Merge pull request #4814 from mensinda/astVisitor

rewriter: Rewrote the meson rewriter - now works with AST modification

6 files changed, 911 insertions, 0 deletions

diff --git a/mesonbuild/ast/__init__.py b/mesonbuild/ast/__init__.py
new file mode 100644
index 0000000..a9370dc
--- /dev/null
+++ b/mesonbuild/ast/__init__.py
@@ -0,0 +1,32 @@
+# Copyright 2019 The Meson development team
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool.
+
+__all__ = [
+    'AstInterpreter',
+    'AstIDGenerator',
+    'AstIndentationGenerator',
+    'AstVisitor',
+    'AstPrinter',
+    'IntrospectionInterpreter',
+    'build_target_functions',
+]
+
+from .interpreter import AstInterpreter
+from .introspection import IntrospectionInterpreter, build_target_functions
+from .visitor import AstVisitor
+from .postprocess import AstIDGenerator, AstIndentationGenerator
+from .printer import AstPrinter
diff --git a/mesonbuild/ast/interpreter.py b/mesonbuild/ast/interpreter.py
new file mode 100644
index 0000000..2071432
--- /dev/null
+++ b/mesonbuild/ast/interpreter.py
@@ -0,0 +1,209 @@
+# Copyright 2016 The Meson development team
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool.
+
+from .. import interpreterbase, mparser, mesonlib
+from .. import environment
+
+from ..interpreterbase import InvalidArguments, BreakRequest, ContinueRequest
+
+import os, sys
+
+class DontCareObject(interpreterbase.InterpreterObject):
+    pass
+
+class MockExecutable(interpreterbase.InterpreterObject):
+    pass
+
+class MockStaticLibrary(interpreterbase.InterpreterObject):
+    pass
+
+class MockSharedLibrary(interpreterbase.InterpreterObject):
+    pass
+
+class MockCustomTarget(interpreterbase.InterpreterObject):
+    pass
+
+class MockRunTarget(interpreterbase.InterpreterObject):
+    pass
+
+ADD_SOURCE = 0
+REMOVE_SOURCE = 1
+
+class AstInterpreter(interpreterbase.InterpreterBase):
+    def __init__(self, source_root, subdir):
+        super().__init__(source_root, subdir)
+        self.visited_subdirs = {}
+        self.assignments = {}
+        self.funcs.update({'project': self.func_do_nothing,
+                           'test': self.func_do_nothing,
+                           'benchmark': self.func_do_nothing,
+                           'install_headers': self.func_do_nothing,
+                           'install_man': self.func_do_nothing,
+                           'install_data': self.func_do_nothing,
+                           'install_subdir': self.func_do_nothing,
+                           'configuration_data': self.func_do_nothing,
+                           'configure_file': self.func_do_nothing,
+                           'find_program': self.func_do_nothing,
+                           'include_directories': self.func_do_nothing,
+                           'add_global_arguments': self.func_do_nothing,
+                           'add_global_link_arguments': self.func_do_nothing,
+                           'add_project_arguments': self.func_do_nothing,
+                           'add_project_link_arguments': self.func_do_nothing,
+                           'message': self.func_do_nothing,
+                           'generator': self.func_do_nothing,
+                           'error': self.func_do_nothing,
+                           'run_command': self.func_do_nothing,
+                           'assert': self.func_do_nothing,
+                           'subproject': self.func_do_nothing,
+                           'dependency': self.func_do_nothing,
+                           'get_option': self.func_do_nothing,
+                           'join_paths': self.func_do_nothing,
+                           'environment': self.func_do_nothing,
+                           'import': self.func_do_nothing,
+                           'vcs_tag': self.func_do_nothing,
+                           'add_languages': self.func_do_nothing,
+                           'declare_dependency': self.func_do_nothing,
+                           'files': self.func_do_nothing,
