From eaff0fc25bfe6f831038953ff5bd8fa2372dba22 Mon Sep 17 00:00:00 2001
From: Yuki Okushi <yuki.okushi@huawei.com>
Date: Fri, 30 Jul 2021 05:35:03 +0900
Subject: [PATCH 1/3] Add a hint that the expressions produce a value

---
 compiler/rustc_lint/src/unused.rs      | 13 +++-
 src/test/ui/lint/fn_must_use.stderr    |  8 ++-
 src/test/ui/lint/must-use-ops.stderr   | 83 +++++++++++++++++++-------
 src/test/ui/lint/unused-borrows.stderr | 23 +++++--
 src/test/ui/unused/issue-85913.rs      | 13 ++++
 src/test/ui/unused/issue-85913.stderr  | 15 +++++
 6 files changed, 125 insertions(+), 30 deletions(-)
 create mode 100644 src/test/ui/unused/issue-85913.rs
 create mode 100644 src/test/ui/unused/issue-85913.stderr

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index c431c048ca0..5437174a683 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -161,7 +161,18 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
 
         if let Some(must_use_op) = must_use_op {
             cx.struct_span_lint(UNUSED_MUST_USE, expr.span, |lint| {
-                lint.build(&format!("unused {} that must be used", must_use_op)).emit()
+                let mut lint = lint.build(&format!("unused {} that must be used", must_use_op));
+                lint.note(&format!("the {} produces a value", must_use_op));
+                if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) {
+                    lint.span_suggestion(
+                        expr.span,
+                        "use `let _ = ...` to ignore it",
+                        format!("let _ = {}", snippet),
+                        Applicability::MachineApplicable,
+                    )
+                    .emit()
+                }
+                lint.emit();
             });
             op_warned = true;
         }
diff --git a/src/test/ui/lint/fn_must_use.stderr b/src/test/ui/lint/fn_must_use.stderr
index d6b1cf3ae1f..75a22823329 100644
--- a/src/test/ui/lint/fn_must_use.stderr
+++ b/src/test/ui/lint/fn_must_use.stderr
@@ -47,13 +47,17 @@ warning: unused comparison that must be used
   --> $DIR/fn_must_use.rs:74:5
    |
 LL |     2 == 3;
-   |     ^^^^^^
+   |     ^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 2 == 3`
+   |
+   = note: the comparison produces a value
 
 warning: unused comparison that must be used
   --> $DIR/fn_must_use.rs:75:5
    |
 LL |     m == n;
-   |     ^^^^^^
+   |     ^^^^^^ help: use `let _ = ...` to ignore it: `let _ = m == n`
+   |
+   = note: the comparison produces a value
 
 warning: 8 warnings emitted
 
diff --git a/src/test/ui/lint/must-use-ops.stderr b/src/test/ui/lint/must-use-ops.stderr
index 3fb80f7e798..73405d02a2e 100644
--- a/src/test/ui/lint/must-use-ops.stderr
+++ b/src/test/ui/lint/must-use-ops.stderr
@@ -2,133 +2,174 @@ warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:12:5
    |
 LL |     val == 1;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val == 1`
    |
 note: the lint level is defined here
   --> $DIR/must-use-ops.rs:5:9
    |
 LL | #![warn(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
+   = note: the comparison produces a value
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:13:5
    |
 LL |     val < 1;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val < 1`
+   |
+   = note: the comparison produces a value
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:14:5
    |
 LL |     val <= 1;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val <= 1`
+   |
+   = note: the comparison produces a value
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:15:5
    |
 LL |     val != 1;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val != 1`
+   |
+   = note: the comparison produces a value
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:16:5
    |
 LL |     val >= 1;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val >= 1`
+   |
+   = note: the comparison produces a value
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:17:5
    |
 LL |     val > 1;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val > 1`
+   |
+   = note: the comparison produces a value
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:20:5
    |
 LL |     val + 2;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val + 2`
+   |
+   = note: the arithmetic operation produces a value
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:21:5
    |
 LL |     val - 2;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val - 2`
+   |
+   = note: the arithmetic operation produces a value
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:22:5
    |
 LL |     val / 2;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val / 2`
+   |
+   = note: the arithmetic operation produces a value
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:23:5
    |
 LL |     val * 2;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val * 2`
+   |
+   = note: the arithmetic operation produces a value
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:24:5
    |
 LL |     val % 2;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val % 2`
+   |
+   = note: the arithmetic operation produces a value
 
