Revert "[clang][pp] adds '#pragma include_instead'"

> `#pragma clang include_instead(<header>)` is a pragma that can be used
> by system headers (and only system headers) to indicate to a tool that
> the file containing said pragma is an implementation-detail header and
> should not be directly included by user code.
>
> The library alternative is very messy code that can be seen in the first
> diff of D106124, and we'd rather avoid that with something more
> universal.
>
> This patch takes the first step by warning a user when they include a
> detail header in their code, and suggests alternative headers that the
> user should include instead. Future work will involve adding a fixit to
> automate the process, as well as cleaning up modules diagnostics to not
> suggest said detail headers. Other tools, such as clangd can also take
> advantage of this pragma to add the correct user headers.
>
> Differential Revision: https://reviews.llvm.org/D106394

This caused compiler crashes in Chromium builds involving PCH and an include
directive with macro expansion, when Token::getLiteralData() returned null. See
the code review for details.

This reverts commit e8a64e5491.

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -300,12 +300,6 @@ def pp_pragma_once_in_main_file : Warning<"#pragma once in main file">,
 def pp_pragma_sysheader_in_main_file : Warning<
   "#pragma system_header ignored in main file">,
   InGroup<DiagGroup<"pragma-system-header-outside-header">>;
-
-def err_pragma_include_instead_not_sysheader : Error<
-  "'#pragma clang include_instead' cannot be used outside of system headers">;
-def err_pragma_include_instead_system_reserved : Error<
-  "header '%0' is an implementation detail; #include %select{'%2'|either '%2' or '%3'|one of %2}1 instead">;
-
 def pp_poisoning_existing_macro : Warning<"poisoning existing macro">;
 def pp_out_of_date_dependency : Warning<
   "current file is older than dependency %0">;

clang/include/clang/Lex/HeaderSearch.h

@@ -20,12 +20,9 @@
 #include "clang/Lex/ModuleMap.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallSet.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Allocator.h"
 #include <cassert>
 #include <cstddef>
@@ -113,14 +110,6 @@ struct HeaderFileInfo {
   /// of the framework.
   StringRef Framework;
 
-  /// List of aliases that this header is known as.
-  /// Most headers should only have at most one alias, but a handful
-  /// have two.
-  llvm::SetVector<llvm::SmallString<32>,
-                  llvm::SmallVector<llvm::SmallString<32>, 2>,
-                  llvm::SmallSet<llvm::SmallString<32>, 2>>
-      Aliases;
-
   HeaderFileInfo()
       : isImport(false), isPragmaOnce(false), DirInfo(SrcMgr::C_User),
         External(false), isModuleHeader(false), isCompilingModuleHeader(false),
@@ -464,10 +453,6 @@ public:
     getFileInfo(File).DirInfo = SrcMgr::C_System;
   }
 
-  void AddFileAlias(const FileEntry *File, StringRef Alias) {
-    getFileInfo(File).Aliases.insert(Alias);
-  }
-
   /// Mark the specified file as part of a module.
   void MarkFileModuleHeader(const FileEntry *FE,
                             ModuleMap::ModuleHeaderRole Role,

clang/include/clang/Lex/Preprocessor.h

@@ -1953,8 +1953,7 @@ public:
   /// This either returns the EOF token and returns true, or
   /// pops a level off the include stack and returns false, at which point the
   /// client should call lex again.
-  bool HandleEndOfFile(Token &Result, SourceLocation Loc,
-                       bool isEndOfMacro = false);
+  bool HandleEndOfFile(Token &Result, bool isEndOfMacro = false);
 
   /// Callback invoked when the current TokenLexer hits the end of its
   /// token stream.
@@ -2364,14 +2363,12 @@ private:
 
