Fixes#204051. I have tried this on the reproducer stated in the ticket.
```
[nix-develop]$ $(nix-build -I nixpkgs=/home/shana/programming/nixpkgs --no-out-link)/tests/foo
running 1 test
test check_module_name ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
```
With Rust 1.61, it is necessary to link to external static/dynamic libaries
when building the rlib that uses them, rather than when linking the final
binary. In fact, it is no longer necessary to specify the libraries to link
when building the final binary, but the library search path flags must still
be included.
According to the Cargo documentation:
> The build script does not have access to the dependencies listed in
> the dependencies or dev-dependencies section (they’re not built
> yet!). Also, build dependencies are not available to the package
> itself unless also explicitly added in the [dependencies] table.
https://doc.rust-lang.org/cargo/reference/build-scripts.html
This change separates linkage of regular dependencies and build
dependencies.
* Make errors include the crate name and make them much more prominent.
* Move more code into lib.sh
* Already source generated logging code and lib.sh in configure
This helps us instruct rustc to build tests instead of binaries. The
actual build will then ONLY produce test executables. This is a first
step towards having rust crate tests within nixpkgs.
We default back to only a single output in test cases since that is the
only reasonable thing to do here.
Producing libraries or binaries in addition to tests would theoretically
be feasible but usually generates different dependency trees. It is very
common to have some libraries in `[dev-depdendencies]` within Cargo.toml
just for your tests. To not start mixing things up going with a
dedicated derivation for the test build sounds like the best choice for
now.
To use this you must provide a proper test dependency chain to
`buildRustCrate` (as you would usually do with your non-test inputs).
And then set the `buildTests` attribute to `true`. The derivation will
then contain all tests that were built in `$out/tests`. All common test
patterns and directories should be supported and tested by this change.
Below is an example how you would run a single test from the derivation.
This commit contains some more examples in the `buildRustCrateTests`
attribute set that might be helpful.
```
let
drv = buildRustCrate {
…
buildTests true;
};
in runCommand "test-my-crate" {} ''
touch $out
exec ${drv}/tests/my-test
''
```
