1 files changed, 157 insertions, 0 deletions
diff --git a/compiler/rustc_hir/src/pat_util.rs b/compiler/rustc_hir/src/pat_util.rs
new file mode 100644
index 000000000..93112199b
--- /dev/null
+++ b/compiler/rustc_hir/src/pat_util.rs
@@ -0,0 +1,157 @@
+use crate::def::{CtorOf, DefKind, Res};
+use crate::def_id::DefId;
+use crate::hir::{self, HirId, PatKind};
+use rustc_data_structures::fx::FxHashSet;
+use rustc_span::hygiene::DesugaringKind;
+use rustc_span::symbol::Ident;
+use rustc_span::Span;
+
+use std::iter::{Enumerate, ExactSizeIterator};
+
+pub struct EnumerateAndAdjust<I> {
+    enumerate: Enumerate<I>,
+    gap_pos: usize,
+    gap_len: usize,
+}
+
+impl<I> Iterator for EnumerateAndAdjust<I>
+where
+    I: Iterator,
+{
+    type Item = (usize, <I as Iterator>::Item);
+
+    fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
+        self.enumerate
+            .next()
+            .map(|(i, elem)| (if i < self.gap_pos { i } else { i + self.gap_len }, elem))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.enumerate.size_hint()
+    }
+}
+
+pub trait EnumerateAndAdjustIterator {
+    fn enumerate_and_adjust(
+        self,
+        expected_len: usize,
+        gap_pos: Option<usize>,
+    ) -> EnumerateAndAdjust<Self>
+    where
+        Self: Sized;
+}
+
+impl<T: ExactSizeIterator> EnumerateAndAdjustIterator for T {
+    fn enumerate_and_adjust(
+        self,
+        expected_len: usize,
+        gap_pos: Option<usize>,
+    ) -> EnumerateAndAdjust<Self>
+    where
+        Self: Sized,
+    {
+        let actual_len = self.len();
+        EnumerateAndAdjust {
+            enumerate: self.enumerate(),
+            gap_pos: gap_pos.unwrap_or(expected_len),
+            gap_len: expected_len - actual_len,
+        }
+    }
+}
+
+impl hir::Pat<'_> {
+    /// Call `f` on every "binding" in a pattern, e.g., on `a` in
+    /// `match foo() { Some(a) => (), None => () }`
+    pub fn each_binding(&self, mut f: impl FnMut(hir::BindingAnnotation, HirId, Span, Ident)) {
+        self.walk_always(|p| {
+            if let PatKind::Binding(binding_mode, _, ident, _) = p.kind {
+                f(binding_mode, p.hir_id, p.span, ident);
+            }
+        });
+    }
+
+    /// Call `f` on every "binding" in a pattern, e.g., on `a` in
+    /// `match foo() { Some(a) => (), None => () }`.
+    ///
+    /// When encountering an or-pattern `p_0 | ... | p_n` only `p_0` will be visited.
+    pub fn each_binding_or_first(
+        &self,
+        f: &mut impl FnMut(hir::BindingAnnotation, HirId, Span, Ident),
+    ) {
+        self.walk(|p| match &p.kind {
+            PatKind::Or(ps) => {
+                ps[0].each_binding_or_first(f);
+                false
+            }
+            PatKind::Binding(bm, _, ident, _) => {
+                f(*bm, p.hir_id, p.span, *ident);
+                true
+            }
+            _ => true,
+        })
+    }
+
+    pub fn simple_ident(&self) -> Option<Ident> {
+        match self.kind {
+            PatKind::Binding(
+                hir::BindingAnnotation::Unannotated | hir::BindingAnnotation::Mutable,
+                _,
+                ident,
+                None,
+            ) => Some(ident),
+            _ => None,
+        }
+    }
+
+    /// Returns variants that are necessary to exist for the pattern to match.
+    pub fn necessary_variants(&self) -> Vec<DefId> {
+        let mut variants = vec![];
+        self.walk(|p| match &p.kind {
+            PatKind::Or(_) => false,
+            PatKind::Path(hir::QPath::Resolved(_, path))
+            | PatKind::TupleStruct(hir::QPath::Resolved(_, path), ..)
+            | PatKind::Struct(hir::QPath::Resolved(_, path), ..) => {
+                if let Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Variant, ..), id) =
+                    path.res
+                {
+                    variants.push(id);
+                }
+                true
+            }
+            _ => true,
+        });
+        // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
+        // the bounds
+        let mut duplicates = FxHashSet::default();
+        variants.retain(|def_id| duplicates.insert(*def_id));
+        variants
+    }
+
+    /// Checks if the pattern contains any `ref` or `ref mut` bindings, and if
+    /// yes whether it contains mutable or just immutables ones.
+    //
+    // FIXME(tschottdorf): this is problematic as the HIR is being scraped, but
+    // ref bindings are be implicit after #42640 (default match binding modes). See issue #44848.
+    pub fn contains_explicit_ref_binding(&self) -> Option<hir::Mutability> {
+        let mut result = None;
+        self.each_binding(|annotation, _, _, _| match annotation {
+            hir::BindingAnnotation::Ref => match result {
+                None | Some(hir::Mutability::Not) => result = Some(hir::Mutability::Not),
+                _ => {}
+            },
+            hir::BindingAnnotation::RefMut => result = Some(hir::Mutability::Mut),
+            _ => {}
+        });
+        result
+    }
+
+    /// If the pattern is `Some(<pat>)` from a desugared for loop, returns the inner pattern
+    pub fn for_loop_some(&self) -> Option<&Self> {
+        if self.span.desugaring_kind() == Some(DesugaringKind::ForLoop) {
+            if let hir::PatKind::Struct(_, [pat_field], _) = self.kind {
+                return Some(pat_field.pat);
+            }
+        }
+        None
+    }
+}