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_tool_lint, lint_array};
   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 pub struct UnusedIoAmount;
  34
  35 impl LintPass for UnusedIoAmount {
  36     fn get_lints(&self) -> LintArray {
  37         lint_array!(UNUSED_IO_AMOUNT)
  38     }
  39
  40     fn name(&self) -> &'static str {
  41         "UnusedIoAmount"
  42     }
  43 }
  44
  45 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedIoAmount {
  46     fn check_stmt(&mut self, cx: &LateContext<'_, '_>, s: &hir::Stmt) {
  47         let expr = match s.node {
  48             hir::StmtKind::Semi(ref expr) | hir::StmtKind::Expr(ref expr) => &**expr,
  49             _ => return,
  50         };
  51
  52         match expr.node {
  53             hir::ExprKind::Match(ref res, _, _) if is_try(cx, expr).is_some() => {
  54                 if let hir::ExprKind::Call(ref func, ref args) = res.node {
  55                     if let hir::ExprKind::Path(ref path) = func.node {
  56                         if match_qpath(path, &paths::TRY_INTO_RESULT) && args.len() == 1 {
  57                             check_method_call(cx, &args[0], expr);
  58                         }
  59                     }
  60                 } else {
  61                     check_method_call(cx, res, expr);
  62                 }
  63             },
  64
  65             hir::ExprKind::MethodCall(ref path, _, ref args) => match &*path.ident.as_str() {
  66                 "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
  67                     check_method_call(cx, &args[0], expr);
  68                 },
  69                 _ => (),
  70             },
  71
  72             _ => (),
  73         }
  74     }
  75 }
  76
  77 fn check_method_call(cx: &LateContext<'_, '_>, call: &hir::Expr, expr: &hir::Expr) {
  78     if let hir::ExprKind::MethodCall(ref path, _, _) = call.node {
  79         let symbol = &*path.ident.as_str();
  80         if match_trait_method(cx, call, &paths::IO_READ) && symbol == "read" {
  81             span_lint(
  82                 cx,
  83                 UNUSED_IO_AMOUNT,
  84                 expr.span,
  85                 "handle read amount returned or use `Read::read_exact` instead",
  86             );
  87         } else if match_trait_method(cx, call, &paths::IO_WRITE) && symbol == "write" {
  88             span_lint(
  89                 cx,
  90                 UNUSED_IO_AMOUNT,
  91                 expr.span,
  92                 "handle written amount returned or use `Write::write_all` instead",
  93             );
  94         }
  95     }
  96 }