReferencedFilesBuilder Builder(SM);
-  for (auto It = Sorted.begin(); It < Sorted.end();) {
-    FileID FID = SM.getFileID(*It);
-    Builder.add(FID, *It);
-    // Cheaply skip over all the other locations from the same FileID.
-    // This avoids lots of redundant Loc->File lookups for the same file.
-    do
-      ++It;
-    while (It != Sorted.end() && SM.isInFileID(*It, FID));
-  }
-
-  // If a header is not self-contained, we consider its symbols a logical part
-  // of the including file. Therefore, mark the parents of all used
-  // non-self-contained FileIDs as used. Perform this on FileIDs rather than
-  // HeaderIDs, as each inclusion of a non-self-contained file is distinct.
-  llvm::DenseSet<FileID> UserFiles;
-  llvm::StringSet<> PublicHeaders;
-  for (FileID ID : Builder.Files) {
-    UserFiles.insert(HeaderResponsible(ID));
-    if (auto PublicHeader = UmbrellaHeader(ID)) {
-      PublicHeaders.insert(*PublicHeader);
-    }
-  }
-
-  llvm::DenseSet<tooling::stdlib::Header> StdlibFiles;
-  for (const auto &Symbol : Locs.Stdlib)
-    for (const auto &Header : Symbol.headers())
-      StdlibFiles.insert(Header);
-
-  return {std::move(UserFiles), std::move(StdlibFiles),
-          std::move(PublicHeaders)};
-}
-
-ReferencedFiles findReferencedFiles(const ReferencedLocations &Locs,
-                                    const IncludeStructure &Includes,
-                                    const CanonicalIncludes &CanonIncludes,
-                                    const SourceManager &SM) {
-  return findReferencedFiles(
-      Locs, SM,
-      [&SM, &Includes](FileID ID) {
-        return headerResponsible(ID, SM, Includes);
-      },
-      [&SM, &CanonIncludes](FileID ID) -> std::optional<StringRef> {
-        auto Entry = SM.getFileEntryRefForID(ID);
-        if (!Entry)
-          return std::nullopt;
-        auto PublicHeader = CanonIncludes.mapHeader(*Entry);
-        if (PublicHeader.empty())
-          return std::nullopt;
-        return PublicHeader;
-      });
-}
 
 std::vector<const Inclusion *>
 getUnused(ParsedAST &AST,
@@ -648,52 +345,6 @@
   return Unused;
 }
 
-#ifndef NDEBUG
-// Is FID a <built-in>, <scratch space> etc?
-static bool isSpecialBuffer(FileID FID, const SourceManager &SM) {
-  const SrcMgr::FileInfo &FI = SM.getSLocEntry(FID).getFile();
-  return FI.getName().startswith("<");
-}
-#endif
-
-llvm::DenseSet<IncludeStructure::HeaderID>
-translateToHeaderIDs(const ReferencedFiles &Files,
-                     const IncludeStructure &Includes,
-                     const SourceManager &SM) {
-  trace::Span Tracer("IncludeCleaner::translateToHeaderIDs");
-  llvm::DenseSet<IncludeStructure::HeaderID> TranslatedHeaderIDs;
-  TranslatedHeaderIDs.reserve(Files.User.size());
-  for (FileID FID : Files.User) {
-    const FileEntry *FE = SM.getFileEntryForID(FID);
-    if (!FE) {
-      assert(isSpecialBuffer(FID, SM));
-      continue;
-    }
-    const auto File = Includes.getID(FE);
-    assert(File);
-    TranslatedHeaderIDs.insert(*File);
-  }
-  for (tooling::stdlib::Header StdlibUsed : Files.Stdlib)
-    for (auto HID : Includes.StdlibHeaders.lookup(StdlibUsed))
-      TranslatedHeaderIDs.insert(HID);
-  return TranslatedHeaderIDs;
-}
-
-// This is the original clangd-own implementation for computing unused
-// #includes. Eventually it will be deprecated and replaced by the
-// include-cleaner-lib-based implementation.
