unused_io_amount: Use span_lint_and_help.

This improves the quality of the genrated output and makes it
more in line with other lint messages.

changelog: [`unused_io_amount`]: Improve help text

Author: nmathewson

clippy_lints/src/unused_io_amount.rs

@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::span_lint;
+use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
 use clippy_utils::{is_try, match_trait_method, paths};
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
@@ -126,32 +126,40 @@ fn check_method_call(cx: &LateContext<'_>, call: &hir::Expr<'_>, expr: &hir::Exp
         };
 
         match (read_trait, write_trait, symbol, is_await) {
-            (true, _, "read", false) => span_lint(
+            (true, _, "read", false) => span_lint_and_help(
                 cx,
                 UNUSED_IO_AMOUNT,
                 expr.span,
-                "read amount is not handled. Use `Read::read_exact` instead",
+                "read amount is not handled",
+                None,
+                "use `Read::read_exact` instead, or handle partial reads",
             ),
-            (true, _, "read", true) => span_lint(
+            (true, _, "read", true) => span_lint_and_help(
                 cx,
                 UNUSED_IO_AMOUNT,
                 expr.span,
-                "read amount is not handled. Use `AsyncReadExt::read_exact` instead",
+                "read amount is not handled",
+                None,
+                "use `AsyncReadExt::read_exact` instead, or handle partial reads",
             ),
             (true, _, "read_vectored", _) => {
                 span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "read amount is not handled");
             },
-            (_, true, "write", false) => span_lint(
+            (_, true, "write", false) => span_lint_and_help(
                 cx,
                 UNUSED_IO_AMOUNT,
                 expr.span,
-                "written amount is not handled. Use `Write::write_all` instead",
+                "written amount is not handled",
+                None,
+                "use `Write::write_all` instead, or handle partial writes",
             ),
-            (_, true, "write", true) => span_lint(
+            (_, true, "write", true) => span_lint_and_help(
                 cx,
                 UNUSED_IO_AMOUNT,
                 expr.span,
-                "written amount is not handled. Use `AsyncWriteExt::write_all` instead",
+                "written amount is not handled",
+                None,
+                "use `AsyncWriteExt::write_all` instead, or handle partial writes",
             ),
             (_, true, "write_vectored", _) => {
                 span_lint(cx, UNUSED_IO_AMOUNT, expr.span, "written amount is not handled");

tests/ui/unused_io_amount.stderr

@@ -1,28 +1,35 @@
-error: written amount is not handled. Use `Write::write_all` instead
+error: written amount is not handled
   --> $DIR/unused_io_amount.rs:9:5
    |
 LL |     s.write(b"test")?;
    |     ^^^^^^^^^^^^^^^^^
    |
    = note: `-D clippy::unused-io-amount` implied by `-D warnings`
+   = help: use `Write::write_all` instead, or handle partial writes
 
-error: read amount is not handled. Use `Read::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:11:5
    |
 LL |     s.read(&mut buf)?;
    |     ^^^^^^^^^^^^^^^^^
+   |
+   = help: use `Read::read_exact` instead, or handle partial reads
 
-error: written amount is not handled. Use `Write::write_all` instead
+error: written amount is not handled
   --> $DIR/unused_io_amount.rs:16:5
    |
 LL |     s.write(b"test").unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `Write::write_all` instead, or handle partial writes
 
-error: read amount is not handled. Use `Read::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:18:5
    |
 LL |     s.read(&mut buf).unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `Read::read_exact` instead, or handle partial reads
 
 error: read amount is not handled
   --> $DIR/unused_io_amount.rs:22:5
@@ -36,25 +43,31 @@ error: written amount is not handled
 LL |     s.write_vectored(&[io::IoSlice::new(&[])])?;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: read amount is not handled. Use `Read::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:30:5
    |
 LL |     reader.read(&mut result).ok()?;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `Read::read_exact` instead, or handle partial reads
 
-error: read amount is not handled. Use `Read::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:39:5
    |
 LL |     reader.read(&mut result).or_else(|err| Err(err))?;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `Read::read_exact` instead, or handle partial reads
 
-error: read amount is not handled. Use `Read::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:51:5
    |
 LL |     reader.read(&mut result).or(Err(Error::Kind))?;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `Read::read_exact` instead, or handle partial reads
 
-error: read amount is not handled. Use `Read::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:58:5
    |
 LL | /     reader
@@ -63,42 +76,56 @@ LL | |         .or(Err(Error::Kind))
 LL | |         .or(Err(Error::Kind))
 LL | |         .expect("error");
    | |________________________^
+   |
+   = help: use `Read::read_exact` instead, or handle partial reads
 
-error: written amount is not handled. Use `AsyncWriteExt::write_all` instead
+error: written amount is not handled
   --> $DIR/unused_io_amount.rs:67:5
    |
 LL |     w.write(b"hello world").await.unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `AsyncWriteExt::write_all` instead, or handle partial writes
 
-error: read amount is not handled. Use `AsyncReadExt::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:72:5
    |
 LL |     r.read(&mut buf[..]).await.unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `AsyncReadExt::read_exact` instead, or handle partial reads
 
-error: written amount is not handled. Use `AsyncWriteExt::write_all` instead
+error: written amount is not handled
   --> $DIR/unused_io_amount.rs:85:9
    |
 LL |         w.write(b"hello world").await?;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `AsyncWriteExt::write_all` instead, or handle partial writes
 
-error: read amount is not handled. Use `AsyncReadExt::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:93:9
    |
 LL |         r.read(&mut buf[..]).await.or(Err(Error::Kind))?;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `AsyncReadExt::read_exact` instead, or handle partial reads
 
-error: written amount is not handled. Use `AsyncWriteExt::write_all` instead
+error: written amount is not handled
   --> $DIR/unused_io_amount.rs:101:5
    |
 LL |     w.write(b"hello world").await.unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `AsyncWriteExt::write_all` instead, or handle partial writes
 
-error: read amount is not handled. Use `AsyncReadExt::read_exact` instead
+error: read amount is not handled
   --> $DIR/unused_io_amount.rs:106:5
    |
 LL |     r.read(&mut buf[..]).await.unwrap();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: use `AsyncReadExt::read_exact` instead, or handle partial reads
 
 error: aborting due to 16 previous errors