 warning: unused logical operation that must be used
   --> $DIR/must-use-ops.rs:27:5
    |
 LL |     true && true;
-   |     ^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = true && true`
+   |
+   = note: the logical operation produces a value
 
 warning: unused logical operation that must be used
   --> $DIR/must-use-ops.rs:28:5
    |
 LL |     false || true;
-   |     ^^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = false || true`
+   |
+   = note: the logical operation produces a value
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:31:5
    |
 LL |     5 ^ val;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 ^ val`
+   |
+   = note: the bitwise operation produces a value
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:32:5
    |
 LL |     5 & val;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 & val`
+   |
+   = note: the bitwise operation produces a value
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:33:5
    |
 LL |     5 | val;
-   |     ^^^^^^^
+   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 | val`
+   |
+   = note: the bitwise operation produces a value
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:34:5
    |
 LL |     5 << val;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 << val`
+   |
+   = note: the bitwise operation produces a value
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:35:5
    |
 LL |     5 >> val;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 >> val`
+   |
+   = note: the bitwise operation produces a value
 
 warning: unused unary operation that must be used
   --> $DIR/must-use-ops.rs:38:5
    |
 LL |     !val;
-   |     ^^^^
+   |     ^^^^ help: use `let _ = ...` to ignore it: `let _ = !val`
+   |
+   = note: the unary operation produces a value
 
 warning: unused unary operation that must be used
   --> $DIR/must-use-ops.rs:39:5
    |
 LL |     -val;
-   |     ^^^^
+   |     ^^^^ help: use `let _ = ...` to ignore it: `let _ = -val`
+   |
+   = note: the unary operation produces a value
 
 warning: unused unary operation that must be used
   --> $DIR/must-use-ops.rs:40:5
    |
 LL |     *val_pointer;
-   |     ^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = *val_pointer`
+   |
+   = note: the unary operation produces a value
 
 warning: 21 warnings emitted
 
diff --git a/src/test/ui/lint/unused-borrows.stderr b/src/test/ui/lint/unused-borrows.stderr
index 24899fe992b..459381b642c 100644
--- a/src/test/ui/lint/unused-borrows.stderr
+++ b/src/test/ui/lint/unused-borrows.stderr
@@ -2,43 +2,54 @@ error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:6:5
    |
 LL |     &42;
-   |     ^^^
+   |     ^^^ help: use `let _ = ...` to ignore it: `let _ = &42`
    |
 note: the lint level is defined here
   --> $DIR/unused-borrows.rs:1:9
    |
 LL | #![deny(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
+   = note: the borrow produces a value
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:9:5
    |
 LL |     &mut foo(42);
-   |     ^^^^^^^^^^^^
+   |     ^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = &mut foo(42)`
+   |
+   = note: the borrow produces a value
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:12:5
    |
 LL |     &&42;
-   |     ^^^^
+   |     ^^^^ help: use `let _ = ...` to ignore it: `let _ = &&42`
+   |
+   = note: the borrow produces a value
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:15:5
    |
 LL |     &&mut 42;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = &&mut 42`
+   |
+   = note: the borrow produces a value
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:18:5
    |
 LL |     &mut &42;
-   |     ^^^^^^^^
+   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = &mut &42`
+   |
+   = note: the borrow produces a value
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:23:5
    |
 LL |     && foo(42);
-   |     ^^^^^^^^^^
+   |     ^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = && foo(42)`
+   |
+   = note: the borrow produces a value
 
 error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/unused/issue-85913.rs b/src/test/ui/unused/issue-85913.rs
new file mode 100644
index 00000000000..7f3817b6ef1
--- /dev/null
+++ b/src/test/ui/unused/issue-85913.rs
@@ -0,0 +1,13 @@
+#![deny(unused_must_use)]
+
+pub fn fun() -> i32 {
+    function() && return 1;
+    //~^ ERROR: unused logical operation that must be used
+    return 0;
+}
+
+fn function() -> bool {
+    true
+}
+
+fn main() {}
diff --git a/src/test/ui/unused/issue-85913.stderr b/src/test/ui/unused/issue-85913.stderr
new file mode 100644
index 00000000000..d5d99f0f7d3
--- /dev/null
+++ b/src/test/ui/unused/issue-85913.stderr
@@ -0,0 +1,15 @@
+error: unused logical operation that must be used
+  --> $DIR/issue-85913.rs:4:5
+   |
+LL |     function() && return 1;
+   |     ^^^^^^^^^^^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = function() && return 1`
+   |
+note: the lint level is defined here
+  --> $DIR/issue-85913.rs:1:9
+   |
+LL | #![deny(unused_must_use)]
+   |         ^^^^^^^^^^^^^^^
+   = note: the logical operation produces a value
+
+error: aborting due to previous error
+

