2018-09-15 07:21:58 +00:00
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use crate::rustc::{declare_tool_lint, hir, lint, lint_array};
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2018-08-27 13:49:54 +00:00
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use crate::utils;
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2018-08-29 12:40:00 +00:00
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use std::fmt;
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2018-08-27 13:49:54 +00:00
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/// **What it does:** Checks for usage of the `offset` pointer method with a `usize` casted to an
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/// `isize`.
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///
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/// **Why is this bad?** If we’re always increasing the pointer address, we can avoid the numeric
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/// cast by using the `add` method instead.
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///
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/// **Known problems:** None
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///
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/// **Example:**
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/// ```rust
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/// let vec = vec![b'a', b'b', b'c'];
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/// let ptr = vec.as_ptr();
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/// let offset = 1_usize;
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///
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/// unsafe { ptr.offset(offset as isize); }
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/// ```
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///
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/// Could be written:
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///
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/// ```rust
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/// let vec = vec![b'a', b'b', b'c'];
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/// let ptr = vec.as_ptr();
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/// let offset = 1_usize;
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///
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/// unsafe { ptr.add(offset); }
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/// ```
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declare_clippy_lint! {
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pub PTR_OFFSET_WITH_CAST,
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2018-08-29 12:02:26 +00:00
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complexity,
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2018-08-27 13:49:54 +00:00
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"uneeded pointer offset cast"
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}
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#[derive(Copy, Clone, Debug)]
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pub struct Pass;
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impl lint::LintPass for Pass {
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fn get_lints(&self) -> lint::LintArray {
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lint_array!(PTR_OFFSET_WITH_CAST)
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}
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}
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impl<'a, 'tcx> lint::LateLintPass<'a, 'tcx> for Pass {
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fn check_expr(&mut self, cx: &lint::LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
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2018-08-29 12:40:00 +00:00
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// Check if the expressions is a ptr.offset or ptr.wrapping_offset method call
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let (receiver_expr, arg_expr, method) = match expr_as_ptr_offset_call(cx, expr) {
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2018-08-27 13:49:54 +00:00
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Some(call_arg) => call_arg,
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None => return,
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};
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2018-08-29 12:40:00 +00:00
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// Check if the argument to the method call is a cast from usize
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2018-08-27 13:49:54 +00:00
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let cast_lhs_expr = match expr_as_cast_from_usize(cx, arg_expr) {
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Some(cast_lhs_expr) => cast_lhs_expr,
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None => return,
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};
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2018-08-29 12:40:00 +00:00
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let msg = format!("use of `{}` with a `usize` casted to an `isize`", method);
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if let Some(sugg) = build_suggestion(cx, method, receiver_expr, cast_lhs_expr) {
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utils::span_lint_and_sugg(cx, PTR_OFFSET_WITH_CAST, expr.span, &msg, "try", sugg);
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2018-08-29 12:12:22 +00:00
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} else {
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2018-08-29 12:40:00 +00:00
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utils::span_lint(cx, PTR_OFFSET_WITH_CAST, expr.span, &msg);
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2018-08-29 12:12:22 +00:00
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}
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2018-08-27 13:49:54 +00:00
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}
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}
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// If the given expression is a cast from a usize, return the lhs of the cast
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fn expr_as_cast_from_usize<'a, 'tcx>(
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cx: &lint::LateContext<'a, 'tcx>,
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expr: &'tcx hir::Expr,
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) -> Option<&'tcx hir::Expr> {
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if let hir::ExprKind::Cast(ref cast_lhs_expr, _) = expr.node {
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if is_expr_ty_usize(cx, &cast_lhs_expr) {
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return Some(cast_lhs_expr);
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}
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}
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None
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}
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2018-08-29 12:40:00 +00:00
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// If the given expression is a ptr::offset or ptr::wrapping_offset method call, return the
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// receiver, the arg of the method call, and the method.
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2018-08-27 13:49:54 +00:00
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fn expr_as_ptr_offset_call<'a, 'tcx>(
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cx: &lint::LateContext<'a, 'tcx>,
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expr: &'tcx hir::Expr,
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2018-08-29 12:40:00 +00:00
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) -> Option<(&'tcx hir::Expr, &'tcx hir::Expr, Method)> {
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2018-08-27 13:49:54 +00:00
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if let hir::ExprKind::MethodCall(ref path_segment, _, ref args) = expr.node {
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2018-08-29 12:40:00 +00:00
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if is_expr_ty_raw_ptr(cx, &args[0]) {
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if path_segment.ident.name == "offset" {
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return Some((&args[0], &args[1], Method::Offset));
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}
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if path_segment.ident.name == "wrapping_offset" {
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return Some((&args[0], &args[1], Method::WrappingOffset));
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}
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2018-08-27 13:49:54 +00:00
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}
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}
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None
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}
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// Is the type of the expression a usize?
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fn is_expr_ty_usize<'a, 'tcx>(
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cx: &lint::LateContext<'a, 'tcx>,
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expr: &hir::Expr,
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) -> bool {
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2018-08-29 12:07:23 +00:00
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cx.tables.expr_ty(expr) == cx.tcx.types.usize
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2018-08-27 13:49:54 +00:00
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}
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// Is the type of the expression a raw pointer?
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fn is_expr_ty_raw_ptr<'a, 'tcx>(
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cx: &lint::LateContext<'a, 'tcx>,
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expr: &hir::Expr,
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) -> bool {
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2018-08-29 12:08:59 +00:00
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cx.tables.expr_ty(expr).is_unsafe_ptr()
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2018-08-27 13:49:54 +00:00
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}
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fn build_suggestion<'a, 'tcx>(
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cx: &lint::LateContext<'a, 'tcx>,
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2018-08-29 12:40:00 +00:00
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method: Method,
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2018-08-27 13:49:54 +00:00
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receiver_expr: &hir::Expr,
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cast_lhs_expr: &hir::Expr,
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2018-08-29 12:12:22 +00:00
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) -> Option<String> {
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2018-08-29 12:42:43 +00:00
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let receiver = utils::snippet_opt(cx, receiver_expr.span)?;
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let cast_lhs = utils::snippet_opt(cx, cast_lhs_expr.span)?;
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Some(format!("{}.{}({})", receiver, method.suggestion(), cast_lhs))
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2018-08-27 13:49:54 +00:00
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}
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2018-08-29 12:40:00 +00:00
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2018-08-29 13:01:05 +00:00
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#[derive(Copy, Clone)]
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2018-08-29 12:40:00 +00:00
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enum Method {
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Offset,
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WrappingOffset,
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}
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impl Method {
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2018-08-29 13:27:32 +00:00
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fn suggestion(self) -> &'static str {
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2018-08-29 13:59:38 +00:00
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match self {
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2018-08-29 12:40:00 +00:00
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Method::Offset => "add",
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Method::WrappingOffset => "wrapping_add",
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}
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}
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}
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impl fmt::Display for Method {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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2018-08-29 13:59:38 +00:00
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match self {
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2018-08-29 12:40:00 +00:00
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Method::Offset => write!(f, "offset"),
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Method::WrappingOffset => write!(f, "wrapping_offset"),
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}
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}
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2018-08-29 12:43:40 +00:00
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}
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