clippy_lints/src/unused_io_amount.rs

   1 use clippy_utils::diagnostics::span_lint;
   2 use clippy_utils::{is_try, match_trait_method, paths};
   3 use rustc_hir as hir;
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   6
   7 declare_clippy_lint! {
   8     /// ### What it does
   9     /// Checks for unused written/read amount.
  10     ///
  11     /// ### Why is this bad?
  12     /// `io::Write::write(_vectored)` and
  13     /// `io::Read::read(_vectored)` are not guaranteed to
  14     /// process the entire buffer. They return how many bytes were processed, which
  15     /// might be smaller
  16     /// than a given buffer's length. If you don't need to deal with
  17     /// partial-write/read, use
  18     /// `write_all`/`read_exact` instead.
  19     ///
  20     /// ### Known problems
  21     /// Detects only common patterns.
  22     ///
  23     /// ### Example
  24     /// ```rust,ignore
  25     /// use std::io;
  26     /// fn foo<W: io::Write>(w: &mut W) -> io::Result<()> {
  27     ///     // must be `w.write_all(b"foo")?;`
  28     ///     w.write(b"foo")?;
  29     ///     Ok(())
  30     /// }
  31     /// ```
  32     pub UNUSED_IO_AMOUNT,
  33     correctness,
  34     "unused written/read amount"
  35 }
  36
  37 declare_lint_pass!(UnusedIoAmount => [UNUSED_IO_AMOUNT]);
  38
  39 impl<'tcx> LateLintPass<'tcx> for UnusedIoAmount {
  40     fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
  41         let expr = match s.kind {
  42             hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr) => expr,
  43             _ => return,
  44         };
  45
  46         match expr.kind {
  47             hir::ExprKind::Match(res, _, _) if is_try(cx, expr).is_some() => {
  48                 if let hir::ExprKind::Call(func, [ref arg_0, ..]) = res.kind {
  49                     if matches!(
  50                         func.kind,
  51                         hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::TryTraitBranch, _))
  52                     ) {
  53                         check_map_error(cx, arg_0, expr);
  54                     }
  55                 } else {
  56                     check_map_error(cx, res, expr);
  57                 }
  58             },
  59             hir::ExprKind::MethodCall(path, _, [ref arg_0, ..], _) => match &*path.ident.as_str() {
  60                 "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
  61                     check_map_error(cx, arg_0, expr);
  62                 },
  63                 _ => (),
  64             },
  65             _ => (),
  66         }
  67     }
  68 }
  69
  70 fn check_map_error(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>) {
  71     let mut call = call;
  72     while let hir::ExprKind::MethodCall(path, _, args, _) = call.kind {
  73         if matches!(&*path.ident.as_str(), "or" | "or_else" | "ok") {
  74             call = &args[0];
  75         } else {
  76             break;
  77         }
  78     }
  79     check_method_call(cx, call, expr);
  80 }
  81
  82 fn check_method_call(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>) {
  83     if let hir::ExprKind::MethodCall(path, _, _, _) = call.kind {
  84         let symbol = &*path.ident.as_str();
  85         let read_trait = match_trait_method(cx, call, &paths::IO_READ);
  86         let write_trait = match_trait_method(cx, call, &paths::IO_WRITE);
  87
  88         match (read_trait, write_trait, symbol) {
  89             (true, _, "read") => span_lint(
  90                 cx,
  91                 UNUSED_IO_AMOUNT,
  92                 expr.span,
  93                 "read amount is not handled. Use `Read::read_exact` instead",
  94             ),
  95             (true, _, "read_vectored") => span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "read amount is not handled"),
  96             (_, true, "write") => span_lint(
  97                 cx,
  98                 UNUSED_IO_AMOUNT,
  99                 expr.span,
 100                 "written amount is not handled. Use `Write::write_all` instead",
 101             ),
 102             (_, true, "write_vectored") => span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "written amount is not handled"),
 103             _ => (),
 104         }
 105     }
 106 }