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| 1 | +use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg}; |
| 2 | +use clippy_utils::source::SpanRangeExt; |
| 3 | +use clippy_utils::sym; |
| 4 | +use rustc_ast::LitKind; |
| 5 | +use rustc_errors::Applicability; |
| 6 | +use rustc_hir::{Expr, ExprKind, UnOp}; |
| 7 | +use rustc_lint::{LateContext, LateLintPass}; |
| 8 | +use rustc_session::declare_lint_pass; |
| 9 | +use std::cmp::Ordering; |
| 10 | +use std::fmt; |
| 11 | + |
| 12 | +declare_clippy_lint! { |
| 13 | + /// ### What it does |
| 14 | + /// Checks for usage of the `offset` pointer method with an integer |
| 15 | + /// literal. |
| 16 | + /// |
| 17 | + /// ### Why is this bad? |
| 18 | + /// The `add` and `sub` methods more accurately express the intent. |
| 19 | + /// |
| 20 | + /// ### Example |
| 21 | + /// ```no_run |
| 22 | + /// let vec = vec![b'a', b'b', b'c']; |
| 23 | + /// let ptr = vec.as_ptr(); |
| 24 | + /// |
| 25 | + /// unsafe { |
| 26 | + /// ptr.offset(-8); |
| 27 | + /// } |
| 28 | + /// ``` |
| 29 | + /// |
| 30 | + /// Could be written: |
| 31 | + /// |
| 32 | + /// ```no_run |
| 33 | + /// let vec = vec![b'a', b'b', b'c']; |
| 34 | + /// let ptr = vec.as_ptr(); |
| 35 | + /// |
| 36 | + /// unsafe { |
| 37 | + /// ptr.sub(8); |
| 38 | + /// } |
| 39 | + /// ``` |
| 40 | + #[clippy::version = "CURRENT_RUSTC_VERSION"] |
| 41 | + pub PTR_OFFSET_BY_LITERAL, |
| 42 | + complexity, |
| 43 | + "unneeded pointer offset" |
| 44 | +} |
| 45 | + |
| 46 | +declare_lint_pass!(PtrOffsetByLiteral => [PTR_OFFSET_BY_LITERAL]); |
| 47 | + |
| 48 | +impl<'tcx> LateLintPass<'tcx> for PtrOffsetByLiteral { |
| 49 | + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| 50 | + // Check if the expressions is a ptr.offset or ptr.wrapping_offset method call |
| 51 | + let Some((receiver_expr, arg_expr, method)) = expr_as_ptr_offset_call(cx, expr) else { |
| 52 | + return; |
| 53 | + }; |
| 54 | + |
| 55 | + // Check if the argument to the method call is a (negated) literal. |
| 56 | + let Some(literal) = expr_as_literal(arg_expr) else { |
| 57 | + return; |
| 58 | + }; |
| 59 | + |
| 60 | + let msg = format!("use of `{method}` with a literal"); |
| 61 | + if let Some(sugg) = build_suggestion(cx, method, receiver_expr, literal) { |
| 62 | + span_lint_and_sugg( |
| 63 | + cx, |
| 64 | + PTR_OFFSET_BY_LITERAL, |
| 65 | + expr.span, |
| 66 | + msg, |
| 67 | + "try", |
| 68 | + sugg, |
| 69 | + Applicability::MachineApplicable, |
| 70 | + ); |
| 71 | + } else { |
| 72 | + span_lint(cx, PTR_OFFSET_BY_LITERAL, expr.span, msg); |
| 73 | + } |
| 74 | + } |
| 75 | +} |
| 76 | + |
| 77 | +fn get_literal_bits<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<u128> { |
| 78 | + let ExprKind::Lit(lit) = expr.kind else { |
| 79 | + return None; |
| 80 | + }; |
| 81 | + |
| 82 | + let LitKind::Int(packed_u128, _) = lit.node else { |
| 83 | + return None; |
| 84 | + }; |
| 85 | + |
| 86 | + Some(packed_u128.get()) |
| 87 | +} |
| 88 | + |
| 89 | +// If the given expression is a (negated) literal, return its value. |
| 90 | +fn expr_as_literal<'tcx>(expr: &'tcx Expr<'tcx>) -> Option<i128> { |
| 91 | + if let Some(literal_bits) = get_literal_bits(expr) { |
| 92 | + // The value must fit in a isize, so we can't have overflow here. |
| 93 | + return Some(literal_bits as i128); |
| 94 | + } |
| 95 | + |
| 96 | + if let ExprKind::Unary(UnOp::Neg, inner) = expr.kind { |
| 97 | + if let Some(literal_bits) = get_literal_bits(inner) { |
| 98 | + return Some(-1 * literal_bits as i128); |
| 99 | + } |
| 100 | + } |
| 101 | + |
| 102 | + None |
| 103 | +} |
| 104 | + |
| 105 | +// If the given expression is a ptr::offset or ptr::wrapping_offset method call, return the |
| 106 | +// receiver, the arg of the method call, and the method. |
| 107 | +fn expr_as_ptr_offset_call<'tcx>( |
| 108 | + cx: &LateContext<'tcx>, |
| 109 | + expr: &'tcx Expr<'_>, |
| 110 | +) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>, Method)> { |
| 111 | + if let ExprKind::MethodCall(path_segment, arg_0, [arg_1], _) = &expr.kind |
| 112 | + && cx.typeck_results().expr_ty(arg_0).is_raw_ptr() |
| 113 | + { |
| 114 | + if path_segment.ident.name == sym::offset { |
| 115 | + return Some((arg_0, arg_1, Method::Offset)); |
| 116 | + } |
| 117 | + if path_segment.ident.name == sym::wrapping_offset { |
| 118 | + return Some((arg_0, arg_1, Method::WrappingOffset)); |
| 119 | + } |
| 120 | + } |
| 121 | + None |
| 122 | +} |
| 123 | + |
| 124 | +fn build_suggestion(cx: &LateContext<'_>, method: Method, receiver_expr: &Expr<'_>, literal: i128) -> Option<String> { |
| 125 | + let receiver = receiver_expr.span.get_source_text(cx)?; |
| 126 | + |
| 127 | + let new_method = match Ord::cmp(&literal, &0) { |
| 128 | + Ordering::Greater => match method { |
| 129 | + Method::Offset => "add", |
| 130 | + Method::WrappingOffset => "wrapping_add", |
| 131 | + }, |
| 132 | + Ordering::Equal => return Some(format!("{receiver}")), |
| 133 | + Ordering::Less => match method { |
| 134 | + Method::Offset => "sub", |
| 135 | + Method::WrappingOffset => "wrapping_sub", |
| 136 | + }, |
| 137 | + }; |
| 138 | + |
| 139 | + let literal = literal.unsigned_abs(); |
| 140 | + Some(format!("{receiver}.{new_method}({literal})")) |
| 141 | +} |
| 142 | + |
| 143 | +#[derive(Copy, Clone)] |
| 144 | +enum Method { |
| 145 | + Offset, |
| 146 | + WrappingOffset, |
| 147 | +} |
| 148 | + |
| 149 | +impl fmt::Display for Method { |
| 150 | + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 151 | + match self { |
| 152 | + Self::Offset => write!(f, "offset"), |
| 153 | + Self::WrappingOffset => write!(f, "wrapping_offset"), |
| 154 | + } |
| 155 | + } |
| 156 | +} |
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