When finding a match expr with multiple arms that requires more, sugg…

…est it

Given

```rust
match Some(42) {
    Some(0) => {}
    Some(1) => {}
}
```

suggest

```rust
match Some(42) {
    Some(0) => {}
    Some(1) => {}
    None | Some(_) => todo!(),
}
```

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -604,6 +604,21 @@ fn non_exhaustive_match<'p, 'tcx>(
                 format!("{}{}{} => todo!()", comma, pre_indentation, pattern),
             ));
         }
+        [.., prev, last] if prev.span.ctxt() == last.span.ctxt() => {
+            if let Ok(snippet) = sm.span_to_snippet(prev.span.between(last.span)) {
+                let comma =
+                    if matches!(last.body.kind, hir::ExprKind::Block(..)) { "" } else { "," };
+                suggestion = Some((
+                    last.span.shrink_to_hi(),
+                    format!(
+                        "{}{}{} => todo!()",
+                        comma,
+                        snippet.strip_prefix(",").unwrap_or(&snippet),
+                        pattern
+                    ),
+                ));
+            }
+        }
         _ => {}
     }
 

src/test/ui/closures/2229_closure_analysis/match/non-exhaustive-match.stderr

@@ -37,7 +37,10 @@ LL |     let _e = || { match e2 { E2::A => (), E2::B => () } };
    |                         ^^ pattern `_` not covered
    |
    = note: the matched value is of type `E2`, which is marked as non-exhaustive
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL |     let _e = || { match e2 { E2::A => (), E2::B => (), _ => todo!() } };
+   |                                                      ++++++++++++++
 
 error[E0505]: cannot move out of `e3` because it is borrowed
   --> $DIR/non-exhaustive-match.rs:46:22

src/test/ui/match/match_non_exhaustive.stderr

@@ -37,7 +37,10 @@ LL |     match e2 { E2::A => (), E2::B => () };
    |           ^^ pattern `_` not covered
    |
    = note: the matched value is of type `E2`, which is marked as non-exhaustive
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL |     match e2 { E2::A => (), E2::B => (), _ => todo!() };
+   |                                        ++++++++++++++
 
 error: aborting due to 3 previous errors
 

src/test/ui/pattern/usefulness/doc-hidden-non-exhaustive.stderr

@@ -5,7 +5,11 @@ LL |     match Foo::A {
    |           ^^^^^^ pattern `_` not covered
    |
    = note: the matched value is of type `Foo`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         Foo::B => {}
+LL +         _ => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `B` not covered
   --> $DIR/doc-hidden-non-exhaustive.rs:14:11
@@ -19,7 +23,11 @@ LL |     B,
    |     - not covered
    |
    = note: the matched value is of type `Foo`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         Foo::C => {}
+LL +         B => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `B` and `_` not covered
   --> $DIR/doc-hidden-non-exhaustive.rs:20:11
@@ -51,7 +59,11 @@ LL |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
    |     ---- not covered
    |
    = note: the matched value is of type `Option<Foo>`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         Some(Foo::A) => {}
+LL +         Some(B) | Some(_) => todo!()
+   |
 
 error: aborting due to 4 previous errors
 

src/test/ui/pattern/usefulness/guards.stderr

@@ -5,7 +5,11 @@ LL |     match 0u8 {
    |           ^^^ pattern `128_u8..=u8::MAX` not covered
    |
    = note: the matched value is of type `u8`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         128 ..= 255 if true => {}
+LL +         128_u8..=u8::MAX => todo!()
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/integer-ranges/exhaustiveness.stderr