From f3c59a8df68fb0d1c40a6788e34b765c29e9cbd0 Mon Sep 17 00:00:00 2001
From: Yuki Okushi <yuki.okushi@huawei.com>
Date: Fri, 30 Jul 2021 05:41:10 +0900
Subject: [PATCH 2/3] Move the `unused` dir to `lint`s subdir

---
 .../ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate.rs    | 0
 .../ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate2.rs   | 0
 .../ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate3.rs   | 0
 .../ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate4.rs   | 0
 .../ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate5.rs   | 0
 src/test/ui/{ => lint}/unused/issue-30730.rs                      | 0
 src/test/ui/{ => lint}/unused/issue-30730.stderr                  | 0
 src/test/ui/{ => lint}/unused/issue-46576.rs                      | 0
 src/test/ui/{ => lint}/unused/issue-46576.stderr                  | 0
 .../{ => unused}/issue-47390-unused-variable-in-struct-pattern.rs | 0
 .../issue-47390-unused-variable-in-struct-pattern.stderr          | 0
 src/test/ui/lint/{ => unused}/issue-54180-unused-ref-field.fixed  | 0
 src/test/ui/lint/{ => unused}/issue-54180-unused-ref-field.rs     | 0
 src/test/ui/lint/{ => unused}/issue-54180-unused-ref-field.stderr | 0
 .../ui/lint/{ => unused}/issue-54538-unused-parens-lint.fixed     | 0
 src/test/ui/lint/{ => unused}/issue-54538-unused-parens-lint.rs   | 0
 .../ui/lint/{ => unused}/issue-54538-unused-parens-lint.stderr    | 0
 src/test/ui/{ => lint}/unused/issue-59896.rs                      | 0
 src/test/ui/{ => lint}/unused/issue-59896.stderr                  | 0
 .../lint/{ => unused}/issue-67691-unused-field-in-or-pattern.rs   | 0
 .../{ => unused}/issue-67691-unused-field-in-or-pattern.stderr    | 0
 src/test/ui/{ => lint}/unused/issue-70041.rs                      | 0
 src/test/ui/{ => lint}/unused/issue-70041.stderr                  | 0
 src/test/ui/lint/{ => unused}/issue-71290-unused-paren-binop.rs   | 0
 .../ui/lint/{ => unused}/issue-74883-unused-paren-baren-yield.rs  | 0
 .../lint/{ => unused}/issue-74883-unused-paren-baren-yield.stderr | 0
 src/test/ui/lint/{ => unused}/issue-81314-unused-span-ident.fixed | 0
 src/test/ui/lint/{ => unused}/issue-81314-unused-span-ident.rs    | 0
 .../ui/lint/{ => unused}/issue-81314-unused-span-ident.stderr     | 0
 src/test/ui/{ => lint}/unused/issue-85913.rs                      | 0
 src/test/ui/{ => lint}/unused/issue-85913.stderr                  | 0
 src/test/ui/lint/{ => unused}/lint-unused-extern-crate.rs         | 0
 src/test/ui/lint/{ => unused}/lint-unused-extern-crate.stderr     | 0
 src/test/ui/lint/{ => unused}/lint-unused-imports.rs              | 0
 src/test/ui/lint/{ => unused}/lint-unused-imports.stderr          | 0
 src/test/ui/lint/{ => unused}/lint-unused-mut-self.fixed          | 0
 src/test/ui/lint/{ => unused}/lint-unused-mut-self.rs             | 0
 src/test/ui/lint/{ => unused}/lint-unused-mut-self.stderr         | 0
 src/test/ui/lint/{ => unused}/lint-unused-mut-variables.rs        | 0
 src/test/ui/lint/{ => unused}/lint-unused-mut-variables.stderr    | 0
 src/test/ui/lint/{ => unused}/lint-unused-variables.rs            | 0
 src/test/ui/lint/{ => unused}/lint-unused-variables.stderr        | 0
 src/test/ui/lint/{ => unused}/must-use-ops.rs                     | 0
 src/test/ui/lint/{ => unused}/must-use-ops.stderr                 | 0
 src/test/ui/lint/{ => unused}/must_use-array.rs                   | 0
 src/test/ui/lint/{ => unused}/must_use-array.stderr               | 0
 src/test/ui/lint/{ => unused}/must_use-in-stdlib-traits.rs        | 0
 src/test/ui/lint/{ => unused}/must_use-in-stdlib-traits.stderr    | 0
 src/test/ui/lint/{ => unused}/must_use-trait.rs                   | 0
 src/test/ui/lint/{ => unused}/must_use-trait.stderr               | 0
 src/test/ui/lint/{ => unused}/must_use-tuple.rs                   | 0
 src/test/ui/lint/{ => unused}/must_use-tuple.stderr               | 0
 src/test/ui/lint/{ => unused}/must_use-unit.rs                    | 0
 src/test/ui/lint/{ => unused}/must_use-unit.stderr                | 0
 src/test/ui/lint/{ => unused}/no-unused-parens-return-block.rs    | 0
 src/test/ui/{ => lint}/unused/unused-attr-macro-rules.rs          | 0
 src/test/ui/{ => lint}/unused/unused-attr-macro-rules.stderr      | 0
 src/test/ui/{ => lint}/unused/unused-attr.rs                      | 0
 src/test/ui/{ => lint}/unused/unused-attr.stderr                  | 0
 src/test/ui/{ => lint}/unused/unused-closure.rs                   | 0
 src/test/ui/{ => lint}/unused/unused-closure.stderr               | 0
 src/test/ui/{ => lint}/unused/unused-doc-comments-edge-cases.rs   | 0
