diff --git a/crates/ra_hir/src/marks.rs b/crates/ra_hir/src/marks.rs
index bbf57004d5b..5b640004288 100644
--- a/crates/ra_hir/src/marks.rs
+++ b/crates/ra_hir/src/marks.rs
@@ -8,4 +8,5 @@ test_utils::marks!(
glob_enum
glob_across_crates
std_prelude
+ match_ergonomics_ref
);
diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index c9a5bc7a100..735cdecb910 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -63,6 +63,30 @@ enum ExprOrPatId {
impl_froms!(ExprOrPatId: ExprId, PatId);
+/// Binding modes inferred for patterns.
+/// https://doc.rust-lang.org/reference/patterns.html#binding-modes
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+enum BindingMode {
+ Move,
+ Ref(Mutability),
+}
+
+impl BindingMode {
+ pub fn convert(annotation: &BindingAnnotation) -> BindingMode {
+ match annotation {
+ BindingAnnotation::Unannotated | BindingAnnotation::Mutable => BindingMode::Move,
+ BindingAnnotation::Ref => BindingMode::Ref(Mutability::Shared),
+ BindingAnnotation::RefMut => BindingMode::Ref(Mutability::Mut),
+ }
+ }
+}
+
+impl Default for BindingMode {
+ fn default() -> Self {
+ BindingMode::Move
+ }
+}
+
/// The result of type inference: A mapping from expressions and patterns to types.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct InferenceResult {
@@ -530,6 +554,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
path: Option<&Path>,
subpats: &[PatId],
expected: &Ty,
+ default_bm: BindingMode,
) -> Ty {
let (ty, def) = self.resolve_variant(path);
@@ -542,13 +567,19 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
.and_then(|d| d.field(self.db, &Name::tuple_field_name(i)))
.map_or(Ty::Unknown, |field| field.ty(self.db))
.subst(&substs);
- self.infer_pat(subpat, &expected_ty);
+ self.infer_pat(subpat, &expected_ty, default_bm);
}
ty
}
- fn infer_struct_pat(&mut self, path: Option<&Path>, subpats: &[FieldPat], expected: &Ty) -> Ty {
+ fn infer_struct_pat(
+ &mut self,
+ path: Option<&Path>,
+ subpats: &[FieldPat],
+ expected: &Ty,
+ default_bm: BindingMode,
+ ) -> Ty {
let (ty, def) = self.resolve_variant(path);
self.unify(&ty, expected);
@@ -559,15 +590,45 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
let matching_field = def.and_then(|it| it.field(self.db, &subpat.name));
let expected_ty =
matching_field.map_or(Ty::Unknown, |field| field.ty(self.db)).subst(&substs);
- self.infer_pat(subpat.pat, &expected_ty);
+ self.infer_pat(subpat.pat, &expected_ty, default_bm);
}
ty
}
- fn infer_pat(&mut self, pat: PatId, expected: &Ty) -> Ty {
+ fn infer_pat(&mut self, pat: PatId, mut expected: &Ty, mut default_bm: BindingMode) -> Ty {
let body = Arc::clone(&self.body); // avoid borrow checker problem
+ let is_non_ref_pat = match &body[pat] {
+ Pat::Tuple(..)
+ | Pat::TupleStruct { .. }
+ | Pat::Struct { .. }
+ | Pat::Range { .. }
+ | Pat::Slice { .. } => true,
+ // TODO: Path/Lit might actually evaluate to ref, but inference is unimplemented.
+ Pat::Path(..) | Pat::Lit(..) => true,
+ Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Missing => false,
+ };
+ if is_non_ref_pat {
+ while let Ty::Ref(inner, mutability) = expected {
+ expected = inner;
+ default_bm = match default_bm {
+ BindingMode::Move => BindingMode::Ref(*mutability),
+ BindingMode::Ref(Mutability::Shared) => BindingMode::Ref(Mutability::Shared),
+ BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(*mutability),
+ }
+ }
+ } else if let Pat::Ref { .. } = &body[pat] {
+ tested_by!(match_ergonomics_ref);
+ // When you encounter a `&pat` pattern, reset to Move.
+ // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
+ default_bm = BindingMode::Move;
+ }
+
+ // Lose mutability.
