lowering: propagate snapshot pop success values in const folding

crates/cairo-lang-lowering/src/optimizations/const_folding.rs

@@ -1325,17 +1325,36 @@ impl<'db, 'mt> ConstFoldingContext<'db, 'mt> {
             let var_info = self.var_info.get(&info.inputs[0].var_id)?;
             let desnapped = try_extract_matches!(var_info.as_ref(), VarInfo::Snapshot)?;
             let element_var_infos = try_extract_matches!(desnapped.as_ref(), VarInfo::Array)?;
-            // TODO(orizi): Propagate success values as well.
             if element_var_infos.is_empty() {
                 let arm = &info.arms[1];
-                self.var_info.insert(arm.var_ids[0], VarInfo::Array(vec![]).into());
+                self.var_info.insert(
+                    arm.var_ids[0],
+                    VarInfo::Snapshot(VarInfo::Array(vec![]).into()).into(),
+                );
                 Some(BlockEnd::Goto(
                     arm.block_id,
                     VarRemapping {
                         remapping: FromIterator::from_iter([(arm.var_ids[0], info.inputs[0])]),
                     },
                 ))
             } else {
+                let (remaining, popped) = if id == self.array_snapshot_pop_front {
+                    (element_var_infos[1..].to_vec(), element_var_infos[0].clone())
+                } else {
+                    let split_idx = element_var_infos.len() - 1;
+                    (element_var_infos[..split_idx].to_vec(), element_var_infos[split_idx].clone())
+                };
+                let arm = &info.arms[0];
+                self.var_info.insert(
+                    arm.var_ids[0],
+                    VarInfo::Snapshot(VarInfo::Array(remaining).into()).into(),
+                );
+                if let Some(popped) = popped {
+                    self.var_info.insert(
+                        arm.var_ids[1],
+                        VarInfo::Box(VarInfo::Snapshot(popped).into()).into(),
+                    );
+                }
                 None
             }
         } else {

crates/cairo-lang-lowering/src/optimizations/test_data/const_folding

@@ -6075,6 +6075,123 @@ End:
 
 //! > ==========================================================================
 
+//! > Span pop_front success propagates remaining snapshot.
+
+//! > test_runner_name
+test_match_optimizer
+
+//! > function_code
+fn foo() -> Option<Box<@felt252>> {
+    let mut snapshot = array![1].span().snapshot;
+    if let Some(_) = array_snapshot_pop_front(ref snapshot) {
+        return array_snapshot_pop_front(ref snapshot);
+    }
+    None
+}
+
+//! > function_name
+foo
+
+//! > module_code
+use core::array::array_snapshot_pop_front;
+
+//! > semantic_diagnostics
+
+//! > before
+Parameters:
+blk0 (root):
+Statements:
+  (v0: core::array::Array::<core::felt252>) <- core::array::array_new::<core::felt252>()
+  (v1: core::felt252) <- 1
+  (v2: core::array::Array::<core::felt252>) <- core::array::array_append::<core::felt252>(v0, v1)
+  (v3: core::array::Array::<core::felt252>, v4: @core::array::Array::<core::felt252>) <- snapshot(v2)
+End:
+  Match(match core::array::array_snapshot_pop_front::<core::felt252>(v4) {
+    Option::Some(v5, v6) => blk1,
+    Option::None(v7) => blk5,
+  })
+
+blk1:
+Statements:
+End:
+  Match(match core::array::array_snapshot_pop_front::<core::felt252>(v5) {
+    Option::Some(v8, v9) => blk2,
+    Option::None(v10) => blk3,
+  })
+
+blk2:
+Statements:
+  (v11: core::option::Option::<core::box::Box::<@core::felt252>>) <- Option::Some(v9)
+End:
+  Goto(blk4, {v11 -> v12})
+
+blk3:
+Statements:
+  (v13: ()) <- struct_construct()
+  (v14: core::option::Option::<core::box::Box::<@core::felt252>>) <- Option::None(v13)
+End:
+  Goto(blk4, {v14 -> v12})
+
+blk4:
+Statements:
+End:
+  Return(v12)
+
+blk5:
+Statements:
+  (v15: ()) <- struct_construct()
+  (v16: core::option::Option::<core::box::Box::<@core::felt252>>) <- Option::None(v15)
+End:
+  Return(v16)
+
+//! > after
+Parameters:
+blk0 (root):
+Statements:
+  (v0: core::array::Array::<core::felt252>) <- core::array::array_new::<core::felt252>()
+  (v1: core::felt252) <- 1
+  (v2: core::array::Array::<core::felt252>) <- core::array::array_append::<core::felt252>(v0, v1)
+  (v3: core::array::Array::<core::felt252>, v4: @core::array::Array::<core::felt252>) <- snapshot(v2)
+End:
+  Match(match core::array::array_snapshot_pop_front::<core::felt252>(v4) {
+    Option::Some(v5, v6) => blk1,
+    Option::None(v7) => blk5,
+  })
+
+blk1:
+Statements:
+End:
+  Goto(blk3, {v5 -> v10})
+
+blk2:
+Statements:
+  (v11: core::option::Option::<core::box::Box::<@core::felt252>>) <- Option::Some(v9)
+End:
+  Goto(blk4, {v11 -> v12})
+
+blk3:
+Statements:
+  (v13: ()) <- struct_construct()
+  (v14: core::option::Option::<core::box::Box::<@core::felt252>>) <- Option::None(v13)
+End:
+  Goto(blk4, {v14 -> v12})
+
+blk4:
+Statements:
+End:
+  Return(v12)
+
+blk5:
+Statements:
+  (v15: ()) <- struct_construct()
+  (v16: core::option::Option::<core::box::Box::<@core::felt252>>) <- Option::None(v15)
+End:
+  Return(v16)
+
+//! > lowering_diagnostics
+
+//! > ==========================================================================
+
 //! > Panic with byte array value.
 
 //! > test_runner_name