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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
use rustc::lint::{Context, LintPass, LintArray};
use rustc::middle::ty;
use syntax::ast;
declare_lint!(STR_TO_STRING, Deny,
"Warn when a String could use to_owned() instead of to_string()");
/// Prefer str.to_owned() over str.to_string()
///
/// The latter creates a `Formatter` and is 5x slower than the former
pub struct StrToStringPass;
impl LintPass for StrToStringPass {
fn get_lints(&self) -> LintArray {
lint_array!(STR_TO_STRING)
}
fn check_expr(&mut self, cx: &Context, expr: &ast::Expr) {
match expr.node {
ast::ExprMethodCall(ref method, _, ref args)
if method.node.name.as_str() == "to_string"
&& is_str(cx, &*args[0]) => {
cx.span_lint(STR_TO_STRING, expr.span,
"str.to_owned() is more efficient than str.to_string(), please use it instead");
},
_ => ()
}
fn is_str(cx: &Context, expr: &ast::Expr) -> bool {
fn walk_ty<'t>(ty: ty::Ty<'t>) -> ty::Ty<'t> {
match ty.sty {
ty::TyRef(_, ref tm) | ty::TyRawPtr(ref tm) => walk_ty(tm.ty),
_ => ty
}
}
match walk_ty(cx.tcx.expr_ty(expr)).sty {
ty::TyStr => true,
_ => false
}
}
}
}
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