text: #!/usr/bin/env python
  # encoding: utf-8
  # Christoph Koke, 2013
  
  """
  Writes the c and cpp compile commands into build/compile_commands.json
  see http://clang.llvm.org/docs/JSONCompilationDatabase.html
  
  Usage:
  
      def configure(conf):
          conf.load('compiler_cxx')
          ...
          conf.load('clang_compilation_database')
  """
  
  import sys, os, json, shlex, pipes
  from waflib import Logs, TaskGen, Task
  
  Task.TaskBase.keep_last_cmd = True
  
  if sys.hexversion >= 0x3030000:
      quote = shlex.quote
  else:
      quote = pipes.quote
  
  
  @TaskGen.feature('c', 'cxx')
  @TaskGen.after_method('process_use')
  def collect_compilation_db_tasks(self):
      "Add a compilation database entry for compiled tasks"
      try:
          clang_db = self.bld.clang_compilation_database_tasks
      except AttributeError:
          clang_db = self.bld.clang_compilation_database_tasks = []
          self.bld.add_post_fun(write_compilation_database)
  
      tup = tuple(y for y in [Task.classes.get(x) for x in ('c', 'cxx')] if y)
      for task in getattr(self, 'compiled_tasks', []):
          if isinstance(task, tup):
              clang_db.append(task)
  
  
  def write_compilation_database(ctx):
      "Write the clang compilation database as JSON"
      database_file = ctx.bldnode.make_node('compile_commands.json')
      Logs.info('Build commands will be stored in %s', database_file.path_from(ctx.path))
      try:
          root = json.load(database_file)
      except IOError:
          root = []
      clang_db = dict((x['file'], x) for x in root)
      for task in getattr(ctx, 'clang_compilation_database_tasks', []):
          try:
              cmd = task.last_cmd
          except AttributeError:
              continue
          directory = getattr(task, 'cwd', ctx.variant_dir)
          f_node = task.inputs[0]
          filename = os.path.relpath(f_node.abspath(), directory)
          cmd = " ".join(map(quote, cmd))
          entry = {
              "directory": directory,
              "command": cmd,
              "file": filename,
          }
          clang_db[filename] = entry
      root = list(clang_db.values())
      database_file.write(json.dumps(root, indent=2))
  