Index: cfe/trunk/docs/JSONCompilationDatabase.rst
===================================================================
--- cfe/trunk/docs/JSONCompilationDatabase.rst
+++ cfe/trunk/docs/JSONCompilationDatabase.rst
@@ -91,3 +91,9 @@
 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.
Index: cfe/trunk/include/clang/Tooling/CompilationDatabase.h
===================================================================
--- cfe/trunk/include/clang/Tooling/CompilationDatabase.h
+++ cfe/trunk/include/clang/Tooling/CompilationDatabase.h
@@ -182,6 +182,11 @@
       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);
Index: cfe/trunk/lib/Tooling/CompilationDatabase.cpp
===================================================================
--- cfe/trunk/lib/Tooling/CompilationDatabase.cpp
+++ cfe/trunk/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 @@
   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 @@
   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 {
 
Index: cfe/trunk/test/Tooling/Inputs/fixed-header.h
===================================================================
--- cfe/trunk/test/Tooling/Inputs/fixed-header.h
+++ cfe/trunk/test/Tooling/Inputs/fixed-header.h
@@ -0,0 +1 @@
+#define SECRET_SYMBOL 1
Index: cfe/trunk/test/Tooling/fixed-database.cpp
===================================================================
--- cfe/trunk/test/Tooling/fixed-database.cpp
+++ cfe/trunk/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, "");