feat(phase-11): Compiler Fundamentals

[davydog187]

Phase 11: Compiler Fundamentals

Goal

Implement core compiler features: multi-assignment, break/goto/labels, do-block scoping, recursive local function support, and break propagation.

Implementation

Codegen (lib/lua/compiler/codegen.ex)

• Multi-assignment in Statement.Assign with RHS-first evaluation and multi-return call expansion
• Statement.Local now uses per-statement var_map register lookup instead of scope.locals, supporting multi-return call expansion
• Statement.LocalFunc emits set_open_upvalue when the local is captured by the inner function (enables recursive local functions)
• New handlers for Statement.Break, Statement.Goto, Statement.Label

Scope Resolver (lib/lua/compiler/scope.ex)

• Statement.Local stores per-statement register assignments in var_map via reg_list
• Statement.Do saves and restores locals and next_register so inner variables don't leak out

Executor (lib/lua/vm/executor.ex)

• :break instruction handler returns {:break, regs, state} signal
• {:goto, label} instruction handler uses find_label/2 to jump forward
• {:label, _name} instruction handler (marker, skip)
• Test handler propagates :break through conditionals to enclosing loops
• while_loop, repeat_loop, numeric_for, generic_for all detect :break and exit
• find_label/2 helper scans forward through instruction list including nested blocks

Changes

• lib/lua/compiler/codegen.ex - multi-assignment, local var_map, recursive local func, break/goto/label
• lib/lua/compiler/scope.ex - per-statement var_map, do-block scope isolation
• lib/lua/vm/executor.ex - break/goto/label handlers, break propagation, find_label helper
• test/lua/compiler/integration_test.exs - unskip recursive local function and do-block scope tests
• test/lua_test.exs - unskip select varargs test

Tests

• Unskipped 3 previously skipped tests that now pass
• All 1126 tests pass, 0 failures

Verification

• mix format completed
• mix compile --warnings-as-errors passes
• mix test --exclude pending passes (0 failures)
• Tests unskipped: 3

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Implements Phase 11 from plan.md