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Phase 28. Audit gap closure (driver errors, edge cases, emitted-syntax checks)

FieldValue
MEPMEP-56 §Phases
StatusLANDED
Started2026-05-29 12:01 (GMT+7)
Landed2026-05-29 12:01 (GMT+7)
Tracking issue—
Tracking PR#22510
Commitd43705737a

Gate​

Three top-level Go tests close the audit gaps left by the per-feature phases:

  • TestPhase28DriverErrorPaths (phase28_driver_errors_test.go): five subtests cover Driver.Build failure branches (parse error, typecheck error, missing source file, unknown target, output-dir is a file). Each subtest asserts a non-nil error and (for the four with stable wording) asserts the message names the failing stage (parse, typecheck, read/no such file/parse, not implemented).
  • TestPhase29EdgeCases (phase29_edge_cases_test.go): 30 subtests build and execute Mochi sources covering collection-boundary, scalar, string-Unicode, query, closure-capture, and previously-uncovered IR-node scenarios (BreakStmt, ContinueStmt, MapValuesExpr, UnNotBool, Panic#code round-trip, ListSortAscExpr, ListSliceExpr, MathCallExpr "ceil", StrConvertExpr, NumCastExpr, MatchStmt Default arm, chained elsif folding, integer-valued float print, Mochi::Runtime::VERSION constant load, Panic#message channel, locked-in BinDivI64 floor-div behaviour) that the per-feature phase tests intentionally kept happy-path only.
  • TestPhase30TargetEmittedSyntax (phase30_target_syntax_test.go): seven subtests run ruby -c against the .rb every non-source build target emits, plus a JSON.parse round-trip against the IRuby notebook and a .gem archive walk that asserts lib/<name>.rb is present byte for byte.
  • TestPhase31Integration (phase31_integration_test.go): five cross-cutting subtests exercise multi-feature programs (closure_over_query_result, nested_hof_filter_then_map_then_reduce, try_catch_around_record_field_access, list_of_records_query, match_arm_returns_distinct_per_variant) that touch two or more phases at once, catching regressions per-feature tests would miss.

Every subtest skips if resolveToolchain cannot find a Ruby; the .gem subtest additionally falls back to $PATH for gem or skips.

Build target / audit decisions​

The audit phase does not change build.go. The audit tests exercise the existing Driver.Build switch (lines 195 to 217) and the per-target functions (buildGem lines 229 to 258, buildBundle lines 270 to 290, buildIRubyNotebook lines 296 to 335, buildTebakoPackage lines 347 to 389, buildTruffleNative lines 400 to 438, buildMRuby lines 450 to 494) and validate their outputs end to end.

Three audit decisions are baked into the test design:

  1. Error-message contracts as a public surface. TestPhase28DriverErrorPaths asserts not just that an error is returned but that the message contains a stage-naming substring (parse, typecheck, not implemented). This locks the error wording into the public contract, so a refactor that renames the stages must update the user-facing message at the same time.
  2. Edge cases through the same execution harness as the happy-path tests. TestPhase29EdgeCases uses the existing runRubyFixture(t, tc, runtimeLib, name, src, want) helper, so an edge-case regression looks identical to a per-feature regression and uses the same -I mochi-runtime/lib invocation. The fixtures cover empty list<int>, empty string, negative arithmetic, a near-int63 integer, Unicode (héllo round-tripping through len and upper), single-element and nested lists, multi-key map and omap round-trips, keys() cardinality, zero-iteration for i in 0..0 and zero-iteration while, a sum-type with three arms exercised through all three (Pos, Neg, Zero), and capture-by-value semantics for a closure over a let.
  3. Syntactic validation that does not require the heavy toolchains. TestPhase30TargetEmittedSyntax runs ruby -c against the emitted .rb for TargetRubyGem, TargetRubyBundle, TargetTebako, TargetTruffleNative, and TargetMRuby. Notebook JSON validity is exercised via a JSON.parse probe. The .gem archive is unpacked via inspectGemContainsLib (defined at the bottom of phase30_target_syntax_test.go, lines 182 to 219), which uses archive/tar to walk the outer tar, identifies data.tar.gz, wraps it in compress/gzip, and walks the inner tar looking for lib/<name>.rb. The two-layer tar (outer plain + inner gzipped) is the documented RubyGems .gem format (the outer also contains metadata.gz and checksums.yaml.gz).

The shared exercise source in TestPhase30TargetEmittedSyntax (a Sign sum type, classify function, name matcher, and a from x in xs select query) is non-trivial on purpose: any syntactic glitch in record / sum / query lowering shows up under ruby -c. A trivial print("hi") source would pass ruby -c even with broken record lowering since no records would be emitted.

