Similar to trybuild, but allows you to test how declarative or procedural macros are expanded.
Please refer to the documentation on docs.rs.
tryexpand
requires cargo-expand to be installed.
Add tryexpand
to your project as a dev-dependency by running
cargo install --dev tryexpand
Then under your crate's tests/
directory, create tests.rs
file containing calls to tryexpand::expand()
and populate the tests/expand/pass/
, tests/expand/checked_pass/
and tests/expand/fail/
directories with corresponding Rust source files under test.
The base of each tryexpand
test suite is the tryexpand::expand()
function, which you pass a list of file paths (or glob patterns) to:
#[test]
pub fn pass() {
tryexpand::expand(
["tests/expand/pass/*.rs"]
).expect_pass();
// or its short-hand (by default `.expect_pass()` is implied):
tryexpand::expand(
["tests/expand/pass/*.rs"]
);
}
By default tryexpand::expand()
assert matched test files to expand successfully.
If instead you want to write tests for macro expansion diagnostics, then will have to add a call to .expect_fail()
:
#[test]
pub fn fail() {
tryexpand::expand(
["tests/expand/fail/*.rs"]
).expect_fail();
}
Additionally you can specify arguments to pass to cargo expand
:
#[test]
tryexpand::expand(
// ...
)
// ...
.args(["--features", "test-feature"])
.expect_pass();
as well as environment variables to set for cargo expand
:
tryexpand::expand(
// ...
)
// ...
.envs([("MY_ENV", "my env var value")])
.expect_pass();
You can also make tryexpand
type-check the expanded code for you (i.e. cargo check
):
tryexpand::expand(
// ...
)
// ...
.and_check()
.expect_pass();
Or you can make tryexpand
run the expanded code for you (i.e. cargo run
):
tryexpand::expand(
// ...
)
// ...
.and_run()
.expect_pass();
Or you can make tryexpand
run the expanded code's included unit tests (if there are any) for you (i.e. cargo test
):
tryexpand::expand(
// ...
)
// ...
.and_run_tests()
.expect_pass();
The test can be run with:
cargo test
While it is possible to run parallel tests it is recommended to run them serially:
cargo test -- --test-threads=1
For debugging purposes you may want to see the output for all tests, not just the failing ones:
cargo test -- --no-capture
Each tryexpand
test will invoke the cargo expand
command (as well as any of the optional follow-up commands: cargo check
, cargo run
, cargo test
) on each of the source files that matches the glob pattern and will compare the expansion result with the corresponding *.out.rs
, *.out.txt
or *.err.txt
snapshot files.
If the environment variable TRYEXPAND=overwrite
is provided (e.g. $ TRYEXPAND=overwrite cargo test
), then snapshot files will be created, or overwritten, if one already exists. Snapshot files should get checked into version control.
Hand-writing snapshot files is not recommended.
When working with multiple expansion test files, it is recommended to specify wildcard (*.rs
) instead of doing a multiple calls to the expand
functions for individual files.
Usage of wildcards for multiple files will group them under a single temporary crate for which dependencies will be built a single time. In contrast, calling expand
functions for each source file will create multiple temporary crates and that will reduce performance as dependencies will be build for each of the temporary crates.
More info on how glob patterns work.
See tests/macro-tests and tests/proc-macro-tests as a reference.
Since each rustc/cargo release might make changes to the emitted diagnostics
it is recommended to run tryexpand
tests using a pinned toolchain, e.g.:
cargo +1.76.0 test <OPTIONS>
For each expand()
-like method call within your tests a temporary and uniquely named Rust project will get generated within $CARGO_TARGET_DIR/target/tests/
.
By default these projects will get deleted upon test completion (regardless of the outcome).
If you wish to take a look at the actual code/projects being expanded you can provide TRYEXPAND_KEEP_ARTIFACTS=1
(e.g. $ TRYEXPAND_KEEP_ARTIFACTS=1 cargo test
) and tryexpand
will skip the cleanup.
By default tryexpand
truncates console output that's longer than 100 lines.
If you wish to temporarily turn this behavior you can provide TRYEXPAND_TRUNCATE_OUTPUT=0
(e.g. $ TRYEXPAND_TRUNCATE_OUTPUT=0 cargo test
) and tryexpand
will produce the full console output.
Please read CONTRIBUTING.md for details on our code of conduct,
and the process for submitting pull requests to us.
We use SemVer for versioning. For the versions available, see the tags on this repository.
This project is licensed under the MIT or Apache-2.0 – see the LICENSE-MIT.md/LICENSE-APACHE.md files for details.
The tryexpand
crate originated as a fork of eupn's macrotest
(crates.io).