Rollup merge of #139035 - nnethercote:PatKind-Missing, r=oli-obk

Add new `PatKind::Missing` variants

To avoid some ugly uses of `kw::Empty` when handling "missing" patterns, e.g. in bare fn tys. Helps with #137978. Details in the individual commits.

r? ``@oli-obk``

10 files changed, 11 insertions, 5 deletions

diff --git a/src/tools/clippy/clippy_lints/src/equatable_if_let.rs b/src/tools/clippy/clippy_lints/src/equatable_if_let.rs
index cd9ab2764ac..3afb687040f 100644
--- a/src/tools/clippy/clippy_lints/src/equatable_if_let.rs
+++ b/src/tools/clippy/clippy_lints/src/equatable_if_let.rs
@@ -45,6 +45,7 @@ fn unary_pattern(pat: &Pat<'_>) -> bool {
         pats.iter().all(unary_pattern)
     }
     match &pat.kind {
+        PatKind::Missing => unreachable!(),
         PatKind::Slice(_, _, _)
         | PatKind::Range(_, _, _)
         | PatKind::Binding(..)
diff --git a/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs b/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs
index 250f17fa902..a21597ffb93 100644
--- a/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/match_same_arms.rs
@@ -253,6 +253,7 @@ fn iter_matching_struct_fields<'a>(
 impl<'a> NormalizedPat<'a> {
     fn from_pat(cx: &LateContext<'_>, arena: &'a DroplessArena, pat: &'a Pat<'_>) -> Self {
         match pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild | PatKind::Binding(.., None) => Self::Wild,
             PatKind::Binding(.., Some(pat))
             | PatKind::Box(pat)
diff --git a/src/tools/clippy/clippy_lints/src/matches/single_match.rs b/src/tools/clippy/clippy_lints/src/matches/single_match.rs
index 56fbd626eef..836c46240ce 100644
--- a/src/tools/clippy/clippy_lints/src/matches/single_match.rs
+++ b/src/tools/clippy/clippy_lints/src/matches/single_match.rs
@@ -406,6 +406,7 @@ impl<'a> PatState<'a> {
                 pats.iter().map(|p| p.pat),
             ),
 
+            PatKind::Missing => unreachable!(),
             PatKind::Wild
             | PatKind::Binding(_, _, _, None)
             | PatKind::Expr(_)
diff --git a/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs b/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
index f43715d6752..8966e6851ac 100644
--- a/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
+++ b/src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs
@@ -224,6 +224,7 @@ fn transform_with_focus_on_idx(alternatives: &mut ThinVec<P<Pat>>, focus_idx: us
 
     // We're trying to find whatever kind (~"constructor") we found in `alternatives[start..]`.
     let changed = match &mut focus_kind {
+        Missing => unreachable!(),
         // These pattern forms are "leafs" and do not have sub-patterns.
         // Therefore they are not some form of constructor `C`,
         // with which a pattern `C(p_0)` may be formed,
diff --git a/src/tools/clippy/clippy_lints/src/utils/author.rs b/src/tools/clippy/clippy_lints/src/utils/author.rs
index 4309cd2c9ab..b7dcd2ffb0e 100644
--- a/src/tools/clippy/clippy_lints/src/utils/author.rs
+++ b/src/tools/clippy/clippy_lints/src/utils/author.rs
@@ -676,6 +676,7 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
         }
 
         match pat.value.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Wild => kind!("Wild"),
             PatKind::Never => kind!("Never"),
             PatKind::Binding(ann, _, name, sub) => {
diff --git a/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs b/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
index eba576392eb..c5dce26143b 100644
--- a/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
+++ b/src/tools/clippy/clippy_utils/src/ast_utils/mod.rs
@@ -33,6 +33,7 @@ pub fn eq_id(l: Ident, r: Ident) -> bool {
 pub fn eq_pat(l: &Pat, r: &Pat) -> bool {
     use PatKind::*;
     match (&l.kind, &r.kind) {
+        (Missing, _) | (_, Missing) => unreachable!(),
         (Paren(l), _) => eq_pat(l, r),
         (_, Paren(r)) => eq_pat(l, r),
         (Wild, Wild) | (Rest, Rest) => true,
diff --git a/src/tools/clippy/clippy_utils/src/hir_utils.rs b/src/tools/clippy/clippy_utils/src/hir_utils.rs
index 9938e64d242..b813cd361ed 100644
--- a/src/tools/clippy/clippy_utils/src/hir_utils.rs
+++ b/src/tools/clippy/clippy_utils/src/hir_utils.rs
@@ -1124,6 +1124,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
     pub fn hash_pat(&mut self, pat: &Pat<'_>) {
         std::mem::discriminant(&pat.kind).hash(&mut self.s);
         match pat.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Binding(BindingMode(by_ref, mutability), _, _, pat) => {
                 std::mem::discriminant(&by_ref).hash(&mut self.s);
                 std::mem::discriminant(&mutability).hash(&mut self.s);
diff --git a/src/tools/clippy/clippy_utils/src/lib.rs b/src/tools/clippy/clippy_utils/src/lib.rs
index 6d2c2a2d692..bcb0f8349e2 100644
--- a/src/tools/clippy/clippy_utils/src/lib.rs
+++ b/src/tools/clippy/clippy_utils/src/lib.rs
@@ -1858,6 +1858,7 @@ pub fn is_refutable(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
     }
 
     match pat.kind {
+        PatKind::Missing => unreachable!(),
         PatKind::Wild | PatKind::Never => false, // If `!` typechecked then the type is empty, so not refutable.
         PatKind::Binding(_, _, _, pat) => pat.is_some_and(|pat| is_refutable(cx, pat)),
         PatKind::Box(pat) | PatKind::Ref(pat, _) => is_refutable(cx, pat),
diff --git a/src/tools/rustfmt/src/items.rs b/src/tools/rustfmt/src/items.rs
index 322af97d9dc..5c3be769f9e 100644
--- a/src/tools/rustfmt/src/items.rs
+++ b/src/tools/rustfmt/src/items.rs
@@ -2442,11 +2442,7 @@ pub(crate) fn span_hi_for_param(context: &RewriteContext<'_>, param: &ast::Param
 }
 
 pub(crate) fn is_named_param(param: &ast::Param) -> bool {
-    if let ast::PatKind::Ident(_, ident, _) = param.pat.kind {
-        ident.name != symbol::kw::Empty
-    } else {
-        true
-    }
+    !matches!(param.pat.kind, ast::PatKind::Missing)
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
diff --git a/src/tools/rustfmt/src/patterns.rs b/src/tools/rustfmt/src/patterns.rs
index 8dc94574503..cb3879f4be8 100644
--- a/src/tools/rustfmt/src/patterns.rs
+++ b/src/tools/rustfmt/src/patterns.rs
@@ -42,6 +42,7 @@ pub(crate) fn is_short_pattern(
 
 fn is_short_pattern_inner(context: &RewriteContext<'_>, pat: &ast::Pat) -> bool {
     match &pat.kind {
+        ast::PatKind::Missing => unreachable!(),
         ast::PatKind::Rest | ast::PatKind::Never | ast::PatKind::Wild | ast::PatKind::Err(_) => {
             true
         }
@@ -100,6 +101,7 @@ impl Rewrite for Pat {
 
     fn rewrite_result(&self, context: &RewriteContext<'_>, shape: Shape) -> RewriteResult {
         match self.kind {
+            PatKind::Missing => unreachable!(),
             PatKind::Or(ref pats) => {
                 let pat_strs = pats
                     .iter()