Files changed​

FilePurpose
transpiler3/ruby/build/phase28_driver_errors_test.goTestPhase28DriverErrorPaths (5 subtests): parse / typecheck / missing-file / unknown-target / out-dir-is-file
transpiler3/ruby/build/phase29_edge_cases_test.goTestPhase29EdgeCases (30 subtests): collection, scalar, string, query, closure boundary scenarios plus uncovered IR nodes + runtime gem assertions (VERSION, Panic#message) + locked floor-div divergence
transpiler3/ruby/build/phase22_test.goExpanded gemspec substring assertions for s.version, s.license, required_ruby_version, summary, authors, add_runtime_dependency constraint, require_paths
transpiler3/ruby/build/phase23_test.goGemfile assertions for mochi-runtime ">= 0.1" version pin and # frozen_string_literal: true header
transpiler3/ruby/build/phase24_test.goNotebook assertions for nbformat_minor (5), kernelspec.display_name, language_info.file_extension, cell execution_count == nil
transpiler3/ruby/build/phase25_test.goTebako press.sh assertions for default image (ghcr.io/tamatebako/...), default Ruby version (3.3.7), --Ruby= flag, full Gemfile
transpiler3/ruby/build/phase26_test.goTruffleNative assertions for --initialize-at-build-time flag and both error-message branches when GRAAL_HOME / native-image are missing
transpiler3/ruby/build/phase27_test.goMRuby build_config.rb assertions for conf.gem core: 'mruby-bin-mrbc', mruby-bin-mruby, and conf.gem '#{__dir__}' directives
transpiler3/ruby/lower/lower.goFloor-div divergence flagged inline at line 1187 (no code change); covered by lock-in test
website/docs/mep/mep-0056.md§3 surface-syntax table extended with anonymous record type Pair = { … }, struct-literal agent constructor, set{…} and omap<K,V> annotation forms, fetch keyword form, json_decode snake_case, int(x) cast form, BinDivI64 known-divergence row
website/docs/implementation/0056/phase-02-scalars.mdFloor-div divergence documented with the lock-in test name
website/docs/implementation/0056/phase-09-datalog.mdSubtest count corrected from 3 to 5
transpiler3/ruby/build/phase30_target_syntax_test.goTestPhase30TargetEmittedSyntax (7 subtests): ruby -c on every emitted .rb, notebook JSON probe, .gem archive walk via inspectGemContainsLib helper
transpiler3/ruby/build/phase31_integration_test.goTestPhase31Integration (5 subtests): cross-cutting programs touching closures + queries + records + try/catch + match together
transpiler3/ruby/build/phase09_test.godl_neq_constraint and dl_not_negation subtests added for previously-untested IsNeq and IsNot paths in datalog.go

Test set​

phase28_driver_errors_test.go:

  • TestPhase28DriverErrorPaths/parse_error, typecheck_error, missing_file, unknown_target, out_dir_is_file.

phase29_edge_cases_test.go:

  • TestPhase29EdgeCases/empty_list_len, empty_string_len, negative_arithmetic, large_integer, unicode_string_ops, list_with_one_element, nested_list, map_get_missing_default, omap_round_trip_multi_key, map_keys_iter_yields_all, for_range_zero_iterations, while_loop_zero_iterations, sum_neg_zero_pos_all_arms, closure_capture_by_value, break_exits_for_range, continue_skips_iteration, map_values_len, not_bool, panic_code_carries_through_catch, list_sort_via_query, list_slice_subscript, math_ceil, str_convert_float, int_cast_from_float, match_default_arm, if_else_if_else_chain, integer_valued_float_print, runtime_version_constant_loads, panic_message_arg_surfaces, negative_int_floor_div_known_divergence.

phase30_target_syntax_test.go:

  • TestPhase30TargetEmittedSyntax/gem, bundle, tebako, truffle_native, mruby, notebook_json_round_trip, gem_unpack_round_trip.

phase31_integration_test.go:

  • TestPhase31Integration/closure_over_query_result, nested_hof_filter_then_map_then_reduce, try_catch_around_record_field_access, list_of_records_query, match_arm_returns_distinct_per_variant.

phase09_test.go (additions):

  • TestPhase9Datalog/dl_neq_constraint, dl_not_negation.

Closeout notes​

Phase 28 was the gap-closure sweep before the MEP closed. The three test files are intentionally separated by audit theme so future contributors can find the right slot for a new regression. Driver errors go in phase28_driver_errors_test.go, language-edge cases go in phase29_edge_cases_test.go, build-target output checks go in phase30_target_syntax_test.go. The .gem walk via archive/tar + compress/gzip was chosen over shelling out to gem unpack because the latter writes to disk and races against the build temp dir, while inspectGemContainsLib runs entirely in memory and is deterministic. The large_integer literal (9223372036854775000) sits just inside int63 to confirm the parser does not truncate near the boundary, and unicode_string_ops covers len on a 5-character string with one non-ASCII codepoint to confirm Ruby's String#length is character-based (which is true on 3.2+ but was not always the case historically).