Test examples in user guide with travis

[Alexander-N]

#385

[konstin]

Please add a note in the readme that extern crate pyo3; is not required when using the 2018 edition

[Alexander-N]

Done

[konstin]

Is this required? I would really like to avoid having to stick with the 2015 edition for the derive only for the doctest. (We should be able pass --extern=2018 to rustdoc to avoid this if it doesn't work otherwise)

[Alexander-N]

Even when passing the edition directly to rustdoc, I get

---- guide/src/class.md - Python_Class::Object_properties (line 232) stdout ----
error[E0433]: failed to resolve: use of undeclared type or module `libc`
  --> guide/src/class.md:240:1
   |
10 | #[pymethods]
   | ^^^^^^^^^^^^ use of undeclared type or module `libc`

thread 'guide/src/class.md - Python_Class::Object_properties (line 232)' panicked at 'couldn't compile the test', src/librustdoc/test.rs:354:13
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

---- guide/src/class.md - Python_Class::Object_properties (line 261) stdout ----
error[E0433]: failed to resolve: use of undeclared type or module `libc`
  --> guide/src/class.md:269:1
   |
10 | #[pymethods]
   | ^^^^^^^^^^^^ use of undeclared type or module `libc`

thread 'guide/src/class.md - Python_Class::Object_properties (line 261)' panicked at 'couldn't compile the test', src/librustdoc/test.rs:354:13

---- guide/src/class.md - Python_Class::Object_properties (line 289) stdout ----
error[E0433]: failed to resolve: use of undeclared type or module `libc`
 --> guide/src/class.md:292:1
  |
5 | #[pyclass]
  | ^^^^^^^^^^ use of undeclared type or module `libc`

thread 'guide/src/class.md - Python_Class::Object_properties (line 289)' panicked at 'couldn't compile the test', src/librustdoc/test.rs:354:13

[konstin]

Thank you! I've left two comments, otherwise it's a that's a big improvement!

[Alexander-N]

On travis I'm getting weird linking errors like /usr/bin/ld: cannot find -lpython3.6m. Any help would be great.

[konstin]

I don't know the exact problem or the solution, but I can give some context: To run the tests, we need to build binaries, which needs to link libpython in the version specified by the build script. Normally the build script also tells the linker the path of libpyhon through rustc-link-search:

pyo3/build.rs

Lines 444 to 448 in d63fac8

	if libpath != "None" {
	println!("cargo:rustc-link-search=native={}", libpath);
	} else if cfg!(target_os = "windows") {
	println!("cargo:rustc-link-search=native={}\\libs", exec_prefix);
	}

This seems to fail here, presumably because the we're calling rustdoc here directly (through docmatic) and not cargo.

It's also possible to add directories to the linker path using environment variables, but that should have already been done by the script that travis runs:

pyo3/ci/travis/setup.sh

Lines 16 to 20 in d63fac8

	PYTHON_LIB=$(python -c "import sysconfig; print(sysconfig.get_config_var('LIBDIR'))")
	export LD_LIBRARY_PATH="$LD_LIBRARY_PATH:$PYTHON_LIB:$HOME/rust/lib"
	echo ${LD_LIBRARY_PATH}

The logs even tell that this path has been set: https://travis-ci.org/PyO3/pyo3/jobs/502189479#L322

I am not really sure what to do here because debugging travis is a tedious task. The quick and dirty solution would be to make the minimum nightly use python 3.5 (which apparently works) and then only run those test in the minimum nightly builds, just like rustfmt and clippy.

[Alexander-N]

Ok, then I would suggest we activate the tests only for Python 3.5 for now. This way we have at least some mechanism in place which prevents the examples to drift from the current API. We could still leave #385 open and look for a better solution.

[konstin]

I think that eventually, we want to either use a fix version of skeptic/docmatic or (which is more likely) write our own small doc tester. But for now this is a really good solution for moving forward with the docs.