3 files changed, 24 insertions, 24 deletions
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 4d17e8c9a..88018b5d9 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -373,12 +373,12 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
        let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =
            db.body_with_source_map(self.owner);
-        let match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {
+        let _match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {
            return;
        } else {
            &infer.type_of_expr[match_expr]
        };
-        // eprintln!("ExprValidator::validate_match2({:?})", match_expr_ty.kind(&Interner));
+        // eprintln!("ExprValidator::validate_match2({:?})", _match_expr_ty.kind(&Interner));
        let pattern_arena = usefulness::PatternArena::clone_from(&body.pats);
        let cx = usefulness::MatchCheckCtx {
diff --git a/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs b/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs
index 2f3555205..d41b95d2f 100644
--- a/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs
+++ b/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs
@@ -143,7 +143,7 @@ impl Constructor {
    /// matrix, unless all of them are.
    pub(super) fn split<'a>(
        &self,
-        pcx: &PatCtxt<'_>,
+        pcx: PatCtxt<'_>,
        ctors: impl Iterator<Item = &'a Constructor> + Clone,
    ) -> SmallVec<[Self; 1]> {
        match self {
@@ -166,7 +166,7 @@ impl Constructor {
    /// this checks for inclusion.
    // We inline because this has a single call site in `Matrix::specialize_constructor`.
    #[inline]
-    pub(super) fn is_covered_by(&self, pcx: &PatCtxt<'_>, other: &Self) -> bool {
+    pub(super) fn is_covered_by(&self, pcx: PatCtxt<'_>, other: &Self) -> bool {
        // This must be kept in sync with `is_covered_by_any`.
        match (self, other) {
            // Wildcards cover anything
@@ -188,7 +188,7 @@ impl Constructor {
    /// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
    /// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
    /// assumed to have been split from a wildcard.
-    fn is_covered_by_any(&self, pcx: &PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
+    fn is_covered_by_any(&self, pcx: PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
        if used_ctors.is_empty() {
            return false;
        }
@@ -236,7 +236,7 @@ pub(super) struct SplitWildcard {
 }
 impl SplitWildcard {
-    pub(super) fn new(pcx: &PatCtxt<'_>) -> Self {
+    pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
        // let cx = pcx.cx;
        // let make_range = |start, end| IntRange(todo!());
@@ -260,7 +260,7 @@ impl SplitWildcard {
    /// do what you want.
    pub(super) fn split<'a>(
        &mut self,
-        pcx: &PatCtxt<'_>,
+        pcx: PatCtxt<'_>,
        ctors: impl Iterator<Item = &'a Constructor> + Clone,
    ) {
        // Since `all_ctors` never contains wildcards, this won't recurse further.
@@ -270,21 +270,21 @@ impl SplitWildcard {
    }
    /// Whether there are any value constructors for this type that are not present in the matrix.
-    fn any_missing(&self, pcx: &PatCtxt<'_>) -> bool {
+    fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
        self.iter_missing(pcx).next().is_some()
    }
    /// Iterate over the constructors for this type that are not present in the matrix.
    pub(super) fn iter_missing<'a>(
        &'a self,
-        pcx: &'a PatCtxt<'_>,
+        pcx: PatCtxt<'a>,
    ) -> impl Iterator<Item = &'a Constructor> {
        self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
    }
    /// Return the set of constructors resulting from splitting the wildcard. As explained at the
    /// top of the file, if any constructors are missing we can ignore the present ones.
-    fn into_ctors(self, pcx: &PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
+    fn into_ctors(self, pcx: PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
        if self.any_missing(pcx) {
            // Some constructors are missing, thus we can specialize with the special `Missing`
            // constructor, which stands for those constructors that are not seen in the matrix,
@@ -313,7 +313,7 @@ impl SplitWildcard {
            //
            // The exception is: if we are at the top-level, for example in an empty match, we
            // sometimes prefer reporting the list of constructors instead of just `_`.