-std::vector<const Inclusion *> computeUnusedIncludes(ParsedAST &AST) {
-  const auto &SM = AST.getSourceManager();
-
-  auto Refs = findReferencedLocations(AST);
-  auto ReferencedFiles =
-      findReferencedFiles(Refs, AST.getIncludeStructure(),
-                          AST.getCanonicalIncludes(), AST.getSourceManager());
-  auto ReferencedHeaders =
-      translateToHeaderIDs(ReferencedFiles, AST.getIncludeStructure(), SM);
-  return getUnused(AST, ReferencedHeaders, ReferencedFiles.SpelledUmbrellas);
-}
-
 IncludeCleanerFindings computeIncludeCleanerFindings(ParsedAST &AST) {
   const auto &SM = AST.getSourceManager();
   const auto &Includes = AST.getIncludeStructure();
@@ -758,17 +409,13 @@
   const Config &Cfg = Config::current();
   IncludeCleanerFindings Findings;
   if (Cfg.Diagnostics.MissingIncludes == Config::IncludesPolicy::Strict ||
-      Cfg.Diagnostics.UnusedIncludes == Config::IncludesPolicy::Experiment) {
+      Cfg.Diagnostics.UnusedIncludes == Config::IncludesPolicy::Strict) {
     // will need include-cleaner results, call it once
     Findings = computeIncludeCleanerFindings(AST);
   }
 
   std::vector<Diag> Result = generateUnusedIncludeDiagnostics(
-      AST.tuPath(),
-      Cfg.Diagnostics.UnusedIncludes == Config::IncludesPolicy::Strict
-          ? computeUnusedIncludes(AST)
-          : Findings.UnusedIncludes,
-      Code);
+      AST.tuPath(), Findings.UnusedIncludes, Code);
   llvm::move(
       generateMissingIncludeDiagnostics(AST, Findings.MissingIncludes, Code),
       std::back_inserter(Result));
diff --git a/clang-tools-extra/clangd/Preamble.cpp b/clang-tools-extra/clangd/Preamble.cpp
--- a/clang-tools-extra/clangd/Preamble.cpp
+++ b/clang-tools-extra/clangd/Preamble.cpp
@@ -128,7 +128,7 @@
     SourceMgr = &CI.getSourceManager();
     Includes.collect(CI);
     if (Config::current().Diagnostics.UnusedIncludes ==
-                Config::IncludesPolicy::Experiment ||
+                Config::IncludesPolicy::Strict ||
             Config::current().Diagnostics.MissingIncludes ==
             Config::IncludesPolicy::Strict)
       Pragmas.record(CI);
diff --git a/clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp b/clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp
--- a/clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp
+++ b/clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp
@@ -38,7 +38,6 @@
 
 using ::testing::AllOf;
 using ::testing::ElementsAre;
-using ::testing::ElementsAreArray;
 using ::testing::IsEmpty;
 using ::testing::Matcher;
 using ::testing::Pointee;
@@ -64,286 +63,6 @@
   return "#pragma once\n" + Code.str();
 }
 
-TEST(IncludeCleaner, ReferencedLocations) {
-  struct TestCase {
-    std::string HeaderCode;
-    std::string MainCode;
-  };
-  TestCase Cases[] = {
-      // DeclRefExpr
-      {
-          "int ^x();",
-          "int y = x();",
-      },
-      // RecordDecl
-      {
-          "class ^X;",
-          "X *y;",
-      },
-      // When definition is available, we don't need to mark forward
-      // declarations as used.
-      {
-          "class ^X {}; class X;",
-          "X *y;",
-      },
-      // We already have forward declaration in the main file, the other
-      // non-definition declarations are not needed.
-      {
-          "class ^X {}; class X;",
-          "class X; X *y;",
-      },
-      // Nested class definition can occur outside of the parent class
-      // definition. Bar declaration should be visible to its definition but
-      // it will always be because we will mark Foo definition as used.
-      {
-          "class ^Foo { class Bar; };",
-          "class Foo::Bar {};",
-      },
-      // TypedefType and UsingDecls
-      {
-          "using ^Integer = int;",
-          "Integer x;",
-      },
-      {
-          "namespace ns { void ^foo(); void ^foo() {} }",
-          "using ns::foo;",
-      },
-      {
-          "namespace ns { void foo(); void foo() {}; }",
-          "using namespace ns;",
-      },
-      {
-          // Refs from UsingTypeLoc and implicit constructor!
