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