+                           'executable': self.func_do_nothing,
+                           'static_library': self.func_do_nothing,
+                           'shared_library': self.func_do_nothing,
+                           'library': self.func_do_nothing,
+                           'build_target': self.func_do_nothing,
+                           'custom_target': self.func_do_nothing,
+                           'run_target': self.func_do_nothing,
+                           'subdir': self.func_subdir,
+                           'set_variable': self.func_do_nothing,
+                           'get_variable': self.func_do_nothing,
+                           'is_variable': self.func_do_nothing,
+                           })
+
+    def func_do_nothing(self, node, args, kwargs):
+        return True
+
+    def func_subdir(self, node, args, kwargs):
+        args = self.flatten_args(args)
+        if len(args) != 1 or not isinstance(args[0], str):
+            sys.stderr.write('Unable to evaluate subdir({}) in AstInterpreter --> Skipping\n'.format(args))
+            return
+
+        prev_subdir = self.subdir
+        subdir = os.path.join(prev_subdir, args[0])
+        absdir = os.path.join(self.source_root, subdir)
+        buildfilename = os.path.join(self.subdir, environment.build_filename)
+        absname = os.path.join(self.source_root, buildfilename)
+        symlinkless_dir = os.path.realpath(absdir)
+        if symlinkless_dir in self.visited_subdirs:
+            sys.stderr.write('Trying to enter {} which has already been visited --> Skipping\n'.format(args[0]))
+            return
+        self.visited_subdirs[symlinkless_dir] = True
+
+        if not os.path.isfile(absname):
+            sys.stderr.write('Unable to find build file {} --> Skipping\n'.format(buildfilename))
+            return
+        with open(absname, encoding='utf8') as f:
+            code = f.read()
+        assert(isinstance(code, str))
+        try:
+            codeblock = mparser.Parser(code, self.subdir).parse()
+        except mesonlib.MesonException as me:
+            me.file = buildfilename
+            raise me
+
+        self.subdir = subdir
+        self.evaluate_codeblock(codeblock)
+        self.subdir = prev_subdir
+
+    def method_call(self, node):
+        return True
+
+    def evaluate_arithmeticstatement(self, cur):
+        return 0
+
+    def evaluate_plusassign(self, node):
+        assert(isinstance(node, mparser.PlusAssignmentNode))
+        if node.var_name not in self.assignments:
+            self.assignments[node.var_name] = []
+        self.assignments[node.var_name] += [node.value] # Save a reference to the value node
+        self.evaluate_statement(node.value) # Evaluate the value just in case
+
+    def evaluate_indexing(self, node):
+        return 0
+
+    def unknown_function_called(self, func_name):
+        pass
+
+    def reduce_arguments(self, args):
+        assert(isinstance(args, mparser.ArgumentNode))
+        if args.incorrect_order():
+            raise InvalidArguments('All keyword arguments must be after positional arguments.')
+        return args.arguments, args.kwargs
+
+    def evaluate_comparison(self, node):
+        return False
+
+    def evaluate_foreach(self, node):
+        try:
+            self.evaluate_codeblock(node.block)
+        except ContinueRequest:
+            pass
+        except BreakRequest:
+            pass
+
+    def evaluate_if(self, node):
+        for i in node.ifs:
+            self.evaluate_codeblock(i.block)
+        if not isinstance(node.elseblock, mparser.EmptyNode):
+            self.evaluate_codeblock(node.elseblock)
+
+    def get_variable(self, varname):
+        return 0
+
+    def assignment(self, node):
+        assert(isinstance(node, mparser.AssignmentNode))
+        self.assignments[node.var_name] = [node.value] # Save a reference to the value node
+        self.evaluate_statement(node.value) # Evaluate the value just in case
+
