Pattern types have their base type as a field

Author: oli-obk

compiler/rustc_middle/src/ty/layout.rs

@@ -839,11 +839,15 @@ where
                 | ty::FnDef(..)
                 | ty::CoroutineWitness(..)
                 | ty::Foreign(..)
-                | ty::Pat(_, _)
                 | ty::Dynamic(_, _) => {
                     bug!("TyAndLayout::field({:?}): not applicable", this)
                 }
 
+                ty::Pat(base, _) => {
+                    assert_eq!(i, 0);
+                    TyMaybeWithLayout::Ty(base)
+                }
+
                 ty::UnsafeBinder(bound_ty) => {
                     let ty = tcx.instantiate_bound_regions_with_erased(bound_ty.into());
                     field_ty_or_layout(TyAndLayout { ty, ..this }, cx, i)

compiler/rustc_ty_utils/src/layout.rs

@@ -350,6 +350,14 @@ fn layout_of_uncached<'tcx>(
                     ty::PatternKind::Or(..) => bug!("patterns cannot have nested or patterns"),
                 },
             }
+            // Pattern types contain their base as their sole field.
+            // This allows the rest of the compiler to process pattern types just like
+            // single field transparent Adts, and only the parts of the compiler that
+            // specifically care about pattern types will have to handle it.
+            layout.fields = FieldsShape::Arbitrary {
+                offsets: [Size::ZERO].into_iter().collect(),
+                memory_index: [0].into_iter().collect(),
+            };
             tcx.mk_layout(layout)
         }
 

tests/ui/type/pattern_types/or_patterns.stderr

@@ -53,7 +53,14 @@ error: layout_of((i8) is (i8::MIN..=-1 | 1..)) = Layout {
                    valid_range: 1..=255,
                },
            ),
-           fields: Primitive,
+           fields: Arbitrary {
+               offsets: [
+                   Size(0 bytes),
+               ],
+               memory_index: [
+                   0,
+               ],
+           },
            largest_niche: Some(
                Niche {
                    offset: Size(0 bytes),
@@ -91,7 +98,14 @@ error: layout_of((i8) is (i8::MIN..=-2 | 0..)) = Layout {
                    valid_range: 0..=254,
                },
            ),
-           fields: Primitive,
+           fields: Arbitrary {
+               offsets: [
+                   Size(0 bytes),
+               ],
+               memory_index: [
+                   0,
+               ],
+           },
            largest_niche: Some(
                Niche {
                    offset: Size(0 bytes),

tests/ui/type/pattern_types/range_patterns.stderr

@@ -57,7 +57,14 @@ error: layout_of((u32) is 1..) = Layout {
                    valid_range: 1..=4294967295,
                },
            ),
-           fields: Primitive,
+           fields: Arbitrary {
+               offsets: [
+                   Size(0 bytes),
+               ],
+               memory_index: [
+                   0,
+               ],
+           },
            largest_niche: Some(
                Niche {
                    offset: Size(0 bytes),
@@ -390,7 +397,14 @@ error: layout_of((i8) is -10..=10) = Layout {
                    valid_range: (..=10) | (246..),
                },
            ),
-           fields: Primitive,
+           fields: Arbitrary {
+               offsets: [
+                   Size(0 bytes),
+               ],
+               memory_index: [
+                   0,
+               ],
+           },
            largest_niche: Some(
                Niche {
                    offset: Size(0 bytes),
@@ -428,7 +442,14 @@ error: layout_of((i8) is i8::MIN..=0) = Layout {
                    valid_range: (..=0) | (128..),
                },
            ),
-           fields: Primitive,
+           fields: Arbitrary {
+               offsets: [
+                   Size(0 bytes),
+               ],
+               memory_index: [
+                   0,
+               ],
+           },
            largest_niche: Some(
                Niche {
                    offset: Size(0 bytes),