@@ -96,7 +96,11 @@ LL |     match 0i8 {
    |           ^^^ pattern `0_i8` not covered
    |
    = note: the matched value is of type `i8`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         1 ..= i8::MAX => {}
+LL +         0_i8 => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `u128::MAX` not covered
   --> $DIR/exhaustiveness.rs:59:8
@@ -144,7 +148,11 @@ LL |     match (0u8, true) {
    |           ^^^^^^^^^^^ pattern `(126_u8..=127_u8, false)` not covered
    |
    = note: the matched value is of type `(u8, bool)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (0 ..= 255, true) => {}
+LL +         (126_u8..=127_u8, false) => todo!()
+   |
 
 error: aborting due to 12 previous errors
 

src/test/ui/pattern/usefulness/integer-ranges/pointer-sized-int.deny.stderr

@@ -153,7 +153,11 @@ LL |     match 0isize {
    = note: the matched value is of type `isize`
    = note: `isize` does not have a fixed maximum value, so a wildcard `_` is necessary to match exhaustively
    = help: add `#![feature(precise_pointer_size_matching)]` to the crate attributes to enable precise `isize` matching
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         1 ..= isize::MAX => {}
+LL +         _ => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: type `usize` is non-empty
   --> $DIR/pointer-sized-int.rs:48:11

src/test/ui/pattern/usefulness/issue-15129.stderr

@@ -5,7 +5,11 @@ LL |     match (T::T1(()), V::V2(true)) {
    |           ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `(T1(()), V2(_))` and `(T2(()), V1(_))` not covered
    |
    = note: the matched value is of type `(T, V)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (T::T2(()), V::V2(b)) => (),
+LL ~         (T1(()), V2(_)) | (T2(()), V1(_)) => todo!(),
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/issue-2111.stderr

@@ -5,7 +5,11 @@ LL |     match (a, b) {
    |           ^^^^^^ patterns `(None, None)` and `(Some(_), Some(_))` not covered
    |
    = note: the matched value is of type `(Option<usize>, Option<usize>)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (Some(_), None) | (None, Some(_)) => {}
+LL +         (None, None) | (Some(_), Some(_)) => todo!()
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/issue-30240.stderr

@@ -18,7 +18,11 @@ LL |     match "world" {
    |           ^^^^^^^ pattern `&_` not covered
    |
    = note: the matched value is of type `&str`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         "hello" => {}
+LL +         &_ => todo!()
+   |
 
 error: aborting due to 2 previous errors
 

src/test/ui/pattern/usefulness/issue-35609.stderr

@@ -102,7 +102,11 @@ LL |     match Some(A) {
    |           ^^^^^^^ patterns `Some(B)`, `Some(C)`, `Some(D)` and 2 more not covered
    |
    = note: the matched value is of type `Option<Enum>`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         None => (),
+LL +         _ => todo!()
+   |
 
 error: aborting due to 8 previous errors
 

src/test/ui/pattern/usefulness/issue-39362.stderr

@@ -10,7 +10,11 @@ LL |       match f {
    |             ^ patterns `Bar { bar: C, .. }`, `Bar { bar: D, .. }`, `Bar { bar: E, .. }` and 1 more not covered
    |
    = note: the matched value is of type `Foo`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         Foo::Bar { bar: Bar::B, .. } => (),
+LL ~         _ => todo!(),
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/issue-4321.stderr

@@ -5,7 +5,11 @@ LL |     println!("foo {:}", match tup {
    |                               ^^^ pattern `(true, false)` not covered
    |
    = note: the matched value is of type `(bool, bool)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (true, true) => "baz",
+LL +         (true, false) => todo!()
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/issue-56379.stderr

@@ -15,7 +15,11 @@ LL |       match Foo::A(true) {
    |             ^^^^^^^^^^^^ patterns `A(false)`, `B(false)` and `C(false)` not covered
    |
    = note: the matched value is of type `Foo`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         Foo::C(true) => {}
+LL +         A(false) | B(false) | C(false) => todo!()
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/issue-72377.stderr

@@ -5,7 +5,11 @@ LL |     match (x, y) {
    |           ^^^^^^ patterns `(A, Some(A))`, `(A, Some(B))`, `(B, Some(B))` and 2 more not covered
    |
    = note: the matched value is of type `(X, Option<X>)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (X::A, Some(X::C)) | (X::C, Some(X::A)) => false,
+LL ~         _ => todo!(),
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/match-arm-statics-2.stderr