-            let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(&pcx.ty);
+            let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
            let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
                Missing
            } else {
@@ -381,8 +381,8 @@ impl Fields {
        Fields::Vec(pats)
    }
-    pub(crate) fn wildcards(pcx: &PatCtxt<'_>, constructor: &Constructor) -> Self {
+    pub(crate) fn wildcards(pcx: PatCtxt<'_>, constructor: &Constructor) -> Self {
-        let ty = &pcx.ty;
+        let ty = pcx.ty;
        let cx = pcx.cx;
        let wildcard_from_ty = |ty| cx.alloc_pat(Pat::Wild, ty);
@@ -446,7 +446,7 @@ impl Fields {
    /// `ty`: `Option<bool>`
    /// `self`: `[false]`
    /// returns `Some(false)`
-    pub(super) fn apply(self, pcx: &PatCtxt<'_>, ctor: &Constructor) -> Pat {
+    pub(super) fn apply(self, pcx: PatCtxt<'_>, ctor: &Constructor) -> Pat {
        let subpatterns_and_indices = self.patterns_and_indices();
        let mut subpatterns = subpatterns_and_indices.iter().map(|&(_, p)| p);
diff --git a/crates/hir_ty/src/diagnostics/pattern/usefulness.rs b/crates/hir_ty/src/diagnostics/pattern/usefulness.rs
index 89e6c6593..7d9ab849b 100644
--- a/crates/hir_ty/src/diagnostics/pattern/usefulness.rs
+++ b/crates/hir_ty/src/diagnostics/pattern/usefulness.rs
@@ -51,11 +51,11 @@ impl<'a> MatchCheckCtx<'a> {
    }
 }
-#[derive(Clone)]
+#[derive(Copy, Clone)]
 pub(super) struct PatCtxt<'a> {
    pub(super) cx: &'a MatchCheckCtx<'a>,
    /// Type of the current column under investigation.
-    pub(super) ty: Ty,
+    pub(super) ty: &'a Ty,
    /// Whether the current pattern is the whole pattern as found in a match arm, or if it's a
    /// subpattern.
    pub(super) is_top_level: bool,
@@ -223,7 +223,7 @@ impl Matrix {
    /// This computes `S(constructor, self)`. See top of the file for explanations.
    fn specialize_constructor(
        &self,
-        pcx: &PatCtxt<'_>,
+        pcx: PatCtxt<'_>,
        ctor: &Constructor,
        ctor_wild_subpatterns: &Fields,
    ) -> Matrix {
@@ -447,7 +447,7 @@ impl Usefulness {
    /// with the results of specializing with the other constructors.
    fn apply_constructor(
        self,
-        pcx: &PatCtxt<'_>,
+        pcx: PatCtxt<'_>,
        matrix: &Matrix,
        ctor: &Constructor,
        ctor_wild_subpatterns: &Fields,
@@ -555,7 +555,7 @@ impl Witness {
    /// pats: [(false, "foo"), 42]  => X { a: (false, "foo"), b: 42 }
    fn apply_constructor(
        mut self,
-        pcx: &PatCtxt<'_>,
+        pcx: PatCtxt<'_>,
        ctor: &Constructor,
        ctor_wild_subpatterns: &Fields,
    ) -> Self {
@@ -623,7 +623,7 @@ fn is_useful(
    // FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476).
    // TODO(iDawer): ty.strip_references()  ?
    let ty = matrix.heads().next().map_or(cx.type_of(v.head()), |r| cx.type_of(r));
-    let pcx = PatCtxt { cx, ty, is_top_level };
+    let pcx = PatCtxt { cx, ty: &ty, is_top_level };
    // If the first pattern is an or-pattern, expand it.
    let ret = if v.head().is_or_pat(cx) {
@@ -657,20 +657,20 @@ fn is_useful(
        // }
        // We split the head constructor of `v`.
