部署ROS2 Crystal版本遇到的一些问题
ROS2的Bouncy版本和Crystal版本有一些不小的差别，所以重新部署时会遇到另外一些问题
环境
- 操作系统：macOS “Mojava” 10.14.5
- 安装方式：二进制包安装
- ROS2版本：Crystal
操作
$ colcon build --symlink-install
现象1
[1.511s] ERROR:colcon.colcon_core.entry_point:Exception loading extension 'colcon_core.shell.bash': cannot import name 'Interpreter' from 'em' (/usr/local/lib/python3.7/site-packages/em/__init__.py)
Traceback (most recent call last):
File "/usr/local/lib/python3.7/site-packages/colcon_core/entry_point.py", line 98, in load_entry_points
extension_type = load_entry_point(entry_point)
File "/usr/local/lib/python3.7/site-packages/colcon_core/entry_point.py", line 140, in load_entry_point
return entry_point.load()
File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2411, in load
return self.resolve()
File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2417, in resolve
module = __import__(self.module_name, fromlist=['__name__'], level=0)
File "/usr/local/lib/python3.7/site-packages/colcon_bash/shell/bash.py", line 13, in <module>
from colcon_core.shell.template import expand_template
File "/usr/local/lib/python3.7/site-packages/colcon_core/shell/template/__init__.py", line 8, in <module>
from em import Interpreter
ImportError: cannot import name 'Interpreter' from 'em' (/usr/local/lib/python3.7/site-packages/em/__init__.py)
解决办法1
谷歌了一些帖子，初步估计这个问题是因为em和empy这两个包在python的包管理器中有同样的名字，如果两个都安装了，默认会找到em，所以出了问题。
-
em是一个终端工具，可以将标准输出的文件或标准输入打印出来，并突出显示与模式匹配的表达式。 -
empy是一个嵌入的python表达式和语句系统。它输入一个源文件，处理并输出，empy可以通过一些特殊的信号或符号来扩展Python的表达式和语句，以及各种特殊的语法形式。这种方式可以允许Python作为标记语言使用，还支持钩子回调、分流录制和回访、动态可链接的过滤器。
事实上ROS2中编译需要的是empy，但出现这个错误时，是因为pip3中同时安装了em，或者仅安装了em。
解决办法就是删除em，并安装empy：
$ pip3 uninstall em
$ pip3 install empy
现象2
--- stderr: examples_rclcpp_minimal_composition
CMake Error at /Users/hanhuijie/ros2_crystal_install/ros2-osx/share/class_loader/cmake/ament_cmake_export_dependencies-extras.cmake:21 (find_package):
By not providing "Findconsole_bridge.cmake" in CMAKE_MODULE_PATH this
project has asked CMake to find a package configuration file provided by
"console_bridge", but CMake did not find one.
Could not find a package configuration file provided by "console_bridge"
with any of the following names:
console_bridgeConfig.cmake
console_bridge-config.cmake
Add the installation prefix of "console_bridge" to CMAKE_PREFIX_PATH or set
"console_bridge_DIR" to a directory containing one of the above files. If
"console_bridge" provides a separate development package or SDK, be sure it
has been installed.
Call Stack (most recent call first):
/Users/hanhuijie/ros2_crystal_install/ros2-osx/share/class_loader/cmake/class_loaderConfig.cmake:38 (include)
CMakeLists.txt:14 (find_package)
解决办法2
这是因为没有安装console_bridge的原因，在MacOS上比较简单，终端brew输入：
$ brew install console_bridge
console_bridge是一个独立于ROS的软件，使用CMake构建，重新实现了rosconsole的功能，即提供日志相关功能的输出接口，但是console_bridge是独立应用，不依赖于ROS。
参考
https://index.ros.org/doc/ros2/Tutorials/Colcon-Tutorial/
https://index.ros.org/doc/ros2/Installation/Crystal/OSX-Install-Binary/