Rollup merge of #118974 - workingjubilee:why-worry-about-enum-abi, r=…

…davidtwco

Annotate panic! reasons during enum layout

Add some reasons to the panics, and use more exhaustive matches.

Also see: #118955

compiler/rustc_abi/src/layout.rs

@@ -382,7 +382,7 @@ pub trait LayoutCalculator {
  *offset += this_offset;
  }
  }
- _ => {
+ FieldsShape::Primitive | FieldsShape::Array { .. } | FieldsShape::Union(..) => {
  panic!("Layout of fields should be Arbitrary for variants")
  }
  }
@@ -600,7 +600,9 @@ pub trait LayoutCalculator {
  variant.size = new_ity_size;
  }
  }
- _ => panic!(),
+ FieldsShape::Primitive | FieldsShape::Array { .. } | FieldsShape::Union(..) => {
+ panic!("encountered a non-arbitrary layout during enum layout")
+ }
  }
  }
  }
@@ -628,7 +630,7 @@ pub trait LayoutCalculator {
  let mut common_prim_initialized_in_all_variants = true;
  for (field_layouts, layout_variant) in iter::zip(variants, &layout_variants) {
  let FieldsShape::Arbitrary { ref offsets, .. } = layout_variant.fields else {
- panic!();
+ panic!("encountered a non-arbitrary layout during enum layout");
  };
  // We skip *all* ZST here and later check if we are good in terms of alignment.
  // This lets us handle some cases involving aligned ZST.
@@ -681,7 +683,7 @@ pub trait LayoutCalculator {
  assert_eq!(memory_index.raw, [0, 1]);
  offsets
  }
- _ => panic!(),
+ _ => panic!("encountered a non-arbitrary layout during enum layout"),
  };
  if pair_offsets[FieldIdx::new(0)] == Size::ZERO
  && pair_offsets[FieldIdx::new(1)] == *offset
@@ -758,7 +760,9 @@ pub trait LayoutCalculator {
  Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
  Variants::Multiple { tag, tag_encoding, tag_field, variants: best_layout.variants }
  }
- _ => panic!(),
+ Variants::Single { .. } => {
+ panic!("encountered a single-variant enum during multi-variant layout")
+ }
  };
  Some(best_layout.layout)
  }
@@ -1154,7 +1158,11 @@ fn univariant<
  assert_eq!(memory_index.raw, [0, 1]);
  offsets
  }
- _ => panic!(),
+ FieldsShape::Primitive
+ | FieldsShape::Array { .. }
+ | FieldsShape::Union(..) => {
+ panic!("encountered a non-arbitrary layout during enum layout")
+ }
  };
  if offsets[i] == pair_offsets[FieldIdx::new(0)]
  && offsets[j] == pair_offsets[FieldIdx::new(1)]