-        let split_ctors = v_ctor.split(&pcx, matrix.head_ctors(cx));
+        let split_ctors = v_ctor.split(pcx, matrix.head_ctors(cx));
        // For each constructor, we compute whether there's a value that starts with it that would
        // witness the usefulness of `v`.
        let start_matrix = matrix;
        let usefulnesses = split_ctors.into_iter().map(|ctor| {
            // debug!("specialize({:?})", ctor);
            // We cache the result of `Fields::wildcards` because it is used a lot.
-            let ctor_wild_subpatterns = Fields::wildcards(&pcx, &ctor);
+            let ctor_wild_subpatterns = Fields::wildcards(pcx, &ctor);
            let spec_matrix =
-                start_matrix.specialize_constructor(&pcx, &ctor, &ctor_wild_subpatterns);
+                start_matrix.specialize_constructor(pcx, &ctor, &ctor_wild_subpatterns);
            let v = v.pop_head_constructor(&ctor_wild_subpatterns, cx);
            let usefulness =
                is_useful(cx, &spec_matrix, &v, witness_preference, is_under_guard, false);
-            usefulness.apply_constructor(&pcx, start_matrix, &ctor, &ctor_wild_subpatterns)
+            usefulness.apply_constructor(pcx, start_matrix, &ctor, &ctor_wild_subpatterns)
        });
        Usefulness::merge(witness_preference, usefulnesses)
    };

diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs index 4d17e8c9a..88018b5d9 100644 --- a/crates/hir_ty/src/diagnostics/expr.rs +++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -373,12 +373,12 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
373	let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =	373	let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =
374	db.body_with_source_map(self.owner);	374	db.body_with_source_map(self.owner);
375		375
376	let match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {	376	let _match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {
377	return;	377	return;
378	} else {	378	} else {
379	&infer.type_of_expr[match_expr]	379	&infer.type_of_expr[match_expr]
380	};	380	};
381	// eprintln!("ExprValidator::validate_match2({:?})", match_expr_ty.kind(&Interner));	381	// eprintln!("ExprValidator::validate_match2({:?})", _match_expr_ty.kind(&Interner));
382		382
383	let pattern_arena = usefulness::PatternArena::clone_from(&body.pats);	383	let pattern_arena = usefulness::PatternArena::clone_from(&body.pats);
384	let cx = usefulness::MatchCheckCtx {	384	let cx = usefulness::MatchCheckCtx {


diff --git a/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs b/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs index 2f3555205..d41b95d2f 100644 --- a/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs +++ b/crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs
@@ -143,7 +143,7 @@ impl Constructor {
143	/// matrix, unless all of them are.	143	/// matrix, unless all of them are.
144	pub(super) fn split<'a>(	144	pub(super) fn split<'a>(
145	&self,	145	&self,
146	pcx: &PatCtxt<'_>,	146	pcx: PatCtxt<'_>,
147	ctors: impl Iterator<Item = &'a Constructor> + Clone,	147	ctors: impl Iterator<Item = &'a Constructor> + Clone,
148	) -> SmallVec<[Self; 1]> {	148	) -> SmallVec<[Self; 1]> {
149	match self {	149	match self {
@@ -166,7 +166,7 @@ impl Constructor {
166	/// this checks for inclusion.	166	/// this checks for inclusion.
167	// We inline because this has a single call site in `Matrix::specialize_constructor`.	167	// We inline because this has a single call site in `Matrix::specialize_constructor`.
168	#[inline]	168	#[inline]
169	pub(super) fn is_covered_by(&self, pcx: &PatCtxt<'_>, other: &Self) -> bool {	169	pub(super) fn is_covered_by(&self, pcx: PatCtxt<'_>, other: &Self) -> bool {
170	// This must be kept in sync with `is_covered_by_any`.	170	// This must be kept in sync with `is_covered_by_any`.
171	match (self, other) {	171	match (self, other) {
172	// Wildcards cover anything	172	// Wildcards cover anything
@@ -188,7 +188,7 @@ impl Constructor {
188	/// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is	188	/// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
189	/// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is	189	/// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
190	/// assumed to have been split from a wildcard.	190	/// assumed to have been split from a wildcard.
