On unused binding in pattern, suggest unit struct/variant with similar name

When encountering a typo in a pattern that gets interpreted as an unused binding, look for unit struct/variant of the same type as the binding:

```
error: unused variable: `Non`
  --> $DIR/binding-typo-2.rs:36:9
   |
LL |         Non => {}
   |         ^^^
   |
help: if this is intentional, prefix it with an underscore
   |
LL |         _Non => {}
   |         +
help: you might have meant to pattern match on the similarly named variant `None`
   |
LL -         Non => {}
LL +         std::prelude::v1::None => {}
   |
```

5 files changed, 189 insertions, 70 deletions

diff --git a/tests/ui/or-patterns/binding-typo-2.rs b/tests/ui/or-patterns/binding-typo-2.rs
index 4dfb84d4f0c..d763ce60ce9 100644
--- a/tests/ui/or-patterns/binding-typo-2.rs
+++ b/tests/ui/or-patterns/binding-typo-2.rs
@@ -17,6 +17,7 @@ fn foo(x: (Lol, Lol)) {
         //~| NOTE: variable not in all patterns
         //~| ERROR: variable `Ban` is assigned to, but never used
         //~| NOTE: consider using `_Ban` instead
+        //~| HELP: you might have meant to pattern match on the similarly named
         _ => {}
     }
     match &x {
@@ -27,15 +28,18 @@ fn foo(x: (Lol, Lol)) {
         //~| NOTE: variable not in all patterns
         //~| ERROR: variable `Ban` is assigned to, but never used
         //~| NOTE: consider using `_Ban` instead
+        //~| HELP: you might have meant to pattern match on the similarly named
         _ => {}
     }
     match Some(42) {
+        Some(_) => {}
         Non => {}
         //~^ ERROR: unused variable: `Non`
         //~| HELP: if this is intentional, prefix it with an underscore
-        _ => {}
+        //~| HELP: you might have meant to pattern match on the similarly named
     }
     match Some(42) {
+        Some(_) => {}
         Non | None => {}
         //~^ ERROR: unused variable: `Non`
         //~| HELP: if this is intentional, prefix it with an underscore
@@ -43,7 +47,7 @@ fn foo(x: (Lol, Lol)) {
         //~| NOTE: pattern doesn't bind `Non`
         //~| NOTE: variable not in all patterns
         //~| HELP: you might have meant to use the similarly named previously used binding `None`
-        _ => {}
+        //~| HELP: you might have meant to pattern match on the similarly named
     }
     match Some(42) {
         Non | Some(_) => {}
@@ -53,14 +57,13 @@ fn foo(x: (Lol, Lol)) {
         //~| NOTE: pattern doesn't bind `Non`
         //~| NOTE: variable not in all patterns
         //~| HELP: you might have meant to use the similarly named unit variant `None`
-        _ => {}
+        //~| HELP: you might have meant to pattern match on the similarly named
     }
 }
 fn bar(x: (Lol, Lol)) {
     use Lol::*;
     use Bat;
     use Bay;
-    use std::option::Option::None;
     match &x {
         (Foo, _) | (Ban, Foo) => {}
         //~^ ERROR: variable `Ban` is not bound in all patterns
@@ -71,6 +74,7 @@ fn bar(x: (Lol, Lol)) {
         //~| NOTE: variable not in all patterns
         //~| ERROR: variable `Ban` is assigned to, but never used
         //~| NOTE: consider using `_Ban` instead
+        //~| HELP: you might have meant to pattern match on the similarly named
         _ => {}
     }
 }
@@ -86,8 +90,21 @@ fn baz(x: (Lol, Lol)) {
         //~| NOTE: variable not in all patterns
         //~| ERROR: variable `Ban` is assigned to, but never used
         //~| NOTE: consider using `_Ban` instead
+        //~| HELP: you might have meant to pattern match on the similarly named
         _ => {}
     }
+    match &x {
+        (Ban, _) => {}
+        //~^ ERROR: unused variable: `Ban`
+        //~| HELP: if this is intentional, prefix it with an underscore
+        //~| HELP: you might have meant to pattern match on the similarly named
+    }
+    match Bay {
+        Ban => {}
+        //~^ ERROR: unused variable: `Ban`
+        //~| HELP: if this is intentional, prefix it with an underscore
+        //~| HELP: you might have meant to pattern match on the similarly named
+    }
 }
 
 fn main() {
diff --git a/tests/ui/or-patterns/binding-typo-2.stderr b/tests/ui/or-patterns/binding-typo-2.stderr
index a2099572485..d683cb2b121 100644
--- a/tests/ui/or-patterns/binding-typo-2.stderr
+++ b/tests/ui/or-patterns/binding-typo-2.stderr
@@ -13,7 +13,48 @@ LL +         (Foo, Bar) | (Bar, Foo) => {}
    |
 
