clippy_lints/src/unused_io_amount.rs

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