+    def flatten_args(self, args, include_unknown_args: bool = False):
+        # Resolve mparser.ArrayNode if needed
+        flattend_args = []
+        temp_args = []
+        if isinstance(args, mparser.ArrayNode):
+            args = [x for x in args.args.arguments]
+        elif isinstance(args, mparser.ArgumentNode):
+            args = [x for x in args.arguments]
+        for i in args:
+            if isinstance(i, mparser.ArrayNode):
+                temp_args += [x for x in i.args.arguments]
+            else:
+                temp_args += [i]
+        for i in temp_args:
+            if isinstance(i, mparser.ElementaryNode) and not isinstance(i, mparser.IdNode):
+                flattend_args += [i.value]
+            elif isinstance(i, (str, bool, int, float)) or include_unknown_args:
+                flattend_args += [i]
+        return flattend_args
+
+    def flatten_kwargs(self, kwargs: object, include_unknown_args: bool = False):
+        flattend_kwargs = {}
+        for key, val in kwargs.items():
+            if isinstance(val, mparser.ElementaryNode):
+                flattend_kwargs[key] = val.value
+            elif isinstance(val, (mparser.ArrayNode, mparser.ArgumentNode)):
+                flattend_kwargs[key] = self.flatten_args(val, include_unknown_args)
+            elif isinstance(val, (str, bool, int, float)) or include_unknown_args:
+                flattend_kwargs[key] = val
+        return flattend_kwargs
diff --git a/mesonbuild/ast/introspection.py b/mesonbuild/ast/introspection.py
new file mode 100644
index 0000000..5d0ec5a
--- /dev/null
+++ b/mesonbuild/ast/introspection.py
@@ -0,0 +1,241 @@
+# Copyright 2018 The Meson development team
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool
+
+from . import AstInterpreter
+from .. import compilers, environment, mesonlib, mparser, optinterpreter
+from .. import coredata as cdata
+from ..interpreterbase import InvalidArguments
+from ..build import Executable, Jar, SharedLibrary, SharedModule, StaticLibrary
+import os
+
+build_target_functions = ['executable', 'jar', 'library', 'shared_library', 'shared_module', 'static_library', 'both_libraries']
+
+class IntrospectionHelper:
+    # mimic an argparse namespace
+    def __init__(self, cross_file):
+        self.cross_file = cross_file
+        self.native_file = None
+        self.cmd_line_options = {}
+
+class IntrospectionInterpreter(AstInterpreter):
+    # Interpreter to detect the options without a build directory
+    # Most of the code is stolen from interperter.Interpreter
+    def __init__(self, source_root, subdir, backend, cross_file=None, subproject='', subproject_dir='subprojects', env=None):
+        super().__init__(source_root, subdir)
+
+        options = IntrospectionHelper(cross_file)
+        self.cross_file = cross_file
+        if env is None:
+            self.environment = environment.Environment(source_root, None, options)
+        else:
+            self.environment = env
+        self.subproject = subproject
+        self.subproject_dir = subproject_dir
+        self.coredata = self.environment.get_coredata()
+        self.option_file = os.path.join(self.source_root, self.subdir, 'meson_options.txt')
+        self.backend = backend
+        self.default_options = {'backend': self.backend}
+        self.project_data = {}
+        self.targets = []
+
+        self.funcs.update({
+            'add_languages': self.func_add_languages,
+            'executable': self.func_executable,
+            'jar': self.func_jar,
+            'library': self.func_library,
+            'project': self.func_project,
+            'shared_library': self.func_shared_lib,
+            'shared_module': self.func_shared_module,
+            'static_library': self.func_static_lib,
+            'both_libraries': self.func_both_lib,
+        })
+
+    def func_project(self, node, args, kwargs):
+        if len(args) < 1:
+            raise InvalidArguments('Not enough arguments to project(). Needs at least the project name.')
