Never pattern in let statement diverges

Author: Nadrieril

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1473,6 +1473,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Type check a `let` statement.
     pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
         self.check_decl(local.into());
+        if local.pat.is_never_pattern() {
+            self.diverges.set(Diverges::Always {
+                span: local.pat.span,
+                custom_note: Some("any code following a never pattern is unreachable"),
+            });
+        }
     }
 
     pub fn check_stmt(&self, stmt: &'tcx hir::Stmt<'tcx>) {

tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.rs

@@ -17,13 +17,14 @@ fn ref_never_arg(&!: &Void) -> u32 {
     //~^ ERROR unreachable statement
 }
 
-//fn never_let() -> u32 {
-//    let ptr: *const Void = std::ptr::null();
-//    unsafe {
-//        let ! = *ptr;
-//    }
-//    println!();
-//}
+fn never_let() -> u32 {
+    let ptr: *const Void = std::ptr::null();
+    unsafe {
+        let ! = *ptr;
+    }
+    println!();
+    //~^ ERROR unreachable statement
+}
 
 fn never_match() -> u32 {
     let ptr: *const Void = std::ptr::null();

tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.stderr

@@ -24,7 +24,18 @@ LL |     println!();
    = note: this error originates in the macro `$crate::print` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: unreachable statement
-  --> $DIR/diverge-causes-unreachable-code.rs:33:5
+  --> $DIR/diverge-causes-unreachable-code.rs:25:5
+   |
+LL |         let ! = *ptr;
+   |             - any code following a never pattern is unreachable
+LL |     }
+LL |     println!();
+   |     ^^^^^^^^^^ unreachable statement
+   |
+   = note: this error originates in the macro `$crate::print` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unreachable statement
+  --> $DIR/diverge-causes-unreachable-code.rs:34:5
    |
 LL |         match *ptr { ! };
    |         ---------------- any code following this `match` expression is unreachable, as all arms diverge
@@ -34,5 +45,5 @@ LL |     println!();
    |
    = note: this error originates in the macro `$crate::print` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 

tests/ui/rfcs/rfc-0000-never_patterns/diverges.rs

@@ -13,12 +13,12 @@ fn never_arg(!: Void) -> u32 {}
 
 fn ref_never_arg(&!: &Void) -> u32 {}
 
-// fn never_let() -> u32 {
-//     let ptr: *const Void = std::ptr::null();
-//     unsafe {
-//         let ! = *ptr;
-//     }
-// }
+fn never_let() -> u32 {
+    let ptr: *const Void = std::ptr::null();
+    unsafe {
+        let ! = *ptr;
+    }
+}
 
 fn never_match() -> u32 {
     let ptr: *const Void = std::ptr::null();