From e1bffbdf66cecc442e8d9e20642df82a155e2aa0 Mon Sep 17 00:00:00 2001 From: Ryan Cumming Date: Mon, 22 Jan 2018 20:58:21 +1100 Subject: [PATCH] Fix spurious warning on empty proc macro crates While attempting to reproduce rust-lang/rust#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. --- src/libsyntax_ext/proc_macro_registrar.rs | 2 +- .../proc-macro/auxiliary/empty-crate.rs | 14 ++++++++++++++ .../run-pass-fulldeps/proc-macro/empty-crate.rs | 17 +++++++++++++++++ 3 files changed, 32 insertions(+), 1 deletion(-) create mode 100644 src/test/run-pass-fulldeps/proc-macro/auxiliary/empty-crate.rs create mode 100644 src/test/run-pass-fulldeps/proc-macro/empty-crate.rs diff --git a/src/libsyntax_ext/proc_macro_registrar.rs b/src/libsyntax_ext/proc_macro_registrar.rs index 8c5276e1d74b5..0ba21e6b366cf 100644 --- a/src/libsyntax_ext/proc_macro_registrar.rs +++ b/src/libsyntax_ext/proc_macro_registrar.rs @@ -381,7 +381,7 @@ fn mk_registrar(cx: &mut ExtCtxt, let __internal = Ident::from_str("__internal"); let registry = Ident::from_str("Registry"); - let registrar = Ident::from_str("registrar"); + let registrar = Ident::from_str("_registrar"); let register_custom_derive = Ident::from_str("register_custom_derive"); let register_attr_proc_macro = Ident::from_str("register_attr_proc_macro"); let register_bang_proc_macro = Ident::from_str("register_bang_proc_macro"); diff --git a/src/test/run-pass-fulldeps/proc-macro/auxiliary/empty-crate.rs b/src/test/run-pass-fulldeps/proc-macro/auxiliary/empty-crate.rs new file mode 100644 index 0000000000000..b45d4bf41d635 --- /dev/null +++ b/src/test/run-pass-fulldeps/proc-macro/auxiliary/empty-crate.rs @@ -0,0 +1,14 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// no-prefer-dynamic + +#![crate_type = "proc-macro"] +#![deny(unused_variables)] diff --git a/src/test/run-pass-fulldeps/proc-macro/empty-crate.rs b/src/test/run-pass-fulldeps/proc-macro/empty-crate.rs new file mode 100644 index 0000000000000..38a2716aee77b --- /dev/null +++ b/src/test/run-pass-fulldeps/proc-macro/empty-crate.rs @@ -0,0 +1,17 @@ +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// aux-build:empty-crate.rs +// ignore-stage1 + +#[macro_use] +extern crate empty_crate; + +fn main() {}