`#[must_use]` for associated functions is supposed to actually work

In the comments of (closed, defunct) pull request #54884, Mazdak
"Centril" Farrokhzad noted that must-use annotations didn't work on an
associated function (what other communities might call a "static
method"). Subsequent logging revealed that in this case we have a
`Def::Method`, whereas the lint pass was only matching on
`Def::Fn`. (One could argue that those def-names are thereby
misleading—must-use for self-ful methods have always worked—but
documenting or reworking that can be left to another day.)

diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index 915b8e7787e998d0d12fb19147172675cda8a236..40bb2faa3623b0f357b983fd3ac0d7d3a9461eca 100644 (file)
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -867,7 +867,7 @@ impl<T: ?Sized> Clone for Rc<T> {
     ///
     /// let five = Rc::new(5);
     ///
-    /// Rc::clone(&five);
+    /// let _ = Rc::clone(&five);
     /// ```
     #[inline]
     fn clone(&self) -> Rc<T> {
@@ -1304,7 +1304,7 @@ impl<T: ?Sized> Clone for Weak<T> {
     ///
     /// let weak_five = Rc::downgrade(&Rc::new(5));
     ///
-    /// Weak::clone(&weak_five);
+    /// let _ = Weak::clone(&weak_five);
     /// ```
     #[inline]
     fn clone(&self) -> Weak<T> {

diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index 9e245fbd7bbe563595a72054a70f69ed72a5dffe..35935861fb18297ef11646d7e26feada3b2c8356 100644 (file)
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -713,7 +713,7 @@ impl<T: ?Sized> Clone for Arc<T> {
     ///
     /// let five = Arc::new(5);
     ///
-    /// Arc::clone(&five);
+    /// let _ = Arc::clone(&five);
     /// ```
     #[inline]
     fn clone(&self) -> Arc<T> {
@@ -1135,7 +1135,7 @@ impl<T: ?Sized> Clone for Weak<T> {
     ///
     /// let weak_five = Arc::downgrade(&Arc::new(5));
     ///
-    /// Weak::clone(&weak_five);
+    /// let _ = Weak::clone(&weak_five);
     /// ```
     #[inline]
     fn clone(&self) -> Weak<T> {

diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index ec3c310c63c4f80c42ec88d65cfed1f1efcd2137..7d178d209672052da3c96d13b16611b572454cb8 100644 (file)
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -80,10 +80,11 @@ fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
                 match callee.node {
                     hir::ExprKind::Path(ref qpath) => {
                         let def = cx.tables.qpath_def(qpath, callee.hir_id);
-                        if let Def::Fn(_) = def {
-                            Some(def)
-                        } else {  // `Def::Local` if it was a closure, for which we
-                            None  // do not currently support must-use linting
+                        match def {
+                            Def::Fn(_) | Def::Method(_) => Some(def),
+                            // `Def::Local` if it was a closure, for which we
+                            // do not currently support must-use linting
+                            _ => None
                         }
                     },
                     _ => None

diff --git a/src/test/run-pass/resolve-pseudo-shadowing.rs b/src/test/run-pass/resolve-pseudo-shadowing.rs
index 071279ae7d818f044555e4fc9935cff20f4d581e..bf6e686bb7bb4a14d5cdda862648d4f12c571917 100644 (file)
--- a/src/test/run-pass/resolve-pseudo-shadowing.rs
+++ b/src/test/run-pass/resolve-pseudo-shadowing.rs
@@ -12,7 +12,7 @@
 
 fn check<Clone>(_c: Clone) {
     fn check2() {
-        <() as std::clone::Clone>::clone(&());
+        let _ = <() as std::clone::Clone>::clone(&());
     }
     check2();
 }

diff --git a/src/test/ui/fn_must_use.rs b/src/test/ui/fn_must_use.rs
index def23046db21d673eefc29ead7f95dcfa45450b4..e3e20bc89b462694f5017f192673898e72cf7ba4 100644 (file)
--- a/src/test/ui/fn_must_use.rs
+++ b/src/test/ui/fn_must_use.rs
@@ -22,6 +22,11 @@ impl MyStruct {
     fn need_to_use_this_method_value(&self) -> usize {
         self.n
     }
+
+    #[must_use]
+    fn need_to_use_this_associated_function_value() -> isize {
+        -1
+    }
 }
 
 trait EvenNature {
@@ -66,6 +71,9 @@ fn main() {
     m.is_even(); // trait method!
     //~^ WARN unused return value
 
+    MyStruct::need_to_use_this_associated_function_value();
+    //~^ WARN unused return value
+
     m.replace(3); // won't warn (annotation needs to be in trait definition)
 
     // comparison methods are `must_use`

diff --git a/src/test/ui/fn_must_use.stderr b/src/test/ui/fn_must_use.stderr
index b5bad22f3dc78b2502353b0b56a4a8671a6180b5..1bce8abbbf055be9f372e6e21833892738580bc6 100644 (file)
--- a/src/test/ui/fn_must_use.stderr
+++ b/src/test/ui/fn_must_use.stderr
@@ -1,5 +1,5 @@
 warning: unused return value of `need_to_use_this_value` which must be used
-  --> $DIR/fn_must_use.rs:60:5
+  --> $DIR/fn_must_use.rs:65:5
    |
 LL |     need_to_use_this_value(); //~ WARN unused return value
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -12,39 +12,45 @@ LL | #![warn(unused_must_use)]
    = note: it's important
 
 warning: unused return value of `MyStruct::need_to_use_this_method_value` which must be used
-  --> $DIR/fn_must_use.rs:65:5
+  --> $DIR/fn_must_use.rs:70:5
    |
 LL |     m.need_to_use_this_method_value(); //~ WARN unused return value
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused return value of `EvenNature::is_even` which must be used
-  --> $DIR/fn_must_use.rs:66:5
+  --> $DIR/fn_must_use.rs:71:5
    |
 LL |     m.is_even(); // trait method!
    |     ^^^^^^^^^^^^
    |
    = note: no side effects
 
+warning: unused return value of `MyStruct::need_to_use_this_associated_function_value` which must be used
+  --> $DIR/fn_must_use.rs:74:5
+   |
+LL |     MyStruct::need_to_use_this_associated_function_value();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 warning: unused return value of `std::cmp::PartialEq::eq` which must be used
-  --> $DIR/fn_must_use.rs:72:5
+  --> $DIR/fn_must_use.rs:80:5
    |
 LL |     2.eq(&3); //~ WARN unused return value
    |     ^^^^^^^^^
 
 warning: unused return value of `std::cmp::PartialEq::eq` which must be used
-  --> $DIR/fn_must_use.rs:73:5
+  --> $DIR/fn_must_use.rs:81:5
    |
 LL |     m.eq(&n); //~ WARN unused return value
    |     ^^^^^^^^^
 
 warning: unused comparison which must be used
-  --> $DIR/fn_must_use.rs:76:5
+  --> $DIR/fn_must_use.rs:84:5
    |
 LL |     2 == 3; //~ WARN unused comparison
    |     ^^^^^^
 
 warning: unused comparison which must be used
-  --> $DIR/fn_must_use.rs:77:5
+  --> $DIR/fn_must_use.rs:85:5
    |
 LL |     m == n; //~ WARN unused comparison
    |     ^^^^^^