+
+        proj_name = args[0]
+        proj_vers = kwargs.get('version', 'undefined')
+        proj_langs = self.flatten_args(args[1:])
+        if isinstance(proj_vers, mparser.ElementaryNode):
+            proj_vers = proj_vers.value
+        if not isinstance(proj_vers, str):
+            proj_vers = 'undefined'
+        self.project_data = {'descriptive_name': proj_name, 'version': proj_vers}
+
+        if os.path.exists(self.option_file):
+            oi = optinterpreter.OptionInterpreter(self.subproject)
+            oi.process(self.option_file)
+            self.coredata.merge_user_options(oi.options)
+
+        def_opts = self.flatten_args(kwargs.get('default_options', []))
+        self.project_default_options = mesonlib.stringlistify(def_opts)
+        self.project_default_options = cdata.create_options_dict(self.project_default_options)
+        self.default_options.update(self.project_default_options)
+        self.coredata.set_default_options(self.default_options, self.subproject, self.environment.cmd_line_options)
+
+        if not self.is_subproject() and 'subproject_dir' in kwargs:
+            spdirname = kwargs['subproject_dir']
+            if isinstance(spdirname, str):
+                self.subproject_dir = spdirname
+        if not self.is_subproject():
+            self.project_data['subprojects'] = []
+            subprojects_dir = os.path.join(self.source_root, self.subproject_dir)
+            if os.path.isdir(subprojects_dir):
+                for i in os.listdir(subprojects_dir):
+                    if os.path.isdir(os.path.join(subprojects_dir, i)):
+                        self.do_subproject(i)
+
+        self.coredata.init_backend_options(self.backend)
+        options = {k: v for k, v in self.environment.cmd_line_options.items() if k.startswith('backend_')}
+
+        self.coredata.set_options(options)
+        self.func_add_languages(None, proj_langs, None)
+
+    def do_subproject(self, dirname):
+        subproject_dir_abs = os.path.join(self.environment.get_source_dir(), self.subproject_dir)
+        subpr = os.path.join(subproject_dir_abs, dirname)
+        try:
+            subi = IntrospectionInterpreter(subpr, '', self.backend, cross_file=self.cross_file, subproject=dirname, subproject_dir=self.subproject_dir, env=self.environment)
+            subi.analyze()
+            subi.project_data['name'] = dirname
+            self.project_data['subprojects'] += [subi.project_data]
+        except:
+            return
+
+    def func_add_languages(self, node, args, kwargs):
+        args = self.flatten_args(args)
+        need_cross_compiler = self.environment.is_cross_build()
+        for lang in sorted(args, key=compilers.sort_clink):
+            lang = lang.lower()
+            if lang not in self.coredata.compilers:
+                self.environment.detect_compilers(lang, need_cross_compiler)
+
+    def build_target(self, node, args, kwargs, targetclass):
+        if not args:
+            return
+        kwargs = self.flatten_kwargs(kwargs, True)
+        name = self.flatten_args(args)[0]
+        srcqueue = [node]
+        if 'sources' in kwargs:
+            srcqueue += kwargs['sources']
+
+        source_nodes = []
+        while srcqueue:
+            curr = srcqueue.pop(0)
+            arg_node = None
+            if isinstance(curr, mparser.FunctionNode):
+                arg_node = curr.args
+            elif isinstance(curr, mparser.ArrayNode):
+                arg_node = curr.args
+            elif isinstance(curr, mparser.IdNode):
+                # Try to resolve the ID and append the node to the queue
+                id = curr.value
+                if id in self.assignments and self.assignments[id]:
+                    node = self.assignments[id][0]
+                    if isinstance(node, (mparser.ArrayNode, mparser.IdNode, mparser.FunctionNode)):
+                        srcqueue += [node]
+            if arg_node is None:
+                continue
+            elemetary_nodes = list(filter(lambda x: isinstance(x, (str, mparser.StringNode)), arg_node.arguments))
+            srcqueue += list(filter(lambda x: isinstance(x, (mparser.FunctionNode, mparser.ArrayNode, mparser.IdNode)), arg_node.arguments))
+            # Pop the first element if the function is a build target function
+            if isinstance(curr, mparser.FunctionNode) and curr.func_name in build_target_functions:
+                elemetary_nodes.pop(0)
+            if elemetary_nodes:
+                source_nodes += [curr]
+
+        # Filter out kwargs from other target types. For example 'soversion'
+        # passed to library() when default_library == 'static'.
