dtolnay
commented
5 years ago This is better than invoking proc macros directly as fn(TokenStream) -> TokenStream from tests for a few reasons:
- It supports testing macro_rules macros as well.
- It does not require factoring testable code out of your
proc-macro = trueentry point crate solely for testing purposes. We can test the proc macro crate directly. - The tool can provide a simple command which automatically updates all the *.expanded.rs files to account for changes in the macro's implementation.
eupn
Similar to what https://github.com/dtolnay/trybuild does for testing compilation failures.
See here and here for a basic test setup leveraging trybuild.
I would expect a very similar setup for testing macro expansion -- with a suite of test cases as *.rs files in some directory, adjacent to expected expanded output in *.expanded.rs files with corresponding names. For each test case the library would set up dependencies and stuff correctly then invoke cargo expand to expand macros and format the expanded code with rustfmt. Then the test case would fail if the expanded and formatted code differs from the expected output in the corresponding *.expanded.rs file.