Replace raw-string OpenACC clause handling and unparse hacks with typed payloads

[ouankou]

Goal

Document and fix the string-heavy OpenACC parsing/unparsing so directives/clauses are structural (enum + typed payloads) with no post-unparse hacks, preserving separators/ordering and failing fast on unknowns.

Problems

• Clause payloads are raw strings (OpenACCClause::addLangExpr, OpenACCVarListClause): async/default_async IDs, device/device_num/num_gangs/num_workers/tile, gang(dim/static/num) args, wait queue lists, routine/bind identifiers, data-like clauses (copy/copyin/copyout/create/present/use_device/link/deviceptr/device_resident/no_create/attach), device selectors, reduction operands, if conditions—none are typed.
• Clause merging (enable_clause_merging) dedups by kind and var string, dropping distinct self/wait/data clauses or altering order; alias spellings aren’t preserved structurally.
• Unparser hacks in OpenACCIRToString.cpp: append space/comma then substr trim; pre-open parens then trim when empty. Spacing is fragile (e.g., copyin(...)create(...)).
• Unknown directives/clauses often flow through generic paths instead of fatal errors, hiding parser/API mismatches.

Impact/Analysis

• Round-trip spacing/separator bugs and payload loss (queues, gang args, async IDs, data lists) because data is stringly and merged. Aliases (pcreate/create, bind identifiers) are not distinguished.
• Spacing hacks make output dependent on every toString appending a trailing space/comma, causing regressions when code changes.

Actionable Plan

1. AST Typing: Add typed structs/enums for all clause payloads (async/default_async IDs, gang args with num/dim/static, wait queue lists with order, bind/routine identifiers, device selectors, device/num_gangs/num_workers/tile, data clause var-sections, reduction operands, if conditions). Record separators and ordering.
2. Grammar layer: Update ANTLR actions to build typed payloads directly; avoid storing raw strings. Add missing enums in OpenACCKinds.h as the single source of truth.
3. IR/C API: Expose structured payloads; remove string reparsing. Unknown kinds/payload mismatches should be fatal.
4. Unparser: Emit from structured data; remove trailing-space/comma substr hacks and only open parens when there is content. Honor recorded separators (comma vs space) and clause order.
5. Merging: Disable or limit clause merging to spec-allowed cases; keep one clause per appearance for self/wait/data unless a semantic merge is explicitly valid.
6. Alias fidelity: Preserve original keyword spelling via typed fields (identifier vs string literal) instead of raw strings.
7. Testing: Strengthen OpenACCV-V round-trip and ctest coverage for async/wait/gang/tile/device/data/reduction/routine/bind cases; require 100% round-trip without spacing hacks.

[ouankou]

• Replace stringly clause payloads with structured types: add OpenACCExpressionItem/OpenACCIdentifier, make async/default_async IDs, wait devnum/queues IDs, gang args, device/num_gangs/num_workers/device_num/tile/vector/vector_length/worker lengths, if/self conditions, routine/bind/cache vars, and data/reduction var lists store text+separator (no post-unparse hacks).
• Update parser actions and merge helpers to build/compare structured payloads directly; keep clause merging off by default for round-trip, but enable merging in built-in test harness to validate normalized output without spacing hacks.
• Ensure merged var lists/devices/use_device deduplicate entries when merging is on; add use_device exit hook and dedup logic for generic expression lists under merging.
• Restore built-in reference outputs from main (normalized, merged form) and keep VV round-trip outputs unchanged; add clause-merging-aware dedup to preserve normalized behavior.
• CI: add concurrency guard to accparser workflow to prevent overlapping runs on the same ref.

See PR #13.

All tests: ctest --output-on-failure.