[Largo]

This retires the code still unchanged since the 2016 import commit (5252433c) and brings IronRuby closer to CRuby 4.0, in five rounds. Today's master (91bb9ecb) is merged in.

2016-era lines (git blame -w, which ignores whitespace changes): 408,361 → 137,549 (−66%). The diff against master is 7,207 files, +24.5k / −280k lines.

Most of the remaining 2016 lines are working code. About 21k are upstream stdlib files identical to CRuby 4.0's, and about 7k are license headers.

Round 1: dead code

• Unused test trees: deleted the vendored 2016 rubyspec/mspec (Tests/mspec), Tests/Legacy, Tests/Experiments, Tests/Interop and Tests/Scripts. Their tests that still check something were ported to Src/IronRuby.Tests first.
• Old build system: deleted Build.proj, make.cmd and the nuspecs; the Makefile and Ruby.sln now drive dotnet build.
• Dead libraries and docs: deleted ParseTree, the 2016 rb-readline (CRuby's readline gem over Reline replaces it), the Tutorial sample, and the 2007 TiddlyWiki docs.
• Dead code paths: removed always-true FEATURE_* #ifs, dead AST nodes, and Ruby 1.8 methods.
• Version info: assemblies carry the release version, and RUBY_REVISION is the git commit.

Round 2: 1.8/1.9-era machinery

• Removed: taint/untrust, $SAFE, RubyCompatibility, the Thread.Abort leftovers and -save/-load.
• Compiler fixes: rescue list evaluation order, a bare rescue calling ===, eval('super') arguments, break from forwarded blocks.
• Library fixes: IO.popen "r+" with binary data, String#chars with U+FFFF, String#succ, const_get, Process.clock_gettime, and the Integer⊕Float out-of-range warnings.
• RbConfig::CONFIG["ruby_version"] is now "4.0.0".

Round 3: CRuby 4.0 conformance

• Stdlib: synced to CRuby 4.0.9 (RubyGems/Bundler 4.0.20), using Util/sync-stdlib.rb.
• Core:
  • CRuby's encoding table;
  • a BigDecimal engine on BigInteger;
  • the platform's errno numbers and texts;
  • object-model fixes (Class.new(Class), 16-digit object ids, method lists hiding CLR members and helpers);
  • Comparable/Enumerable → IComparable/IEnumerable.
• Error messages: CRuby 4.0 wording.
• Prelude: about 725 dead lines removed.

Round 4: follow-ups

• System::Int64/BigInteger name their CLR types again.
• Library methods:
  • keyword-parameter arity errors match CRuby ([Keywords]);
  • called names through aliases ([CalledName], [SameRubyMethod]);
  • no sticky keyword-hash mark ([ReceivesKeywords]).
• Encodings: regexp character offsets on Shift_JIS/EUC-JP, UTF-16/32 padding, converters.
• New API: IO#timeout, Thread#set_trace_func, ObjectSpace.count_objects, GC.stat_heap, did_you_mean (lazy), Enumerator::Producer, Process::Waiter.
• Ractor: the Ruby 4.0 API on CLR threads.
• Startup: the precompiled startup library builds again (ir -e 1: 0.65 s → 0.49 s on the R2R host). A new DLR patch, 0103, keeps backtraces when rethrowing.
• Platform: open/fcntl flags, File.lchmod, UDP after ICMP errors, connect timeouts per CRuby Bug #22223, regenerated AOT subclasses.
• Regressions from rounds 1–3, found by a full ruby/spec run, are fixed.