   // Pragmas.
   void HandlePragmaDirective(PragmaIntroducer Introducer);
-  void ResolvePragmaIncludeInstead(SourceLocation Location) const;
 
 public:
   void HandlePragmaOnce(Token &OnceTok);
   void HandlePragmaMark(Token &MarkTok);
   void HandlePragmaPoison();
   void HandlePragmaSystemHeader(Token &SysHeaderTok);
-  void HandlePragmaIncludeInstead(Token &Tok);
   void HandlePragmaDependency(Token &DependencyTok);
   void HandlePragmaPushMacro(Token &Tok);
   void HandlePragmaPopMacro(Token &Tok);

clang/include/clang/Lex/PreprocessorLexer.h

@@ -14,13 +14,11 @@
 #ifndef LLVM_CLANG_LEX_PREPROCESSORLEXER_H
 #define LLVM_CLANG_LEX_PREPROCESSORLEXER_H
 
-#include "clang/Basic/SourceLocation.h"
-#include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/MultipleIncludeOpt.h"
 #include "clang/Lex/Token.h"
+#include "clang/Basic/SourceLocation.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringMap.h"
 #include <cassert>
 
 namespace clang {
@@ -76,13 +74,6 @@ protected:
   /// we are currently in.
   SmallVector<PPConditionalInfo, 4> ConditionalStack;
 
-  struct IncludeInfo {
-    const FileEntry *File;
-    SourceLocation Location;
-  };
-  // A complete history of all the files included by the current file.
-  llvm::StringMap<IncludeInfo> IncludeHistory;
-
   PreprocessorLexer() : FID() {}
   PreprocessorLexer(Preprocessor *pp, FileID fid);
   virtual ~PreprocessorLexer() = default;
@@ -184,15 +175,6 @@ public:
     ConditionalStack.clear();
     ConditionalStack.append(CL.begin(), CL.end());
   }
-
-  void addInclude(StringRef Filename, const FileEntry &File,
-                  SourceLocation Location) {
-    IncludeHistory.insert({Filename, {&File, Location}});
-  }
-
-  const llvm::StringMap<IncludeInfo> &getIncludeHistory() const {
-    return IncludeHistory;
-  }
 };
 
 } // namespace clang

clang/lib/Lex/Lexer.cpp

@@ -2811,11 +2811,11 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
     ConditionalStack.pop_back();
   }
 
-  SourceLocation EndLoc = getSourceLocation(BufferEnd);
   // C99 5.1.1.2p2: If the file is non-empty and didn't end in a newline, issue
   // a pedwarn.
   if (CurPtr != BufferStart && (CurPtr[-1] != '\n' && CurPtr[-1] != '\r')) {
     DiagnosticsEngine &Diags = PP->getDiagnostics();
+    SourceLocation EndLoc = getSourceLocation(BufferEnd);
     unsigned DiagID;
 
     if (LangOpts.CPlusPlus11) {
@@ -2838,7 +2838,7 @@ bool Lexer::LexEndOfFile(Token &Result, const char *CurPtr) {
   BufferPtr = CurPtr;
 
   // Finally, let the preprocessor handle this.
-  return PP->HandleEndOfFile(Result, EndLoc, isPragmaLexer());
+  return PP->HandleEndOfFile(Result, isPragmaLexer());
 }
 
 /// isNextPPTokenLParen - Return 1 if the next unexpanded token lexed from

clang/lib/Lex/PPDirectives.cpp

@@ -2022,12 +2022,6 @@ Preprocessor::ImportAction Preprocessor::HandleHeaderIncludeOrImport(
       IsFrameworkFound, IsImportDecl, IsMapped, LookupFrom, LookupFromFile,
       LookupFilename, RelativePath, SearchPath, SuggestedModule, isAngled);
 
-  // Record the header's filename for later use.
-  if (File)
-    CurLexer->addInclude(
-        {FilenameTok.getLiteralData(), FilenameTok.getLength()},
-        File->getFileEntry(), FilenameLoc);
-
   if (usingPCHWithThroughHeader() && SkippingUntilPCHThroughHeader) {
     if (File && isPCHThroughHeader(&File->getFileEntry()))
       SkippingUntilPCHThroughHeader = false;

clang/lib/Lex/PPLexerChange.cpp

@@ -12,7 +12,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Basic/FileManager.h"
-#include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/LexDiagnostic.h"
@@ -23,7 +22,6 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBufferRef.h"
 #include "llvm/Support/Path.h"
-
 using namespace clang;
 
 //===----------------------------------------------------------------------===//
@@ -301,46 +299,10 @@ void Preprocessor::diagnoseMissingHeaderInUmbrellaDir(const Module &Mod) {
   }
 }
 
