rust-clippy/clippy_lints/src/ptr_offset_with_cast.rs

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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// 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.
use crate::utils;
use rustc::{declare_tool_lint, hir, lint, lint_array};
use rustc_errors::Applicability;
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use std::fmt;
/// **What it does:** Checks for usage of the `offset` pointer method with a `usize` casted to an
/// `isize`.
///
/// **Why is this bad?** If were always increasing the pointer address, we can avoid the numeric
/// cast by using the `add` method instead.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// let vec = vec![b'a', b'b', b'c'];
/// let ptr = vec.as_ptr();
/// let offset = 1_usize;
///
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/// unsafe {
/// ptr.offset(offset as isize);
/// }
/// ```
///
/// Could be written:
///
/// ```rust
/// let vec = vec![b'a', b'b', b'c'];
/// let ptr = vec.as_ptr();
/// let offset = 1_usize;
///
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/// unsafe {
/// ptr.add(offset);
/// }
/// ```
declare_clippy_lint! {
pub PTR_OFFSET_WITH_CAST,
complexity,
"unneeded pointer offset cast"
}
#[derive(Copy, Clone, Debug)]
pub struct Pass;
impl lint::LintPass for Pass {
fn get_lints(&self) -> lint::LintArray {
lint_array!(PTR_OFFSET_WITH_CAST)
}
}
impl<'a, 'tcx> lint::LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &lint::LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
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// Check if the expressions is a ptr.offset or ptr.wrapping_offset method call
let (receiver_expr, arg_expr, method) = match expr_as_ptr_offset_call(cx, expr) {
Some(call_arg) => call_arg,
None => return,
};
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// Check if the argument to the method call is a cast from usize
let cast_lhs_expr = match expr_as_cast_from_usize(cx, arg_expr) {
Some(cast_lhs_expr) => cast_lhs_expr,
None => return,
};
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let msg = format!("use of `{}` with a `usize` casted to an `isize`", method);
if let Some(sugg) = build_suggestion(cx, method, receiver_expr, cast_lhs_expr) {
utils::span_lint_and_sugg(
cx,
PTR_OFFSET_WITH_CAST,
expr.span,
&msg,
"try",
sugg,
Applicability::MachineApplicable,
);
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} else {
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utils::span_lint(cx, PTR_OFFSET_WITH_CAST, expr.span, &msg);
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}
}
}
// If the given expression is a cast from a usize, return the lhs of the cast
fn expr_as_cast_from_usize<'a, 'tcx>(
cx: &lint::LateContext<'a, 'tcx>,
expr: &'tcx hir::Expr,
) -> Option<&'tcx hir::Expr> {
if let hir::ExprKind::Cast(ref cast_lhs_expr, _) = expr.node {
if is_expr_ty_usize(cx, &cast_lhs_expr) {
return Some(cast_lhs_expr);
}
}
None
}
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// If the given expression is a ptr::offset or ptr::wrapping_offset method call, return the
// receiver, the arg of the method call, and the method.
fn expr_as_ptr_offset_call<'a, 'tcx>(
cx: &lint::LateContext<'a, 'tcx>,
expr: &'tcx hir::Expr,
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) -> Option<(&'tcx hir::Expr, &'tcx hir::Expr, Method)> {
if let hir::ExprKind::MethodCall(ref path_segment, _, ref args) = expr.node {
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if is_expr_ty_raw_ptr(cx, &args[0]) {
if path_segment.ident.name == "offset" {
return Some((&args[0], &args[1], Method::Offset));
}
if path_segment.ident.name == "wrapping_offset" {
return Some((&args[0], &args[1], Method::WrappingOffset));
}
}
}
None
}
// Is the type of the expression a usize?
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fn is_expr_ty_usize<'a, 'tcx>(cx: &lint::LateContext<'a, 'tcx>, expr: &hir::Expr) -> bool {
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cx.tables.expr_ty(expr) == cx.tcx.types.usize
}
// Is the type of the expression a raw pointer?
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fn is_expr_ty_raw_ptr<'a, 'tcx>(cx: &lint::LateContext<'a, 'tcx>, expr: &hir::Expr) -> bool {
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cx.tables.expr_ty(expr).is_unsafe_ptr()
}
fn build_suggestion<'a, 'tcx>(
cx: &lint::LateContext<'a, 'tcx>,
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method: Method,
receiver_expr: &hir::Expr,
cast_lhs_expr: &hir::Expr,
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) -> Option<String> {
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let receiver = utils::snippet_opt(cx, receiver_expr.span)?;
let cast_lhs = utils::snippet_opt(cx, cast_lhs_expr.span)?;
Some(format!("{}.{}({})", receiver, method.suggestion(), cast_lhs))
}
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#[derive(Copy, Clone)]
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enum Method {
Offset,
WrappingOffset,
}
impl Method {
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fn suggestion(self) -> &'static str {
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match self {
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Method::Offset => "add",
Method::WrappingOffset => "wrapping_add",
}
}
}
impl fmt::Display for Method {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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match self {
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Method::Offset => write!(f, "offset"),
Method::WrappingOffset => write!(f, "wrapping_offset"),
}
}
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}