 .../ui/{ => lint}/unused/unused-doc-comments-edge-cases.stderr    | 0
 src/test/ui/{ => lint}/unused/unused-doc-comments-for-macros.rs   | 0
 .../ui/{ => lint}/unused/unused-doc-comments-for-macros.stderr    | 0
 src/test/ui/{ => lint}/unused/unused-macro-rules.rs               | 0
 src/test/ui/{ => lint}/unused/unused-macro-rules.stderr           | 0
 src/test/ui/{ => lint}/unused/unused-macro-with-bad-frag-spec.rs  | 0
 .../ui/{ => lint}/unused/unused-macro-with-bad-frag-spec.stderr   | 0
 .../ui/{ => lint}/unused/unused-macro-with-follow-violation.rs    | 0
 .../{ => lint}/unused/unused-macro-with-follow-violation.stderr   | 0
 src/test/ui/{ => lint}/unused/unused-macro.rs                     | 0
 src/test/ui/{ => lint}/unused/unused-macro.stderr                 | 0
 .../ui/{ => lint}/unused/unused-mut-warning-captured-var.fixed    | 0
 src/test/ui/{ => lint}/unused/unused-mut-warning-captured-var.rs  | 0
 .../ui/{ => lint}/unused/unused-mut-warning-captured-var.stderr   | 0
 src/test/ui/{ => lint}/unused/unused-result.rs                    | 0
 src/test/ui/{ => lint}/unused/unused-result.stderr                | 0
 src/test/ui/{ => lint}/unused/useless-comment.rs                  | 0
 src/test/ui/{ => lint}/unused/useless-comment.stderr              | 0
 80 files changed, 0 insertions(+), 0 deletions(-)
 rename src/test/ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate.rs (100%)
 rename src/test/ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate2.rs (100%)
 rename src/test/ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate3.rs (100%)
 rename src/test/ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate4.rs (100%)
 rename src/test/ui/lint/{ => unused}/auxiliary/lint_unused_extern_crate5.rs (100%)
 rename src/test/ui/{ => lint}/unused/issue-30730.rs (100%)
 rename src/test/ui/{ => lint}/unused/issue-30730.stderr (100%)
 rename src/test/ui/{ => lint}/unused/issue-46576.rs (100%)
 rename src/test/ui/{ => lint}/unused/issue-46576.stderr (100%)
 rename src/test/ui/lint/{ => unused}/issue-47390-unused-variable-in-struct-pattern.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-47390-unused-variable-in-struct-pattern.stderr (100%)
 rename src/test/ui/lint/{ => unused}/issue-54180-unused-ref-field.fixed (100%)
 rename src/test/ui/lint/{ => unused}/issue-54180-unused-ref-field.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-54180-unused-ref-field.stderr (100%)
 rename src/test/ui/lint/{ => unused}/issue-54538-unused-parens-lint.fixed (100%)
 rename src/test/ui/lint/{ => unused}/issue-54538-unused-parens-lint.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-54538-unused-parens-lint.stderr (100%)
 rename src/test/ui/{ => lint}/unused/issue-59896.rs (100%)
 rename src/test/ui/{ => lint}/unused/issue-59896.stderr (100%)
 rename src/test/ui/lint/{ => unused}/issue-67691-unused-field-in-or-pattern.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-67691-unused-field-in-or-pattern.stderr (100%)
 rename src/test/ui/{ => lint}/unused/issue-70041.rs (100%)
 rename src/test/ui/{ => lint}/unused/issue-70041.stderr (100%)
 rename src/test/ui/lint/{ => unused}/issue-71290-unused-paren-binop.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-74883-unused-paren-baren-yield.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-74883-unused-paren-baren-yield.stderr (100%)
 rename src/test/ui/lint/{ => unused}/issue-81314-unused-span-ident.fixed (100%)
 rename src/test/ui/lint/{ => unused}/issue-81314-unused-span-ident.rs (100%)
 rename src/test/ui/lint/{ => unused}/issue-81314-unused-span-ident.stderr (100%)
 rename src/test/ui/{ => lint}/unused/issue-85913.rs (100%)
 rename src/test/ui/{ => lint}/unused/issue-85913.stderr (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-extern-crate.rs (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-extern-crate.stderr (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-imports.rs (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-imports.stderr (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-mut-self.fixed (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-mut-self.rs (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-mut-self.stderr (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-mut-variables.rs (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-mut-variables.stderr (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-variables.rs (100%)
 rename src/test/ui/lint/{ => unused}/lint-unused-variables.stderr (100%)
 rename src/test/ui/lint/{ => unused}/must-use-ops.rs (100%)
 rename src/test/ui/lint/{ => unused}/must-use-ops.stderr (100%)
