Fix let_unit_value to lint when explicit unit type annotation is present

clippy_lints/src/unit_types/let_unit_value.rs

@@ -33,13 +33,6 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, format_args: &FormatArgsStorag
             return;
         }
 
-        // skip `let _: () = { ... }`
-        if let Some(ty) = local.ty
-            && let TyKind::Tup([]) = ty.kind
-        {
-            return;
-        }
-
         if (local.ty.is_some_and(|ty| !matches!(ty.kind, TyKind::Infer(())))
             || matches!(local.pat.kind, PatKind::Tuple([], ddpos) if ddpos.as_opt_usize().is_none()))
             && expr_needs_inferred_result(cx, init)

tests/ui/crashes/ice-8821.fixed

@@ -0,0 +1,9 @@
+#![warn(clippy::let_unit_value)]
+
+fn f() {}
+static FN: fn() = f;
+
+fn main() {
+    FN();
+    //~^ ERROR: this let-binding has unit value
+}

tests/ui/crashes/ice-8821.rs

@@ -1,10 +1,9 @@
-//@ check-pass
-
 #![warn(clippy::let_unit_value)]
 
 fn f() {}
 static FN: fn() = f;
 
 fn main() {
     let _: () = FN();
+    //~^ ERROR: this let-binding has unit value
 }

tests/ui/crashes/ice-8821.stderr

@@ -0,0 +1,16 @@
+error: this let-binding has unit value
+  --> tests/ui/crashes/ice-8821.rs:7:5
+   |
+LL |     let _: () = FN();
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::let-unit-value` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::let_unit_value)]`
+help: omit the `let` binding
+   |
+LL -     let _: () = FN();
+LL +     FN();
+   |
+
+error: aborting due to 1 previous error
+

tests/ui/let_unit.fixed

@@ -18,14 +18,17 @@ fn main() {
     let _y = 1; // this is fine
     let _z = ((), 1); // this as well
     if true {
-        // do not lint this, since () is explicit
+        // do not lint these, since () is explicit
         let _a = ();
         let () = returns_unit();
         let () = ();
         () = returns_unit();
         () = ();
         let _a: () = ();
-        let _a: () = returns_unit();
+
+        // should lint: explicit type annotation is redundant
+        returns_unit();
+        //~^ let_unit_value
     }
 
     consume_units_with_for_loop(); // should be fine as well
@@ -90,27 +93,33 @@ fn _returns_generic() {
     }
 
     let _: () = f();
-    let x: () = f();
+    let _: () = f();
+    //~^ ERROR: this let-binding has unit value
 
     let _: () = f2(0i32);
-    let x: () = f2(0i32);
+    let _: () = f2(0i32);
+    //~^ ERROR: this let-binding has unit value
 
-    let _: () = f3(());
-    let x: () = f3(());
+    f3(());
+    //~^ ERROR: this let-binding has unit value
+    f3(());
+    //~^ ERROR: this let-binding has unit value
 
     fn f4<T>(mut x: Vec<T>) -> T {
         x.pop().unwrap()
     }
     let _: () = f4(vec![()]);
-    let x: () = f4(vec![()]);
+    let _: () = f4(vec![()]);
+    //~^ ERROR: this let-binding has unit value
 
     let _: () = {
         let x = 5;
         f2(x)
     };
 
     let _: () = if true { f() } else { f2(0) };
-    let x: () = if true { f() } else { f2(0) };
+    let _: () = if true { f() } else { f2(0) };
+    //~^ ERROR: this let-binding has unit value
 
     match Some(0) {
         //~^ let_unit_value
@@ -160,7 +169,8 @@ fn _returns_generic() {
         {
             let _: () = x;
             let _: () = y;
-            let _: () = z;
+            z;
+            //~^ ERROR: this let-binding has unit value
             let _: () = x1;
             let _: () = x2;
             let _: () = opt;

tests/ui/let_unit.rs

@@ -18,14 +18,17 @@ fn main() {
     let _y = 1; // this is fine
     let _z = ((), 1); // this as well
     if true {
-        // do not lint this, since () is explicit
+        // do not lint these, since () is explicit
         let _a = ();
         let () = returns_unit();
         let () = ();
         () = returns_unit();
         () = ();
         let _a: () = ();
+
+        // should lint: explicit type annotation is redundant
         let _a: () = returns_unit();
+        //~^ let_unit_value
     }
 
     consume_units_with_for_loop(); // should be fine as well
@@ -91,18 +94,23 @@ fn _returns_generic() {
 
     let _: () = f();
     let x: () = f();
+    //~^ ERROR: this let-binding has unit value
 