-          "struct ^A {}; using B = A; using ^C = B;",
-          "C a;",
-      },
-      {"namespace ns { template<typename T> class A {}; } using ns::^A;",
-       "A<int>* a;"},
-      {"namespace ns { template<typename T> class A {}; } using ns::^A;",
-       R"cpp(
-          template <template <typename> class T> class X {};
-          X<A> x;
-        )cpp"},
-      {R"cpp(
-          namespace ns { template<typename T> class A {}; }
-          namespace absl {using ns::^A;}
-       )cpp",
-       R"cpp(
-          template <template <typename> class T> class X {};
-          X<absl::A> x;
-       )cpp"},
-      {R"cpp(
-          namespace ns { template<typename T> struct ^A { ^A(T); }; }
-          using ns::^A;
-       )cpp",
-       "A CATD(123);"},
-      {
-          "typedef bool ^Y; template <typename T> struct ^X {};",
-          "X<Y> x;",
-      },
-      {
-          // https://github.com/clangd/clangd/issues/1036
-          R"cpp(
-            struct ^Base { void ^base(); };
-            template <int> struct ^Derived : Base {};
-          )cpp",
-          R"cpp(
-            class Holder {
-              void foo() { Member.base(); }
-              Derived<0> Member;
-            };
-          )cpp",
-      },
-      {
-          "struct Foo; struct ^Foo{}; typedef Foo ^Bar;",
-          "Bar b;",
-      },
-      {
-          "namespace ns { class X; }; using ns::^X;",
-          "X *y;",
-      },
-      // MemberExpr
-      {
-          "struct ^X{int ^a;}; X ^foo();",
-          "int y = foo().a;",
-      },
-      // Expr (type is traversed)
-      {
-          "class ^X{}; X ^foo();",
-          "auto bar() { return foo(); }",
-      },
-      // Redecls
-      {
-          "void ^foo(); void ^foo() {} void ^foo();",
-          "void bar() { foo(); }",
-      },
-      // Constructor
-      {
-          "struct ^X { ^X(int) {} int ^foo(); };",
-          "auto x = X(42); auto y = x.foo();",
-      },
-      // Function
-      {
-          "void ^foo();",
-          "void foo() {}",
-      },
-      {
-          "void foo() {}",
-          "void foo();",
-      },
-      {
-          "inline void ^foo() {}",
-          "void bar() { foo(); }",
-      },
-      {
-          "int ^foo(char); int ^foo(float);",
-          "template<class T> int x = foo(T{});",
-      },
-      // Static function
-      {
-          "struct ^X { static bool ^foo(); }; bool X::^foo() {}",
-          "auto b = X::foo();",
-      },
-      // TemplateRecordDecl
-      {
-          "template <typename> class ^X;",
-          "X<int> *y;",
-      },
-      // Type name not spelled out in code
-      {
-          "class ^X{}; X ^getX();",
-          "auto x = getX();",
-      },
-      // Enums
-      {
-          "enum ^Color { ^Red = 42, Green = 9000};",
-          "int MyColor = Red;",
-      },
-      {
-          "struct ^X { enum ^Language { ^CXX = 42, Python = 9000}; };",
-          "int Lang = X::CXX;",
-      },
-      // Macros
-      {
-          "#define ^CONSTANT 42",
-          "int Foo = CONSTANT;",
-      },
-      {
-          "#define ^FOO x",
-          "#define BAR FOO",
-      },
-      {
-          "#define INNER 42\n"
-          "#define ^OUTER INNER",
-          "int answer = OUTER;",
-      },
-      {
-          "#define ^ANSWER 42\n"
-          "#define ^SQUARE(X) X * X",
-          "int sq = SQUARE(ANSWER);",
-      },
-      {
-          "#define ^FOO\n"
-          "#define ^BAR",
-          "#if 0\n"
-          "#if FOO\n"
-          "BAR\n"
-          "#endif\n"
-          "#endif",
-      },
-      // Misc
-      {
-          "enum class ^Color : int;",
-          "enum class Color : int {};",
-      },
-      {
-          "enum class Color : int {};",
-          "enum class Color : int;",
-      },
-      {
-          "enum class ^Color;",
-          "Color c;",
-      },
-      {
-          "enum class ^Color : int;",
-          "Color c;",
-      },
-      {
-          "enum class ^Color : char;",
-          "Color *c;",
-      },
-      {
-          "enum class ^Color : char {};",
-          "Color *c;",
-      },
-  };
-  for (const TestCase &T : Cases) {
-    TestTU TU;
-    TU.Code = T.MainCode;
-    Annotations Header(T.HeaderCode);
-    TU.HeaderCode = Header.code().str();
-    TU.ExtraArgs.push_back("-std=c++17");
-    auto AST = TU.build();
-
-    std::vector<Position> Points;
-    for (const auto &Loc : findReferencedLocations(AST).User) {
-      if (AST.getSourceManager().getBufferName(Loc).endswith(
-              TU.HeaderFilename)) {
-        Points.push_back(offsetToPosition(
-            TU.HeaderCode, AST.getSourceManager().getFileOffset(Loc)));
-      }
-    }
-    llvm::sort(Points);
-
-    EXPECT_EQ(Points, Header.points()) << T.HeaderCode << "\n---\n"
-                                       << T.MainCode;
-  }
-}
-
-TEST(IncludeCleaner, Stdlib) {
-  // Smoke tests only for finding used symbols/headers.
