clippy_lints/src/unused_io_amount.rs

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