src/tools/clippy/clippy_lints/src/unused_io_amount.rs

   1 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
   2 use clippy_utils::{is_try, match_trait_method, paths};
   3 use rustc_hir as hir;
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   6
   7 declare_clippy_lint! {
   8     /// ### What it does
   9     /// Checks for unused written/read amount.
  10     ///
  11     /// ### Why is this bad?
  12     /// `io::Write::write(_vectored)` and
  13     /// `io::Read::read(_vectored)` are not guaranteed to
  14     /// process the entire buffer. They return how many bytes were processed, which
  15     /// might be smaller
  16     /// than a given buffer's length. If you don't need to deal with
  17     /// partial-write/read, use
  18     /// `write_all`/`read_exact` instead.
  19     ///
  20     /// When working with asynchronous code (either with the `futures`
  21     /// crate or with `tokio`), a similar issue exists for
  22     /// `AsyncWriteExt::write()` and `AsyncReadExt::read()` : these
  23     /// functions are also not guaranteed to process the entire
  24     /// buffer.  Your code should either handle partial-writes/reads, or
  25     /// call the `write_all`/`read_exact` methods on those traits instead.
  26     ///
  27     /// ### Known problems
  28     /// Detects only common patterns.
  29     ///
  30     /// ### Examples
  31     /// ```rust,ignore
  32     /// use std::io;
  33     /// fn foo<W: io::Write>(w: &mut W) -> io::Result<()> {
  34     ///     // must be `w.write_all(b"foo")?;`
  35     ///     w.write(b"foo")?;
  36     ///     Ok(())
  37     /// }
  38     /// ```
  39     #[clippy::version = "pre 1.29.0"]
  40     pub UNUSED_IO_AMOUNT,
  41     correctness,
  42     "unused written/read amount"
  43 }
  44
  45 declare_lint_pass!(UnusedIoAmount => [UNUSED_IO_AMOUNT]);
  46
  47 impl<'tcx> LateLintPass<'tcx> for UnusedIoAmount {
  48     fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
  49         let expr = match s.kind {
  50             hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr) => expr,
  51             _ => return,
  52         };
  53
  54         match expr.kind {
  55             hir::ExprKind::Match(res, _, _) if is_try(cx, expr).is_some() => {
  56                 if let hir::ExprKind::Call(func, [ref arg_0, ..]) = res.kind {
  57                     if matches!(
  58                         func.kind,
  59                         hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::TryTraitBranch, ..))
  60                     ) {
  61                         check_map_error(cx, arg_0, expr);
  62                     }
  63                 } else {
  64                     check_map_error(cx, res, expr);
  65                 }
  66             },
  67             hir::ExprKind::MethodCall(path, [ref arg_0, ..], _) => match path.ident.as_str() {
  68                 "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
  69                     check_map_error(cx, arg_0, expr);
  70                 },
  71                 _ => (),
  72             },
  73             _ => (),
  74         }
  75     }
  76 }
  77
  78 /// If `expr` is an (e).await, return the inner expression "e" that's being
  79 /// waited on.  Otherwise return None.
  80 fn try_remove_await<'a>(expr: &'a hir::Expr<'a>) -> Option<&hir::Expr<'a>> {
  81     if let hir::ExprKind::Match(expr, _, hir::MatchSource::AwaitDesugar) = expr.kind {
  82         if let hir::ExprKind::Call(func, [ref arg_0, ..]) = expr.kind {
  83             if matches!(
  84                 func.kind,
  85                 hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::IntoFutureIntoFuture, ..))
  86             ) {
  87                 return Some(arg_0);
  88             }
  89         }
  90     }
  91
  92     None
  93 }
  94
  95 fn check_map_error(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>) {
  96     let mut call = call;
  97     while let hir::ExprKind::MethodCall(path, args, _) = call.kind {
  98         if matches!(path.ident.as_str(), "or" | "or_else" | "ok") {
  99             call = &args[0];
 100         } else {
 101             break;
 102         }
 103     }
 104
 105     if let Some(call) = try_remove_await(call) {
 106         check_method_call(cx, call, expr, true);
 107     } else {
 108         check_method_call(cx, call, expr, false);
 109     }
 110 }
 111
 112 fn check_method_call(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>, is_await: bool) {
 113     if let hir::ExprKind::MethodCall(path, _, _) = call.kind {
 114         let symbol = path.ident.as_str();
 115         let read_trait = if is_await {
 116             match_trait_method(cx, call, &paths::FUTURES_IO_ASYNCREADEXT)
 117                 || match_trait_method(cx, call, &paths::TOKIO_IO_ASYNCREADEXT)
 118         } else {
 119             match_trait_method(cx, call, &paths::IO_READ)
 120         };
 121         let write_trait = if is_await {
 122             match_trait_method(cx, call, &paths::FUTURES_IO_ASYNCWRITEEXT)
 123                 || match_trait_method(cx, call, &paths::TOKIO_IO_ASYNCWRITEEXT)
 124         } else {
 125             match_trait_method(cx, call, &paths::IO_WRITE)
 126         };
 127
 128         match (read_trait, write_trait, symbol, is_await) {
 129             (true, _, "read", false) => span_lint_and_help(
 130                 cx,
 131                 UNUSED_IO_AMOUNT,
 132                 expr.span,
 133                 "read amount is not handled",
 134                 None,
 135                 "use `Read::read_exact` instead, or handle partial reads",
 136             ),
 137             (true, _, "read", true) => span_lint_and_help(
 138                 cx,
 139                 UNUSED_IO_AMOUNT,
 140                 expr.span,
 141                 "read amount is not handled",
 142                 None,
 143                 "use `AsyncReadExt::read_exact` instead, or handle partial reads",
 144             ),
 145             (true, _, "read_vectored", _) => {
 146                 span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "read amount is not handled");
 147             },
 148             (_, true, "write", false) => span_lint_and_help(
 149                 cx,
 150                 UNUSED_IO_AMOUNT,
 151                 expr.span,
 152                 "written amount is not handled",
 153                 None,
 154                 "use `Write::write_all` instead, or handle partial writes",
 155             ),
 156             (_, true, "write", true) => span_lint_and_help(
 157                 cx,
 158                 UNUSED_IO_AMOUNT,
 159                 expr.span,
 160                 "written amount is not handled",
 161                 None,
 162                 "use `AsyncWriteExt::write_all` instead, or handle partial writes",
 163             ),
 164             (_, true, "write_vectored", _) => {
 165                 span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "written amount is not handled");
 166             },
 167             _ => (),
 168         }
 169     }
 170 }