+        kwargs = {k: v for k, v in kwargs.items() if k in targetclass.known_kwargs}
+
+        is_cross = False
+        objects = []
+        empty_sources = [] # Passing the unresolved sources list causes errors
+        target = targetclass(name, self.subdir, self.subproject, is_cross, empty_sources, objects, self.environment, kwargs)
+
+        self.targets += [{
+            'name': target.get_basename(),
+            'id': target.get_id(),
+            'type': target.get_typename(),
+            'defined_in': os.path.normpath(os.path.join(self.source_root, self.subdir, environment.build_filename)),
+            'subdir': self.subdir,
+            'build_by_default': target.build_by_default,
+            'sources': source_nodes,
+            'kwargs': kwargs,
+            'node': node,
+        }]
+
+        return
+
+    def build_library(self, node, args, kwargs):
+        default_library = self.coredata.get_builtin_option('default_library')
+        if default_library == 'shared':
+            return self.build_target(node, args, kwargs, SharedLibrary)
+        elif default_library == 'static':
+            return self.build_target(node, args, kwargs, StaticLibrary)
+        elif default_library == 'both':
+            return self.build_target(node, args, kwargs, SharedLibrary)
+
+    def func_executable(self, node, args, kwargs):
+        return self.build_target(node, args, kwargs, Executable)
+
+    def func_static_lib(self, node, args, kwargs):
+        return self.build_target(node, args, kwargs, StaticLibrary)
+
+    def func_shared_lib(self, node, args, kwargs):
+        return self.build_target(node, args, kwargs, SharedLibrary)
+
+    def func_both_lib(self, node, args, kwargs):
+        return self.build_target(node, args, kwargs, SharedLibrary)
+
+    def func_shared_module(self, node, args, kwargs):
+        return self.build_target(node, args, kwargs, SharedModule)
+
+    def func_library(self, node, args, kwargs):
+        return self.build_library(node, args, kwargs)
+
+    def func_jar(self, node, args, kwargs):
+        return self.build_target(node, args, kwargs, Jar)
+
+    def func_build_target(self, node, args, kwargs):
+        if 'target_type' not in kwargs:
+            return
+        target_type = kwargs.pop('target_type')
+        if isinstance(target_type, mparser.ElementaryNode):
+            target_type = target_type.value
+        if target_type == 'executable':
+            return self.build_target(node, args, kwargs, Executable)
+        elif target_type == 'shared_library':
+            return self.build_target(node, args, kwargs, SharedLibrary)
+        elif target_type == 'static_library':
+            return self.build_target(node, args, kwargs, StaticLibrary)
+        elif target_type == 'both_libraries':
+            return self.build_target(node, args, kwargs, SharedLibrary)
+        elif target_type == 'library':
+            return self.build_library(node, args, kwargs)
+        elif target_type == 'jar':
+            return self.build_target(node, args, kwargs, Jar)
+
+    def is_subproject(self):
+        return self.subproject != ''
+
+    def analyze(self):
+        self.load_root_meson_file()
+        self.sanity_check_ast()
+        self.parse_project()
+        self.run()
diff --git a/mesonbuild/ast/postprocess.py b/mesonbuild/ast/postprocess.py
new file mode 100644
index 0000000..e913b4f
--- /dev/null
+++ b/mesonbuild/ast/postprocess.py
@@ -0,0 +1,86 @@
+# Copyright 2019 The Meson development team
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool
+
+from . import AstVisitor
+from .. import mparser
+
+class AstIndentationGenerator(AstVisitor):
+    def __init__(self):
+        self.level = 0
+
+    def visit_default_func(self, node: mparser.BaseNode):
+        # Store the current level in the node
+        node.level = self.level
+
+    def visit_ArrayNode(self, node: mparser.ArrayNode):
+        self.visit_default_func(node)
+        self.level += 1
+        node.args.accept(self)
+        self.level -= 1
+
+    def visit_DictNode(self, node: mparser.DictNode):
+        self.visit_default_func(node)
+        self.level += 1