191	fn is_covered_by_any(&self, pcx: &PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {	191	fn is_covered_by_any(&self, pcx: PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
192	if used_ctors.is_empty() {	192	if used_ctors.is_empty() {
193	return false;	193	return false;
194	}	194	}
@@ -236,7 +236,7 @@ pub(super) struct SplitWildcard {
236	}	236	}
237		237
238	impl SplitWildcard {	238	impl SplitWildcard {
239	pub(super) fn new(pcx: &PatCtxt<'_>) -> Self {	239	pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
240	// let cx = pcx.cx;	240	// let cx = pcx.cx;
241	// let make_range = \|start, end\| IntRange(todo!());	241	// let make_range = \|start, end\| IntRange(todo!());
242		242
@@ -260,7 +260,7 @@ impl SplitWildcard {
260	/// do what you want.	260	/// do what you want.
261	pub(super) fn split<'a>(	261	pub(super) fn split<'a>(
262	&mut self,	262	&mut self,
263	pcx: &PatCtxt<'_>,	263	pcx: PatCtxt<'_>,
264	ctors: impl Iterator<Item = &'a Constructor> + Clone,	264	ctors: impl Iterator<Item = &'a Constructor> + Clone,
265	) {	265	) {
266	// Since `all_ctors` never contains wildcards, this won't recurse further.	266	// Since `all_ctors` never contains wildcards, this won't recurse further.
@@ -270,21 +270,21 @@ impl SplitWildcard {
270	}	270	}
271		271
272	/// Whether there are any value constructors for this type that are not present in the matrix.	272	/// Whether there are any value constructors for this type that are not present in the matrix.
273	fn any_missing(&self, pcx: &PatCtxt<'_>) -> bool {	273	fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
274	self.iter_missing(pcx).next().is_some()	274	self.iter_missing(pcx).next().is_some()
275	}	275	}
276		276
277	/// Iterate over the constructors for this type that are not present in the matrix.	277	/// Iterate over the constructors for this type that are not present in the matrix.
278	pub(super) fn iter_missing<'a>(	278	pub(super) fn iter_missing<'a>(
279	&'a self,	279	&'a self,
280	pcx: &'a PatCtxt<'_>,	280	pcx: PatCtxt<'a>,
281	) -> impl Iterator<Item = &'a Constructor> {	281	) -> impl Iterator<Item = &'a Constructor> {
282	self.all_ctors.iter().filter(move \|ctor\| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))	282	self.all_ctors.iter().filter(move \|ctor\| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
283	}	283	}
284		284
285	/// Return the set of constructors resulting from splitting the wildcard. As explained at the	285	/// Return the set of constructors resulting from splitting the wildcard. As explained at the
286	/// top of the file, if any constructors are missing we can ignore the present ones.	286	/// top of the file, if any constructors are missing we can ignore the present ones.
287	fn into_ctors(self, pcx: &PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {	287	fn into_ctors(self, pcx: PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
288	if self.any_missing(pcx) {	288	if self.any_missing(pcx) {
289	// Some constructors are missing, thus we can specialize with the special `Missing`	289	// Some constructors are missing, thus we can specialize with the special `Missing`
290	// constructor, which stands for those constructors that are not seen in the matrix,	290	// constructor, which stands for those constructors that are not seen in the matrix,
@@ -313,7 +313,7 @@ impl SplitWildcard {
313	//	313	//
314	// The exception is: if we are at the top-level, for example in an empty match, we	314	// The exception is: if we are at the top-level, for example in an empty match, we
315	// sometimes prefer reporting the list of constructors instead of just `_`.	315	// sometimes prefer reporting the list of constructors instead of just `_`.
