Reland "[clang] Refactor to remove clangDriver dependency from clangFrontend and flangFrontend" (#169599)

This relands #165277 by reverting #169397.
This also relands the corresponding Bazel port by reverting #169410.

The original revert was due to a report of a broken build, which was
later resolved by fully clearing the build directory.

Author: naveen-seth

clang-tools-extra/clangd/CompileCommands.cpp

@@ -132,8 +132,7 @@ std::optional<std::string> detectSysroot() {
 
 std::string detectStandardResourceDir() {
   static int StaticForMainAddr; // Just an address in this process.
-  return CompilerInvocation::GetResourcesPath("clangd",
-                                              (void *)&StaticForMainAddr);
+  return GetResourcesPath("clangd", (void *)&StaticForMainAddr);
 }
 
 // The path passed to argv[0] is important:

clang-tools-extra/clangd/Compiler.cpp

@@ -9,6 +9,7 @@
 #include "Compiler.h"
 #include "support/Logger.h"
 #include "clang/Basic/TargetInfo.h"
+#include "clang/Driver/CreateInvocationFromArgs.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Serialization/PCHContainerOperations.h"

clang/docs/ReleaseNotes.rst

@@ -84,6 +84,8 @@ Potentially Breaking Changes
 - Downstream projects that previously linked only against ``clangDriver`` may
   now (also) need to link against the new ``clangOptions`` library, since
   options-related code has been moved out of the Driver into a separate library.
+- The ``clangFrontend`` library no longer depends on ``clangDriver``, which may
+  break downstream projects that relied on this transitive dependency.
 
 C/C++ Language Potentially Breaking Changes
 -------------------------------------------

clang/include/clang/Driver/CommonArgs.h

@@ -291,16 +291,6 @@ void handleVectorizeLoopsArgs(const llvm::opt::ArgList &Args,
 void handleVectorizeSLPArgs(const llvm::opt::ArgList &Args,
                             llvm::opt::ArgStringList &CmdArgs);
 
-// Parse -mprefer-vector-width=. Return the Value string if well-formed.
-// Otherwise, return an empty string and issue a diagnosic message if needed.
-StringRef parseMPreferVectorWidthOption(clang::DiagnosticsEngine &Diags,
-                                        const llvm::opt::ArgList &Args);
-
-// Parse -mrecip. Return the Value string if well-formed.
-// Otherwise, return an empty string and issue a diagnosic message if needed.
-StringRef parseMRecipOption(clang::DiagnosticsEngine &Diags,
-                            const llvm::opt::ArgList &Args);
-
 // Convert ComplexRangeKind to a string that can be passed as a frontend option.
 std::string complexRangeKindToStr(LangOptions::ComplexRangeKind Range);
 

clang/include/clang/Driver/CreateASTUnitFromArgs.h

@@ -0,0 +1,80 @@
+//===-- CreateInvocationFromArgs.h - Create an ASTUnit from Args-*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Utility for creating an ASTUnit from a vector of command line arguments.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_DRIVER_CREATEASTUNITFROMARGS_H
+#define LLVM_CLANG_DRIVER_CREATEASTUNITFROMARGS_H
+
+#include "clang/Frontend/ASTUnit.h"
+
+namespace clang {
+
+/// Create an ASTUnit from a vector of command line arguments, which must
+/// specify exactly one source file.
+///
+/// \param ArgBegin - The beginning of the argument vector.
+///
+/// \param ArgEnd - The end of the argument vector.
+///
+/// \param PCHContainerOps - The PCHContainerOperations to use for loading and
+/// creating modules.
+///
+/// \param Diags - The diagnostics engine to use for reporting errors; its
+/// lifetime is expected to extend past that of the returned ASTUnit.
+///
+/// \param ResourceFilesPath - The path to the compiler resource files.
+///
+/// \param StorePreamblesInMemory - Whether to store PCH in memory. If false,
+/// PCH are stored in temporary files.
+///
+/// \param PreambleStoragePath - The path to a directory, in which to create
+/// temporary PCH files. If empty, the default system temporary directory is
+/// used. This parameter is ignored if \p StorePreamblesInMemory is true.
+///
+/// \param ModuleFormat - If provided, uses the specific module format.
+///
+/// \param ErrAST - If non-null and parsing failed without any AST to return
+/// (e.g. because the PCH could not be loaded), this accepts the ASTUnit
+/// mainly to allow the caller to see the diagnostics.
+///
+/// \param VFS - A llvm::vfs::FileSystem to be used for all file accesses.
+/// Note that preamble is saved to a temporary directory on a RealFileSystem,
+/// so in order for it to be loaded correctly, VFS should have access to
+/// it(i.e., be an overlay over RealFileSystem). RealFileSystem will be used
+/// if \p VFS is nullptr.
+///
+// FIXME: Move OnlyLocalDecls, UseBumpAllocator to setters on the ASTUnit, we
+// shouldn't need to specify them at construction time.
+std::unique_ptr<ASTUnit> CreateASTUnitFromCommandLine(
+    const char **ArgBegin, const char **ArgEnd,
+    std::shared_ptr<PCHContainerOperations> PCHContainerOps,
+    std::shared_ptr<DiagnosticOptions> DiagOpts,
+    IntrusiveRefCntPtr<DiagnosticsEngine> Diags, StringRef ResourceFilesPath,
+    bool StorePreamblesInMemory = false,
+    StringRef PreambleStoragePath = StringRef(), bool OnlyLocalDecls = false,
+    CaptureDiagsKind CaptureDiagnostics = CaptureDiagsKind::None,
+    ArrayRef<ASTUnit::RemappedFile> RemappedFiles = {},
+    bool RemappedFilesKeepOriginalName = true,
+    unsigned PrecompilePreambleAfterNParses = 0,
+    TranslationUnitKind TUKind = TU_Complete,
+    bool CacheCodeCompletionResults = false,
+    bool IncludeBriefCommentsInCodeCompletion = false,
+    bool AllowPCHWithCompilerErrors = false,
+    SkipFunctionBodiesScope SkipFunctionBodies = SkipFunctionBodiesScope::None,
+    bool SingleFileParse = false, bool UserFilesAreVolatile = false,
+    bool ForSerialization = false, bool RetainExcludedConditionalBlocks = false,
+    std::optional<StringRef> ModuleFormat = std::nullopt,
+    std::unique_ptr<ASTUnit> *ErrAST = nullptr,
+    IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS = nullptr);
+
+} // namespace clang
+
+#endif // LLVM_CLANG_DRIVER_CREATEASTUNITFROMARGS_H