+        node.args.accept(self)
+        self.level -= 1
+
+    def visit_MethodNode(self, node: mparser.MethodNode):
+        self.visit_default_func(node)
+        node.source_object.accept(self)
+        self.level += 1
+        node.args.accept(self)
+        self.level -= 1
+
+    def visit_FunctionNode(self, node: mparser.FunctionNode):
+        self.visit_default_func(node)
+        self.level += 1
+        node.args.accept(self)
+        self.level -= 1
+
+    def visit_ForeachClauseNode(self, node: mparser.ForeachClauseNode):
+        self.visit_default_func(node)
+        self.level += 1
+        node.items.accept(self)
+        node.block.accept(self)
+        self.level -= 1
+
+    def visit_IfClauseNode(self, node: mparser.IfClauseNode):
+        self.visit_default_func(node)
+        for i in node.ifs:
+            i.accept(self)
+        if node.elseblock:
+            self.level += 1
+            node.elseblock.accept(self)
+            self.level -= 1
+
+    def visit_IfNode(self, node: mparser.IfNode):
+        self.visit_default_func(node)
+        self.level += 1
+        node.condition.accept(self)
+        node.block.accept(self)
+        self.level -= 1
+
+class AstIDGenerator(AstVisitor):
+    def __init__(self):
+        self.counter = {}
+
+    def visit_default_func(self, node: mparser.BaseNode):
+        name = type(node).__name__
+        if name not in self.counter:
+            self.counter[name] = 0
+        node.ast_id = name + '#' + str(self.counter[name])
+        self.counter[name] += 1
diff --git a/mesonbuild/ast/printer.py b/mesonbuild/ast/printer.py
new file mode 100644
index 0000000..60e0b0d
--- /dev/null
+++ b/mesonbuild/ast/printer.py
@@ -0,0 +1,203 @@
+# Copyright 2019 The Meson development team
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool
+
+from .. import mparser
+from . import AstVisitor
+import re
+
+arithmic_map = {
+    'add': '+',
+    'sub': '-',
+    'mod': '%',
+    'mul': '*',
+    'div': '/'
+}
+
+class AstPrinter(AstVisitor):
+    def __init__(self, indent: int = 2, arg_newline_cutoff: int = 5):
+        self.result = ''
+        self.indent = indent
+        self.arg_newline_cutoff = arg_newline_cutoff
+        self.ci = ''
+        self.is_newline = True
+        self.last_level = 0
+
+    def post_process(self):
+        self.result = re.sub(r'\s+\n', '\n', self.result)
+
+    def append(self, data: str, node: mparser.BaseNode):
+        level = 0
+        if node and hasattr(node, 'level'):
+            level = node.level
+        else:
+            level = self.last_level
+        self.last_level = level
+        if self.is_newline:
+            self.result += ' ' * (level * self.indent)
+        self.result += data
+        self.is_newline = False
+
+    def append_padded(self, data: str, node: mparser.BaseNode):
+        if self.result[-1] not in [' ', '\n']:
+            data = ' ' + data
+        self.append(data + ' ', node)
+
+    def newline(self):
+        self.result += '\n'
+        self.is_newline = True
+
+    def visit_BooleanNode(self, node: mparser.BooleanNode):
+        self.append('true' if node.value else 'false', node)
+
+    def visit_IdNode(self, node: mparser.IdNode):
+        self.append(node.value, node)
+
+    def visit_NumberNode(self, node: mparser.NumberNode):
+        self.append(str(node.value), node)
+
+    def visit_StringNode(self, node: mparser.StringNode):
+        self.append("'" + node.value + "'", node)
+
+    def visit_ContinueNode(self, node: mparser.ContinueNode):
+        self.append('continue', node)
+
+    def visit_BreakNode(self, node: mparser.BreakNode):
+        self.append('break', node)
+
+    def visit_ArrayNode(self, node: mparser.ArrayNode):
+        self.append('[', node)
+        node.args.accept(self)
+        self.append(']', node)
+
+    def visit_DictNode(self, node: mparser.DictNode):
+        self.append('{', node)
+        node.args.accept(self)
+        self.append('}', node)
+
+    def visit_OrNode(self, node: mparser.OrNode):
+        node.left.accept(self)
+        self.append_padded('or', node)
+        node.right.accept(self)
+
