Rollup merge of #109390 - cbeuw:aggregate-lit, r=oli-obk

Custom MIR: Support aggregate expressions

Add support for tuple, array and ADT expressions in custom mir

r? `````@oli-obk````` or `````@tmiasko````` or `````@JakobDegen`````

compiler/rustc_middle/src/mir/syntax.rs

@@ -1165,7 +1165,7 @@ pub enum AggregateKind<'tcx> {
     Tuple,
 
     /// The second field is the variant index. It's equal to 0 for struct
-    /// and union expressions. The fourth field is
+    /// and union expressions. The last field is the
     /// active field number and is present only for union expressions
     /// -- e.g., for a union expression `SomeUnion { c: .. }`, the
     /// active field index would identity the field `c`

compiler/rustc_mir_build/src/build/custom/parse/instruction.rs

@@ -166,6 +166,28 @@ impl<'tcx, 'body> ParseCtxt<'tcx, 'body> {
                 let cast_kind = mir_cast_kind(source_ty, expr.ty);
                 Ok(Rvalue::Cast(cast_kind, source, expr.ty))
             },
+            ExprKind::Tuple { fields } => Ok(
+                Rvalue::Aggregate(
+                    Box::new(AggregateKind::Tuple),
+                    fields.iter().map(|e| self.parse_operand(*e)).collect::<Result<_, _>>()?
+                )
+            ),
+            ExprKind::Array { fields } => {
+                let elem_ty = expr.ty.builtin_index().expect("ty must be an array");
+                Ok(Rvalue::Aggregate(
+                    Box::new(AggregateKind::Array(elem_ty)),
+                    fields.iter().map(|e| self.parse_operand(*e)).collect::<Result<_, _>>()?
+                ))
+            },
+            ExprKind::Adt(box AdtExpr{ adt_def, variant_index, substs, fields, .. }) => {
+                let is_union = adt_def.is_union();
+                let active_field_index = is_union.then(|| fields[0].name.index());
+
+                Ok(Rvalue::Aggregate(
+                    Box::new(AggregateKind::Adt(adt_def.did(), *variant_index, substs, None, active_field_index)),
+                    fields.iter().map(|f| self.parse_operand(f.expr)).collect::<Result<_, _>>()?
+                ))
+            },
             _ => self.parse_operand(expr_id).map(Rvalue::Use),
         )
     }