Auto merge of #5027 - sinkuu:vectored_io, r=phansch

Lint vectored IO in unused_io_amount lint

`read_vectored` & `write_vectored` require handling returned value likewise non-vectored methods. https://github.com/rust-lang/rust/issues/68041

---

changelog: lint vectored IO in `unused_io_amount` lint

clippy_lints/src/unused_io_amount.rs

@@ -6,8 +6,8 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 declare_clippy_lint! {
     /// **What it does:** Checks for unused written/read amount.
     ///
-    /// **Why is this bad?** `io::Write::write` and `io::Read::read` are not
+    /// **Why is this bad?** `io::Write::write(_vectored)` and
-    /// guaranteed to
+    /// `io::Read::read(_vectored)` are not guaranteed to
     /// process the entire buffer. They return how many bytes were processed, which
     /// might be smaller
     /// than a given buffer's length. If you don't need to deal with
@@ -67,20 +67,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedIoAmount {
 fn check_method_call(cx: &LateContext<'_, '_>, call: &hir::Expr<'_>, expr: &hir::Expr<'_>) {
     if let hir::ExprKind::MethodCall(ref path, _, _) = call.kind {
         let symbol = &*path.ident.as_str();
-        if match_trait_method(cx, call, &paths::IO_READ) && symbol == "read" {
+        let read_trait = match_trait_method(cx, call, &paths::IO_READ);
-            span_lint(
+        let write_trait = match_trait_method(cx, call, &paths::IO_WRITE);
+
+        match (read_trait, write_trait, symbol) {
+            (true, _, "read") => span_lint(
                 cx,
                 UNUSED_IO_AMOUNT,
                 expr.span,
-                "handle read amount returned or use `Read::read_exact` instead",
+                "read amount is not handled. Use `Read::read_exact` instead",
-            );
+            ),
-        } else if match_trait_method(cx, call, &paths::IO_WRITE) && symbol == "write" {
+            (true, _, "read_vectored") => span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "read amount is not handled"),
-            span_lint(
+            (_, true, "write") => span_lint(
                 cx,
                 UNUSED_IO_AMOUNT,
                 expr.span,
-                "handle written amount returned or use `Write::write_all` instead",
+                "written amount is not handled. Use `Write::write_all` instead",
-            );
+            ),
+            (_, true, "write_vectored") => span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "written amount is not handled"),
+            _ => (),
         }
     }
 }

tests/ui/unused_io_amount.rs

@@ -16,4 +16,10 @@ fn unwrap<T: io::Read + io::Write>(s: &mut T) {
     s.read(&mut buf).unwrap();
 }
 
+fn vectored<T: io::Read + io::Write>(s: &mut T) -> io::Result<()> {
+    s.read_vectored(&mut [io::IoSliceMut::new(&mut [])])?;
+    s.write_vectored(&[io::IoSlice::new(&[])])?;
+    Ok(())
+}
+
 fn main() {}

tests/ui/unused_io_amount.stderr

@@ -1,4 +1,4 @@
-error: handle written amount returned or use `Write::write_all` instead
+error: written amount is not handled. Use `Write::write_all` instead
   --> $DIR/unused_io_amount.rs:7:5
    |
 LL |     s.write(b"test")?;
@@ -6,23 +6,35 @@ LL |     s.write(b"test")?;
    |
    = note: `-D clippy::unused-io-amount` implied by `-D warnings`
 
-error: handle read amount returned or use `Read::read_exact` instead
+error: read amount is not handled. Use `Read::read_exact` instead
   --> $DIR/unused_io_amount.rs:9:5
    |
 LL |     s.read(&mut buf)?;
    |     ^^^^^^^^^^^^^^^^^
 
-error: handle written amount returned or use `Write::write_all` instead
+error: written amount is not handled. Use `Write::write_all` instead
   --> $DIR/unused_io_amount.rs:14:5
    |
 LL |     s.write(b"test").unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: handle read amount returned or use `Read::read_exact` instead
+error: read amount is not handled. Use `Read::read_exact` instead
   --> $DIR/unused_io_amount.rs:16:5
    |
 LL |     s.read(&mut buf).unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: read amount is not handled
+  --> $DIR/unused_io_amount.rs:20:5
+   |
+LL |     s.read_vectored(&mut [io::IoSliceMut::new(&mut [])])?;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: written amount is not handled
+  --> $DIR/unused_io_amount.rs:21:5
+   |
+LL |     s.write_vectored(&[io::IoSlice::new(&[])])?;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors