Added a custom launch substitution to modify YAML parameters based on…

… launch params - lifecycle version (ros-navigation#771)

* Initial version copied from old code

* Code now installs

You can `import nav2_common.launch.rewritten_yaml` now.

* Bring RewrittenYaml class into launch scope like other launch packages do

This lets you say:
`from nav2_common.launch import RewrittenYaml`
instead of
`from nav2_common.launch.rewritten_yaml import RewrittenYaml`

* Add support for converting strings to non-string values in YAML

By the time RewrittenYaml gets the rewrite values, they've already been
resolved to strings. This is a problem for use_sim_time because the
code only accepts bools. To work around this RewrritenYaml has an option
to convert all values to an actual type.

* Add dependency in nav2_bringup package so it doesn't get forgotten.

nav2_bringup/package.xml

@@ -16,6 +16,7 @@
 
   <exec_depend>launch_ros</exec_depend>
   <exec_depend>navigation2</exec_depend>
+  <exec_depend>nav2_common</exec_depend>
 
   <test_depend>ament_lint_common</test_depend>
   <test_depend>ament_lint_auto</test_depend>

nav2_common/CMakeLists.txt

@@ -3,6 +3,9 @@ cmake_minimum_required(VERSION 3.5)
 project(nav2_common NONE)
 
 find_package(ament_cmake_core REQUIRED)
+find_package(ament_cmake_python REQUIRED)
+
+ament_python_install_package(nav2_common)
 
 ament_package(
   CONFIG_EXTRAS "nav2_common-extras.cmake"

nav2_common/nav2_common/launch/__init__.py

@@ -0,0 +1 @@
+from .rewritten_yaml import RewrittenYaml

nav2_common/nav2_common/launch/rewritten_yaml.py

@@ -0,0 +1,98 @@
+from typing import Dict
+from typing import List
+from typing import Text
+import yaml
+import tempfile
+import launch
+
+class DictItemReference:
+  def __init__(self, dictionary, key):
+    self.dictionary = dictionary
+    self.dictKey = key
+
+  def key(self):
+      return self.dictKey
+
+  def setValue(self, value):
+      self.dictionary[self.dictKey] = value
+
+class RewrittenYaml(launch.Substitution):
+  """
+  Substitution that modifies the given Yaml file.
+  """
+
+  def __init__(self,
+    source_file: launch.SomeSubstitutionsType,
+    rewrites: Dict,
+    convert_types = False) -> None:
+    super().__init__()
+
+    from launch.utilities import normalize_to_list_of_substitutions  # import here to avoid loop
+    self.__source_file = normalize_to_list_of_substitutions(source_file)
+    self.__rewrites = {}
+    self.__convert_types = convert_types
+    for key in rewrites:
+        self.__rewrites[key] = normalize_to_list_of_substitutions(rewrites[key])
+
+  @property
+  def name(self) -> List[launch.Substitution]:
+    """Getter for name."""
+    return self.__source_file
+
+  def describe(self) -> Text:
+    """Return a description of this substitution as a string."""
+    return ''
+
+  def perform(self, context: launch.LaunchContext) -> Text:
+    yaml_filename = launch.utilities.perform_substitutions(context, self.name)
+    rewritten_yaml = tempfile.NamedTemporaryFile(mode='w', delete=False)
+    resolved_rewrites = self.resolve_rewrites(context)
+    data = yaml.load(open(yaml_filename, 'r'))
+    self.substitute_values(data, resolved_rewrites)
+    yaml.dump(data, rewritten_yaml)
+    rewritten_yaml.close()
+    return rewritten_yaml.name
+
+  def resolve_rewrites(self, context):
+    resolved = {}
+    for key in self.__rewrites:
+      resolved[key] = launch.utilities.perform_substitutions(context, self.__rewrites[key])
+    return resolved
+
+  def substitute_values(self, yaml, rewrites):
+    for key in self.getYamlKeys(yaml):
+      if key.key() in rewrites:
+        raw_value = rewrites[key.key()]
+        key.setValue(self.convert(raw_value))
+
+  def getYamlKeys(self, yamlData):
+    try:
+      for key in yamlData.keys():
+        for k in self.getYamlKeys(yamlData[key]):
+          yield k
+        yield DictItemReference(yamlData, key)
+    except AttributeError:
+      return
+
+  def convert(self, text_value):
+    if self.__convert_types:
+      # try converting to float
+      try:
+        return float(text_value)
+      except ValueError:
+        pass
+
+      # try converting to int
+      try:
+        return int(text_value)
+      except ValueError:
+        pass
+
+      # try converting to bool
+      if text_value.lower() == "true":
+        return True
+      if text_value.lower() == "false":
+        return False
+
+      #nothing else worked so fall through and return text
+    return text_value

nav2_common/package.xml

@@ -9,6 +9,8 @@
 
   <buildtool_depend>ament_cmake_core</buildtool_depend>
 
+  <build_depend>ament_cmake_python</build_depend>
+
   <buildtool_export_depend>ament_cmake_core</buildtool_export_depend>
 
   <export>