-  // Details of Decl -> stdlib::Symbol -> stdlib::Headers mapping tested there.
-  auto TU = TestTU::withHeaderCode(R"cpp(
-    namespace std { class error_code {}; }
-    class error_code {};
-    namespace nonstd { class error_code {}; }
-  )cpp");
-  struct {
-    llvm::StringRef Code;
-    std::vector<llvm::StringRef> Symbols;
-    std::vector<llvm::StringRef> Headers;
-  } Tests[] = {
-      {"std::error_code x;", {"std::error_code"}, {"<system_error>"}},
-      {"error_code x;", {}, {}},
-      {"nonstd::error_code x;", {}, {}},
-  };
-
-  for (const auto &Test : Tests) {
-    TU.Code = Test.Code.str();
-    ParsedAST AST = TU.build();
-    std::vector<tooling::stdlib::Symbol> WantSyms;
-    for (const auto &SymName : Test.Symbols) {
-      auto QName = splitQualifiedName(SymName);
-      auto Sym = tooling::stdlib::Symbol::named(QName.first, QName.second);
-      EXPECT_TRUE(Sym) << SymName;
-      WantSyms.push_back(*Sym);
-    }
-    std::vector<tooling::stdlib::Header> WantHeaders;
-    for (const auto &HeaderName : Test.Headers) {
-      auto Header = tooling::stdlib::Header::named(HeaderName);
-      EXPECT_TRUE(Header) << HeaderName;
-      WantHeaders.push_back(*Header);
-    }
-
-    ReferencedLocations Locs = findReferencedLocations(AST);
-    EXPECT_THAT(Locs.Stdlib, ElementsAreArray(WantSyms));
-    ReferencedFiles Files =
-        findReferencedFiles(Locs, AST.getIncludeStructure(),
-                            AST.getCanonicalIncludes(), AST.getSourceManager());
-    EXPECT_THAT(Files.Stdlib, ElementsAreArray(WantHeaders));
-  }
-}
-
 MATCHER_P(writtenInclusion, Written, "") {
   if (arg.Written != Written)
     *result_listener << arg.Written;
@@ -372,8 +91,6 @@
   TU.AdditionalFiles["queue"] = "#include <bits>";
   TU.ExtraArgs = {"-isystem", testRoot()};
   auto AST = TU.build();
-  EXPECT_THAT(computeUnusedIncludes(AST),
-              ElementsAre(Pointee(writtenInclusion("<queue>"))));
   IncludeCleanerFindings Findings = computeIncludeCleanerFindings(AST);
   EXPECT_THAT(Findings.UnusedIncludes,
               ElementsAre(Pointee(writtenInclusion("<queue>"))));
@@ -408,11 +125,6 @@
   TU.ExtraArgs.push_back("-isystem" + testPath("system"));
   TU.Code = MainFile.str();
   ParsedAST AST = TU.build();
-  EXPECT_THAT(
-      computeUnusedIncludes(AST),
-      UnorderedElementsAre(Pointee(writtenInclusion("\"unused.h\"")),
-                           Pointee(writtenInclusion("\"dir/unused.h\""))));
-
   IncludeCleanerFindings Findings = computeIncludeCleanerFindings(AST);
   EXPECT_THAT(
       Findings.UnusedIncludes,
@@ -544,142 +256,6 @@
                           "#include <vector>\n", "#include <vector>")))));
 }
 
-TEST(IncludeCleaner, VirtualBuffers) {
-  TestTU TU;
-  TU.Code = R"cpp(
-    #include "macros.h"
-
-    using flags::FLAGS_FOO;
-
-    // CLI will come from a define, __cplusplus is a built-in. In both cases, they
-    // come from non-existent files.
