fix(derive-encode): emit friendly compile errors instead of panicking#307
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lohitkolluri wants to merge 1 commit into
Open
fix(derive-encode): emit friendly compile errors instead of panicking#307lohitkolluri wants to merge 1 commit into
lohitkolluri wants to merge 1 commit into
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The proc-macro derives panicked for unsupported shapes (unnamed/unit struct, enum, union, unknown `#[prometheus(...)] attribute) and the bad-attribute case was inside a closure, which produced a confusing `error: proc-macro derive panicked` diagnostic that pointed users at the proc-macro internals rather than the `#[derive(...)] line they needed to fix. Replace all `panic!` calls with `compile_error!` so users see a direct diagnostic that points to the offending `#[derive(...)] line. For the unknown-attribute case, validate attributes in a pre-pass so the derive can return a `compile_error!` token stream before generating the impl. Add a trybuild `compile_fail` test that exercises each error path and pins the expected diagnostics. Signed-off-by: Lohit Kolluri <lohitkolluri@gmail.com>
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Summary
Replace
panic!calls in theEncodeLabelSetandEncodeLabelValueproc-macro derives withcompile_error!so unsupported shapes surface a direct diagnostic that points to the#[derive(...)]line the user wrote, instead of the currenterror: proc-macro derive panickedmessage that points into the proc-macro internals.Full changes
panic!sites inderive-encode/src/lib.rsnow emitcompile_error!tokens.#[prometheus(...)]attributes (which previously panicked inside a closure) are validated in a pre-pass so the derive can return acompile_error!token stream before generating the impl.compile_failtest inderive-encode/tests/build/friendly-compilation-error-msg.rscovers unnamed struct, unit struct, enum, union, and unknown-attribute paths. The expected.stderris committed alongside it.Testing
cargo test -p prometheus-client-derive-encode --test libpasses deterministically (with and withoutTRYBUILD=overwrite).cargo clippy -p prometheus-client-derive-encode --all-targets -- -D warningsclean.cargo fmt --check -p prometheus-client-derive-encodeclean.Notes
For valid inputs the derive behavior is unchanged. The new diagnostics are user-facing; no downstream tooling currently parses these derive errors, so this is not a breaking change.
Issues
Closes #269