Fix codegen panic on messages containing nested extend blocks#181
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`_walk_message` in pb-jelly-gen looked up a non-existent field "extension_type" on `DescriptorProto`. The actual field for nested extensions is named "extension" (number 6), per google/protobuf/descriptor.proto. The bug was dormant because no existing pb-test fixture had a nested `extend` block, but it fires on real-world editions 2023 protos such as upstream google/protobuf/sample_messages_edition.proto, which nest extends inside `MessageSetCorrectExtension*`. The file-level walker (`_walk_file`) already used the correct field name; only the per-message walker was wrong. Adds a regression proto (`pb-test/.../nested_extensions.proto`) containing a message with a nested extend block. Without the fix, running pb_test_gen panics at codegen.rs with `called Option::unwrap() on a None value`; with the fix, codegen and the integration test pass. Co-authored-by: Cursor <cursoragent@cursor.com>
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Co-authored-by: Cursor <cursoragent@cursor.com>
The verify_generated_files test (run with VALIDATE=1 in CI) compares generated Rust against .expected snapshots checked into the repo. Adding the new nested_extensions.proto fixture without its snapshot caused CI to fail with NotFound when reading the missing nested_extensions.rs.expected file. Generate the missing snapshot and update lib.rs.expected to declare the new module. Co-authored-by: Cursor <cursoragent@cursor.com>
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Summary
pb-jelly-gen's message walker (_walk_messageincodegen.rs) panicked withcalled Option::unwrap() on a None valuewhenever it encountered a message containing a nestedextendblock.The walker was looking up a field named
"extension_type"onDescriptorProto, but the actual field for nested extensions is named"extension"(number 6) — seegoogle/protobuf/descriptor.proto.get_field("extension_type")returnedNone, and the immediate.unwrap()panicked.The file-level walker (
_walk_file) already used the correct field name, so top-levelextendblocks were unaffected. Only nested extends triggered the bug.Why this surfaced now
The bug was dormant because no existing
pb-testfixture exercised a nestedextendblock. It fires on real-world protos — most notably upstream protobuf v29'sgoogle/protobuf/sample_messages_edition.proto, which nests extends insideMessageSetCorrectExtension*. Anyone pulling protobuf v29 protos into apb-jelly-genbuild hits the panic immediately.Test plan
cd pb-test/pb_test_gen && cargo run— codegen succeedscd pb-test && cargo test— integration tests passpanic on the new fixture, proving the test catches the
regression.