Add Group action for partitioning collections by field

[KrisSimon]

Migrated from GitLab MR !224 (open)
feature/group-action → main
Originally created: 2026-04-02
Author: Kris Simon
Labels: 0.9

Summary

• Adds the Group action to ARO's data pipeline operations (ARO-0018)
• Syntax: Group the <result> from <collection> by "fieldName".
• Partitions a collection into a dictionary mapping each unique field value to its array of matching items

Changes

• Parser: Extended ByClause to accept string literals (by "field") in addition to regex patterns
• Runtime: New GroupAction in DataPipelineActionsModule with streaming support
• Compiler: aro_action_group bridge function + LLVM extern declaration
• LSP: Completion entry for Group action
• Editor: Syntax highlighting in VS Code and IntelliJ TextMate grammars
• Tests: 7 new unit tests covering grouping, missing fields, empty collections, error cases
• Docs: Updated ARO-0018 proposal, Book chapters (DataPipelines, Actions, AppendixA, AppendixB), Website docs
• Examples: GroupDemo example + 18_DataProcessing data processing application

Test plan

• All 1583 tests pass (7 new Group action tests)
• aro check ./Examples/GroupDemo passes
• aro run ./Examples/GroupDemo produces correct grouped output
• aro check ./Examples/18_DataProcessing passes

🤖 Generated with Claude Code

[KrisSimon]

implemented in 0.9 upstream