Add explanations and suggestions to `irrefutable_let_patterns` lint

6 files changed, 54 insertions, 5 deletions

diff --git a/src/test/ui/closures/2229_closure_analysis/diagnostics/closure-origin-single-variant-diagnostics.stderr b/src/test/ui/closures/2229_closure_analysis/diagnostics/closure-origin-single-variant-diagnostics.stderr
index 5c7a56c7ced..8586dfd9186 100644
--- a/src/test/ui/closures/2229_closure_analysis/diagnostics/closure-origin-single-variant-diagnostics.stderr
+++ b/src/test/ui/closures/2229_closure_analysis/diagnostics/closure-origin-single-variant-diagnostics.stderr
@@ -17,6 +17,8 @@ LL | |         }
    | |_________^
    |
    = note: `#[warn(irrefutable_let_patterns)]` on by default
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
 
 error[E0382]: use of moved value: `c`
   --> $DIR/closure-origin-single-variant-diagnostics.rs:25:13
diff --git a/src/test/ui/expr/if/if-let.stderr b/src/test/ui/expr/if/if-let.stderr
index 468e913a773..c64c9093ee5 100644
--- a/src/test/ui/expr/if/if-let.stderr
+++ b/src/test/ui/expr/if/if-let.stderr
@@ -10,6 +10,8 @@ LL | |     });
    | |_______- in this macro invocation
    |
    = note: `#[warn(irrefutable_let_patterns)]` on by default
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: irrefutable `if let` pattern
@@ -23,6 +25,8 @@ LL | |         println!("irrefutable pattern");
 LL | |     });
    | |_______- in this macro invocation
    |
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: irrefutable `if let` pattern
@@ -32,6 +36,9 @@ LL | /     if let a = 1 {
 LL | |         println!("irrefutable pattern");
 LL | |     }
    | |_____^
+   |
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
 
 warning: irrefutable `if let` pattern
   --> $DIR/if-let.rs:30:5
@@ -44,6 +51,9 @@ LL | |     } else {
 LL | |         println!("else in irrefutable `if let`");
 LL | |     }
    | |_____^
+   |
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
 
 warning: irrefutable `if let` pattern
   --> $DIR/if-let.rs:40:12
@@ -53,6 +63,9 @@ LL |       } else if let a = 1 {
 LL | |         println!("irrefutable pattern");
 LL | |     }
    | |_____^
+   |
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
 
 warning: irrefutable `if let` pattern
   --> $DIR/if-let.rs:46:12
@@ -62,6 +75,9 @@ LL |       } else if let a = 1 {
 LL | |         println!("irrefutable pattern");
 LL | |     }
    | |_____^
+   |
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
 
 warning: 6 warnings emitted
 
diff --git a/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.rs b/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.rs
index c1cfa4695c9..7549eae7016 100644
--- a/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.rs
+++ b/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.rs
@@ -1,3 +1,6 @@
+#![feature(if_let_guard)]
+#![allow(incomplete_features)]
+
 #![deny(irrefutable_let_patterns)]
 
 fn main() {
@@ -6,4 +9,9 @@ fn main() {
     while let _ = 5 { //~ ERROR irrefutable `while let` pattern
         break;
     }
+
+    match 5 {
+        _ if let _ = 2 => {} //~ ERROR irrefutable `if let` guard pattern
+        _ => {}
+    }
 }
diff --git a/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.stderr b/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.stderr
index 1de30f7db06..d6926ee12ee 100644
--- a/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.stderr
+++ b/src/test/ui/pattern/usefulness/deny-irrefutable-let-patterns.stderr
@@ -1,22 +1,36 @@
 error: irrefutable `if let` pattern
-  --> $DIR/deny-irrefutable-let-patterns.rs:4:5
+  --> $DIR/deny-irrefutable-let-patterns.rs:7:5
    |
 LL |     if let _ = 5 {}
    |     ^^^^^^^^^^^^^^^
    |
 note: the lint level is defined here
-  --> $DIR/deny-irrefutable-let-patterns.rs:1:9
+  --> $DIR/deny-irrefutable-let-patterns.rs:4:9
    |
 LL | #![deny(irrefutable_let_patterns)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this pattern will always match, so the `if let` is useless
+   = help: consider replacing the `if let` with a `let`
 
 error: irrefutable `while let` pattern
-  --> $DIR/deny-irrefutable-let-patterns.rs:6:5
+  --> $DIR/deny-irrefutable-let-patterns.rs:9:5
    |
 LL | /     while let _ = 5 {
 LL | |         break;
 LL | |     }
    | |_____^
+   |
+   = note: this pattern will always match, so the loop will never exit
+   = help: consider instead using a `loop { ... }` with a `let` inside it
+
+error: irrefutable `if let` guard pattern
+  --> $DIR/deny-irrefutable-let-patterns.rs:14:18
+   |
+LL |         _ if let _ = 2 => {}
+   |                  ^
+   |
+   = note: this pattern will always match, so the guard is useless
+   = help: consider removing the guard and adding a `let` inside the match arm
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/rfc-2294-if-let-guard/warns.stderr b/src/test/ui/rfc-2294-if-let-guard/warns.stderr
index 33fa25d32fb..c7627f1c3c5 100644
--- a/src/test/ui/rfc-2294-if-let-guard/warns.stderr
+++ b/src/test/ui/rfc-2294-if-let-guard/warns.stderr
@@ -1,4 +1,4 @@
-error: irrefutable `if let` guard
+error: irrefutable `if let` guard pattern
   --> $DIR/warns.rs:7:24
    |
 LL |         Some(x) if let () = x => {}
@@ -9,6 +9,8 @@ note: the lint level is defined here
    |
 LL | #[deny(irrefutable_let_patterns)]
    |        ^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this pattern will always match, so the guard is useless
+   = help: consider removing the guard and adding a `let` inside the match arm
 
 error: unreachable pattern
   --> $DIR/warns.rs:16:25
diff --git a/src/test/ui/while-let.stderr b/src/test/ui/while-let.stderr
index 6538b9fbe6f..04e77bf9470 100644
--- a/src/test/ui/while-let.stderr
+++ b/src/test/ui/while-let.stderr
@@ -10,6 +10,8 @@ LL | |     });
    | |_______- in this macro invocation
    |
    = note: `#[warn(irrefutable_let_patterns)]` on by default
+   = note: this pattern will always match, so the loop will never exit
+   = help: consider instead using a `loop { ... }` with a `let` inside it
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: irrefutable `while let` pattern
@@ -23,6 +25,8 @@ LL | |         println!("irrefutable pattern");
 LL | |     });
    | |_______- in this macro invocation
    |
+   = note: this pattern will always match, so the loop will never exit
+   = help: consider instead using a `loop { ... }` with a `let` inside it
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 warning: irrefutable `while let` pattern
@@ -33,6 +37,9 @@ LL | |         println!("irrefutable pattern");
 LL | |         break;
 LL | |     }
    | |_____^
+   |
+   = note: this pattern will always match, so the loop will never exit
+   = help: consider instead using a `loop { ... }` with a `let` inside it
 
 warning: 3 warnings emitted