-void Preprocessor::ResolvePragmaIncludeInstead(
-    const SourceLocation Location) const {
-  assert(Location.isValid());
-  if (CurLexer == nullptr)
-    return;
-
-  if (SourceMgr.isInSystemHeader(Location))
-    return;
-
-  for (const auto &Include : CurLexer->getIncludeHistory()) {
-    StringRef Filename = Include.getKey();
-    const PreprocessorLexer::IncludeInfo &Info = Include.getValue();
-    ArrayRef<SmallString<32>> Aliases =
-        HeaderInfo.getFileInfo(Info.File).Aliases.getArrayRef();
-
-    if (Aliases.empty())
-      continue;
-
-    switch (Aliases.size()) {
-    case 1:
-      Diag(Info.Location, diag::err_pragma_include_instead_system_reserved)
-          << Filename << 0 << Aliases[0];
-      continue;
-    case 2:
-      Diag(Info.Location, diag::err_pragma_include_instead_system_reserved)
-          << Filename << 1 << Aliases[0] << Aliases[1];
-      continue;
-    default: {
-      Diag(Info.Location, diag::err_pragma_include_instead_system_reserved)
-          << Filename << 2 << ("{'" + llvm::join(Aliases, "', '") + "'}");
-    }
-    }
-  }
-}
-
 /// HandleEndOfFile - This callback is invoked when the lexer hits the end of
 /// the current file.  This either returns the EOF token or pops a level off
 /// the include stack and keeps going.
-bool Preprocessor::HandleEndOfFile(Token &Result, SourceLocation EndLoc,
-                                   bool isEndOfMacro) {
+bool Preprocessor::HandleEndOfFile(Token &Result, bool isEndOfMacro) {
   assert(!CurTokenLexer &&
          "Ending a file when currently in a macro!");
 
@@ -410,9 +372,6 @@ bool Preprocessor::HandleEndOfFile(Token &Result, SourceLocation EndLoc,
     }
   }
 
-  if (EndLoc.isValid())
-    ResolvePragmaIncludeInstead(EndLoc);
-
   // Complain about reaching a true EOF within arc_cf_code_audited.
   // We don't want to complain about reaching the end of a macro
   // instantiation or a _Pragma.
@@ -601,7 +560,7 @@ bool Preprocessor::HandleEndOfTokenLexer(Token &Result) {
     TokenLexerCache[NumCachedTokenLexers++] = std::move(CurTokenLexer);
 
   // Handle this like a #include file being popped off the stack.
-  return HandleEndOfFile(Result, {}, true);
+  return HandleEndOfFile(Result, true);
 }
 
 /// RemoveTopOfLexerStack - Pop the current lexer/macro exp off the top of the

clang/lib/Lex/Pragma.cpp

@@ -13,7 +13,6 @@
 
 #include "clang/Lex/Pragma.h"
 #include "clang/Basic/Diagnostic.h"
-#include "clang/Basic/DiagnosticLex.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
@@ -36,12 +35,11 @@
 #include "clang/Lex/TokenLexer.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Timer.h"
@@ -497,88 +495,43 @@ void Preprocessor::HandlePragmaSystemHeader(Token &SysHeaderTok) {
                         SrcMgr::C_System);
 }
 
-static llvm::Optional<Token> LexHeader(Preprocessor &PP,
-                                       Optional<FileEntryRef> &File,
-                                       bool SuppressIncludeNotFoundError) {
+/// HandlePragmaDependency - Handle \#pragma GCC dependency "foo" blah.
+void Preprocessor::HandlePragmaDependency(Token &DependencyTok) {
   Token FilenameTok;
-  if (PP.LexHeaderName(FilenameTok, /*AllowConcatenation*/ false))
-    return llvm::None;
+  if (LexHeaderName(FilenameTok, /*AllowConcatenation*/false))
+    return;
 
   // If the next token wasn't a header-name, diagnose the error.
   if (FilenameTok.isNot(tok::header_name)) {
-    PP.Diag(FilenameTok.getLocation(), diag::err_pp_expects_filename);
-    return llvm::None;
+    Diag(FilenameTok.getLocation(), diag::err_pp_expects_filename);
+    return;
   }
 
