Remove comments from yaml file before applying substitutions

[ivanpauno]

Fixes ros2/ros2#1317.

I'm not sure if it's the best solution, but it's one.

[iuhilnehc-ynos]

It seems to break a case, which I am not sure if it's a correct case, that could be parsed successfully before.

/**:
  ros__parameters:
    mix_subs: "$(command pwd) $(dirname)"

before:

$ ros2 param get /parameter_blackboard mix_subs
String value is: /home/chenlh/Projects/ROS2/ros2-master /home/chenlh/Projects/ROS2/ros2-master/install/share/demo_nodes_cpp/launch/topics

after using 95d4699:

$ ros2 launch demo_nodes_cpp parameter_blackboard.xml
[INFO] [launch]: All log files can be found below /home/chenlh/.ros/log/2022-08-30-11-39-18-674265-OptiPlex-7080-460434
[INFO] [launch]: Default logging verbosity is set to INFO
tree Tree(template, [Tree(fragment, [Token(UNQUOTED_STRING, 'demo_nodes_cpp')])])
tree Tree(template, [Tree(fragment, [Token(UNQUOTED_STRING, 'parameter_blackboard')])])
tree Tree(template, [Tree(fragment, [Token(UNQUOTED_STRING, 'parameter_file_with_substitutions.yaml')])])
tree Tree(template, [Tree(fragment, [Token(UNQUOTED_STRING, '/**:\n  ros__parameters:\n    mix_subs: ')]), Tree(fragment, [Tree(substitution, [Token(IDENTIFIER, 'command'), Tree(arguments, [Tree(value, [Tree(part, [Token(UNQUOTED_RSTRING, 'pwd')])])])])]), Tree(fragment, [Token(UNQUOTED_STRING, ' ')]), Tree(fragment, [Tree(substitution, [Token(IDENTIFIER, 'dirname')])]), Tree(fragment, [Token(UNQUOTED_STRING, '\n')])])
[ERROR] [launch]: Caught exception in launch (see debug for traceback): The substituted parameter file is not a valid yaml file

[iuhilnehc-ynos]

It seems that we need to invoke yaml.safe_dump with default_style='"', and then to support the yaml tag for !!int, !!float in the rcl which will be similar to ros2/rcl#999.

the data is dumped with default_style='"', and then parsed by substitutions.
"/**":
  "ros__parameters":
    "array":
    - !!int "1"
    - !!int "2"
    - !!int "3"
    "double": !!float "3.141592653"
    "filename": "run /home/chenlh/Projects/ROS2/ros2-master/install/share/demo_nodes_cpp/launch/topics/parameter_blackboard.xml on 2022年 08月 30日 星期二 13:50:26 CST
"
    "filename2": "2022年 08月 30日 星期二 13:50:26 CST
 /home/chenlh/Projects/ROS2/ros2-master/install/share/demo_nodes_cpp/launch/topics/parameter_blackboard.xml"
    "float": !!float "3.1"
    "int": !!int "3"

[ivanpauno]

@iuhilnehc-ynos thanks for showing an example when the PR doesn't work correctly.

It seems that we need to invoke yaml.safe_dump with default_style='"'

This will cause issues in yaml files like:

/**:
  ros__parameters:
    my_integer: $(env MY_INTEGER)

[iuhilnehc-ynos]

A better way to fix this issue might need to update the grammar.lark to ignore the comment. I am not familiar with lark.

After referring to https://github.com/ros2/rosidl/blob/51811962c832745f531968d351af3d1af45cd238/rosidl_parser/rosidl_parser/grammar.lark#L30, I updated the `grammar.lark` with ```patch diff --git a/launch/share/launch/frontend/grammar.lark b/launch/share/launch/frontend/grammar.lark index 740c2c4..e2d45f5 100644 --- a/launch/share/launch/frontend/grammar.lark +++ b/launch/share/launch/frontend/grammar.lark @@ -4,6 +4,9 @@ %import common.LETTER %import common.WS

+COMMENT: "#" /[^\n]/*
+%ignore COMMENT
+
IDENTIFIER: LETTER (LETTER | DIGIT | "_" | "-")*

I am not sure if it covers all comment cases. I have tested the following cases, and it seems good with the result.
yaml file:

```yaml
# int: $(env MY_INT)
/**:
  ros__parameters:
    # int: $(env MY_INT)
    filename: "run $(filename) on $(command date)"   # int: $(env MY_INT)
    filename2: "$(command date) $(filename) #fdas"
    filename3: $(env MY_INT) $(filename) #fdas
    filename4: $(env MY_INT) # $(filename) #fdas
    int2: $(env MY_INT)