M2compiler-V2/docs/summary_m2comp_step6.md

m2comp step 6 — WITH + CASE (tag: m2comp-step6)

Statement-level gap closed with v1 lowering recipes, ported to the tree-walking backend: WITH opens a record scope (bare fields, nesting, any record designator incl. a[i]), CASE lowers to compare-chains over int/char selectors (ranges, multi-labels, ELSE). Suite 61/61 (56 inherited + 2 run + 3 reject); new keywords WITH/CASE/| (token numbers shifted, Msg regenerated, no test depends on numbers).

What was built

• src/AST: nkWith (record designator + stmts), nkCase (selector + arm chain + else), nkCaseArm (label chain + body), nkRange (num = lo, op = hi, both folded) + constructors and KindName entries.
• Grammar: WithStat (record check 215, PushRecord/PopScope around the body), CaseStat (ordinal selector check 213, EqCheck per label, ConstFold per bound with 230 on non-constant, ranges via ..), wired into Stat.
• src/SymTab: ConstFold accepts nkChar (char labels and char bounds; no other change needed — PushRecord and EqCheck already existed for this).
• src/MGen: WITH address-temp stack (withTmps/withTyps, max 8, reset per module); EmitWith evaluates any record designator once; bare WITH-fields (aux = KindField, no tag) resolve in load/address paths via top-down search (stores flow through the generic address path); EmitCase evaluates the selector once and emits per-label Eq (ranges: Ge+Le+And) Jz-chains into arm bodies.
• run_tests.sh: expect_fail gained an optional .LST message argument (existing single-arg calls unchanged).

Tests — 61/61

t_with 51 (fields, nested WITH, a[i] argument); t_case 138 (multi-labels, 4..6 range, ELSE, char selector, fallthrough-free arms). Rejections: WITH on INTEGER (215), record selector (213), variable label (230).

Bugs found (all fixed, all covered)

• None in the compiler: the three rejections "aborted" only inside the suite because the new test lines passed bare filenames to expect_fail (it takes tests/-prefixed paths), so the driver HALTed on "Could not open input file". Fixed the lines; no compiler change.