 rename src/test/ui/lint/{ => unused}/must_use-array.rs (100%)
 rename src/test/ui/lint/{ => unused}/must_use-array.stderr (100%)
 rename src/test/ui/lint/{ => unused}/must_use-in-stdlib-traits.rs (100%)
 rename src/test/ui/lint/{ => unused}/must_use-in-stdlib-traits.stderr (100%)
 rename src/test/ui/lint/{ => unused}/must_use-trait.rs (100%)
 rename src/test/ui/lint/{ => unused}/must_use-trait.stderr (100%)
 rename src/test/ui/lint/{ => unused}/must_use-tuple.rs (100%)
 rename src/test/ui/lint/{ => unused}/must_use-tuple.stderr (100%)
 rename src/test/ui/lint/{ => unused}/must_use-unit.rs (100%)
 rename src/test/ui/lint/{ => unused}/must_use-unit.stderr (100%)
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diff --git a/src/test/ui/lint/auxiliary/lint_unused_extern_crate.rs b/src/test/ui/lint/unused/auxiliary/lint_unused_extern_crate.rs
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diff --git a/src/test/ui/lint/issue-67691-unused-field-in-or-pattern.rs b/src/test/ui/lint/unused/issue-67691-unused-field-in-or-pattern.rs
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diff --git a/src/test/ui/lint/issue-71290-unused-paren-binop.rs b/src/test/ui/lint/unused/issue-71290-unused-paren-binop.rs
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diff --git a/src/test/ui/lint/issue-74883-unused-paren-baren-yield.rs b/src/test/ui/lint/unused/issue-74883-unused-paren-baren-yield.rs
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diff --git a/src/test/ui/lint/lint-unused-extern-crate.rs b/src/test/ui/lint/unused/lint-unused-extern-crate.rs
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rename from src/test/ui/unused/unused-macro-with-bad-frag-spec.stderr
rename to src/test/ui/lint/unused/unused-macro-with-bad-frag-spec.stderr
diff --git a/src/test/ui/unused/unused-macro-with-follow-violation.rs b/src/test/ui/lint/unused/unused-macro-with-follow-violation.rs
similarity index 100%
rename from src/test/ui/unused/unused-macro-with-follow-violation.rs
rename to src/test/ui/lint/unused/unused-macro-with-follow-violation.rs
diff --git a/src/test/ui/unused/unused-macro-with-follow-violation.stderr b/src/test/ui/lint/unused/unused-macro-with-follow-violation.stderr
similarity index 100%
rename from src/test/ui/unused/unused-macro-with-follow-violation.stderr
rename to src/test/ui/lint/unused/unused-macro-with-follow-violation.stderr
diff --git a/src/test/ui/unused/unused-macro.rs b/src/test/ui/lint/unused/unused-macro.rs
similarity index 100%
rename from src/test/ui/unused/unused-macro.rs
rename to src/test/ui/lint/unused/unused-macro.rs
diff --git a/src/test/ui/unused/unused-macro.stderr b/src/test/ui/lint/unused/unused-macro.stderr
similarity index 100%
rename from src/test/ui/unused/unused-macro.stderr
rename to src/test/ui/lint/unused/unused-macro.stderr
diff --git a/src/test/ui/unused/unused-mut-warning-captured-var.fixed b/src/test/ui/lint/unused/unused-mut-warning-captured-var.fixed
similarity index 100%
rename from src/test/ui/unused/unused-mut-warning-captured-var.fixed
rename to src/test/ui/lint/unused/unused-mut-warning-captured-var.fixed
diff --git a/src/test/ui/unused/unused-mut-warning-captured-var.rs b/src/test/ui/lint/unused/unused-mut-warning-captured-var.rs
similarity index 100%
rename from src/test/ui/unused/unused-mut-warning-captured-var.rs
rename to src/test/ui/lint/unused/unused-mut-warning-captured-var.rs
diff --git a/src/test/ui/unused/unused-mut-warning-captured-var.stderr b/src/test/ui/lint/unused/unused-mut-warning-captured-var.stderr
similarity index 100%
rename from src/test/ui/unused/unused-mut-warning-captured-var.stderr
rename to src/test/ui/lint/unused/unused-mut-warning-captured-var.stderr
diff --git a/src/test/ui/unused/unused-result.rs b/src/test/ui/lint/unused/unused-result.rs
similarity index 100%
rename from src/test/ui/unused/unused-result.rs
rename to src/test/ui/lint/unused/unused-result.rs
diff --git a/src/test/ui/unused/unused-result.stderr b/src/test/ui/lint/unused/unused-result.stderr
similarity index 100%
rename from src/test/ui/unused/unused-result.stderr
rename to src/test/ui/lint/unused/unused-result.stderr
diff --git a/src/test/ui/unused/useless-comment.rs b/src/test/ui/lint/unused/useless-comment.rs
similarity index 100%
rename from src/test/ui/unused/useless-comment.rs
rename to src/test/ui/lint/unused/useless-comment.rs
diff --git a/src/test/ui/unused/useless-comment.stderr b/src/test/ui/lint/unused/useless-comment.stderr
similarity index 100%
rename from src/test/ui/unused/useless-comment.stderr
rename to src/test/ui/lint/unused/useless-comment.stderr