   // Reserve a buffer to get the spelling.
   SmallString<128> FilenameBuffer;
   bool Invalid = false;
-  StringRef Filename = PP.getSpelling(FilenameTok, FilenameBuffer, &Invalid);
+  StringRef Filename = getSpelling(FilenameTok, FilenameBuffer, &Invalid);
   if (Invalid)
-    return llvm::None;
+    return;
 
   bool isAngled =
-      PP.GetIncludeFilenameSpelling(FilenameTok.getLocation(), Filename);
+    GetIncludeFilenameSpelling(FilenameTok.getLocation(), Filename);
   // If GetIncludeFilenameSpelling set the start ptr to null, there was an
   // error.
   if (Filename.empty())
-    return llvm::None;
+    return;
 
   // Search include directories for this file.
   const DirectoryLookup *CurDir;
-  File = PP.LookupFile(FilenameTok.getLocation(), Filename, isAngled, nullptr,
-                       nullptr, CurDir, nullptr, nullptr, nullptr, nullptr,
-                       nullptr);
+  Optional<FileEntryRef> File =
+      LookupFile(FilenameTok.getLocation(), Filename, isAngled, nullptr,
+                 nullptr, CurDir, nullptr, nullptr, nullptr, nullptr, nullptr);
   if (!File) {
     if (!SuppressIncludeNotFoundError)
-      PP.Diag(FilenameTok, diag::err_pp_file_not_found) << Filename;
-    return llvm::None;
-  }
-
-  return FilenameTok;
-}
-
-/// HandlePragmaIncludeInstead - Handle \#pragma clang include_instead(header).
-void Preprocessor::HandlePragmaIncludeInstead(Token &Tok) {
-  // Get the current file lexer we're looking at.  Ignore _Pragma 'files' etc.
-  PreprocessorLexer *TheLexer = getCurrentFileLexer();
-
-  if (!SourceMgr.isInSystemHeader(Tok.getLocation())) {
-    Diag(Tok, diag::err_pragma_include_instead_not_sysheader);
+      Diag(FilenameTok, diag::err_pp_file_not_found) << Filename;
     return;
   }
 
-  Lex(Tok);
-  if (Tok.isNot(tok::l_paren)) {
-    Diag(Tok, diag::err_expected) << "(";
-    return;
-  }
-
-  Optional<FileEntryRef> File;
-  llvm::Optional<Token> FilenameTok =
-      LexHeader(*this, File, SuppressIncludeNotFoundError);
-  if (!FilenameTok)
-    return;
-
-  Lex(Tok);
-  if (Tok.isNot(tok::r_paren)) {
-    Diag(Tok, diag::err_expected) << ")";
-    return;
-  }
-
-  HeaderInfo.AddFileAlias(
-      TheLexer->getFileEntry(),
-      {FilenameTok->getLiteralData(), FilenameTok->getLength()});
-}
-
-/// HandlePragmaDependency - Handle \#pragma GCC dependency "foo" blah.
-void Preprocessor::HandlePragmaDependency(Token &DependencyTok) {
-  Optional<FileEntryRef> File;
-  llvm::Optional<Token> FilenameTok =
-      LexHeader(*this, File, SuppressIncludeNotFoundError);
-  if (!FilenameTok)
-    return;
-
   const FileEntry *CurFile = getCurrentFileLexer()->getFileEntry();
 
   // If this file is older than the file it depends on, emit a diagnostic.
@@ -594,7 +547,7 @@ void Preprocessor::HandlePragmaDependency(Token &DependencyTok) {
     // Remove the trailing ' ' if present.
     if (!Message.empty())
       Message.erase(Message.end()-1);
-    Diag(*FilenameTok, diag::pp_out_of_date_dependency) << Message;
+    Diag(FilenameTok, diag::pp_out_of_date_dependency) << Message;
   }
 }
 
@@ -1069,18 +1022,6 @@ struct PragmaSystemHeaderHandler : public PragmaHandler {
   }
 };
 
-/// PragmaIncludeInsteadHandler - "\#pragma clang include_instead(header)" marks
-/// the current file as non-includable if the including header is not a system
-/// header.
-struct PragmaIncludeInsteadHandler : public PragmaHandler {
-  PragmaIncludeInsteadHandler() : PragmaHandler("include_instead") {}
-
-  void HandlePragma(Preprocessor &PP, PragmaIntroducer Introducer,
-                    Token &IIToken) override {
-    PP.HandlePragmaIncludeInstead(IIToken);
-  }
-};
-
 struct PragmaDependencyHandler : public PragmaHandler {
   PragmaDependencyHandler() : PragmaHandler("dependency") {}
 
