Allow tests to read data dynamically from a package

[huonw]

E.g. https://github.com/kmcallister/html5ever has tests that dynamically, at test time, (#431) construct tests from the test-case descriptions in https://github.com/html5lib/html5lib-tests submodule. At the moment it is using Makefiles to build, and just passes around an environment variable to point to the right place (i.e. the root directory) allowing the test runner to reach into the html5lib-tests folder at runtime.

Cargo doesn't provide an easy way to do this, other than relying on the position of the test runner binary itself. It would be nice to either enforce this position so we can rely on it, or, better, pass an environment variable pointing at the right place (while both building and running tests, maybe).

(Or something else that achieves the same goal.)

[SimonSapin]

I’d like to generalize this request to all programs, not just tests. Program may want to ship resources (images, stylesheets, documents, …) other than code, for use at runtime. Currently, include_str!() and include_bin!() can be used for this, but they bloat the program’s binaries and require re-building the program when any resource changes.

Rust and Cargo should have a set of conventions (and possibly some library support) for having arbitrary files somewhere the program can use them with std::io::File::open. For programs "installed" on Linux, this probably should be in /usr/share/.

[alexcrichton]

In terms of installation, that's going to have to be a bridge that we cross at a later date. In terms of extending this to non-tests, would the environment variable solution work ok?

[SimonSapin]

So cargo run would take care of setting that variable? Yeah, that would work.

[alexcrichton]

Yeah basically all cargo subprocesses (compilation, tests, running, etc) would have the environment variable.