clippy_lints/src/unused_io_amount.rs

   1 use crate::utils::{is_try, match_qpath, match_trait_method, paths, span_lint};
   2 use rustc::hir;
   3 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use rustc::{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` and `io::Read::read` are not
  10     /// 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<'a, 'tcx> LateLintPass<'a, '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 let hir::ExprKind::Path(ref path) = func.kind {
  46                         if match_qpath(path, &paths::TRY_INTO_RESULT) && args.len() == 1 {
  47                             check_method_call(cx, &args[0], expr);
  48                         }
  49                     }
  50                 } else {
  51                     check_method_call(cx, res, expr);
  52                 }
  53             },
  54
  55             hir::ExprKind::MethodCall(ref path, _, ref args) => match &*path.ident.as_str() {
  56                 "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
  57                     check_method_call(cx, &args[0], expr);
  58                 },
  59                 _ => (),
  60             },
  61
  62             _ => (),
  63         }
  64     }
  65 }
  66
  67 fn check_method_call(cx: &LateContext<'_, '_>, call: &hir::Expr, expr: &hir::Expr) {
  68     if let hir::ExprKind::MethodCall(ref path, _, _) = call.kind {
  69         let symbol = &*path.ident.as_str();
  70         if match_trait_method(cx, call, &paths::IO_READ) && symbol == "read" {
  71             span_lint(
  72                 cx,
  73                 UNUSED_IO_AMOUNT,
  74                 expr.span,
  75                 "handle read amount returned or use `Read::read_exact` instead",
  76             );
  77         } else if match_trait_method(cx, call, &paths::IO_WRITE) && symbol == "write" {
  78             span_lint(
  79                 cx,
  80                 UNUSED_IO_AMOUNT,
  81                 expr.span,
  82                 "handle written amount returned or use `Write::write_all` instead",
  83             );
  84         }
  85     }
  86 }