From 55f4564dbd4dbe3984540e615e4cd083d9eb9055 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ali=C3=A9nore=20Bouttefeux?= <alienore.bouttefeux@gmail.com>
Date: Fri, 16 Apr 2021 20:12:16 +0200
Subject: [PATCH] improve unused_io_amount

---
 clippy_lints/src/unused_io_amount.rs | 51 +++++++++++++++++-----------
 tests/ui/unused_io_amount.rs         |  9 ++++-
 tests/ui/unused_io_amount.stderr     | 20 +++++++----
 3 files changed, 52 insertions(+), 28 deletions(-)

diff --git a/clippy_lints/src/unused_io_amount.rs b/clippy_lints/src/unused_io_amount.rs
index 5e8e530f480f..3e5a0bcc78d0 100644
--- a/clippy_lints/src/unused_io_amount.rs
+++ b/clippy_lints/src/unused_io_amount.rs
@@ -67,27 +67,38 @@ impl<'tcx> LateLintPass<'tcx> for UnusedIoAmount {
 }
 
 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();
-        let read_trait = match_trait_method(cx, call, &paths::IO_READ);
-        let write_trait = match_trait_method(cx, call, &paths::IO_WRITE);
+    if let hir::ExprKind::MethodCall(ref path, _, ref args, _) = call.kind {
+        match &*path.ident.as_str() {
+            "ok" | "or" | "or_else" => {
+                check_method_call(cx, &args[0], expr);
+            },
+            _ => {
+                let symbol = &*path.ident.as_str();
+                let read_trait = match_trait_method(cx, call, &paths::IO_READ);
+                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,
-                "read amount is not handled. Use `Read::read_exact` instead",
-            ),
-            (true, _, "read_vectored") => span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "read amount is not handled"),
-            (_, true, "write") => span_lint(
-                cx,
-                UNUSED_IO_AMOUNT,
-                expr.span,
-                "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"),
-            _ => (),
+                match (read_trait, write_trait, symbol) {
+                    (true, _, "read") => span_lint(
+                        cx,
+                        UNUSED_IO_AMOUNT,
+                        expr.span,
+                        "read amount is not handled. Use `Read::read_exact` instead",
+                    ),
+                    (true, _, "read_vectored") => {
+                        span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "read amount is not handled")
+                    },
+                    (_, true, "write") => span_lint(
+                        cx,
+                        UNUSED_IO_AMOUNT,
+                        expr.span,
+                        "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")
+                    },
+                    _ => (),
+                }
+            },
         }
     }
 }
diff --git a/tests/ui/unused_io_amount.rs b/tests/ui/unused_io_amount.rs
index ebaba9629db1..136143b62f2c 100644
--- a/tests/ui/unused_io_amount.rs
+++ b/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 +22,11 @@ fn vectored<T: io::Read + io::Write>(s: &mut T) -> io::Result<()> {
     Ok(())
 }
 
+fn test(file: &str) -> Option<()> {
+    let mut reader = std::fs::File::open(file).ok()?;
+    let mut result = [0u8; 0];
+    reader.read(&mut result).ok()?;
+    Some(())
+}
+
 fn main() {}
diff --git a/tests/ui/unused_io_amount.stderr b/tests/ui/unused_io_amount.stderr
index 5219d63980b4..74e1c0ef9e15 100644
--- a/tests/ui/unused_io_amount.stderr
+++ b/tests/ui/unused_io_amount.stderr
@@ -1,5 +1,5 @@
 error: written amount is not handled. Use `Write::write_all` instead
-  --> $DIR/unused_io_amount.rs:7:5
+  --> $DIR/unused_io_amount.rs:8:5
    |
 LL |     s.write(b"test")?;
    |     ^^^^^^^^^^^^^^^^^
@@ -7,34 +7,40 @@ LL |     s.write(b"test")?;
    = note: `-D clippy::unused-io-amount` implied by `-D warnings`
 
 error: read amount is not handled. Use `Read::read_exact` instead
-  --> $DIR/unused_io_amount.rs:9:5
+  --> $DIR/unused_io_amount.rs:10:5
    |
 LL |     s.read(&mut buf)?;
    |     ^^^^^^^^^^^^^^^^^
 
 error: written amount is not handled. Use `Write::write_all` instead
-  --> $DIR/unused_io_amount.rs:14:5
+  --> $DIR/unused_io_amount.rs:15:5
    |
 LL |     s.write(b"test").unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: read amount is not handled. Use `Read::read_exact` instead
-  --> $DIR/unused_io_amount.rs:16:5
+  --> $DIR/unused_io_amount.rs:17:5
    |
 LL |     s.read(&mut buf).unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: read amount is not handled
-  --> $DIR/unused_io_amount.rs:20:5
+  --> $DIR/unused_io_amount.rs:21:5
    |
 LL |     s.read_vectored(&mut [io::IoSliceMut::new(&mut [])])?;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: written amount is not handled
-  --> $DIR/unused_io_amount.rs:21:5
+  --> $DIR/unused_io_amount.rs:22:5
    |
 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:29:5
+   |
+LL |     reader.read(&mut result).ok()?;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 7 previous errors