     let _: () = f2(0i32);
     let x: () = f2(0i32);
+    //~^ ERROR: this let-binding has unit value
 
     let _: () = f3(());
+    //~^ ERROR: this let-binding has unit value
     let x: () = f3(());
+    //~^ ERROR: this let-binding has unit value
 
     fn f4<T>(mut x: Vec<T>) -> T {
         x.pop().unwrap()
     }
     let _: () = f4(vec![()]);
     let x: () = f4(vec![()]);
+    //~^ ERROR: this let-binding has unit value
 
     let _: () = {
         let x = 5;
@@ -111,6 +119,7 @@ fn _returns_generic() {
 
     let _: () = if true { f() } else { f2(0) };
     let x: () = if true { f() } else { f2(0) };
+    //~^ ERROR: this let-binding has unit value
 
     let x = match Some(0) {
         //~^ let_unit_value
@@ -161,6 +170,7 @@ fn _returns_generic() {
             let _: () = x;
             let _: () = y;
             let _: () = z;
+            //~^ ERROR: this let-binding has unit value
             let _: () = x1;
             let _: () = x2;
             let _: () = opt;

tests/ui/let_unit.stderr

@@ -13,7 +13,19 @@ LL +     println!("x");
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:65:5
+  --> tests/ui/let_unit.rs:30:9
+   |
+LL |         let _a: () = returns_unit();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: omit the `let` binding
+   |
+LL -         let _a: () = returns_unit();
+LL +         returns_unit();
+   |
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:68:5
    |
 LL | /     let _ = v
 LL | |
@@ -31,7 +43,63 @@ LL +     v
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:115:5
+  --> tests/ui/let_unit.rs:96:5
+   |
+LL |     let x: () = f();
+   |     ^^^^-^^^^^^^^^^^
+   |         |
+   |         help: use a wildcard binding: `_`
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:100:5
+   |
+LL |     let x: () = f2(0i32);
+   |     ^^^^-^^^^^^^^^^^^^^^^
+   |         |
+   |         help: use a wildcard binding: `_`
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:103:5
+   |
+LL |     let _: () = f3(());
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+help: omit the `let` binding
+   |
+LL -     let _: () = f3(());
+LL +     f3(());
+   |
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:105:5
+   |
+LL |     let x: () = f3(());
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+help: omit the `let` binding
+   |
+LL -     let x: () = f3(());
+LL +     f3(());
+   |
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:112:5
+   |
+LL |     let x: () = f4(vec![()]);
+   |     ^^^^-^^^^^^^^^^^^^^^^^^^^
+   |         |
+   |         help: use a wildcard binding: `_`
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:121:5
+   |
+LL |     let x: () = if true { f() } else { f2(0) };
+   |     ^^^^-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |         |
+   |         help: use a wildcard binding: `_`
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:124:5
    |
 LL | /     let x = match Some(0) {
 LL | |
@@ -49,7 +117,19 @@ LL +     match Some(0) {
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:195:9
+  --> tests/ui/let_unit.rs:172:13
+   |
+LL |             let _: () = z;
+   |             ^^^^^^^^^^^^^^
+   |
+help: omit the `let` binding
+   |
+LL -             let _: () = z;
+LL +             z;
+   |
+
+error: this let-binding has unit value
+  --> tests/ui/let_unit.rs:205:9
    |
 LL |         let res = returns_unit();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -63,7 +143,7 @@ LL ~         returns_result(()).unwrap();
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:208:5
+  --> tests/ui/let_unit.rs:218:5
    |
 LL |     let res = returns_unit();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -77,7 +157,7 @@ LL ~     takes_unit(());
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:216:14
+  --> tests/ui/let_unit.rs:226:14
    |
 LL |         _ => _ = returns_unit(),
    |              ^^^^^^^^^^^^^^^^^^
@@ -89,7 +169,7 @@ LL +         _ => returns_unit(),
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:220:5
+  --> tests/ui/let_unit.rs:230:5
    |
 LL |     _ = if true {}
    |     ^^^^^^^^^^^^^^
@@ -101,7 +181,7 @@ LL +     if true {}
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:225:5
+  --> tests/ui/let_unit.rs:235:5
    |
 LL |     let res = eprintln!("I return unit");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -115,7 +195,7 @@ LL ~     takes_unit(());
    |
 
 error: this let-binding has unit value
-  --> tests/ui/let_unit.rs:235:5
+  --> tests/ui/let_unit.rs:245:5
    |
 LL |     let value = println!();
    |     ^^^^^^^^^^^^^^^^^^^^^^^
@@ -128,5 +208,5 @@ LL |
 LL ~     Foo { value: () };
    |
 
-error: aborting due to 9 previous errors
+error: aborting due to 17 previous errors