clippy_lints/src/unused_io_amount.rs

   1 use crate::utils::{is_try, match_qpath, match_trait_method, paths, span_lint};
   2 use rustc::declare_lint_pass;
   3 use rustc::hir;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc_session::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` and `io::Read::read` are not
  11     /// 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<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedIoAmount {
  37     fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
  38         let expr = match s.kind {
  39             hir::StmtKind::Semi(ref expr) | hir::StmtKind::Expr(ref expr) => &**expr,
  40             _ => return,
  41         };
  42
  43         match expr.kind {
  44             hir::ExprKind::Match(ref res, _, _) if is_try(expr).is_some() => {
  45                 if let hir::ExprKind::Call(ref func, ref args) = res.kind {
  46                     if let hir::ExprKind::Path(ref path) = func.kind {
  47                         if match_qpath(path, &paths::TRY_INTO_RESULT) && args.len() == 1 {
  48                             check_method_call(cx, &args[0], expr);
  49                         }
  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         if match_trait_method(cx, call, &paths::IO_READ) && symbol == "read" {
  72             span_lint(
  73                 cx,
  74                 UNUSED_IO_AMOUNT,
  75                 expr.span,
  76                 "handle read amount returned or use `Read::read_exact` instead",
  77             );
  78         } else if match_trait_method(cx, call, &paths::IO_WRITE) && symbol == "write" {
  79             span_lint(
  80                 cx,
  81                 UNUSED_IO_AMOUNT,
  82                 expr.span,
  83                 "handle written amount returned or use `Write::write_all` instead",
  84             );
  85         }
  86     }
  87 }