clippy_lints/src/unused_io_amount.rs

   1 use rustc::lint::*;
   2 use rustc::hir;
   3 use utils::{span_lint, match_qpath, match_trait_method, is_try, paths};
   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_lint! {
  27     pub UNUSED_IO_AMOUNT,
  28     Deny,
  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, _) |
  44             hir::StmtExpr(ref expr, _) => &**expr,
  45             _ => return,
  46         };
  47
  48         match expr.node {
  49             hir::ExprMatch(ref res, _, _) if is_try(expr).is_some() => {
  50                 if let hir::ExprCall(ref func, ref args) = res.node {
  51                     if let hir::ExprPath(ref path) = func.node {
  52                         if match_qpath(path, &paths::TRY_INTO_RESULT) && args.len() == 1 {
  53                             check_method_call(cx, &args[0], expr);
  54                         }
  55                     }
  56                 } else {
  57                     check_method_call(cx, res, expr);
  58                 }
  59             },
  60
  61             hir::ExprMethodCall(ref path, _, ref args) => {
  62                 match &*path.name.as_str() {
  63                     "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
  64                         check_method_call(cx, &args[0], expr);
  65                     },
  66                     _ => (),
  67                 }
  68             },
  69
  70             _ => (),
  71         }
  72     }
  73 }
  74
  75 fn check_method_call(cx: &LateContext, call: &hir::Expr, expr: &hir::Expr) {
  76     if let hir::ExprMethodCall(ref path, _, _) = call.node {
  77         let symbol = &*path.name.as_str();
  78         if match_trait_method(cx, call, &paths::IO_READ) && symbol == "read" {
  79             span_lint(
  80                 cx,
  81                 UNUSED_IO_AMOUNT,
  82                 expr.span,
  83                 "handle read amount returned or use `Read::read_exact` instead",
  84             );
  85         } else if match_trait_method(cx, call, &paths::IO_WRITE) && symbol == "write" {
  86             span_lint(
  87                 cx,
  88                 UNUSED_IO_AMOUNT,
  89                 expr.span,
  90                 "handle written amount returned or use `Write::write_all` instead",
  91             );
  92         }
  93     }
  94 }