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| 1 | +use clippy_utils::{ |
| 2 | + diagnostics::{span_lint, span_lint_and_sugg}, |
| 3 | + higher::{get_vec_init_kind, VecInitKind}, |
| 4 | + source::snippet, |
| 5 | + visitors::expr_visitor_no_bodies, |
| 6 | +}; |
| 7 | +use hir::{intravisit::Visitor, ExprKind, Local, PatKind, PathSegment, QPath, StmtKind}; |
| 8 | +use rustc_errors::Applicability; |
| 9 | +use rustc_hir as hir; |
| 10 | +use rustc_lint::{LateContext, LateLintPass}; |
| 11 | +use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| 12 | + |
| 13 | +declare_clippy_lint! { |
| 14 | + /// ### What it does |
| 15 | + /// This lint catches reads into a zero-length `Vec`. |
| 16 | + /// Especially in the case of a call to `with_capacity`, this lint warns that read |
| 17 | + /// gets the number of bytes from the `Vec`'s length, not its capacity. |
| 18 | + /// |
| 19 | + /// ### Why is this bad? |
| 20 | + /// Reading zero bytes is almost certainly not the intended behavior. |
| 21 | + /// |
| 22 | + /// ### Known problems |
| 23 | + /// In theory, a very unusual read implementation could assign some semantic meaning |
| 24 | + /// to zero-byte reads. But it seems exceptionally unlikely that code intending to do |
| 25 | + /// a zero-byte read would allocate a `Vec` for it. |
| 26 | + /// |
| 27 | + /// ### Example |
| 28 | + /// ```rust |
| 29 | + /// use std::io; |
| 30 | + /// fn foo<F: io::Read>(mut f: F) { |
| 31 | + /// let mut data = Vec::with_capacity(100); |
| 32 | + /// f.read(&mut data).unwrap(); |
| 33 | + /// } |
| 34 | + /// ``` |
| 35 | + /// Use instead: |
| 36 | + /// ```rust |
| 37 | + /// use std::io; |
| 38 | + /// fn foo<F: io::Read>(mut f: F) { |
| 39 | + /// let mut data = Vec::with_capacity(100); |
| 40 | + /// data.resize(100, 0); |
| 41 | + /// f.read(&mut data).unwrap(); |
| 42 | + /// } |
| 43 | + /// ``` |
| 44 | + #[clippy::version = "1.63.0"] |
| 45 | + pub READ_ZERO_BYTE_VEC, |
| 46 | + correctness, |
| 47 | + "checks for reads into a zero-length `Vec`" |
| 48 | +} |
| 49 | +declare_lint_pass!(ReadZeroByteVec => [READ_ZERO_BYTE_VEC]); |
| 50 | + |
| 51 | +impl<'tcx> LateLintPass<'tcx> for ReadZeroByteVec { |
| 52 | + fn check_block(&mut self, cx: &LateContext<'tcx>, block: &hir::Block<'tcx>) { |
| 53 | + for (idx, stmt) in block.stmts.iter().enumerate() { |
| 54 | + if !stmt.span.from_expansion() |
| 55 | + // matches `let v = Vec::new();` |
| 56 | + && let StmtKind::Local(local) = stmt.kind |
| 57 | + && let Local { pat, init: Some(init), .. } = local |
| 58 | + && let PatKind::Binding(_, _, ident, _) = pat.kind |
| 59 | + && let Some(vec_init_kind) = get_vec_init_kind(cx, init) |
| 60 | + { |
| 61 | + // finds use of `_.read(&mut v)` |
| 62 | + let mut read_found = false; |
| 63 | + let mut visitor = expr_visitor_no_bodies(|expr| { |
| 64 | + if let ExprKind::MethodCall(path, [_self, arg], _) = expr.kind |
| 65 | + && let PathSegment { ident: read_or_read_exact, .. } = *path |
| 66 | + && matches!(read_or_read_exact.as_str(), "read" | "read_exact") |
| 67 | + && let ExprKind::AddrOf(_, hir::Mutability::Mut, inner) = arg.kind |
| 68 | + && let ExprKind::Path(QPath::Resolved(None, inner_path)) = inner.kind |
| 69 | + && let [inner_seg] = inner_path.segments |
| 70 | + && ident.name == inner_seg.ident.name |
| 71 | + { |
| 72 | + read_found = true; |
| 73 | + } |
| 74 | + !read_found |
| 75 | + }); |
| 76 | + |
| 77 | + let next_stmt_span; |
| 78 | + if idx == block.stmts.len() - 1 { |
| 79 | + // case { .. stmt; expr } |
| 80 | + if let Some(e) = block.expr { |
| 81 | + visitor.visit_expr(e); |
| 82 | + next_stmt_span = e.span; |
| 83 | + } else { |
| 84 | + return; |
| 85 | + } |
| 86 | + } else { |
| 87 | + // case { .. stmt; stmt; .. } |
| 88 | + let next_stmt = &block.stmts[idx + 1]; |
| 89 | + visitor.visit_stmt(next_stmt); |
| 90 | + next_stmt_span = next_stmt.span; |
| 91 | + } |
| 92 | + drop(visitor); |
| 93 | + |
| 94 | + if read_found && !next_stmt_span.from_expansion() { |
| 95 | + let applicability = Applicability::MaybeIncorrect; |
| 96 | + match vec_init_kind { |
| 97 | + VecInitKind::WithConstCapacity(len) => { |
| 98 | + span_lint_and_sugg( |
| 99 | + cx, |
| 100 | + READ_ZERO_BYTE_VEC, |
| 101 | + next_stmt_span, |
| 102 | + "reading zero byte data to `Vec`", |
| 103 | + "try", |
| 104 | + format!("{}.resize({}, 0); {}", |
| 105 | + ident.as_str(), |
| 106 | + len, |
| 107 | + snippet(cx, next_stmt_span, "..") |
| 108 | + ), |
| 109 | + applicability, |
| 110 | + ); |
| 111 | + } |
| 112 | + VecInitKind::WithExprCapacity(hir_id) => { |
| 113 | + let e = cx.tcx.hir().expect_expr(hir_id); |
| 114 | + span_lint_and_sugg( |
| 115 | + cx, |
| 116 | + READ_ZERO_BYTE_VEC, |
| 117 | + next_stmt_span, |
| 118 | + "reading zero byte data to `Vec`", |
| 119 | + "try", |
| 120 | + format!("{}.resize({}, 0); {}", |
| 121 | + ident.as_str(), |
| 122 | + snippet(cx, e.span, ".."), |
| 123 | + snippet(cx, next_stmt_span, "..") |
| 124 | + ), |
| 125 | + applicability, |
| 126 | + ); |
| 127 | + } |
| 128 | + _ => { |
| 129 | + span_lint( |
| 130 | + cx, |
| 131 | + READ_ZERO_BYTE_VEC, |
| 132 | + next_stmt_span, |
| 133 | + "reading zero byte data to `Vec`", |
| 134 | + ); |
| 135 | + |
| 136 | + } |
| 137 | + } |
| 138 | + } |
| 139 | + } |
| 140 | + } |
| 141 | + } |
| 142 | +} |
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