liveness: Warn about unused captured variables

src/test/ui/closures/closure-immutable-outer-variable.fixed

@@ -8,6 +8,6 @@ fn foo(mut f: Box<dyn FnMut()>) {
 
 fn main() {
     let mut y = true;
-    foo(Box::new(move || y = false) as Box<_>);
+    foo(Box::new(move || y = !y) as Box<_>);
     //~^ ERROR cannot assign to `y`, as it is not declared as mutable
 }

src/test/ui/closures/closure-immutable-outer-variable.rs

@@ -8,6 +8,6 @@ fn foo(mut f: Box<dyn FnMut()>) {
 
 fn main() {
     let y = true;
-    foo(Box::new(move || y = false) as Box<_>);
+    foo(Box::new(move || y = !y) as Box<_>);
     //~^ ERROR cannot assign to `y`, as it is not declared as mutable
 }

src/test/ui/closures/closure-immutable-outer-variable.stderr

@@ -3,8 +3,8 @@ error[E0594]: cannot assign to `y`, as it is not declared as mutable
    |
 LL |     let y = true;
    |         - help: consider changing this to be mutable: `mut y`
-LL |     foo(Box::new(move || y = false) as Box<_>);
-   |                          ^^^^^^^^^ cannot assign
+LL |     foo(Box::new(move || y = !y) as Box<_>);
+   |                          ^^^^^^ cannot assign
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-11958.rs

@@ -1,5 +1,4 @@
 // run-pass
-#![forbid(warnings)]
 
 // We shouldn't need to rebind a moved upvar as mut if it's already
 // marked as mut
@@ -7,4 +6,6 @@
 pub fn main() {
     let mut x = 1;
     let _thunk = Box::new(move|| { x = 2; });
+    //~^ WARN value assigned to `x` is never read
+    //~| WARN unused variable: `x`
 }

src/test/ui/issues/issue-11958.stderr

@@ -0,0 +1,20 @@
+warning: value assigned to `x` is never read
+  --> $DIR/issue-11958.rs:8:36
+   |
+LL |     let _thunk = Box::new(move|| { x = 2; });
+   |                                    ^
+   |
+   = note: `#[warn(unused_assignments)]` on by default
+   = help: maybe it is overwritten before being read?
+
+warning: unused variable: `x`
+  --> $DIR/issue-11958.rs:8:36
+   |
+LL |     let _thunk = Box::new(move|| { x = 2; });
+   |                                    ^
+   |
+   = note: `#[warn(unused_variables)]` on by default
+   = help: did you mean to capture by reference instead?
+
+warning: 2 warnings emitted
+