+    def visit_AndNode(self, node: mparser.AndNode):
+        node.left.accept(self)
+        self.append_padded('and', node)
+        node.right.accept(self)
+
+    def visit_ComparisonNode(self, node: mparser.ComparisonNode):
+        node.left.accept(self)
+        self.append_padded(mparser.comparison_map[node.ctype], node)
+        node.right.accept(self)
+
+    def visit_ArithmeticNode(self, node: mparser.ArithmeticNode):
+        node.left.accept(self)
+        self.append_padded(arithmic_map[node.operation], node)
+        node.right.accept(self)
+
+    def visit_NotNode(self, node: mparser.NotNode):
+        self.append_padded('not', node)
+        node.value.accept(self)
+
+    def visit_CodeBlockNode(self, node: mparser.CodeBlockNode):
+        for i in node.lines:
+            i.accept(self)
+            self.newline()
+
+    def visit_IndexNode(self, node: mparser.IndexNode):
+        self.append('[', node)
+        node.index.accept(self)
+        self.append(']', node)
+
+    def visit_MethodNode(self, node: mparser.MethodNode):
+        node.source_object.accept(self)
+        self.append('.' + node.name + '(', node)
+        node.args.accept(self)
+        self.append(')', node)
+
+    def visit_FunctionNode(self, node: mparser.FunctionNode):
+        self.append(node.func_name + '(', node)
+        node.args.accept(self)
+        self.append(')', node)
+
+    def visit_AssignmentNode(self, node: mparser.AssignmentNode):
+        self.append(node.var_name + ' = ', node)
+        node.value.accept(self)
+
+    def visit_PlusAssignmentNode(self, node: mparser.PlusAssignmentNode):
+        self.append(node.var_name + ' += ', node)
+        node.value.accept(self)
+
+    def visit_ForeachClauseNode(self, node: mparser.ForeachClauseNode):
+        varnames = [x.value for x in node.varnames]
+        self.append_padded('foreach', node)
+        self.append_padded(', '.join(varnames), node)
+        self.append_padded(':', node)
+        node.items.accept(self)
+        self.newline()
+        node.block.accept(self)
+        self.append('endforeach', node)
+
+    def visit_IfClauseNode(self, node: mparser.IfClauseNode):
+        prefix = ''
+        for i in node.ifs:
+            self.append_padded(prefix + 'if', node)
+            prefix = 'el'
+            i.accept(self)
+        if node.elseblock:
+            self.append('else', node)
+            node.elseblock.accept(self)
+        self.append('endif', node)
+
+    def visit_UMinusNode(self, node: mparser.UMinusNode):
+        self.append_padded('-', node)
+        node.value.accept(self)
+
+    def visit_IfNode(self, node: mparser.IfNode):
+        node.condition.accept(self)
+        self.newline()
+        node.block.accept(self)
+
+    def visit_TernaryNode(self, node: mparser.TernaryNode):
+        node.condition.accept(self)
+        self.append_padded('?', node)
+        node.trueblock.accept(self)
+        self.append_padded(':', node)
+        node.falseblock.accept(self)
+
+    def visit_ArgumentNode(self, node: mparser.ArgumentNode):
+        break_args = True if (len(node.arguments) + len(node.kwargs)) > self.arg_newline_cutoff else False
+        for i in node.arguments + list(node.kwargs.values()):
+            if not isinstance(i, mparser.ElementaryNode):
+                break_args = True
+        if break_args:
+            self.newline()
+        for i in node.arguments:
+            i.accept(self)
+            self.append(', ', node)
+            if break_args:
+                self.newline()
+        for key, val in node.kwargs.items():
+            self.append(key, node)
+            self.append_padded(':', node)
+            val.accept(self)
+            self.append(', ', node)
+            if break_args:
+                self.newline()
+        if break_args:
+            self.result = re.sub(r', \n$', '\n', self.result)
+        else:
+            self.result = re.sub(r', $', '', self.result)
diff --git a/mesonbuild/ast/visitor.py b/mesonbuild/ast/visitor.py
new file mode 100644
index 0000000..c8769d4
--- /dev/null
+++ b/mesonbuild/ast/visitor.py
@@ -0,0 +1,140 @@
+# Copyright 2019 The Meson development team
