8000 Fix hygene issue when deriving Debug by Phlosioneer · Pull Request #48934 · rust-lang/rust · GitHub
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Fix hygene issue when deriving Debug #48934

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Merged
merged 1 commit into from
Mar 13, 2018
Merged

Fix hygene issue when deriving Debug #48934

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Fix hygene issue when deriving Debug 
The code for several of the core traits doesn't use hygenic macros.
This isn't a problem, except for the Debug trait, which is the only
one that uses a variable, named "builder".

Variables can't share names with unit structs, so attempting to
[derive(Debug)] on any type while a unit struct with the name
"builder" was in scope would result in an error.

This commit just changes the name of the variable to
"__debug_trait_builder", because I couldn't figure out how to get a
list of all unit structs in-scope from within the derive expansion
function. If someone wants to have a unit struct with
the exact name "__debug_trait_builder", they'll just have to do it
without a [derive(Debug)].
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@Phlosioneer
Phlosioneer committed Mar 11, 2018
commit c033c6e47c1a84e2902c75a1b5ec161362f34f18
2 changes: 1 addition & 1 deletion src/libsyntax_ext/deriving/debug.rs
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Expand Up @@ -70,7 +70,7 @@ fn show_substructure(cx: &mut ExtCtxt, span: Span, substr: &Substructure) -> P<E
// We want to make sure we have the ctxt set so that we can use unstable methods
let span = span.with_ctxt(cx.backtrace());
let name = cx.expr_lit(span, ast::LitKind::Str(ident.name, ast::StrStyle::Cooked));
let builder = Ident::from_str("builder");
let builder = Ident::from_str("__debug_trait_builder");
let builder_expr = cx.expr_ident(span, builder.clone());

let fmt = substr.nonself_args[0].clone();
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17 changes: 17 additions & 0 deletions src/test/run-pass/issue-42453.rs
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@@ -0,0 +1,17 @@
// Copyright 2014 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#[derive(Debug)]
struct builder;

fn main() {

}

0