 error[E0408]: variable `Ban` is not bound in all patterns
-  --> $DIR/binding-typo-2.rs:23:9
+  --> $DIR/binding-typo-2.rs:24:9
+   |
+LL |         (Foo, _) | (Ban, Foo) => {}
+   |         ^^^^^^^^    --- variable not in all patterns
+   |         |
+   |         pattern doesn't bind `Ban`
+   |
+help: you might have meant to use the similarly named unit variant `Bar`
+   |
+LL -         (Foo, _) | (Ban, Foo) => {}
+LL +         (Foo, _) | (Bar, Foo) => {}
+   |
+
+error[E0408]: variable `Non` is not bound in all patterns
+  --> $DIR/binding-typo-2.rs:43:15
+   |
+LL |         Non | None => {}
+   |         ---   ^^^^ pattern doesn't bind `Non`
+   |         |
+   |         variable not in all patterns
+   |
+help: you might have meant to use the similarly named previously used binding `None`
+   |
+LL |         None | None => {}
+   |            +
+
+error[E0408]: variable `Non` is not bound in all patterns
+  --> $DIR/binding-typo-2.rs:53:15
+   |
+LL |         Non | Some(_) => {}
+   |         ---   ^^^^^^^ pattern doesn't bind `Non`
+   |         |
+   |         variable not in all patterns
+   |
+help: you might have meant to use the similarly named unit variant `None`
+   |
+LL -         Non | Some(_) => {}
+LL +         core::option::Option::None | Some(_) => {}
+   |
+
+error[E0408]: variable `Ban` is not bound in all patterns
+  --> $DIR/binding-typo-2.rs:68:9
    |
 LL |         (Foo, _) | (Ban, Foo) => {}
    |         ^^^^^^^^    --- variable not in all patterns
@@ -28,39 +69,31 @@ LL +         (Foo, _) | (Bar, Foo) => {}
 help: you might have meant to use the similarly named unit struct `Bay`
    |
 LL -         (Foo, _) | (Ban, Foo) => {}
-LL +         (Foo, _) | (::Bay, Foo) => {}
+LL +         (Foo, _) | (Bay, Foo) => {}
    |
 help: you might have meant to use the similarly named constant `Bat`
    |
 LL -         (Foo, _) | (Ban, Foo) => {}
-LL +         (Foo, _) | (::Bat, Foo) => {}
+LL +         (Foo, _) | (Bat, Foo) => {}
    |
 
-error[E0408]: variable `Non` is not bound in all patterns
-  --> $DIR/binding-typo-2.rs:41:16
-   |
-LL |         (Non | None)=> {}
-   |          ---   ^^^^ pattern doesn't bind `Non`
-   |          |
-   |          variable not in all patterns
+error[E0408]: variable `Ban` is not bound in all patterns
+  --> $DIR/binding-typo-2.rs:85:9
    |
-help: you might have meant to use the similarly named previously used binding `None`
+LL |         (Foo, _) | (Ban, Foo) => {}
+   |         ^^^^^^^^    --- variable not in all patterns
+   |         |
+   |         pattern doesn't bind `Ban`
    |
-LL |         (None | None)=> {}
-   |             +
-
-error[E0408]: variable `Non` is not bound in all patterns
-  --> $DIR/binding-typo-2.rs:51:16
+help: you might have meant to use the similarly named unit variant `Bar`
    |
-LL |         (Non | Some(_))=> {}
-   |          ---   ^^^^^^^ pattern doesn't bind `Non`
-   |          |
-   |          variable not in all patterns
+LL -         (Foo, _) | (Ban, Foo) => {}
+LL +         (Foo, _) | (Bar, Foo) => {}
    |
-help: you might have meant to use the similarly named unit variant `None`
+help: you might have meant to use the similarly named constant `Bat`
    |
-LL -         (Non | Some(_))=> {}
-LL +         (core::option::Option::None | Some(_))=> {}
+LL -         (Foo, _) | (Ban, Foo) => {}
+LL +         (Foo, _) | (Bat, Foo) => {}
    |
 
 error: variable `Ban` is assigned to, but never used
@@ -75,33 +108,131 @@ note: the lint level is defined here
    |
 LL | #![deny(unused_variables)]
    |         ^^^^^^^^^^^^^^^^
+help: you might have meant to pattern match on the similarly named variant `Bar`
+   |
+LL -         (Foo, Bar) | (Ban, Foo) => {}
+LL +         (Foo, Bar) | (Lol::Bar, Foo) => {}
+   |
 
