Fix spurious warning on empty proc macro crates #47655
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While attempting to reproduce #47086 I noticed the following warning: ```shell > rustc /dev/null --crate-type proc-macro warning: unused variable: `registrar` --> /dev/null:0:1 ``` As there are no macros to register the automatically generated registrar function for the crate has no body. As a result its `registrar` argument is unused triggering the above warning. The warning is confusing and not easily actionable by the developer. It could also be triggered legitimately by e.g. having all of the macros in a crate #[cfg]'ed out. Fix by naming the generated argument `_registrar` inside `mk_registrar()`. This suppresses the unused variable warning.
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@bors: r+ rollup Thanks! |
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📌 Commit e1bffbd has been approved by |
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…ty-proc-macro-crate, r=alexcrichton Fix spurious warning on empty proc macro crates While attempting to reproduce rust-lang#47086 I noticed the following warning: ```shell > rustc /dev/null --crate-type proc-macro warning: unused variable: `registrar` --> /dev/null:0:1 ``` As there are no macros to register the automatically generated registrar function for the crate has no body. As a result its `registrar` argument is unused triggering the above warning. The warning is confusing and not easily actionable by the developer. It could also be triggered legitimately by e.g. having all of the macros in a crate #[cfg]'ed out. Fix by naming the generated argument `_registrar` inside `mk_registrar()`. This suppresses the unused variable warning.
kennytm
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Jan 31, 2018
…source-line, r=estebank Avoid underflow in render_source_line While testing rust-lang#47655 I was able to make the compiler panic when it's compiled with debug assertions: ```shell > rustc /dev/null --crate-type proc-macro error: internal compiler error: unexpected panic note: the compiler unexpectedly panicked. this is a bug. note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports note: rustc 1.25.0-dev running on x86_64-apple-darwin note: run with `RUST_BACKTRACE=1` for a backtrace thread 'rustc' panicked at 'attempt to subtract with overflow', librustc_errors/emitter.rs:287:49 ``` Without debug assertions the following warning is emitted: ```shell > rustc /dev/null --crate-type proc-macro warning: unused variable: `registrar` --> /dev/null:0:1 | | = note: #[warn(unused_variables)] on by default = note: to avoid this warning, consider using `_registrar` instead ``` The panic is due to the unused variable warning being spanned to `/dev/null:0:1`. When `render_source_line` subtracts 1 from the line number to look up the source line it panics due to underflow. Without debug assertions this would wrap and cause us to return a blank string instead. Fix by explicitly testing for 0 and exiting early. I'm unsure how to automatically test this now that rust-lang#46655 has been approved.
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While attempting to reproduce #47086 I noticed the following warning:
As there are no macros to register the automatically generated registrar function for the crate has no body. As a result its
registrarargument is unused triggering the above warning.The warning is confusing and not easily actionable by the developer. It could also be triggered legitimately by e.g. having all of the macros in a crate #[cfg]'ed out.
Fix by naming the generated argument
_registrarinsidemk_registrar(). This suppresses the unused variable warning.