[Tooling] Use FixedCompilationDatabase when compile_flags.txt is fo…

…und.

Summary:
This is an alternative to JSONCompilationDatabase for simple projects that
don't use a build system such as CMake.
(You can also drop one in ~, to make your tools use e.g. C++11 by default)

There's no facility for varying flags per-source-file or per-machine.
Possibly this could be accommodated backwards-compatibly using cpp, but even if
not the simplicity seems worthwhile for the cases that are addressed.

Tested with clangd, works great! (requires clangd restart)

Reviewers: klimek

Subscribers: ilya-biryukov, cfe-commits

Differential Revision: https://reviews.llvm.org/D39799

llvm-svn: 317777

clang/docs/JSONCompilationDatabase.rst

@@ -91,3 +91,9 @@ The convention is to name the file compile\_commands.json and put it at
 the top of the build directory. Clang tools are pointed to the top of
 the build directory to detect the file and use the compilation database
 to parse C++ code in the source tree.
+
+Alternatives
+============
+For simple projects, Clang tools also recognize a compile_flags.txt file.
+This should contain one flag per line. The same flags will be used to compile
+any file.

clang/include/clang/Tooling/CompilationDatabase.h

@@ -182,6 +182,11 @@ class FixedCompilationDatabase : public CompilationDatabase {
       int &Argc, const char *const *Argv, std::string &ErrorMsg,
       Twine Directory = ".");
 
+  /// Reads flags from the given file, one-per line.
+  /// Returns nullptr and sets ErrorMessage if we can't read the file.
+  static std::unique_ptr<FixedCompilationDatabase>
+  loadFromFile(StringRef Path, std::string &ErrorMsg);
+
   /// \brief Constructs a compilation data base from a specified directory
   /// and command line.
   FixedCompilationDatabase(Twine Directory, ArrayRef<std::string> CommandLine);

clang/lib/Tooling/CompilationDatabase.cpp

@@ -10,6 +10,9 @@
 //  This file contains implementations of the CompilationDatabase base class
 //  and the FixedCompilationDatabase.
 //
+//  FIXME: Various functions that take a string &ErrorMessage should be upgraded
+//  to Expected.
+//
 //===----------------------------------------------------------------------===//
 
 #include "clang/Tooling/CompilationDatabase.h"
@@ -26,6 +29,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Support/Host.h"
+#include "llvm/Support/LineIterator.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 #include <sstream>
@@ -302,8 +306,22 @@ FixedCompilationDatabase::loadFromCommandLine(int &Argc,
   std::vector<std::string> StrippedArgs;
   if (!stripPositionalArgs(CommandLine, StrippedArgs, ErrorMsg))
     return nullptr;
-  return std::unique_ptr<FixedCompilationDatabase>(
-      new FixedCompilationDatabase(Directory, StrippedArgs));
+  return llvm::make_unique<FixedCompilationDatabase>(Directory, StrippedArgs);
+}
+
+std::unique_ptr<FixedCompilationDatabase>
+FixedCompilationDatabase::loadFromFile(StringRef Path, std::string &ErrorMsg) {
+  ErrorMsg.clear();
+  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> File =
+      llvm::MemoryBuffer::getFile(Path);
+  if (std::error_code Result = File.getError()) {
+    ErrorMsg = "Error while opening fixed database: " + Result.message();
+    return nullptr;
+  }
+  std::vector<std::string> Args{llvm::line_iterator(**File),
+                                llvm::line_iterator()};
+  return llvm::make_unique<FixedCompilationDatabase>(
+      llvm::sys::path::parent_path(Path), std::move(Args));
 }
 
 FixedCompilationDatabase::
@@ -334,6 +352,22 @@ FixedCompilationDatabase::getAllCompileCommands() const {
   return std::vector<CompileCommand>();
 }
 
+namespace {
+
+class FixedCompilationDatabasePlugin : public CompilationDatabasePlugin {
+  std::unique_ptr<CompilationDatabase>
+  loadFromDirectory(StringRef Directory, std::string &ErrorMessage) override {
+    SmallString<1024> DatabasePath(Directory);
+    llvm::sys::path::append(DatabasePath, "compile_flags.txt");
+    return FixedCompilationDatabase::loadFromFile(DatabasePath, ErrorMessage);
+  }
+};
+
+static CompilationDatabasePluginRegistry::Add<FixedCompilationDatabasePlugin>
+X("fixed-compilation-database", "Reads plain-text flags file");
+
+} // namespace
+
 namespace clang {
 namespace tooling {
 

clang/test/Tooling/Inputs/fixed-header.h

@@ -0,0 +1 @@
+#define SECRET_SYMBOL 1

clang/test/Tooling/fixed-database.cpp

@@ -0,0 +1,18 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/Src
+// RUN: cp "%s" "%t/Src/test.cpp"
+// RUN: mkdir -p %t/Include
+// RUN: cp "%S/Inputs/fixed-header.h" "%t/Include/"
+// -I flag is relative to %t (where compile_flags is), not Src/.
+// RUN: echo '-IInclude/' >> %t/compile_flags.txt
+// RUN: echo "-Dklazz=class" >> %t/compile_flags.txt
+// RUN: echo '-std=c++11' >> %t/compile_flags.txt
+// RUN: clang-check "%t/Src/test.cpp" 2>&1
+// RUN: not clang-check "%s" 2>&1 | FileCheck "%s" -check-prefix=NODB
+
+// NODB: unknown type name 'klazz'
+klazz F{};
+
+// NODB: 'fixed-header.h' file not found
+#include "fixed-header.h"
+static_assert(SECRET_SYMBOL == 1, "");