From 924eddf30d0e72b61aa753daf8dc0c75790a8730 Mon Sep 17 00:00:00 2001
From: Yuki Okushi <yuki.okushi@huawei.com>
Date: Sat, 31 Jul 2021 06:21:52 +0900
Subject: [PATCH 3/3] Apply review suggestion

---
 compiler/rustc_lint/src/unused.rs           |  17 +--
 src/test/ui/lint/fn_must_use.stderr         |  14 +-
 src/test/ui/lint/unused-borrows.stderr      |  42 ++++--
 src/test/ui/lint/unused/issue-85913.stderr  |   7 +-
 src/test/ui/lint/unused/must-use-ops.stderr | 147 ++++++++++++++------
 5 files changed, 157 insertions(+), 70 deletions(-)

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 5437174a683..2b580452a60 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -162,16 +162,13 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
         if let Some(must_use_op) = must_use_op {
             cx.struct_span_lint(UNUSED_MUST_USE, expr.span, |lint| {
                 let mut lint = lint.build(&format!("unused {} that must be used", must_use_op));
-                lint.note(&format!("the {} produces a value", must_use_op));
-                if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) {
-                    lint.span_suggestion(
-                        expr.span,
-                        "use `let _ = ...` to ignore it",
-                        format!("let _ = {}", snippet),
-                        Applicability::MachineApplicable,
-                    )
-                    .emit()
-                }
+                lint.span_label(expr.span, &format!("the {} produces a value", must_use_op));
+                lint.span_suggestion_verbose(
+                    expr.span.shrink_to_lo(),
+                    "use `let _ = ...` to ignore the resulting value",
+                    "let _ = ".to_string(),
+                    Applicability::MachineApplicable,
+                );
                 lint.emit();
             });
             op_warned = true;
diff --git a/src/test/ui/lint/fn_must_use.stderr b/src/test/ui/lint/fn_must_use.stderr
index 75a22823329..6a5fdac4d91 100644
--- a/src/test/ui/lint/fn_must_use.stderr
+++ b/src/test/ui/lint/fn_must_use.stderr
@@ -47,17 +47,23 @@ warning: unused comparison that must be used
   --> $DIR/fn_must_use.rs:74:5
    |
 LL |     2 == 3;
-   |     ^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 2 == 3`
+   |     ^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 2 == 3;
+   |     ^^^^^^^
 
