Unused io amount detects .read().ok()?

clippy_lints/src/unused_io_amount.rs

@@ -47,25 +47,35 @@ impl<'tcx> LateLintPass<'tcx> for UnusedIoAmount {
  func.kind,
  hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::TryIntoResult, _))
  ) {
- check_method_call(cx, &args[0], expr);
+ check_map_error(cx, &args[0], expr);
  }
  } else {
- check_method_call(cx, res, expr);
+ check_map_error(cx, res, expr);
  }
  },
-
  hir::ExprKind::MethodCall(path, _, args, _) => match &*path.ident.as_str() {
  "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
- check_method_call(cx, &args[0], expr);
+ check_map_error(cx, &args[0], expr);
  },
  _ => (),
  },
-
  _ => (),
  }
  }
 }
 
+fn check_map_error(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>) {
+ let mut call = call;
+ while let hir::ExprKind::MethodCall(ref path, _, ref args, _) = call.kind {
+ if matches!(&*path.ident.as_str(), "or" | "or_else" | "ok") {
+ call = &args[0];
+ } else {
+ break;
+ }
+ }
+ check_method_call(cx, call, expr);
+}
+
 fn check_method_call(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>) {
  if let hir::ExprKind::MethodCall(path, _, _, _) = call.kind {
  let symbol = &*path.ident.as_str();

tests/ui/unused_io_amount.rs

@@ -1,7 +1,7 @@
 #![allow(dead_code)]
 #![warn(clippy::unused_io_amount)]
 
-use std::io;
+use std::io::{self, Read};
 
 fn question_mark<T: io::Read + io::Write>(s: &mut T) -> io::Result<()> {
  s.write(b"test")?;
@@ -22,4 +22,43 @@ fn vectored<T: io::Read + io::Write>(s: &mut T) -> io::Result<()> {
  Ok(())
 }
 
+fn ok(file: &str) -> Option<()> {
+ let mut reader = std::fs::File::open(file).ok()?;
+ let mut result = [0u8; 0];
+ reader.read(&mut result).ok()?;
+ Some(())
+}
+
+#[allow(clippy::redundant_closure)]
+#[allow(clippy::bind_instead_of_map)]
+fn or_else(file: &str) -> io::Result<()> {
+ let mut reader = std::fs::File::open(file)?;
+ let mut result = [0u8; 0];
+ reader.read(&mut result).or_else(|err| Err(err))?;
+ Ok(())
+}
+
+#[derive(Debug)]
+enum Error {
+ Kind,
+}
+
+fn or(file: &str) -> Result<(), Error> {
+ let mut reader = std::fs::File::open(file).unwrap();
+ let mut result = [0u8; 0];
+ reader.read(&mut result).or(Err(Error::Kind))?;
+ Ok(())
+}
+
+fn combine_or(file: &str) -> Result<(), Error> {
+ let mut reader = std::fs::File::open(file).unwrap();
+ let mut result = [0u8; 0];
+ reader
+ .read(&mut result)
+ .or(Err(Error::Kind))
+ .or(Err(Error::Kind))
+ .expect("error");
+ Ok(())
+}
+
 fn main() {}

tests/ui/unused_io_amount.stderr

@@ -36,5 +36,33 @@ error: written amount is not handled
 LL | s.write_vectored(&[io::IoSlice::new(&[])])?;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 6 previous errors
+error: read amount is not handled. Use `Read::read_exact` instead
+ --> $DIR/unused_io_amount.rs:28:5
+ |
+LL | reader.read(&mut result).ok()?;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: read amount is not handled. Use `Read::read_exact` instead
+ --> $DIR/unused_io_amount.rs:37:5
+ |
+LL | reader.read(&mut result).or_else(|err| Err(err))?;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: read amount is not handled. Use `Read::read_exact` instead
+ --> $DIR/unused_io_amount.rs:49:5
+ |
+LL | reader.read(&mut result).or(Err(Error::Kind))?;
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: read amount is not handled. Use `Read::read_exact` instead
+ --> $DIR/unused_io_amount.rs:56:5
+ |
+LL | / reader
+LL | | .read(&mut result)
+LL | | .or(Err(Error::Kind))
+LL | | .or(Err(Error::Kind))
+LL | | .expect("error");
+ | |________________________^
+
+error: aborting due to 10 previous errors