clippy_lints/src/unused_io_amount.rs

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