 warning: unused comparison that must be used
   --> $DIR/fn_must_use.rs:75:5
    |
 LL |     m == n;
-   |     ^^^^^^ help: use `let _ = ...` to ignore it: `let _ = m == n`
+   |     ^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = m == n;
+   |     ^^^^^^^
 
 warning: 8 warnings emitted
 
diff --git a/src/test/ui/lint/unused-borrows.stderr b/src/test/ui/lint/unused-borrows.stderr
index 459381b642c..e91e02df476 100644
--- a/src/test/ui/lint/unused-borrows.stderr
+++ b/src/test/ui/lint/unused-borrows.stderr
@@ -2,54 +2,72 @@ error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:6:5
    |
 LL |     &42;
-   |     ^^^ help: use `let _ = ...` to ignore it: `let _ = &42`
+   |     ^^^ the borrow produces a value
    |
 note: the lint level is defined here
   --> $DIR/unused-borrows.rs:1:9
    |
 LL | #![deny(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
-   = note: the borrow produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = &42;
+   |     ^^^^^^^
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:9:5
    |
 LL |     &mut foo(42);
-   |     ^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = &mut foo(42)`
+   |     ^^^^^^^^^^^^ the borrow produces a value
    |
-   = note: the borrow produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = &mut foo(42);
+   |     ^^^^^^^
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:12:5
    |
 LL |     &&42;
-   |     ^^^^ help: use `let _ = ...` to ignore it: `let _ = &&42`
+   |     ^^^^ the borrow produces a value
    |
-   = note: the borrow produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = &&42;
+   |     ^^^^^^^
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:15:5
    |
 LL |     &&mut 42;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = &&mut 42`
+   |     ^^^^^^^^ the borrow produces a value
    |
-   = note: the borrow produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = &&mut 42;
+   |     ^^^^^^^
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:18:5
    |
 LL |     &mut &42;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = &mut &42`
+   |     ^^^^^^^^ the borrow produces a value
    |
-   = note: the borrow produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = &mut &42;
+   |     ^^^^^^^
 
 error: unused borrow that must be used
   --> $DIR/unused-borrows.rs:23:5
    |
 LL |     && foo(42);
-   |     ^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = && foo(42)`
+   |     ^^^^^^^^^^ the borrow produces a value
    |
-   = note: the borrow produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = && foo(42);
+   |     ^^^^^^^
 
 error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/lint/unused/issue-85913.stderr b/src/test/ui/lint/unused/issue-85913.stderr
index d5d99f0f7d3..4835cfae46f 100644
--- a/src/test/ui/lint/unused/issue-85913.stderr
+++ b/src/test/ui/lint/unused/issue-85913.stderr
@@ -2,14 +2,17 @@ error: unused logical operation that must be used
   --> $DIR/issue-85913.rs:4:5
    |
 LL |     function() && return 1;
-   |     ^^^^^^^^^^^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = function() && return 1`
+   |     ^^^^^^^^^^^^^^^^^^^^^^ the logical operation produces a value
    |
 note: the lint level is defined here
   --> $DIR/issue-85913.rs:1:9
    |
 LL | #![deny(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
-   = note: the logical operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = function() && return 1;
+   |     ^^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/lint/unused/must-use-ops.stderr b/src/test/ui/lint/unused/must-use-ops.stderr
index 73405d02a2e..4dd739088b9 100644
--- a/src/test/ui/lint/unused/must-use-ops.stderr
+++ b/src/test/ui/lint/unused/must-use-ops.stderr
@@ -2,174 +2,237 @@ warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:12:5
    |
 LL |     val == 1;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val == 1`
+   |     ^^^^^^^^ the comparison produces a value
    |
 note: the lint level is defined here
   --> $DIR/must-use-ops.rs:5:9
    |
 LL | #![warn(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val == 1;
+   |     ^^^^^^^
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:13:5
    |
 LL |     val < 1;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val < 1`
+   |     ^^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val < 1;
+   |     ^^^^^^^
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:14:5
    |
 LL |     val <= 1;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val <= 1`
+   |     ^^^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val <= 1;
+   |     ^^^^^^^
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:15:5
    |
 LL |     val != 1;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val != 1`
+   |     ^^^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val != 1;
+   |     ^^^^^^^
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:16:5
    |
 LL |     val >= 1;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val >= 1`
+   |     ^^^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val >= 1;
+   |     ^^^^^^^
 