@@ -1993,7 +1934,6 @@ void Preprocessor::RegisterBuiltinPragmas() {
   // #pragma clang ...
   AddPragmaHandler("clang", new PragmaPoisonHandler());
   AddPragmaHandler("clang", new PragmaSystemHeaderHandler());
-  AddPragmaHandler("clang", new PragmaIncludeInsteadHandler());
   AddPragmaHandler("clang", new PragmaDebugHandler());
   AddPragmaHandler("clang", new PragmaDependencyHandler());
   AddPragmaHandler("clang", new PragmaDiagnosticHandler("clang"));

clang/test/Preprocessor/Inputs/include_instead/bad-syntax.h

@@ -1,7 +0,0 @@
-#pragma GCC system_header
-
-#pragma clang include_instead <include_instead/public-before.h>
-// expected-error@-1{{expected (}}
-
-#pragma clang include_instead(<include_instead/public-after.h>]
-// expected-error@-1{{expected )}}

clang/test/Preprocessor/Inputs/include_instead/file-not-found.h

@@ -1,3 +0,0 @@
-#pragma GCC system_header
-#pragma clang include_instead(<include_instead/does_not_exist.h>)
-// expected-error@-1{{'include_instead/does_not_exist.h' file not found}}

clang/test/Preprocessor/Inputs/include_instead/non-system-header.h

@@ -1,2 +0,0 @@
-#pragma clang include_instead(<include_instead/public1.h>)
-// expected-error@-1{{'#pragma clang include_instead' cannot be used outside of system headers}}

clang/test/Preprocessor/Inputs/include_instead/private-x.h

@@ -1,4 +0,0 @@
-#include <include_instead/private1.h>
-
-#pragma GCC system_header
-#pragma clang include_instead(<include_instead/public-gcc-system-header-before-includes.h>)

clang/test/Preprocessor/Inputs/include_instead/private1.h

@@ -1,2 +0,0 @@
-#pragma GCC system_header
-#pragma clang include_instead(<include_instead/public-before.h>)

clang/test/Preprocessor/Inputs/include_instead/private2.h

@@ -1,4 +0,0 @@
-#pragma GCC system_header
-
-#pragma clang include_instead(<include_instead/public-before.h>)
-#pragma clang include_instead("include_instead/public-after.h")

clang/test/Preprocessor/Inputs/include_instead/private3.h

@@ -1,5 +0,0 @@
-#pragma GCC system_header
-
-#pragma clang include_instead(<include_instead/public-after.h>)
-#pragma clang include_instead(<include_instead/public-empty.h>)
-#pragma clang include_instead("include_instead/public-before.h")

clang/test/Preprocessor/Inputs/include_instead/public-after.h

@@ -1,2 +0,0 @@
-#include <include_instead/private2.h>
-#pragma GCC system_header

clang/test/Preprocessor/Inputs/include_instead/public-before.h

@@ -1,5 +0,0 @@
-#pragma GCC system_header
-
-#include <include_instead/private1.h> // no warning expected
-#include <include_instead/private2.h> // no warning expected
-#include <include_instead/private3.h> // no warning expected

clang/test/Preprocessor/Inputs/include_instead/public-empty.h

@@ -1 +0,0 @@
-// This file simply needs to exist.

clang/test/Preprocessor/include_instead.cpp

@@ -1,16 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -I %S/Inputs %s
-
-#include <include_instead/bad-syntax.h>
-#include <include_instead/non-system-header.h>
-
-#include <include_instead/private1.h>
-// expected-error@-1{{header '<include_instead/private1.h>' is an implementation detail; #include '<include_instead/public-before.h>' instead}}
-
-#include "include_instead/private2.h"
-// expected-error@-1{{header '"include_instead/private2.h"' is an implementation detail; #include either '<include_instead/public-before.h>' or '"include_instead/public-after.h"' instead}}
-
-#include <include_instead/private3.h>
-// expected-error@-1{{header '<include_instead/private3.h>' is an implementation detail; #include one of {'<include_instead/public-after.h>', '<include_instead/public-empty.h>', '"include_instead/public-before.h"'} instead}}
-
-#include <include_instead/public-before.h>
-#include <include_instead/public-after.h>

clang/test/Preprocessor/include_instead_file_not_found.cpp

@@ -1,2 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -I %S/Inputs %s
-#include <include_instead/file-not-found.h>