clang/include/clang/Driver/CreateInvocationFromArgs.h

@@ -0,0 +1,76 @@
+//===--- CreateInvocationFromArgs.h - CompilerInvocation from Args --------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Utility for creating a CompilerInvocation from command-line arguments, for
+// tools to use in preparation to parse a file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_DRIVER_CREATEINVOCATIONFROMARGS_H
+#define LLVM_CLANG_DRIVER_CREATEINVOCATIONFROMARGS_H
+
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/LLVM.h"
+#include "llvm/Support/VirtualFileSystem.h"
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace clang {
+
+class CompilerInvocation;
+class DiagnosticsEngine;
+
+/// Optional inputs to createInvocation.
+struct CreateInvocationOptions {
+  /// Receives diagnostics encountered while parsing command-line flags.
+  /// If not provided, these are printed to stderr.
+  IntrusiveRefCntPtr<DiagnosticsEngine> Diags = nullptr;
+  /// Used e.g. to probe for system headers locations.
+  /// If not provided, the real filesystem is used.
+  /// FIXME: the driver does perform some non-virtualized IO.
+  IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS = nullptr;
+  /// Whether to attempt to produce a non-null (possibly incorrect) invocation
+  /// if any errors were encountered.
+  /// By default, always return null on errors.
+  bool RecoverOnError = false;
+  /// Allow the driver to probe the filesystem for PCH files.
+  /// This is used to replace -include with -include-pch in the cc1 args.
+  /// FIXME: ProbePrecompiled=true is a poor, historical default.
+  /// It misbehaves if the PCH file is from GCC, has the wrong version, etc.
+  bool ProbePrecompiled = false;
+  /// If set, the target is populated with the cc1 args produced by the driver.
+  /// This may be populated even if createInvocation returns nullptr.
+  std::vector<std::string> *CC1Args = nullptr;
+};
+
+/// Interpret clang arguments in preparation to parse a file.
+///
+/// This simulates a number of steps Clang takes when its driver is invoked:
+/// - choosing actions (e.g compile + link) to run
+/// - probing the system for settings like standard library locations
+/// - spawning a cc1 subprocess to compile code, with more explicit arguments
+/// - in the cc1 process, assembling those arguments into a CompilerInvocation
+///   which is used to configure the parser
+///
+/// This simulation is lossy, e.g. in some situations one driver run would
+/// result in multiple parses. (Multi-arch, CUDA, ...).
+/// This function tries to select a reasonable invocation that tools should use.
+///
+/// Args[0] should be the driver name, such as "clang" or "/usr/bin/g++".
+/// Absolute path is preferred - this affects searching for system headers.
+///
+/// May return nullptr if an invocation could not be determined.
+/// See CreateInvocationOptions::RecoverOnError to try harder!
+std::unique_ptr<CompilerInvocation>
+createInvocation(ArrayRef<const char *> Args,
+                 CreateInvocationOptions Opts = {});
+
+} // namespace clang
+
+#endif // LLVM_CLANG_DRIVER_CREATEINVOCATIONFROMARGS_H

clang/include/clang/Driver/Driver.h

@@ -406,10 +406,6 @@ class Driver {
                               SmallString<128> &CrashDiagDir);
 
 public:
-  /// Takes the path to a binary that's either in bin/ or lib/ and returns
-  /// the path to clang's resource directory.
-  static std::string GetResourcesPath(StringRef BinaryPath);
-
   Driver(StringRef ClangExecutable, StringRef TargetTriple,
          DiagnosticsEngine &Diags, std::string Title = "clang LLVM compiler",
          IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS = nullptr);