 error: variable `Ban` is assigned to, but never used
-  --> $DIR/binding-typo-2.rs:23:21
+  --> $DIR/binding-typo-2.rs:24:21
    |
 LL |         (Foo, _) | (Ban, Foo) => {}
    |                     ^^^
    |
    = note: consider using `_Ban` instead
+help: you might have meant to pattern match on the similarly named variant `Bar`
+   |
+LL -         (Foo, _) | (Ban, Foo) => {}
+LL +         (Foo, _) | (Lol::Bar, Foo) => {}
+   |
 
 error: unused variable: `Non`
-  --> $DIR/binding-typo-2.rs:35:9
+  --> $DIR/binding-typo-2.rs:36:9
    |
 LL |         Non => {}
-   |         ^^^ help: if this is intentional, prefix it with an underscore: `_Non`
+   |         ^^^
+   |
+help: if this is intentional, prefix it with an underscore
+   |
+LL |         _Non => {}
+   |         +
+help: you might have meant to pattern match on the similarly named variant `None`
+   |
+LL -         Non => {}
+LL +         std::prelude::v1::None => {}
+   |
 
 error: unused variable: `Non`
-  --> $DIR/binding-typo-2.rs:41:10
+  --> $DIR/binding-typo-2.rs:43:9
+   |
+LL |         Non | None => {}
+   |         ^^^
+   |
+help: if this is intentional, prefix it with an underscore
+   |
+LL |         _Non | None => {}
+   |         +
+help: you might have meant to pattern match on the similarly named variant `None`
+   |
+LL -         Non | None => {}
+LL +         std::prelude::v1::None | None => {}
    |
-LL |         (Non | None)=> {}
-   |          ^^^ help: if this is intentional, prefix it with an underscore: `_Non`
 
 error: unused variable: `Non`
-  --> $DIR/binding-typo-2.rs:51:10
+  --> $DIR/binding-typo-2.rs:53:9
+   |
+LL |         Non | Some(_) => {}
+   |         ^^^
+   |
+help: if this is intentional, prefix it with an underscore
+   |
+LL |         _Non | Some(_) => {}
+   |         +
+help: you might have meant to pattern match on the similarly named variant `None`
+   |
+LL -         Non | Some(_) => {}
+LL +         std::prelude::v1::None | Some(_) => {}
+   |
+
+error: variable `Ban` is assigned to, but never used
+  --> $DIR/binding-typo-2.rs:68:21
+   |
+LL |         (Foo, _) | (Ban, Foo) => {}
+   |                     ^^^
+   |
+   = note: consider using `_Ban` instead
+help: you might have meant to pattern match on the similarly named variant `Bar`
+   |
+LL -         (Foo, _) | (Ban, Foo) => {}
+LL +         (Foo, _) | (Lol::Bar, Foo) => {}
+   |
+
+error: variable `Ban` is assigned to, but never used
+  --> $DIR/binding-typo-2.rs:85:21
+   |
+LL |         (Foo, _) | (Ban, Foo) => {}
+   |                     ^^^
+   |
+   = note: consider using `_Ban` instead
+help: you might have meant to pattern match on the similarly named variant `Bar`
+   |
+LL -         (Foo, _) | (Ban, Foo) => {}
+LL +         (Foo, _) | (Lol::Bar, Foo) => {}
+   |
+
+error: unused variable: `Ban`
+  --> $DIR/binding-typo-2.rs:97:10
+   |
+LL |         (Ban, _) => {}
+   |          ^^^
+   |
+help: if this is intentional, prefix it with an underscore
+   |
+LL |         (_Ban, _) => {}
+   |          +
+help: you might have meant to pattern match on the similarly named variant `Bar`
+   |
+LL -         (Ban, _) => {}
+LL +         (Lol::Bar, _) => {}
+   |
+
+error: unused variable: `Ban`
+  --> $DIR/binding-typo-2.rs:103:9
+   |
+LL |         Ban => {}
+   |         ^^^
+   |
+help: if this is intentional, prefix it with an underscore
+   |
+LL |         _Ban => {}
+   |         +
+help: you might have meant to pattern match on the similarly named struct `Bay`
+   |
+LL -         Ban => {}
+LL +         Bay => {}
    |
-LL |         (Non | Some(_))=> {}
-   |          ^^^ help: if this is intentional, prefix it with an underscore: `_Non`
 
-error: aborting due to 9 previous errors
+error: aborting due to 15 previous errors
 
