This Month in Our Test Infra: March 2025 issue

The Rust test system, called compiletest, now lets you match compiler diagnostics that appear after a line of code. Previously you could only match diagnostics that happened on the same line or earlier. This is useful when a test file contains code that is not valid Rust, so you cannot put a comment after the line to match the error. compiletest also added a new way to match diagnostics that don’t have a line number. Instead of using the older //@ error-pattern, you can write //~? ERROR message at the end of the file. This tells the test runner to look for an error with that exact message, even if the compiler didn’t attach a line number to it. If you run tests that use the old //@ error-pattern, the new system will now require you to add a //~ annotation anyway, so you don’t accidentally ignore errors. Finally, the bootstrap tool that builds Rust now uses a file called bootstrap.toml instead of config.toml. This avoids confusion with Cargo’s own configuration file.