feature: install only dependencies of a specific type

[Aposhian]

Many package managers such as npm and cargo allow for selectively installing a specific class of dependencies, such as dependencies and devDependencies.

package.xml files conveniently provide multiple tags to classify what dependencies are needed for:

• <build_depend>
• <exec_depend>
• <test_depend>

However, rosdep doesn't support a way to only install build_depend dependencies, or only exec_depend and test_depend dependencies. This is very frustrating for scenarios where you only want to build, or only want to execute.

For example, in CI, I want a build step to install all build dependencies and compile binaries. I transfer those binaries over to a test step where I want to install exec and test dependencies so I can run tests, and then I transfer the binaries over to a final binary deployment that only installs exec dependencies.

Yes, this is technically possible by manually specifying packages to install, or by using --skip-keys, but that defeats the purpose of having a package.xml file with these nice, self-documenting tags.

Here is what the usage could look like:

rosdep install --from-paths <src-dir> --build-depend

or

rosdep install --from-paths <src-dir> --exec-depend --test-depend

And the default behavior could be to install everything if none of these flags are specified. <depend> tags would also get installed no matter what. So adding these flags would not break backward compatibility.

I would love to work on a PR for this.

[christophebedard]

There's an open PR for that: #789

[Aposhian]

Thanks, didn't find that in my searching.