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Show better warning for trying to cast non-u8 scalar to char
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GuillaumeGomez committed Feb 10, 2018
1 parent 932c736 commit 0cccd9a
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17 changes: 17 additions & 0 deletions src/librustc_lint/types.rs
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
#![allow(non_snake_case)]

use rustc::hir::def_id::DefId;
use rustc::hir::map as hir_map;
use rustc::ty::subst::Substs;
use rustc::ty::{self, AdtKind, Ty, TyCtxt};
use rustc::ty::layout::{self, LayoutOf};
Expand Down Expand Up @@ -176,6 +177,22 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeLimits {
_ => bug!(),
};
if lit_val < min || lit_val > max {
let parent_id = cx.tcx.hir.get_parent_node(e.id);
if let hir_map::NodeExpr(parent_expr) = cx.tcx.hir.get(parent_id) {
if let hir::ExprCast(..) = parent_expr.node {
if let ty::TyChar = cx.tables.expr_ty(parent_expr).sty {
let mut err = cx.struct_span_lint(
OVERFLOWING_LITERALS,
parent_expr.span,
"only u8 can be casted into char");
err.span_suggestion(parent_expr.span,
&"use a char literal instead",
format!("'\\u{{{:X}}}'", lit_val));
err.emit();
return
}
}
}
cx.span_lint(OVERFLOWING_LITERALS,
e.span,
&format!("literal out of range for {:?}", t));
Expand Down
20 changes: 20 additions & 0 deletions src/test/ui/cast_char.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
// 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 <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.

#![deny(overflowing_literals)]

fn main() {
const XYZ: char = 0x1F888 as char;
//~^ ERROR only u8 can be casted into char
const XY: char = 129160 as char;
//~^ ERROR only u8 can be casted into char
const ZYX: char = '\u{01F888}';
println!("{}", XYZ);
}
20 changes: 20 additions & 0 deletions src/test/ui/cast_char.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
error: only u8 can be casted into char
--> $DIR/cast_char.rs:14:23
|
14 | const XYZ: char = 0x1F888 as char;
| ^^^^^^^^^^^^^^^ help: use a char literal instead: `'/u{1F888}'`
|
note: lint level defined here
--> $DIR/cast_char.rs:11:9
|
11 | #![deny(overflowing_literals)]
| ^^^^^^^^^^^^^^^^^^^^

error: only u8 can be casted into char
--> $DIR/cast_char.rs:16:22
|
16 | const XY: char = 129160 as char;
| ^^^^^^^^^^^^^^ help: use a char literal instead: `'/u{1F888}'`

error: aborting due to 2 previous errors

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