There was a mismatch between a `self.macro_context_level += 1` and the
corresponding `self.macro_context_level -= 1`, which resulted in an
`usize` underflow (panic in debug mode, wrong behaviour in release
mode).
This fixes it and adds a relevant assertion and test. In order to
properly test library mode extraction, a special option enforcing that
on source code as well is added.
Since we dropped checked in toolchain files for tests requiring nightly,
the `setup.sh` script was not doing its job of setting up the toolchains
and the `rust-src` component, occasionally leading to test failures.
Rather than fixing the version separately for each test, we can just
request to use a nightly in the `options.yml` file, with the specific
version hard-coded in `qltest.rs`. We can update it if we need to.
It's better to have a single nightly version for all tests that require
it, in order to avoid downloading more versions than necessary.
This adds the possibility to add a special `proc_macro.rs` source file
to QL tests, which will be generated into a `proc_macro` crate the
usual `lib` crate depends on.
This allow to define procedural macros in QL tests, and is here used to
move the `macro-expansion` integration test to be a language test
instead.
As the generated manifests involved were starting to get a bit complex,
they are now generated from a `mustache` template.
The target file created by `cargo check` was causing problems in
language tests.
We might want to also ignore `target` by default in the production
indexing, but I'll leave that for further discussion.
Also accept `options.yml` and `options.yaml` files as well for test options,
to get YAML syntax highlighting. In a follow up PR we might make the extension
mandatory.
