3 files changed, 51 insertions, 3 deletions
diff --git a/crates/ra_hir_ty/src/_match.rs b/crates/ra_hir_ty/src/_match.rs
index a64be9848..688026a04 100644
--- a/crates/ra_hir_ty/src/_match.rs
+++ b/crates/ra_hir_ty/src/_match.rs
@@ -194,9 +194,10 @@ use smallvec::{smallvec, SmallVec};
 use crate::{
    db::HirDatabase,
    expr::{Body, Expr, Literal, Pat, PatId},
-    InferenceResult,
+    ApplicationTy, InferenceResult, Ty, TypeCtor,
 };
-use hir_def::{adt::VariantData, EnumVariantId, VariantId};
+use hir_def::{adt::VariantData, AdtId, EnumVariantId, VariantId};
+use ra_arena::Idx;
 #[derive(Debug, Clone, Copy)]
 /// Either a pattern from the source code being analyzed, represented as
@@ -512,6 +513,7 @@ pub enum Usefulness {
 }
 pub struct MatchCheckCtx<'a> {
+    pub match_expr: Idx<Expr>,
    pub body: Arc<Body>,
    pub infer: Arc<InferenceResult>,
    pub db: &'a dyn HirDatabase,
@@ -530,6 +532,16 @@ pub(crate) fn is_useful(
    matrix: &Matrix,
    v: &PatStack,
 ) -> MatchCheckResult<Usefulness> {
+    // Handle the special case of enums with no variants. In that case, no match
+    // arm is useful.
+    if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) =
+        cx.infer[cx.match_expr].strip_references()
+    {
+        if cx.db.enum_data(*enum_id).variants.is_empty() {
+            return Ok(Usefulness::NotUseful);
+        }
+    }
    if v.is_empty() {
        let result = if matrix.is_empty() { Usefulness::Useful } else { Usefulness::NotUseful };
@@ -1618,6 +1630,32 @@ mod tests {
        check_no_diagnostic(content);
    }
+    #[test]
+    fn enum_never() {
+        let content = r"
+            enum Never {}
+            fn test_fn(never: Never) {
+                match never {}
+            }
+        ";
+        check_no_diagnostic(content);
+    }
+    #[test]
+    fn enum_never_ref() {
+        let content = r"
+            enum Never {}
+            fn test_fn(never: &Never) {
+                match never {}
+            }
+        ";
+        check_no_diagnostic(content);
+    }
 }
 #[cfg(test)]
diff --git a/crates/ra_hir_ty/src/expr.rs b/crates/ra_hir_ty/src/expr.rs
index 21abbcf1e..fd59f4320 100644
--- a/crates/ra_hir_ty/src/expr.rs
+++ b/crates/ra_hir_ty/src/expr.rs
@@ -156,7 +156,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
            None => return,
        };
-        let cx = MatchCheckCtx { body, infer: infer.clone(), db };
+        let cx = MatchCheckCtx { match_expr, body, infer: infer.clone(), db };
        let pats = arms.iter().map(|arm| arm.pat);
        let mut seen = Matrix::empty();
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 18f74d3b1..2677f3af2 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -680,6 +680,16 @@ impl Ty {
        }
    }
+    pub fn strip_references(&self) -> &Ty {
+        let mut t: &Ty = self;
+        while let Ty::Apply(ApplicationTy { ctor: TypeCtor::Ref(_mutability), parameters }) = t {
+            t = parameters.as_single();
+        }
+        t
+    }
    pub fn as_adt(&self) -> Option<(AdtId, &Substs)> {
        match self {
            Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(adt_def), parameters }) => {

