simplify must-use lint slightly

Author: jdonszelmann

clippy_lints/src/functions/must_use.rs

@@ -124,32 +124,16 @@ fn check_needless_must_use(
         } else {
             // When there are multiple attributes, it is not sufficient to simply make `must_use` empty, see
             // issue #12320.
-            span_lint_and_then(
+            // FIXME(jdonszelmann): this used to give a machine-applicable fix. However, it was super fragile,
+            // honestly looked incorrect, and is a little hard to support for a little bit now. Some day this could be
+            // re-added.
+            span_lint_and_help(
                 cx,
-                MUST_USE_UNIT,
+                DOUBLE_MUST_USE,
                 fn_header_span,
                 "this unit-returning function has a `#[must_use]` attribute",
-                |diag| {
-                    let mut attrs_without_must_use = attrs.to_vec();
-                    attrs_without_must_use.retain(|a| a.id() != attr.id());
-                    let sugg_str = attrs_without_must_use
-                        .iter()
-                        .map(|a| {
-                            if a.value_str().is_none() {
-                                return a.name_or_empty().to_string();
-                            }
-                            format!("{} = \"{}\"", a.name_or_empty(), a.value_str().unwrap())
-                        })
-                        .collect::<Vec<_>>()
-                        .join(", ");
-
-                    diag.span_suggestion(
-                        attrs[0].span().with_hi(attrs[attrs.len() - 1].span().hi()),
-                        "change these attributes to",
-                        sugg_str,
-                        Applicability::MachineApplicable,
-                    );
-                },
+                Some(attr.span()),
+                "remove `must_use`",
             );
         }
     } else if attr.value_str().is_none() && is_must_use_ty(cx, return_ty(cx, item_id)) {

tests/ui/must_use_unit.fixed

@@ -24,8 +24,3 @@ fn main() {
     );
 }
 
-#[cfg_attr(all(), )]
-fn issue_12320() {}
-
-#[cfg_attr(all(), deprecateddoc = "foo", doc = "foo", must_use)]
-fn issue_12320_2() {}

tests/ui/must_use_unit.rs

@@ -27,8 +27,3 @@ fn main() {
     );
 }
 
-#[cfg_attr(all(), must_use, deprecated)]
-fn issue_12320() {}
-
-#[cfg_attr(all(), deprecated, doc = "foo", must_use)]
-fn issue_12320_2() {}

tests/ui/must_use_unit.stderr

@@ -25,23 +25,5 @@ LL | #[must_use = "With note"]
 LL | pub fn must_use_with_note() {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-[Unparsed(AttrItem { path: AttrPath { segments: [must_use#0], span: tests/ui/must_use_unit.rs:30:19: 30:27 (#0) }, args: Empty, id: HashIgnoredAttrId { attr_id: AttrId(9) }, style: Outer, span: tests/ui/must_use_unit.rs:30:19: 30:27 (#0) }), Parsed(Deprecation { deprecation: Deprecation { since: Unspecified, note: None, suggestion: None }, span: tests/ui/must_use_unit.rs:30:29: 30:39 (#0) })]
-error: this unit-returning function has a `#[must_use]` attribute
-  --> tests/ui/must_use_unit.rs:31:1
-   |
-LL | #[cfg_attr(all(), must_use, deprecated)]
-   |                   -------------------- help: change these attributes to
-LL | fn issue_12320() {}
-   | ^^^^^^^^^^^^^^^^
-
-[Unparsed(AttrItem { path: AttrPath { segments: [doc#0], span: tests/ui/must_use_unit.rs:33:31: 33:34 (#0) }, args: Eq { eq_span: tests/ui/must_use_unit.rs:33:35: 33:36 (#0), expr: MetaItemLit { symbol: "foo", suffix: None, kind: Str("foo", Cooked), span: tests/ui/must_use_unit.rs:33:37: 33:42 (#0) } }, id: HashIgnoredAttrId { attr_id: AttrId(12) }, style: Outer, span: tests/ui/must_use_unit.rs:33:31: 33:42 (#0) }), Unparsed(AttrItem { path: AttrPath { segments: [must_use#0], span: tests/ui/must_use_unit.rs:33:44: 33:52 (#0) }, args: Empty, id: HashIgnoredAttrId { attr_id: AttrId(13) }, style: Outer, span: tests/ui/must_use_unit.rs:33:44: 33:52 (#0) }), Parsed(Deprecation { deprecation: Deprecation { since: Unspecified, note: None, suggestion: None }, span: tests/ui/must_use_unit.rs:33:19: 33:29 (#0) })]
-error: this unit-returning function has a `#[must_use]` attribute
-  --> tests/ui/must_use_unit.rs:34:1
-   |
-LL | #[cfg_attr(all(), deprecated, doc = "foo", must_use)]
-   |                             -- help: change these attributes to: `doc = "foo",`
-LL | fn issue_12320_2() {}
-   | ^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 5 previous errors
+error: aborting due to 3 previous errors
 

tests/ui/must_use_unit_12320.rs

@@ -0,0 +1,11 @@
+//@aux-build:proc_macros.rs
+//@no-rustfix
+
+#![warn(clippy::must_use_unit)]
+#![allow(clippy::unused_unit)]
+
+#[cfg_attr(all(), must_use, deprecated)]
+fn issue_12320() {}
+
+#[cfg_attr(all(), deprecated, doc = "foo", must_use)]
+fn issue_12320_2() {}

tests/ui/must_use_unit_12320.stderr

@@ -0,0 +1,28 @@
+error: this unit-returning function has a `#[must_use]` attribute
+  --> tests/ui/must_use_unit_12320.rs:8:1
+   |
+LL | fn issue_12320() {}
+   | ^^^^^^^^^^^^^^^^
+   |
+help: remove `must_use`
+  --> tests/ui/must_use_unit_12320.rs:7:19
+   |
+LL | #[cfg_attr(all(), must_use, deprecated)]
+   |                   ^^^^^^^^
+   = note: `-D clippy::double-must-use` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::double_must_use)]`
+
+error: this unit-returning function has a `#[must_use]` attribute
+  --> tests/ui/must_use_unit_12320.rs:11:1
+   |
+LL | fn issue_12320_2() {}
+   | ^^^^^^^^^^^^^^^^^^
+   |
+help: remove `must_use`
+  --> tests/ui/must_use_unit_12320.rs:10:44
+   |
+LL | #[cfg_attr(all(), deprecated, doc = "foo", must_use)]
+   |                                            ^^^^^^^^
+
+error: aborting due to 2 previous errors
+