 For more information about this error, try `rustc --explain E0408`.
diff --git a/tests/ui/or-patterns/binding-typo.fixed b/tests/ui/or-patterns/binding-typo.fixed
index 2902ca30393..f209ad644db 100644
--- a/tests/ui/or-patterns/binding-typo.fixed
+++ b/tests/ui/or-patterns/binding-typo.fixed
@@ -1,6 +1,6 @@
 // Issue #51976
 //@ run-rustfix
-#![deny(unused_variables)] //~ NOTE: the lint level is defined here
+#![allow(unused_variables)] // allowed so we don't get overlapping suggestions
 enum Lol {
     Foo,
     Bar,
@@ -14,8 +14,6 @@ fn foo(x: (Lol, Lol)) {
         //~| HELP: you might have meant to use the similarly named previously used binding `Bar`
         //~| NOTE: pattern doesn't bind `Ban`
         //~| NOTE: variable not in all patterns
-        //~| ERROR: variable `Ban` is assigned to, but never used
-        //~| NOTE: consider using `_Ban` instead
         _ => {}
     }
     match &x {
@@ -24,8 +22,6 @@ fn foo(x: (Lol, Lol)) {
         //~| HELP: you might have meant to use the similarly named unit variant `Bar`
         //~| NOTE: pattern doesn't bind `Ban`
         //~| NOTE: variable not in all patterns
-        //~| ERROR: variable `Ban` is assigned to, but never used
-        //~| NOTE: consider using `_Ban` instead
         _ => {}
     }
 }
diff --git a/tests/ui/or-patterns/binding-typo.rs b/tests/ui/or-patterns/binding-typo.rs
index 2ffe0e45c83..6be9b801a0d 100644
--- a/tests/ui/or-patterns/binding-typo.rs
+++ b/tests/ui/or-patterns/binding-typo.rs
@@ -1,6 +1,6 @@
 // Issue #51976
 //@ run-rustfix
-#![deny(unused_variables)] //~ NOTE: the lint level is defined here
+#![allow(unused_variables)] // allowed so we don't get overlapping suggestions
 enum Lol {
     Foo,
     Bar,
@@ -14,8 +14,6 @@ fn foo(x: (Lol, Lol)) {
         //~| HELP: you might have meant to use the similarly named previously used binding `Bar`
         //~| NOTE: pattern doesn't bind `Ban`
         //~| NOTE: variable not in all patterns
-        //~| ERROR: variable `Ban` is assigned to, but never used
-        //~| NOTE: consider using `_Ban` instead
         _ => {}
     }
     match &x {
@@ -24,8 +22,6 @@ fn foo(x: (Lol, Lol)) {
         //~| HELP: you might have meant to use the similarly named unit variant `Bar`
         //~| NOTE: pattern doesn't bind `Ban`
         //~| NOTE: variable not in all patterns
-        //~| ERROR: variable `Ban` is assigned to, but never used
-        //~| NOTE: consider using `_Ban` instead
         _ => {}
     }
 }
diff --git a/tests/ui/or-patterns/binding-typo.stderr b/tests/ui/or-patterns/binding-typo.stderr
index f90301d2cee..fb6d5f71209 100644
--- a/tests/ui/or-patterns/binding-typo.stderr
+++ b/tests/ui/or-patterns/binding-typo.stderr
@@ -13,7 +13,7 @@ LL +         (Foo, Bar) | (Bar, Foo) => {}
    |
 
 error[E0408]: variable `Ban` is not bound in all patterns
-  --> $DIR/binding-typo.rs:22:9
+  --> $DIR/binding-typo.rs:20:9
    |
 LL |         (Foo, _) | (Ban, Foo) => {}
    |         ^^^^^^^^    --- variable not in all patterns
@@ -26,27 +26,6 @@ LL -         (Foo, _) | (Ban, Foo) => {}
 LL +         (Foo, _) | (Bar, Foo) => {}
    |
 
-error: variable `Ban` is assigned to, but never used
-  --> $DIR/binding-typo.rs:12:23
-   |
-LL |         (Foo, Bar) | (Ban, Foo) => {}
-   |                       ^^^
-   |
-   = note: consider using `_Ban` instead
-note: the lint level is defined here
-  --> $DIR/binding-typo.rs:3:9
-   |
-LL | #![deny(unused_variables)]
-   |         ^^^^^^^^^^^^^^^^
-
-error: variable `Ban` is assigned to, but never used
-  --> $DIR/binding-typo.rs:22:21
-   |
-LL |         (Foo, _) | (Ban, Foo) => {}
-   |                     ^^^
-   |
-   = note: consider using `_Ban` instead
-
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0408`.