vatsrahul1001 opened a new pull request, #67720:
URL: https://github.com/apache/airflow/pull/67720
Closes #67714.
## What was broken
Open `@task_group` rendered with vertically-stacked internals and edges
crossing the boundary in confusing ways whenever an internal task had a direct
dependency on a node outside the group (an "escape edge" that bypassed the
group's entry/exit interface). Dag execution was unaffected — purely a UI
rendering issue.
The reporter's minimal repro: with only `entry`/`exit` wired across the
group boundary, Graph view rendered correctly. Adding two lines like
`group_result["a2"] >> final_task_result` made the group's children stack
vertically and dependency edges wrap around the boundary.
## Root cause
Two interacting bugs in the ELK graph-layout refactor from #65031:
1. **`hasUniformExternalConnectivity` was too lenient.** It fired whenever
externally-connected children separately shared the same external *sources* OR
the same external *targets*, instead of the canonical fan-in/fan-out pattern
where every child has the same full `(sources, targets)` profile. The
reporter's group had `a1` as an "entry" (external source `{start}`) and
`a2`/`a3`/`group_done` as "exits" (external target `{final_task}`) — different
profiles per child. The lenient check still returned `true`, triggering the
collapse path on a group where the author had deliberately wired explicit
escape edges.
2. **`rewriteGroupEdges` was tuned for closed groups.** When the collapse
path fired on an *open* group, it dropped all of the group's internal edges —
leaving ELK with no internal-layout information for the children. That's what
produced the vertical stacking.
## Fix
* Tighten `hasUniformExternalConnectivity` to require every
externally-connected child to share the same full `(sources, targets)` profile.
Mixed entry/exit shapes (like the reporter's repro) now fall back to rendering
individual crossing edges, preserving the author's explicit dependency intent.
The canonical "cleanup group" fan-in/fan-out pattern that the optimization was
designed for (every child has same upstream AND same downstream) still triggers
the collapse.
* Add a `preserveInternal` option to `rewriteGroupEdges`. The open-group
call site sets it so the collapse optimization preserves internal edges for the
subsequent extraction loop; the closed-group call site keeps the default (drop
internals — they're not laid out when the group is collapsed).
## Tests
New `elkGraphUtils.test.ts` covers:
- `hasUniformExternalConnectivity` — vanilla TaskGroup, mixed-profile #67714
trigger, canonical fan-in/fan-out
- `generateElkGraph` for the #67714 repro: internal edges preserved AND
escape edges rendered individually
- `generateElkGraph` for the canonical fan-in/fan-out shape: collapse still
fires, internal edges kept (exercises `preserveInternal: true`)
- `generateElkGraph` regression guards: simple open TaskGroup, closed
TaskGroup
Verified the new tests fail against `main` without the fix and pass with it.
## Risk
Targeted change to one file plus its new test. No API or schema changes.
Behaviour change boundary is `hasUniformExternalConnectivity`'s return value on
mixed-profile groups, which previously collapsed to a group-level edge and now
renders individual edges. Closed groups and canonical fan-in/fan-out groups
behave identically to before.
cc @bbovenzi (author of #65031, original Graph-layout refactor)
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