-    int y = CLI + __cplusplus;
-
-    int concat(a, b) = 42;
-    )cpp";
-  // The pasting operator in combination with DEFINE_FLAG will create
-  // ScratchBuffer with `flags::FLAGS_FOO` that will have FileID but not
-  // FileEntry.
-  TU.AdditionalFiles["macros.h"] = R"cpp(
-    #ifndef MACROS_H
-    #define MACROS_H
-
-    #define DEFINE_FLAG(X) \
-    namespace flags { \
-    int FLAGS_##X; \
-    } \
-
-    DEFINE_FLAG(FOO)
-
-    #define ab x
-    #define concat(x, y) x##y
-
-    #endif // MACROS_H
-    )cpp";
-  TU.ExtraArgs = {"-DCLI=42"};
-  ParsedAST AST = TU.build();
-  auto &SM = AST.getSourceManager();
-  auto &Includes = AST.getIncludeStructure();
-
-  auto ReferencedFiles = findReferencedFiles(
-      findReferencedLocations(AST), Includes, AST.getCanonicalIncludes(), SM);
-  llvm::StringSet<> ReferencedFileNames;
-  for (FileID FID : ReferencedFiles.User)
-    ReferencedFileNames.insert(
-        SM.getPresumedLoc(SM.getLocForStartOfFile(FID)).getFilename());
-  // Note we deduped the names as _number_ of <built-in>s is uninteresting.
-  EXPECT_THAT(ReferencedFileNames.keys(),
-              UnorderedElementsAre("<built-in>", "<scratch space>",
-                                   testPath("macros.h")));
-
-  // Should not crash due to FileIDs that are not headers.
-  auto ReferencedHeaders = translateToHeaderIDs(ReferencedFiles, Includes, SM);
-  std::vector<llvm::StringRef> ReferencedHeaderNames;
-  for (IncludeStructure::HeaderID HID : ReferencedHeaders)
-    ReferencedHeaderNames.push_back(Includes.getRealPath(HID));
-  // Non-header files are gone at this point.
-  EXPECT_THAT(ReferencedHeaderNames, ElementsAre(testPath("macros.h")));
-
-  // Sanity check.
-  EXPECT_THAT(
-      getUnused(AST, ReferencedHeaders, ReferencedFiles.SpelledUmbrellas),
-      IsEmpty());
-}
-
-TEST(IncludeCleaner, DistinctUnguardedInclusions) {
-  TestTU TU;
-  TU.Code = R"cpp(
-    #include "bar.h"
-    #include "foo.h"
-
-    int LocalFoo = foo::Variable;
-    )cpp";
-  TU.AdditionalFiles["foo.h"] = R"cpp(
-    #pragma once
-    namespace foo {
-    #include "unguarded.h"
-    }
-    )cpp";
-  TU.AdditionalFiles["bar.h"] = R"cpp(
-    #pragma once
-    namespace bar {
-    #include "unguarded.h"
-    }
-    )cpp";
-  TU.AdditionalFiles["unguarded.h"] = R"cpp(
-    constexpr int Variable = 42;
-    )cpp";
-
-  ParsedAST AST = TU.build();
-
-  auto ReferencedFiles = findReferencedFiles(
-      findReferencedLocations(AST), AST.getIncludeStructure(),
-      AST.getCanonicalIncludes(), AST.getSourceManager());
-  llvm::StringSet<> ReferencedFileNames;
-  auto &SM = AST.getSourceManager();
-  for (FileID FID : ReferencedFiles.User)
-    ReferencedFileNames.insert(
-        SM.getPresumedLoc(SM.getLocForStartOfFile(FID)).getFilename());
-  // Note that we have uplifted the referenced files from non self-contained
-  // headers to header-guarded ones.