src/test/ui/liveness/liveness-upvars.rs

@@ -0,0 +1,108 @@
+// edition:2018
+// check-pass
+#![warn(unused)]
+#![allow(unreachable_code)]
+
+pub fn unintentional_copy_one() {
+    let mut last = None;
+    let mut f = move |s| {
+        last = Some(s); //~  WARN value assigned to `last` is never read
+                        //~| WARN unused variable: `last`
+    };
+    f("a");
+    f("b");
+    f("c");
+    dbg!(last.unwrap());
+}
+
+pub fn unintentional_copy_two() {
+    let mut sum = 0;
+    (1..10).for_each(move |x| {
+        sum += x; //~ WARN unused variable: `sum`
+    });
+    dbg!(sum);
+}
+
+pub fn f() {
+    let mut c = 0;
+
+    // Captured by value, but variable is dead on entry.
+    move || {
+        c = 1; //~ WARN value captured by `c` is never read
+        println!("{}", c);
+    };
+    let _ = async move {
+        c = 1; //~ WARN value captured by `c` is never read
+        println!("{}", c);
+    };
+
+    // Read and written to, but never actually used.
+    move || {
+        c += 1; //~ WARN unused variable: `c`
+    };
+    let _ = async move {
+        c += 1; //~  WARN value assigned to `c` is never read
+                //~| WARN unused variable: `c`
+    };
+
+    move || {
+        println!("{}", c);
+        // Value is read by closure itself on later invocations.
+        c += 1;
+    };
+    let b = Box::new(42);
+    move || {
+        println!("{}", c);
+        // Never read because this is FnOnce closure.
+        c += 1; //~  WARN value assigned to `c` is never read
+        drop(b);
+    };
+    let _ = async move {
+        println!("{}", c);
+        // Never read because this is a generator.
+        c += 1; //~  WARN value assigned to `c` is never read
+    };
+}
+
+pub fn nested() {
+    let mut d = None;
+    let mut e = None;
+    || {
+        || {
+            d = Some("d1"); //~ WARN value assigned to `d` is never read
+            d = Some("d2");
+        };
+        move || {
+            e = Some("e1"); //~  WARN value assigned to `e` is never read
+                            //~| WARN unused variable: `e`
+            e = Some("e2"); //~  WARN value assigned to `e` is never read
+        };
+    };
+}
+
+pub fn g<T: Default>(mut v: T) {
+    |r| {
+        if r {
+            v = T::default(); //~ WARN value assigned to `v` is never read
+        } else {
+            drop(v);
+        }
+    };
+}
+
+pub fn h<T: Copy + Default + std::fmt::Debug>() {
+    let mut z = T::default();
+    move |b| {
+        loop {
+            if b {
+                z = T::default(); //~  WARN value assigned to `z` is never read
+                                  //~| WARN unused variable: `z`
+            } else {
+                return;
+            }
+        }
+        dbg!(z);
+    };
+}
+
+fn main() {}

src/test/ui/liveness/liveness-upvars.stderr

@@ -0,0 +1,150 @@
+warning: value assigned to `last` is never read
+  --> $DIR/liveness-upvars.rs:9:9
+   |
+LL |         last = Some(s);
+   |         ^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/liveness-upvars.rs:3:9
+   |
+LL | #![warn(unused)]
+   |         ^^^^^^
+   = note: `#[warn(unused_assignments)]` implied by `#[warn(unused)]`
+   = help: maybe it is overwritten before being read?
+
+warning: unused variable: `last`
+  --> $DIR/liveness-upvars.rs:9:9
+   |
+LL |         last = Some(s);
+   |         ^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/liveness-upvars.rs:3:9
+   |
+LL | #![warn(unused)]
+   |         ^^^^^^
+   = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
+   = help: did you mean to capture by reference instead?
+
+warning: unused variable: `sum`
+  --> $DIR/liveness-upvars.rs:21:9
+   |
+LL |         sum += x;
+   |         ^^^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: value captured by `c` is never read
+  --> $DIR/liveness-upvars.rs:31:9
+   |
+LL |         c = 1;
+   |         ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: value captured by `c` is never read
+  --> $DIR/liveness-upvars.rs:35:9
+   |
+LL |         c = 1;
+   |         ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: unused variable: `c`
+  --> $DIR/liveness-upvars.rs:41:9
+   |
+LL |         c += 1;
+   |         ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: value assigned to `c` is never read
+  --> $DIR/liveness-upvars.rs:44:9
+   |
+LL |         c += 1;
+   |         ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: unused variable: `c`
+  --> $DIR/liveness-upvars.rs:44:9
+   |
+LL |         c += 1;
+   |         ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: value assigned to `c` is never read
+  --> $DIR/liveness-upvars.rs:57:9
+   |
+LL |         c += 1;
+   |         ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: value assigned to `c` is never read
+  --> $DIR/liveness-upvars.rs:63:9
+   |
+LL |         c += 1;
+   |         ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: value assigned to `d` is never read
+  --> $DIR/liveness-upvars.rs:72:13
+   |
+LL |             d = Some("d1");
+   |             ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: value assigned to `e` is never read
+  --> $DIR/liveness-upvars.rs:76:13
+   |
+LL |             e = Some("e1");
+   |             ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: value assigned to `e` is never read
+  --> $DIR/liveness-upvars.rs:78:13
+   |
+LL |             e = Some("e2");
+   |             ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: unused variable: `e`
+  --> $DIR/liveness-upvars.rs:76:13
+   |
+LL |             e = Some("e1");
+   |             ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: value assigned to `v` is never read
+  --> $DIR/liveness-upvars.rs:86:13
+   |
+LL |             v = T::default();
+   |             ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: value assigned to `z` is never read
+  --> $DIR/liveness-upvars.rs:98:17
+   |
+LL |                 z = T::default();
+   |                 ^
+   |
+   = help: maybe it is overwritten before being read?
+
+warning: unused variable: `z`
+  --> $DIR/liveness-upvars.rs:98:17
+   |
+LL |                 z = T::default();
+   |                 ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: 17 warnings emitted
+