@@ -5,7 +5,11 @@ LL |     match (true, false) {
    |           ^^^^^^^^^^^^^ pattern `(true, false)` not covered
    |
    = note: the matched value is of type `(bool, bool)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (false, true) => (),
+LL +         (true, false) => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `Some(Some(West))` not covered
   --> $DIR/match-arm-statics-2.rs:29:11
@@ -22,7 +26,11 @@ LL |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
    |     not covered
    |
    = note: the matched value is of type `Option<Option<Direction>>`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         None => (),
+LL +         Some(Some(West)) => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `Foo { bar: Some(North), baz: NewBool(true) }` not covered
   --> $DIR/match-arm-statics-2.rs:48:11
@@ -37,7 +45,11 @@ LL |       match (Foo { bar: Some(North), baz: NewBool(true) }) {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `Foo { bar: Some(North), baz: NewBool(true) }` not covered
    |
    = note: the matched value is of type `Foo`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         Foo { bar: Some(EAST), .. } => (),
+LL +         Foo { bar: Some(North), baz: NewBool(true) } => todo!()
+   |
 
 error: aborting due to 3 previous errors
 

src/test/ui/pattern/usefulness/match-privately-empty.stderr

@@ -10,7 +10,11 @@ LL |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
    |     ---- not covered
    |
    = note: the matched value is of type `Option<Private>`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         }) => {}
+LL +         Some(Private { misc: true, .. }) => todo!()
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/match-slice-patterns.stderr

@@ -5,7 +5,11 @@ LL |     match list {
    |           ^^^^ pattern `&[_, Some(_), .., None, _]` not covered
    |
    = note: the matched value is of type `&[Option<()>]`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         &[.., Some(_), _] => {}
+LL ~         &[_, Some(_), .., None, _] => todo!(),
+   |
 
 error: aborting due to previous error
 

src/test/ui/pattern/usefulness/non-exhaustive-match-nested.stderr

@@ -5,7 +5,11 @@ LL |     match (l1, l2) {
    |           ^^^^^^^^ pattern `(Some(&[]), Err(_))` not covered
    |
    = note: the matched value is of type `(Option<&[T]>, Result<&[T], ()>)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         (None, Ok(&[_, _, ..])) => "None, Ok(at least two elements)",
+LL +         (Some(&[]), Err(_)) => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `A(C)` not covered
   --> $DIR/non-exhaustive-match-nested.rs:15:11
@@ -20,7 +24,11 @@ LL |     match x {
    |           ^ pattern `A(C)` not covered
    |
    = note: the matched value is of type `T`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         T::B => { panic!("goodbye"); }
+LL +         A(C) => todo!()
+   |
 
 error: aborting due to 2 previous errors
 

src/test/ui/pattern/usefulness/non-exhaustive-match.stderr

@@ -67,7 +67,11 @@ LL |     match (T::A, T::A) {
    |           ^^^^^^^^^^^^ patterns `(A, A)` and `(B, B)` not covered
    |
    = note: the matched value is of type `(T, T)`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~       (T::B, T::A) => {}
+LL +       (A, A) | (B, B) => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `B` not covered
   --> $DIR/non-exhaustive-match.rs:22:11
@@ -95,7 +99,11 @@ LL |     match *vec {
    |           ^^^^ pattern `[]` not covered
    |
    = note: the matched value is of type `[Option<isize>]`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         [None] => {}
+LL +         [] => todo!()
+   |
 
 error[E0004]: non-exhaustive patterns: `[_, _, _, _, ..]` not covered
   --> $DIR/non-exhaustive-match.rs:46:11
@@ -104,7 +112,11 @@ LL |     match *vec {
    |           ^^^^ pattern `[_, _, _, _, ..]` not covered
    |
    = note: the matched value is of type `[f32]`
-   = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+   |
+LL ~         [] => (),
+LL +         [_, _, _, _, ..] => todo!()
+   |
 
 error: aborting due to 8 previous errors