diff --git a/crates/ra_hir_ty/src/_match.rs b/crates/ra_hir_ty/src/_match.rs index a64be9848..688026a04 100644 --- a/crates/ra_hir_ty/src/_match.rs +++ b/crates/ra_hir_ty/src/_match.rs
@@ -194,9 +194,10 @@ use smallvec::{smallvec, SmallVec};
194	use crate::{	194	use crate::{
195	db::HirDatabase,	195	db::HirDatabase,
196	expr::{Body, Expr, Literal, Pat, PatId},	196	expr::{Body, Expr, Literal, Pat, PatId},
197	InferenceResult,	197	ApplicationTy, InferenceResult, Ty, TypeCtor,
198	};	198	};
199	use hir_def::{adt::VariantData, EnumVariantId, VariantId};	199	use hir_def::{adt::VariantData, AdtId, EnumVariantId, VariantId};
		200	use ra_arena::Idx;
200		201
201	#[derive(Debug, Clone, Copy)]	202	#[derive(Debug, Clone, Copy)]
202	/// Either a pattern from the source code being analyzed, represented as	203	/// Either a pattern from the source code being analyzed, represented as
@@ -512,6 +513,7 @@ pub enum Usefulness {
512	}	513	}
513		514
514	pub struct MatchCheckCtx<'a> {	515	pub struct MatchCheckCtx<'a> {
		516	pub match_expr: Idx<Expr>,
515	pub body: Arc<Body>,	517	pub body: Arc<Body>,
516	pub infer: Arc<InferenceResult>,	518	pub infer: Arc<InferenceResult>,
517	pub db: &'a dyn HirDatabase,	519	pub db: &'a dyn HirDatabase,
@@ -530,6 +532,16 @@ pub(crate) fn is_useful(
530	matrix: &Matrix,	532	matrix: &Matrix,
531	v: &PatStack,	533	v: &PatStack,
532	) -> MatchCheckResult<Usefulness> {	534	) -> MatchCheckResult<Usefulness> {
		535	// Handle the special case of enums with no variants. In that case, no match
		536	// arm is useful.
		537	if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) =
		538	cx.infer[cx.match_expr].strip_references()
		539	{
		540	if cx.db.enum_data(*enum_id).variants.is_empty() {
		541	return Ok(Usefulness::NotUseful);
		542	}
		543	}
		544
533	if v.is_empty() {	545	if v.is_empty() {
534	let result = if matrix.is_empty() { Usefulness::Useful } else { Usefulness::NotUseful };	546	let result = if matrix.is_empty() { Usefulness::Useful } else { Usefulness::NotUseful };
535		547
@@ -1618,6 +1630,32 @@ mod tests {
1618		1630
1619	check_no_diagnostic(content);	1631	check_no_diagnostic(content);
1620	}	1632	}
		1633
		1634	#[test]
		1635	fn enum_never() {
		1636	let content = r"
		1637	enum Never {}
		1638
		1639	fn test_fn(never: Never) {
		1640	match never {}
		1641	}
		1642	";
		1643
		1644	check_no_diagnostic(content);
		1645	}
		1646
		1647	#[test]
		1648	fn enum_never_ref() {
		1649	let content = r"
		1650	enum Never {}
		1651
		1652	fn test_fn(never: &Never) {
		1653	match never {}
		1654	}
		1655	";
		1656
		1657	check_no_diagnostic(content);
		1658	}
1621	}	1659	}
1622		1660
1623	#[cfg(test)]	1661	#[cfg(test)]


diff --git a/crates/ra_hir_ty/src/expr.rs b/crates/ra_hir_ty/src/expr.rs index 21abbcf1e..fd59f4320 100644 --- a/crates/ra_hir_ty/src/expr.rs +++ b/crates/ra_hir_ty/src/expr.rs
@@ -156,7 +156,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
156	None => return,	156	None => return,
157	};	157	};
158		158
159	let cx = MatchCheckCtx { body, infer: infer.clone(), db };	159	let cx = MatchCheckCtx { match_expr, body, infer: infer.clone(), db };
160	let pats = arms.iter().map(\|arm\| arm.pat);	160	let pats = arms.iter().map(\|arm\| arm.pat);
161		161
162	let mut seen = Matrix::empty();	162	let mut seen = Matrix::empty();


diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs index 18f74d3b1..2677f3af2 100644 --- a/crates/ra_hir_ty/src/lib.rs +++ b/crates/ra_hir_ty/src/lib.rs
@@ -680,6 +680,16 @@ impl Ty {
680	}	680	}
681	}	681	}
682		682
		683	pub fn strip_references(&self) -> &Ty {
		684	let mut t: &Ty = self;
		685
		686	while let Ty::Apply(ApplicationTy { ctor: TypeCtor::Ref(_mutability), parameters }) = t {
		687	t = parameters.as_single();
		688	}
		689
		690	t
		691	}
		692
683	pub fn as_adt(&self) -> Option<(AdtId, &Substs)> {	693	pub fn as_adt(&self) -> Option<(AdtId, &Substs)> {
684	match self {	694	match self {
685	Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(adt_def), parameters }) => {	695	Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(adt_def), parameters }) => {