316	let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(&pcx.ty);	316	let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
317	let ctor = if !self.matrix_ctors.is_empty() \|\| report_when_all_missing {	317	let ctor = if !self.matrix_ctors.is_empty() \|\| report_when_all_missing {
318	Missing	318	Missing
319	} else {	319	} else {
@@ -381,8 +381,8 @@ impl Fields {
381	Fields::Vec(pats)	381	Fields::Vec(pats)
382	}	382	}
383		383
384	pub(crate) fn wildcards(pcx: &PatCtxt<'_>, constructor: &Constructor) -> Self {	384	pub(crate) fn wildcards(pcx: PatCtxt<'_>, constructor: &Constructor) -> Self {
385	let ty = &pcx.ty;	385	let ty = pcx.ty;
386	let cx = pcx.cx;	386	let cx = pcx.cx;
387	let wildcard_from_ty = \|ty\| cx.alloc_pat(Pat::Wild, ty);	387	let wildcard_from_ty = \|ty\| cx.alloc_pat(Pat::Wild, ty);
388		388
@@ -446,7 +446,7 @@ impl Fields {
446	/// `ty`: `Option<bool>`	446	/// `ty`: `Option<bool>`
447	/// `self`: `[false]`	447	/// `self`: `[false]`
448	/// returns `Some(false)`	448	/// returns `Some(false)`
449	pub(super) fn apply(self, pcx: &PatCtxt<'_>, ctor: &Constructor) -> Pat {	449	pub(super) fn apply(self, pcx: PatCtxt<'_>, ctor: &Constructor) -> Pat {
450	let subpatterns_and_indices = self.patterns_and_indices();	450	let subpatterns_and_indices = self.patterns_and_indices();
451	let mut subpatterns = subpatterns_and_indices.iter().map(\|&(_, p)\| p);	451	let mut subpatterns = subpatterns_and_indices.iter().map(\|&(_, p)\| p);
452		452


diff --git a/crates/hir_ty/src/diagnostics/pattern/usefulness.rs b/crates/hir_ty/src/diagnostics/pattern/usefulness.rs index 89e6c6593..7d9ab849b 100644 --- a/crates/hir_ty/src/diagnostics/pattern/usefulness.rs +++ b/crates/hir_ty/src/diagnostics/pattern/usefulness.rs
@@ -51,11 +51,11 @@ impl<'a> MatchCheckCtx<'a> {
51	}	51	}
52	}	52	}
53		53
54	#[derive(Clone)]	54	#[derive(Copy, Clone)]
55	pub(super) struct PatCtxt<'a> {	55	pub(super) struct PatCtxt<'a> {
56	pub(super) cx: &'a MatchCheckCtx<'a>,	56	pub(super) cx: &'a MatchCheckCtx<'a>,
57	/// Type of the current column under investigation.	57	/// Type of the current column under investigation.
58	pub(super) ty: Ty,	58	pub(super) ty: &'a Ty,
59	/// Whether the current pattern is the whole pattern as found in a match arm, or if it's a	59	/// Whether the current pattern is the whole pattern as found in a match arm, or if it's a
60	/// subpattern.	60	/// subpattern.
61	pub(super) is_top_level: bool,	61	pub(super) is_top_level: bool,
@@ -223,7 +223,7 @@ impl Matrix {
223	/// This computes `S(constructor, self)`. See top of the file for explanations.	223	/// This computes `S(constructor, self)`. See top of the file for explanations.
224	fn specialize_constructor(	224	fn specialize_constructor(
225	&self,	225	&self,
226	pcx: &PatCtxt<'_>,	226	pcx: PatCtxt<'_>,
227	ctor: &Constructor,	227	ctor: &Constructor,
228	ctor_wild_subpatterns: &Fields,	228	ctor_wild_subpatterns: &Fields,
229	) -> Matrix {	229	) -> Matrix {
@@ -447,7 +447,7 @@ impl Usefulness {
447	/// with the results of specializing with the other constructors.	447	/// with the results of specializing with the other constructors.