-  EXPECT_THAT(ReferencedFileNames.keys(),
-              UnorderedElementsAre(testPath("foo.h")));
-}
-
-TEST(IncludeCleaner, NonSelfContainedHeaders) {
-  TestTU TU;
-  TU.Code = R"cpp(
-    #include "foo.h"
-
-    int LocalFoo = Variable;
-    )cpp";
-  TU.AdditionalFiles["foo.h"] = R"cpp(
-    #pragma once
-    #include "indirection.h"
-    )cpp";
-  TU.AdditionalFiles["indirection.h"] = R"cpp(
-    #include "unguarded.h"
-    )cpp";
-  TU.AdditionalFiles["unguarded.h"] = R"cpp(
-    constexpr int Variable = 42;
-    )cpp";
-
-  ParsedAST AST = TU.build();
-
-  auto ReferencedFiles = findReferencedFiles(
-      findReferencedLocations(AST), AST.getIncludeStructure(),
-      AST.getCanonicalIncludes(), AST.getSourceManager());
-  llvm::StringSet<> ReferencedFileNames;
-  auto &SM = AST.getSourceManager();
-  for (FileID FID : ReferencedFiles.User)
-    ReferencedFileNames.insert(
-        SM.getPresumedLoc(SM.getLocForStartOfFile(FID)).getFilename());
-  // Note that we have uplifted the referenced files from non self-contained
-  // headers to header-guarded ones.
-  EXPECT_THAT(ReferencedFileNames.keys(),
-              UnorderedElementsAre(testPath("foo.h")));
-}
-
 TEST(IncludeCleaner, IWYUPragmas) {
   TestTU TU;
   TU.Code = R"cpp(
@@ -697,52 +273,10 @@
     void foo() {}
   )cpp");
   Config Cfg;
-  Cfg.Diagnostics.UnusedIncludes = Config::IncludesPolicy::Experiment;
+  Cfg.Diagnostics.UnusedIncludes = Config::IncludesPolicy::Strict;
   WithContextValue Ctx(Config::Key, std::move(Cfg));
   ParsedAST AST = TU.build();
-
-  auto ReferencedFiles = findReferencedFiles(
-      findReferencedLocations(AST), AST.getIncludeStructure(),
-      AST.getCanonicalIncludes(), AST.getSourceManager());
-  EXPECT_EQ(ReferencedFiles.SpelledUmbrellas.size(), 1u);
-  EXPECT_EQ(ReferencedFiles.SpelledUmbrellas.begin()->getKey(), "\"public.h\"");
-  EXPECT_EQ(ReferencedFiles.User.size(), 2u);
-  EXPECT_TRUE(
-      ReferencedFiles.User.contains(AST.getSourceManager().getMainFileID()));
-  EXPECT_TRUE(
-      ReferencedFiles.User.contains(AST.getSourceManager().getMainFileID()));
-  EXPECT_THAT(AST.getDiagnostics(), llvm::ValueIs(IsEmpty()));
-  EXPECT_THAT(computeUnusedIncludes(AST), IsEmpty());
-  IncludeCleanerFindings Findings = computeIncludeCleanerFindings(AST);
-  EXPECT_THAT(Findings.UnusedIncludes, IsEmpty());
-}
-
-TEST(IncludeCleaner, RecursiveInclusion) {
-  TestTU TU;
-  TU.Code = R"cpp(
-    #include "foo.h"
-
-    void baz() {
-      foo();
-    }
-    )cpp";
-  TU.AdditionalFiles["foo.h"] = R"cpp(
-    #ifndef FOO_H
-    #define FOO_H
-
-    void foo() {}
-
-    #include "bar.h"
-
-    #endif
-  )cpp";
-  TU.AdditionalFiles["bar.h"] = guard(R"cpp(
-    #include "foo.h"
-  )cpp");
-  ParsedAST AST = TU.build();
-
   EXPECT_THAT(AST.getDiagnostics(), llvm::ValueIs(IsEmpty()));
-  EXPECT_THAT(computeUnusedIncludes(AST), IsEmpty());
   IncludeCleanerFindings Findings = computeIncludeCleanerFindings(AST);
   EXPECT_THAT(Findings.UnusedIncludes, IsEmpty());
 }
@@ -768,7 +302,6 @@
   EXPECT_THAT(AST.getDiagnostics(), llvm::ValueIs(IsEmpty()));
   // FIXME: This is not correct: foo.h is unused but is not diagnosed as such
   // because we ignore headers with IWYU export pragmas for now.
-  EXPECT_THAT(computeUnusedIncludes(AST), IsEmpty());
   IncludeCleanerFindings Findings = computeIncludeCleanerFindings(AST);
   EXPECT_THAT(Findings.UnusedIncludes, IsEmpty());
 }