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fix: Preserve offset for CFG edges when serializing to JSON #2606

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Merged
merged 5 commits into from
Oct 2, 2025
Merged

fix: Preserve offset for CFG edges when serializing to JSON #2606

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4a2aefa
Add failing test case.
cqc-alec Oct 2, 2025
c37f5fc
Preserve offset for CFG edges.
cqc-alec Oct 2, 2025
1c30510
Tell miri to ignore test.
cqc-alec Oct 2, 2025
2cfa31f
Apply offset for all non-order edges.
cqc-alec Oct 2, 2025
8796750
Fix comment.
cqc-alec Oct 2, 2025
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3 changes: 2 additions & 1 deletion hugr-core/src/hugr/serialize.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -215,7 +215,8 @@ impl TryFrom<&Hugr> for SerHugrLatest {
let op = hugr.get_optype(node);
let is_value_port = offset < op.value_port_count(dir);
let is_static_input = op.static_port(dir).is_some_and(|p| p.index() == offset);
let offset = (is_value_port || is_static_input).then_some(offset as u32);
let is_cfg_edge = op.is_dataflow_block();
let offset = (is_value_port || is_static_input || is_cfg_edge).then_some(offset as u32);
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@aborgna-q aborgna-q Oct 2, 2025 •
edited
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This is too restraining.
The bug happens any time we have more than one non-df ports, so it would be safer to do

Suggested change
let is_cfg_edge = op.is_dataflow_block();
let offset = (is_value_port || is_static_input || is_cfg_edge).then_some(offset as u32);
let multiple_other_ports = op.non_df_port_count(dir) > 1;
let offset = (is_value_port || is_static_input || multiple_other_ports).then_some(offset as u32);

Alternatively, always encode the offset 🤷

It's not a breaking serialization change either way since the decoding logic works fine if the offset is already defined

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@cqc-alec cqc-alec Oct 2, 2025

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Yeah, my first idea was to encode the offset always, but this broke some round-trip tests in hugr-py for hugrs containing order edges.

I will try your suggestion.

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@aborgna-q aborgna-q Oct 2, 2025 •
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Ah, seems like hugr-py uses None only for order edges. (The fn comment seems wrong here, only order edges have offset -1)

hugr/hugr-py/src/hugr/hugr/base.py

Lines 971 to 980 in 70ee1cb

def _constrain_offset(self, p: P) -> PortOffset | None:
"""Constrain an offset to be a valid encoded port offset.
Order edges and control flow edges should be encoded without an offset.
"""
if p.offset < 0:
assert p.offset == -1, "Only order edges are allowed with offset < 0"
return None
else:
return p.offset

If we wanted to follow that here then we can check

let other_port_is_not_order = op.other_port_kind(dir) != EdgeKind::StateOrder;
let offset = (is_value_port || is_static_input || other_port_is_not_order).then_some(offset as u32);

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@cqc-alec cqc-alec Oct 2, 2025

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Right, thanks. I've gone with your second suggestion. I tried the first, but ran into some round-tripping failures using testfiles exported by guppylang. With this second idea, all seems good. (Also checked that it still fixes #2592 .)

(node_rekey[&node], offset)
};

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25 changes: 25 additions & 0 deletions hugr-core/src/hugr/serialize/test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ use crate::builder::{
Container, DFGBuilder, Dataflow, DataflowHugr, DataflowSubContainer, HugrBuilder,
ModuleBuilder, endo_sig, inout_sig, test::closed_dfg_root_hugr,
};
use crate::envelope::{EnvelopeConfig, read_envelope, write_envelope};
use crate::extension::ExtensionRegistry;
use crate::extension::prelude::Noop;
use crate::extension::prelude::{bool_t, qb_t, usize_t};
Expand All @@ -16,15 +17,21 @@ use crate::hugr::validate::ValidationError;
use crate::hugr::views::ExtractionResult;
use crate::ops::custom::{ExtensionOp, OpaqueOp, OpaqueOpError};
use crate::ops::{self, DFG, Input, Module, Output, Value, dataflow::IOTrait};
use crate::package::Package;
use crate::std_extensions::arithmetic::float_types::float64_type;
use crate::std_extensions::arithmetic::int_types::{ConstInt, INT_TYPES};
use crate::std_extensions::logic::LogicOp;
use crate::std_extensions::std_reg;
use crate::test_file;
use crate::types::type_param::TypeParam;
use crate::types::{
FuncValueType, PolyFuncType, PolyFuncTypeRV, Signature, SumType, Type, TypeArg, TypeBound,
TypeRV,
};
use crate::{OutgoingPort, Visibility, type_row};
use std::fs::File;
use std::io::{BufReader, Cursor};

use std::sync::LazyLock;

use itertools::Itertools;
Expand Down Expand Up @@ -625,6 +632,24 @@ fn std_extensions_valid() {
}
}

#[test]
// https://github.com/CQCL/hugr/issues/2600
fn cfg_edge_ordering() {
let pkg: Package = Package::load(
BufReader::new(File::open(test_file!("issue-2600.hugr")).unwrap()),
None,
)
.unwrap();
pkg.validate().unwrap();

let mut data1: Vec<u8> = Vec::new();
let _ = write_envelope(&mut data1, &pkg, EnvelopeConfig::text());

let buff1 = Cursor::new(data1);
let (_, pkg1) = read_envelope(buff1, &std_reg()).unwrap();
pkg1.validate().unwrap();
}

mod proptest {
use super::check_testing_roundtrip;
use super::{NodeSer, SimpleOpDef};
Expand Down
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