 warning: unused comparison that must be used
   --> $DIR/must-use-ops.rs:17:5
    |
 LL |     val > 1;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val > 1`
+   |     ^^^^^^^ the comparison produces a value
    |
-   = note: the comparison produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val > 1;
+   |     ^^^^^^^
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:20:5
    |
 LL |     val + 2;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val + 2`
+   |     ^^^^^^^ the arithmetic operation produces a value
    |
-   = note: the arithmetic operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val + 2;
+   |     ^^^^^^^
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:21:5
    |
 LL |     val - 2;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val - 2`
+   |     ^^^^^^^ the arithmetic operation produces a value
    |
-   = note: the arithmetic operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val - 2;
+   |     ^^^^^^^
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:22:5
    |
 LL |     val / 2;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val / 2`
+   |     ^^^^^^^ the arithmetic operation produces a value
    |
-   = note: the arithmetic operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val / 2;
+   |     ^^^^^^^
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:23:5
    |
 LL |     val * 2;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val * 2`
+   |     ^^^^^^^ the arithmetic operation produces a value
    |
-   = note: the arithmetic operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val * 2;
+   |     ^^^^^^^
 
 warning: unused arithmetic operation that must be used
   --> $DIR/must-use-ops.rs:24:5
    |
 LL |     val % 2;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = val % 2`
+   |     ^^^^^^^ the arithmetic operation produces a value
    |
-   = note: the arithmetic operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = val % 2;
+   |     ^^^^^^^
 
 warning: unused logical operation that must be used
   --> $DIR/must-use-ops.rs:27:5
    |
 LL |     true && true;
-   |     ^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = true && true`
+   |     ^^^^^^^^^^^^ the logical operation produces a value
    |
-   = note: the logical operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = true && true;
+   |     ^^^^^^^
 
 warning: unused logical operation that must be used
   --> $DIR/must-use-ops.rs:28:5
    |
 LL |     false || true;
-   |     ^^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = false || true`
+   |     ^^^^^^^^^^^^^ the logical operation produces a value
    |
-   = note: the logical operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = false || true;
+   |     ^^^^^^^
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:31:5
    |
 LL |     5 ^ val;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 ^ val`
+   |     ^^^^^^^ the bitwise operation produces a value
    |
-   = note: the bitwise operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 5 ^ val;
+   |     ^^^^^^^
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:32:5
    |
 LL |     5 & val;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 & val`
+   |     ^^^^^^^ the bitwise operation produces a value
    |
-   = note: the bitwise operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 5 & val;
+   |     ^^^^^^^
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:33:5
    |
 LL |     5 | val;
-   |     ^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 | val`
+   |     ^^^^^^^ the bitwise operation produces a value
    |
-   = note: the bitwise operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 5 | val;
+   |     ^^^^^^^
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:34:5
    |
 LL |     5 << val;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 << val`
+   |     ^^^^^^^^ the bitwise operation produces a value
    |
-   = note: the bitwise operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 5 << val;
+   |     ^^^^^^^
 
 warning: unused bitwise operation that must be used
   --> $DIR/must-use-ops.rs:35:5
    |
 LL |     5 >> val;
-   |     ^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = 5 >> val`
+   |     ^^^^^^^^ the bitwise operation produces a value
    |
-   = note: the bitwise operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 5 >> val;
+   |     ^^^^^^^
 
 warning: unused unary operation that must be used
   --> $DIR/must-use-ops.rs:38:5
    |
 LL |     !val;
-   |     ^^^^ help: use `let _ = ...` to ignore it: `let _ = !val`
+   |     ^^^^ the unary operation produces a value
    |
-   = note: the unary operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = !val;
+   |     ^^^^^^^
 
 warning: unused unary operation that must be used
   --> $DIR/must-use-ops.rs:39:5
    |
 LL |     -val;
-   |     ^^^^ help: use `let _ = ...` to ignore it: `let _ = -val`
+   |     ^^^^ the unary operation produces a value
    |
-   = note: the unary operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = -val;
+   |     ^^^^^^^
 
 warning: unused unary operation that must be used
   --> $DIR/must-use-ops.rs:40:5
    |
 LL |     *val_pointer;
-   |     ^^^^^^^^^^^^ help: use `let _ = ...` to ignore it: `let _ = *val_pointer`
+   |     ^^^^^^^^^^^^ the unary operation produces a value
    |
-   = note: the unary operation produces a value
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = *val_pointer;
+   |     ^^^^^^^
 
 warning: 21 warnings emitted