fix(elixir): Phoenix channel extraction is unreachable in both branches

[henry-hz]

Refs #1729 (defect 2 of 4).

The bug

Neither half of extract_channels_elixir() can fire, so an Elixir project produces zero Channel nodes regardless of how much Phoenix.PubSub or Phoenix.Channel it uses.

docs/elixir-lsp/PLAN.md §1.2 currently records this path as "Phoenix channels/PubSub (works today)", which is what prompted me to write it up rather than just patch it.

Emit side

elixir_process_call() reads:

TSNode args = ts_node_child_by_field_name(call, TS_FIELD("arguments"));

tree-sitter-elixir defines no arguments field — its whole field set is key, left, operand, operator, quoted_start, quoted_end, right, target, value. args is always null, so elixir_emit_second_arg() returns early every time.

Listener side

} else if (strcmp(kind, "def") == 0) {
    elixir_process_function_def(ctx, node);
}

There is no def node type in the grammar — an Elixir definition is a call whose target is the macro name. That branch is unreachable, and elixir_process_function_def() compounds it by reading name and parameters fields that also do not exist.

The fix

• a positional arguments fallback, mirroring elixir_call_args() which extract_defs.c has always used for the same reason
• dispatch on call + a def-macro target instead of the phantom def node type
• elixir_process_function_def() now takes the def call, unwraps a when guard, and reads the head's name and parameters positionally — so guarded clauses like def handle_in(e, p, s) when is_map(s) are caught too
• the callee lookup accepts target or child(0), matching what extract_defs.c does

Test

elixir_channels_pubsub_and_handle_in covers Phoenix.PubSub.broadcast, Phoenix.PubSub.subscribe, a bare push emit, and two handle_in listener clauses, one guarded.

Verification

• make -f Makefile.cbm test-focused TEST_SUITES="extraction registry lang_contract grammar_regression grammar_labels repro_language_registry repro_call_node_manifest" → 388 passed, 0 failed
• CALLS-breadth contract across 53 languages unaffected; every change is inside the Elixir path
• clang-format --dry-run --Werror clean on extract_channels.c. tests/ left unformatted, per its exclusion from LINT_SRCS

Independent of #1721 — these can land in either order.

Submitted as a bug fix under the CONTRIBUTING exception for focused bug fixes.

🤖 Generated with Claude Code

https://claude.ai/code/session_01DpDDX9sFC16mQ9U9wQ3WNd

[github-actions]

Thanks for opening this — it has been seen, and it is queued.

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Current review status: working through a backlog. 0.9.1-rc.1 is out, so the release freeze that held reviews is over — but it left a large queue of open pull requests behind it, and we are reading through them oldest-first. The background is in discussion #1144.

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