448	fn apply_constructor(	448	fn apply_constructor(
449	self,	449	self,
450	pcx: &PatCtxt<'_>,	450	pcx: PatCtxt<'_>,
451	matrix: &Matrix,	451	matrix: &Matrix,
452	ctor: &Constructor,	452	ctor: &Constructor,
453	ctor_wild_subpatterns: &Fields,	453	ctor_wild_subpatterns: &Fields,
@@ -555,7 +555,7 @@ impl Witness {
555	/// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }	555	/// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
556	fn apply_constructor(	556	fn apply_constructor(
557	mut self,	557	mut self,
558	pcx: &PatCtxt<'_>,	558	pcx: PatCtxt<'_>,
559	ctor: &Constructor,	559	ctor: &Constructor,
560	ctor_wild_subpatterns: &Fields,	560	ctor_wild_subpatterns: &Fields,
561	) -> Self {	561	) -> Self {
@@ -623,7 +623,7 @@ fn is_useful(
623	// FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476).	623	// FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476).
624	// TODO(iDawer): ty.strip_references() ?	624	// TODO(iDawer): ty.strip_references() ?
625	let ty = matrix.heads().next().map_or(cx.type_of(v.head()), \|r\| cx.type_of(r));	625	let ty = matrix.heads().next().map_or(cx.type_of(v.head()), \|r\| cx.type_of(r));
626	let pcx = PatCtxt { cx, ty, is_top_level };	626	let pcx = PatCtxt { cx, ty: &ty, is_top_level };
627		627
628	// If the first pattern is an or-pattern, expand it.	628	// If the first pattern is an or-pattern, expand it.
629	let ret = if v.head().is_or_pat(cx) {	629	let ret = if v.head().is_or_pat(cx) {
@@ -657,20 +657,20 @@ fn is_useful(
657	// }	657	// }
658		658
659	// We split the head constructor of `v`.	659	// We split the head constructor of `v`.
660	let split_ctors = v_ctor.split(&pcx, matrix.head_ctors(cx));	660	let split_ctors = v_ctor.split(pcx, matrix.head_ctors(cx));
661	// For each constructor, we compute whether there's a value that starts with it that would	661	// For each constructor, we compute whether there's a value that starts with it that would
662	// witness the usefulness of `v`.	662	// witness the usefulness of `v`.
663	let start_matrix = matrix;	663	let start_matrix = matrix;
664	let usefulnesses = split_ctors.into_iter().map(\|ctor\| {	664	let usefulnesses = split_ctors.into_iter().map(\|ctor\| {
665	// debug!("specialize({:?})", ctor);	665	// debug!("specialize({:?})", ctor);
666	// We cache the result of `Fields::wildcards` because it is used a lot.	666	// We cache the result of `Fields::wildcards` because it is used a lot.
667	let ctor_wild_subpatterns = Fields::wildcards(&pcx, &ctor);	667	let ctor_wild_subpatterns = Fields::wildcards(pcx, &ctor);
668	let spec_matrix =	668	let spec_matrix =
669	start_matrix.specialize_constructor(&pcx, &ctor, &ctor_wild_subpatterns);	669	start_matrix.specialize_constructor(pcx, &ctor, &ctor_wild_subpatterns);
670	let v = v.pop_head_constructor(&ctor_wild_subpatterns, cx);	670	let v = v.pop_head_constructor(&ctor_wild_subpatterns, cx);
671	let usefulness =	671	let usefulness =
672	is_useful(cx, &spec_matrix, &v, witness_preference, is_under_guard, false);	672	is_useful(cx, &spec_matrix, &v, witness_preference, is_under_guard, false);
673	usefulness.apply_constructor(&pcx, start_matrix, &ctor, &ctor_wild_subpatterns)	673	usefulness.apply_constructor(pcx, start_matrix, &ctor, &ctor_wild_subpatterns)
674	});	674	});
675	Usefulness::merge(witness_preference, usefulnesses)	675	Usefulness::merge(witness_preference, usefulnesses)
676	};	676	};