+ let default_bm = default_bm;
+ let expected = expected;
+
let ty = match &body[pat] {
Pat::Tuple(ref args) => {
let expectations = match *expected {
@@ -579,7 +640,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
let inner_tys = args
.iter()
.zip(expectations_iter)
- .map(|(&pat, ty)| self.infer_pat(pat, ty))
+ .map(|(&pat, ty)| self.infer_pat(pat, ty, default_bm))
.collect::<Vec<_>>()
.into();
@@ -595,14 +656,14 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
}
_ => &Ty::Unknown,
};
- let subty = self.infer_pat(*pat, expectation);
+ let subty = self.infer_pat(*pat, expectation, default_bm);
Ty::Ref(subty.into(), *mutability)
}
Pat::TupleStruct { path: ref p, args: ref subpats } => {
- self.infer_tuple_struct_pat(p.as_ref(), subpats, expected)
+ self.infer_tuple_struct_pat(p.as_ref(), subpats, expected, default_bm)
}
Pat::Struct { path: ref p, args: ref fields } => {
- self.infer_struct_pat(p.as_ref(), fields, expected)
+ self.infer_struct_pat(p.as_ref(), fields, expected, default_bm)
}
Pat::Path(path) => {
// TODO use correct resolver for the surrounding expression
@@ -610,17 +671,21 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
self.infer_path_expr(&resolver, &path, pat.into()).unwrap_or(Ty::Unknown)
}
Pat::Bind { mode, name: _name, subpat } => {
+ let mode = if mode == &BindingAnnotation::Unannotated {
+ default_bm
+ } else {
+ BindingMode::convert(mode)
+ };
let inner_ty = if let Some(subpat) = subpat {
- self.infer_pat(*subpat, expected)
+ self.infer_pat(*subpat, expected, default_bm)
} else {
expected.clone()
};
let inner_ty = self.insert_type_vars_shallow(inner_ty);
let bound_ty = match mode {
- BindingAnnotation::Ref => Ty::Ref(inner_ty.clone().into(), Mutability::Shared),
- BindingAnnotation::RefMut => Ty::Ref(inner_ty.clone().into(), Mutability::Mut),
- BindingAnnotation::Mutable | BindingAnnotation::Unannotated => inner_ty.clone(),
+ BindingMode::Ref(mutability) => Ty::Ref(inner_ty.clone().into(), mutability),
+ BindingMode::Move => inner_ty.clone(),
};
let bound_ty = self.resolve_ty_as_possible(&mut vec![], bound_ty);
self.write_pat_ty(pat, bound_ty);
@@ -700,7 +765,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
}
Expr::For { iterable, body, pat } => {
let _iterable_ty = self.infer_expr(*iterable, &Expectation::none());
- self.infer_pat(*pat, &Ty::Unknown);
+ self.infer_pat(*pat, &Ty::Unknown, BindingMode::default());
self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
Ty::unit()
}
@@ -714,7 +779,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
} else {
Ty::Unknown
};
- self.infer_pat(*arg_pat, &expected);
+ self.infer_pat(*arg_pat, &expected, BindingMode::default());
}
// TODO: infer lambda type etc.
@@ -807,7 +872,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
for arm in arms {
for &pat in &arm.pats {
- let _pat_ty = self.infer_pat(pat, &input_ty);
+ let _pat_ty = self.infer_pat(pat, &input_ty, BindingMode::default());
}
if let Some(guard_expr) = arm.guard {
self.infer_expr(guard_expr, &Expectation::has_type(Ty::Bool));
@@ -1007,7 +1072,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
decl_ty
};
- self.infer_pat(*pat, &ty);
+ self.infer_pat(*pat, &ty, BindingMode::default());
}
Statement::Expr(expr) => {
self.infer_expr(*expr, &Expectation::none());
@@ -1023,7 +1088,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
for (type_ref, pat) in signature.params().iter().zip(body.params()) {
let ty = self.make_ty(type_ref);
- self.infer_pat(*pat, &ty);
+ self.infer_pat(*pat, &ty, BindingMode::default());
}
self.return_ty = self.make_ty(signature.ret_type());
}
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index acae71c266d..0f2172ddfc7 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -830,6 +830,60 @@ fn test(x: &i32) {
);
}
+#[test]
+fn infer_pattern_match_ergonomics() {
+ assert_snapshot_matches!(
+ infer(r#"
+struct A<T>(T);
+
+fn test() {
+ let A(n) = &A(1);
+ let A(n) = &mut A(1);
+}
+"#),
+ @r###"
+[28; 79) '{ ...(1); }': ()
+[38; 42) 'A(n)': A<i32>
+[40; 41) 'n': &i32
+[45; 50) '&A(1)': &A<i32>
+[46; 47) 'A': A<i32>(T) -> A<T>
+[46; 50) 'A(1)': A<i32>
+[48; 49) '1': i32
+[60; 64) 'A(n)': A<i32>
+[62; 63) 'n': &mut i32
+[67; 76) '&mut A(1)': &mut A<i32>
+[72; 73) 'A': A<i32>(T) -> A<T>
+[72; 76) 'A(1)': A<i32>
+[74; 75) '1': i32"###
+ );
+}
+
+#[test]
+fn infer_pattern_match_ergonomics_ref() {
+ covers!(match_ergonomics_ref);
+ assert_snapshot_matches!(
+ infer(r#"
+fn test() {
+ let v = &(1, &2);
+ let (_, &w) = v;
+}
+"#),
+ @r###"
+[11; 57) '{ ...= v; }': ()
+[21; 22) 'v': &(i32, &i32)
+[25; 33) '&(1, &2)': &(i32, &i32)
+[26; 33) '(1, &2)': (i32, &i32)
+[27; 28) '1': i32
+[30; 32) '&2': &i32
+[31; 32) '2': i32
+[43; 50) '(_, &w)': (i32, &i32)
+[44; 45) '_': i32
+[47; 49) '&w': &i32
+[48; 49) 'w': i32
+[53; 54) 'v': &(i32, &i32)"###
+ );
+}
+
#[test]
fn infer_adt_pattern() {
assert_snapshot_matches!(