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print-type-sizes: skip field printing for primitives #89329

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Oct 6, 2021
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print-type-sizes: skip field printing for primitives #89329

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7 changes: 5 additions & 2 deletions compiler/rustc_middle/src/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1805,8 +1805,11 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {

match layout.variants {
Variants::Single { index } => {
debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variants[index].ident);
if !adt_def.variants.is_empty() {
if !adt_def.variants.is_empty() && layout.fields != FieldsShape::Primitive {
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Why is variants non-empty here? Primitives aren't enums.

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FieldsShape describes how fields are located in memory, with Primitive used for things that have no fields, including the never type.

Variants that are uninhabited and have ZST fields only are consider to be absent. Layout computation omits absents variants entirely. If all variants of an enum are absent, the layout of a never type is used (Variants::Single, FieldsShape::Primitive).

debug!(
"print-type-size `{:#?}` variant {}",
layout, adt_def.variants[index].ident
);
let variant_def = &adt_def.variants[index];
let fields: Vec<_> = variant_def.fields.iter().map(|f| f.ident.name).collect();
record(
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2 changes: 1 addition & 1 deletion src/test/ui/print_type_sizes/uninhabited.rs
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Expand Up @@ -11,5 +11,5 @@
fn start(_: isize, _: *const *const u8) -> isize {
let _x: Option<!> = None;
let _y: Result<u32, !> = Ok(42);
0
let _z: Result<!, !> = loop {};
}
1 change: 1 addition & 0 deletions src/test/ui/print_type_sizes/uninhabited.stdout
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Expand Up @@ -3,3 +3,4 @@ print-type-size variant `Ok`: 4 bytes
print-type-size field `.0`: 4 bytes
print-type-size type: `std::option::Option<!>`: 0 bytes, alignment: 1 bytes
print-type-size variant `None`: 0 bytes
print-type-size type: `std::result::Result<!, !>`: 0 bytes, alignment: 1 bytes