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This class contains the basic functionality needed to run any interpreter
+# or an interpreter-based tool
+
+from .. import mparser
+
+class AstVisitor:
+    def __init__(self):
+        pass
+
+    def visit_default_func(self, node: mparser.BaseNode):
+        pass
+
+    def visit_BooleanNode(self, node: mparser.BooleanNode):
+        self.visit_default_func(node)
+
+    def visit_IdNode(self, node: mparser.IdNode):
+        self.visit_default_func(node)
+
+    def visit_NumberNode(self, node: mparser.NumberNode):
+        self.visit_default_func(node)
+
+    def visit_StringNode(self, node: mparser.StringNode):
+        self.visit_default_func(node)
+
+    def visit_ContinueNode(self, node: mparser.ContinueNode):
+        self.visit_default_func(node)
+
+    def visit_BreakNode(self, node: mparser.BreakNode):
+        self.visit_default_func(node)
+
+    def visit_ArrayNode(self, node: mparser.ArrayNode):
+        self.visit_default_func(node)
+        node.args.accept(self)
+
+    def visit_DictNode(self, node: mparser.DictNode):
+        self.visit_default_func(node)
+        node.args.accept(self)
+
+    def visit_EmptyNode(self, node: mparser.EmptyNode):
+        self.visit_default_func(node)
+
+    def visit_OrNode(self, node: mparser.OrNode):
+        self.visit_default_func(node)
+        node.left.accept(self)
+        node.right.accept(self)
+
+    def visit_AndNode(self, node: mparser.AndNode):
+        self.visit_default_func(node)
+        node.left.accept(self)
+        node.right.accept(self)
+
+    def visit_ComparisonNode(self, node: mparser.ComparisonNode):
+        self.visit_default_func(node)
+        node.left.accept(self)
+        node.right.accept(self)
+
+    def visit_ArithmeticNode(self, node: mparser.ArithmeticNode):
+        self.visit_default_func(node)
+        node.left.accept(self)
+        node.right.accept(self)
+
+    def visit_NotNode(self, node: mparser.NotNode):
+        self.visit_default_func(node)
+        node.value.accept(self)
+
+    def visit_CodeBlockNode(self, node: mparser.CodeBlockNode):
+        self.visit_default_func(node)
+        for i in node.lines:
+            i.accept(self)
+
+    def visit_IndexNode(self, node: mparser.IndexNode):
+        self.visit_default_func(node)
+        node.index.accept(self)
+
+    def visit_MethodNode(self, node: mparser.MethodNode):
+        self.visit_default_func(node)
+        node.source_object.accept(self)
+        node.args.accept(self)
+
+    def visit_FunctionNode(self, node: mparser.FunctionNode):
+        self.visit_default_func(node)
+        node.args.accept(self)
+
+    def visit_AssignmentNode(self, node: mparser.AssignmentNode):
+        self.visit_default_func(node)
+        node.value.accept(self)
+
+    def visit_PlusAssignmentNode(self, node: mparser.PlusAssignmentNode):
+        self.visit_default_func(node)
+        node.value.accept(self)
+
+    def visit_ForeachClauseNode(self, node: mparser.ForeachClauseNode):
+        self.visit_default_func(node)
+        node.items.accept(self)
+        node.block.accept(self)
+
+    def visit_IfClauseNode(self, node: mparser.IfClauseNode):
+        self.visit_default_func(node)
+        for i in node.ifs:
+            i.accept(self)
+        if node.elseblock:
+            node.elseblock.accept(self)
+
+    def visit_UMinusNode(self, node: mparser.UMinusNode):
+        self.visit_default_func(node)
+        node.value.accept(self)
+
+    def visit_IfNode(self, node: mparser.IfNode):
+        self.visit_default_func(node)
+        node.condition.accept(self)
+        node.block.accept(self)
+
+    def visit_TernaryNode(self, node: mparser.TernaryNode):
+        self.visit_default_func(node)
+        node.condition.accept(self)
+        node.trueblock.accept(self)
+        node.falseblock.accept(self)
+
+    def visit_ArgumentNode(self, node: mparser.ArgumentNode):
+        self.visit_default_func(node)
+        for i in node.arguments:
+            i.accept(self)
+        for i in node.commas:
+            pass
+        for val in node.kwargs.values():
+            val.accept(self)