Round 5: conformance and performance

• Performance:
  • the keyword-mark checks cost nothing measurable;
  • const_get/const_defined? are back to their pre-round-1 speed;
  • the Util/bench geomean over 63 benchmarks is 0.984× the start of round 5, where pre-round-1 is 1.038×.
• Backtraces:
  • correct lines in compiled (hot) code;
  • re-raise frames;
  • library frames and labels follow CRuby's rule (a probe of ~210 raising snippets went from 104 differences to 39).
• Error reports: did_you_mean suggests locals (NameError#local_variables); error_highlight is on by default; SyntaxError reports read "syntax errors found" with prism's annotated snippet, and syntax_suggest is on. All byte-identical to CRuby on the cases checked.
• Ractor isolation: globals, class variables, class-level ivars, constants with unshareable values, ractor-local $stdout/$VERBOSE, isolated procs, require in main. 146 of 153 checks in CRuby's bootstraptest/test_ractor.rb pass; the checks cost nothing until a Ractor starts.
• Method#arity/#parameters: match CRuby for all but 46 of 2,111 core methods (41 of them Set), via an InternalMethods.Generated.cs signature table.
• Fiber: resume/transfer keywords, CRuby's Fiber errors and storage, IO#write_nonblock with non-Strings, and a RubyBufferedStream offset bug.
• .NET interop: overloads are chosen by a Ruby Array's items (String.Join(",", [1, 2]), LINQ Sum), bignums prefer double, Nullable[T].new works, BigInteger-only members and snake_case CLR names work on Integers.
• Hidden state: about 55 prelude constants hidden (Module#__hide_constant__), internal ivars of Set, Random, Enumerator and others hidden (Marshal stays byte-compatible), autoloads for core classes answer nil, and Enumerator names are fixed.
• ruby/spec fixes: mspec's fixnum_max helper now covers IronRuby (default.mspec), a Net::HTTP hang (IO#read after gets on a socket) is fixed, and Thread#status at thread start is fixed.

Merge with master (91bb9ecb)

• master's C# Rational/Complex are kept, with this branch's conventions on top: hidden helpers, the Numeric owner for dup/clone, "to" wording, and [Keywords] for exception:.
• Integer()/Float() stay this branch's C# methods.
• BasicObject#equal? keeps master's identity method while staying one method with #== to Ruby.
• 1.step(by:, to:) keywords and the Range#first arity were fixed after the merge.
• ruby/spec slices show no regressions against either parent (core/rational, complex, integer, range, numeric, kernel conversions, basicobject, language).

Testing (final tree d15f678b)

• IronRuby.Tests on net10.0: PASSED, 0 failures. net8.0 and net10.0 build with no compiler warnings.
• Prism sweeps: 847/847, 491/491, 314/314, 0 failed. The generated files come out unchanged when regenerated.
• CRuby-diff scripts (encodings, BigDecimal, Zlib, error messages, keyword hashes, hot-code backtraces, did_you_mean/error_highlight/SyntaxError, Rational/Complex): byte-identical output.
• ruby/spec at dda28d04/b79c65ed, LANG=C.UTF-8 (README Status):

suite	examples	failing
language	2935	1 (wording, below)
command_line	175	0
security	34	0
library	6011	0
core	23130	44: 20 ObjectSpace.each_object (needs -X:ObjectSpace), 24 wording

Decision for the reviewer

"can't convert X to Y (X#m gives Z)" matches CRuby 4.0 exactly, which the README names as the reference. The pinned ruby/spec expects the 4.1 wording "into" from engines other than CRuby < 4.1; CRuby 4.0.9 fails the same examples. CI doesn't gate on the spec run. Reverting means changing one format string in RubyExceptions.CreateReturnTypeError, one prelude line, and the test expectations that pinned the old wording.

Not verified here

• Windows and macOS: the errno tables and the macOS/FreeBSD/arm/powerpc open/fcntl values come from the platform headers, untested on those systems.

Known follow-ups

• Line tracking: correct lines in compiled code add 4–10% on pure call microbenchmarks (super_call, lambda_call, yield). Cheaper variants would lose other threads' Thread#backtrace frames or the fiber-reclamation guarantees.
• Ractor: moved Strings/Arrays/Hashes passed to built-ins aren't rejected.
• Thread#raise and fibers: a Thread#raise arriving just as a thread resumes a fiber can land in the wrong one (intermittent).
• Identity on large numbers: (2**64).equal?(2**64) is true (from master's value-type identity rule); CRuby says false.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KPwZf4gAJD4kdk9eEzGgYM