[pseudo] Use the pseudoCXX library in fuzzer.

[hokein]

Summary

Get rid of the tedious grammar command-flag handling, and simply the
code.

[sammccall]

As discussed offline:

• this should really be a cross-cutting change for all tools
• we're going to have multiple grammars or variants (e.g. c, c++, obj-c)
• it would be nice to preserve the ability for tools to use a grammar from a file

This all points at having a library shared between {fuzzer, clang-pseudo, benchmark} that supports --grammar=cxx and --grammar=/some/path.

It needs to depend on CXX but isn't itself CXX, so I think it's a new library. Maybe clangPseudoCLI? I think for now the easiest thing is for the library to define the cl::opt flags and just expose functions to get the "current" grammar. (And maybe langopts should go there too)

clang-tools-extra/pseudo/fuzzer/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   FuzzerCLI
   Support
   )
 
 add_llvm_fuzzer(clang-pseudo-fuzzer
   Fuzzer.cpp
   DUMMY_MAIN Main.cpp
   )
 
 target_link_libraries(clang-pseudo-fuzzer
   PRIVATE
   clangPseudo
+  clangPseudoCXX
   clangPseudoGrammar
   )

clang-tools-extra/pseudo/fuzzer/Fuzzer.cpp

 //===-- Fuzzer.cpp - Fuzz the pseudoparser --------------------------------===//
 //
 // 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 "clang-pseudo/DirectiveTree.h"
 #include "clang-pseudo/Forest.h"
 #include "clang-pseudo/GLR.h"
 #include "clang-pseudo/Grammar.h"
 #include "clang-pseudo/LRTable.h"
 #include "clang-pseudo/Token.h"
+#include "clang-pseudo/cxx/CXX.h"
 #include "clang/Basic/LangOptions.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 
 namespace clang {
 namespace pseudo {
 namespace {
 
 class Fuzzer {
   clang::LangOptions LangOpts = clang::pseudo::genericLangOpts();
-  std::unique_ptr<Grammar> G;
-  LRTable T;
   bool Print;
 
 public:
-  Fuzzer(llvm::StringRef GrammarPath, bool Print) : Print(Print) {
-    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> GrammarText =
-        llvm::MemoryBuffer::getFile(GrammarPath);
-    if (std::error_code EC = GrammarText.getError()) {
-      llvm::errs() << "Error: can't read grammar file '" << GrammarPath
-                   << "': " << EC.message() << "\n";
-      std::exit(1);
-    }
-    std::vector<std::string> Diags;
-    G = Grammar::parseBNF(GrammarText->get()->getBuffer(), Diags);
-    if (!Diags.empty()) {
-      for (const auto &Diag : Diags)
-        llvm::errs() << Diag << "\n";
-      std::exit(1);
-    }
-    T = LRTable::buildSLR(*G);
-  }
+  Fuzzer(bool Print) : Print(Print) {}
 
   void operator()(llvm::StringRef Code) {
     std::string CodeStr = Code.str(); // Must be null-terminated.
     auto RawStream = lex(CodeStr, LangOpts);
     auto DirectiveStructure = DirectiveTree::parse(RawStream);
     clang::pseudo::chooseConditionalBranches(DirectiveStructure, RawStream);
     // FIXME: strip preprocessor directives
     auto ParseableStream =
         clang::pseudo::stripComments(cook(RawStream, LangOpts));
 
     clang::pseudo::ForestArena Arena;
     clang::pseudo::GSS GSS;
+    const auto &G = cxx::getGrammar();
+    const LRTable &T = cxx::getLRTable();
     auto &Root =
-        glrParse(ParseableStream, clang::pseudo::ParseParams{*G, T, Arena, GSS},
-                 *G->findNonterminal("translation-unit"));
+        glrParse(ParseableStream, clang::pseudo::ParseParams{G, T, Arena, GSS},
+                 static_cast<SymbolID>(cxx::Symbol::translation_unit));
     if (Print)
-      llvm::outs() << Root.dumpRecursive(*G);
+      llvm::outs() << Root.dumpRecursive(G);
   }
 };
 
 Fuzzer *Fuzz = nullptr;
 
 } // namespace
 } // namespace pseudo
 } // namespace clang
 
 extern "C" {
 
 // Set up the fuzzer from command line flags:
 //  -grammar=<file> (required) - path to cxx.bnf
 //  -print                     - used for testing the fuzzer
 int LLVMFuzzerInitialize(int *Argc, char ***Argv) {
-  llvm::StringRef GrammarFile;
   bool PrintForest = false;
   auto ConsumeArg = [&](llvm::StringRef Arg) -> bool {
-    if (Arg.consume_front("-grammar=")) {
-      GrammarFile = Arg;
-      return true;
-    } else if (Arg == "-print") {
+    if (Arg == "-print") {
       PrintForest = true;
       return true;
     }
     return false;
   };
   *Argc = std::remove_if(*Argv + 1, *Argv + *Argc, ConsumeArg) - *Argv;
 
-  if (GrammarFile.empty()) {
-    fprintf(stderr, "Fuzzer needs -grammar=/path/to/cxx.bnf\n");
-    exit(1);
-  }
-  clang::pseudo::Fuzz = new clang::pseudo::Fuzzer(GrammarFile, PrintForest);
+  clang::pseudo::Fuzz = new clang::pseudo::Fuzzer(PrintForest);
   return 0;
 }
 
 int LLVMFuzzerTestOneInput(uint8_t *Data, size_t Size) {
   (*clang::pseudo::Fuzz)(llvm::StringRef(reinterpret_cast<char *>(Data), Size));
   return 0;
 }
 }