src/test/ui/unboxed-closures/unboxed-closures-counter-not-moved.rs

@@ -1,5 +1,4 @@
 // run-pass
-#![allow(unused_variables)]
 // Test that we mutate a counter on the stack only when we expect to.
 
 fn call<F>(f: F) where F : FnOnce() {
@@ -13,7 +12,7 @@ fn main() {
     call(|| {
         // Move `y`, but do not move `counter`, even though it is read
         // by value (note that it is also mutated).
-        for item in y {
+        for item in y { //~ WARN unused variable: `item`
             let v = counter;
             counter += v;
         }
@@ -22,7 +21,8 @@ fn main() {
 
     call(move || {
         // this mutates a moved copy, and hence doesn't affect original
-        counter += 1;
+        counter += 1; //~  WARN value assigned to `counter` is never read
+                      //~| WARN unused variable: `counter`
     });
     assert_eq!(counter, 88);
 }

src/test/ui/unboxed-closures/unboxed-closures-counter-not-moved.stderr

@@ -0,0 +1,27 @@
+warning: unused variable: `item`
+  --> $DIR/unboxed-closures-counter-not-moved.rs:15:13
+   |
+LL |         for item in y {
+   |             ^^^^ help: if this is intentional, prefix it with an underscore: `_item`
+   |
+   = note: `#[warn(unused_variables)]` on by default
+
+warning: value assigned to `counter` is never read
+  --> $DIR/unboxed-closures-counter-not-moved.rs:24:9
+   |
+LL |         counter += 1;
+   |         ^^^^^^^
+   |
+   = note: `#[warn(unused_assignments)]` on by default
+   = help: maybe it is overwritten before being read?
+
+warning: unused variable: `counter`
+  --> $DIR/unboxed-closures-counter-not-moved.rs:24:9
+   |
+LL |         counter += 1;
+   |         ^^^^^^^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: 3 warnings emitted
+

src/test/ui/unboxed-closures/unboxed-closures-move-mutable.rs

@@ -13,11 +13,11 @@ fn set(x: &mut usize) { *x = 42; }
 fn main() {
     {
         let mut x = 0_usize;
-        move || x += 1;
+        move || x += 1; //~ WARN unused variable: `x`
     }
     {
         let mut x = 0_usize;
-        move || x += 1;
+        move || x += 1; //~ WARN unused variable: `x`
     }
     {
         let mut x = 0_usize;

src/test/ui/unboxed-closures/unboxed-closures-move-mutable.stderr

@@ -0,0 +1,19 @@
+warning: unused variable: `x`
+  --> $DIR/unboxed-closures-move-mutable.rs:16:17
+   |
+LL |         move || x += 1;
+   |                 ^
+   |
+   = note: `#[warn(unused_variables)]` on by default
+   = help: did you mean to capture by reference instead?
+
+warning: unused variable: `x`
+  --> $DIR/unboxed-closures-move-mutable.rs:20:17
+   |
+LL |         move || x += 1;
+   |                 ^
+   |
+   = help: did you mean to capture by reference instead?
+
+warning: 2 warnings emitted
+