build: add option to generate a clang compilation database

The compilation database is a JSON file[1] storing all compilation flags. That
is useful for tools using libclang for code completion and error reporting
(for example: YouCompleteMe for vim).

[1]: http://clang.llvm.org/docs/JSONCompilationDatabase.html

waftools/clang_compilation_database.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python
+# encoding: utf-8
+# Christoph Koke, 2013
+# Original source: waflib/extras/clang_compilation_database.py from
+# waf git 15d14c7bdf2e (New BSD License)
+
+"""
+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
+from waflib.Tools import c, cxx
+
+if sys.hexversion >= 0x3030000:
+        quote = shlex.quote
+else:
+        quote = pipes.quote
+
+@TaskGen.feature('*')
+@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)
+
+        for task in getattr(self, 'compiled_tasks', []):
+                if isinstance(task, (c.c, cxx.cxx)):
+                        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))

wscript

@@ -84,6 +84,11 @@ build_options = [
         'name': '--test',
         'desc': 'test suite (using cmocka)',
         'func': check_pkg_config('cmocka >= 0.4.1'),
+    }, {
+        'name': '--clang-database',
+        'desc': 'generate a clang compilation database',
+        'func': check_true,
+        'default': 'disable',
     }
 ]
 
@@ -891,6 +896,9 @@ def configure(ctx):
     if not ctx.dependency_satisfied('build-date'):
         ctx.env.CFLAGS += ['-DNO_BUILD_TIMESTAMPS']
 
+    if ctx.dependency_satisfied('clang-database'):
+        ctx.load('clang_compilation_database')
+
     ctx.store_dependencies_lists()
 
 def build(ctx):