February 2026 - ruby-core - ml.ruby-lang.org

[ruby-core:123958] [Ruby Feature#21720] Add a native Binary Heap / Priority Queue to Ruby's Standard Library (heapify, heappush, heappop)
by rahulk501 (Rahul Kumar) 11 Jun '26

11 Jun '26

Issue #21720 has been reported by rahulk501 (Rahul Kumar). ---------------------------------------- Feature #21720: Add a native Binary Heap / Priority Queue to Ruby's Standard Library (heapify, heappush, heappop) https://bugs.ruby-lang.org/issues/21720 * Author: rahulk501 (Rahul Kumar) * Status: Open ---------------------------------------- **Title:** Add a native Binary Heap / Priority Queue to Ruby's Standard Library (`heapify`, `heappush`, `heappop`) **Problem** Ruby currently lacks a native binary heap / priority queue data structure in the standard library. Users frequently reimplement heaps manually, or install third-party gems, simply to access common operations such as: * `heapify` * `heappush` * `heappop` * efficient priority queues Meanwhile, languages like Python provide a standard `heapq` module which is widely used in algorithms, AI, scheduling, job queues, pathfinding, graph traversal, and competitive programming. Because Ruby does not include a heap implementation, developers often write ad-hoc, buggy, or inconsistent versions of a heap. This leads to fragmentation and duplication. **Proposal** Introduce a lightweight `Heap` or `BinaryHeap` class to Ruby’s standard library with the following minimal API: ```ruby heap = Heap.new(array = []) heap.push(value) heap.pop # returns smallest (min-heap) heap.peek heap.size ``` Or a module-based functional API similar to Python’s `heapq`: ```ruby Heap.heapify(array) Heap.heappush(array, value) Heap.heappop(array) ``` Both designs are simple and allow backward-compatible extension. **Why include it in the standard library?** 1. Heaps are a *fundamental data structure*—used in sorting, algorithms, scheduling, and timers. 2. Many languages include them natively (Python, C++ via STL `priority_queue`, Java, Go, Rust `BinaryHeap`). 3. Adding it reduces unnecessary reimplementations in user codebases. 4. A small heap implementation adds little maintenance burden. 5. Existing Ruby solutions (gems like `algorithms`, `priority_queue`, custom code) are not universally available and often exceed what users need. **Reference Implementation (pure Ruby, minimal example)** ```ruby module Heap def self.heapify(arr) (arr.length / 2 - 1).downto(0) { |i| sift_down(arr, i) } arr end def self.heappush(arr, value) arr << value sift_up(arr, arr.length - 1) end def self.heappop(arr) return nil if arr.empty? arr[0], arr[-1] = arr[-1], arr[0] min = arr.pop sift_down(arr, 0) min end def self.sift_up(arr, i) while i > 0 p = (i - 1) / 2 break if arr[p] <= arr[i] arr[p], arr[i] = arr[i], arr[p] i = p end end def self.sift_down(arr, i) n = arr.length loop do left = 2 * i + 1 right = 2 * i + 2 smallest = i smallest = left if left < n && arr[left] < arr[smallest] smallest = right if right < n && arr[right] < arr[smallest] break if smallest == i arr[i], arr[smallest] = arr[smallest], arr[i] i = smallest end end private_class_method :sift_up, :sift_down end ``` **Optional C implementation** If accepted, I am willing to provide a minimal C version for performance parity with other stdlib containers. **Compatibility** No breaking changes expected. Naming avoids conflict with existing libraries. **Conclusion** Adding a tiny, well-defined heap structure would strengthen Ruby’s built-in algorithmic tools, reduce duplicated code across the ecosystem, and align Ruby with other mainstream languages. -- https://bugs.ruby-lang.org/

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[ruby-core:111678] [Ruby master Feature#19315] Lazy substrings in CRuby
by Eregon (Benoit Daloze) 11 Jun '26

11 Jun '26

Issue #19315 has been reported by Eregon (Benoit Daloze). ---------------------------------------- Feature #19315: Lazy substrings in CRuby https://bugs.ruby-lang.org/issues/19315 * Author: Eregon (Benoit Daloze) * Status: Open * Priority: Normal ---------------------------------------- CRuby should implement lazy substrings, i.e., "abcdef"[1..3] must not copy bytes. Currently CRuby only reuse the char* if the substring is until the end of the buffer. But it should also work wherever the substring starts and ends. Yes, it means RSTRING_PTR() might need to allocate to \0-terminate, so be it, it's worth it. There is already code for this (`SHARABLE_MIDDLE_SUBSTRING`), but it's disabled by default and `RSTRING_PTR()` needs to be changed to deal with this. It seems a good idea to introduce a variant of `RSTRING_PTR` which doesn't guarantee \0-termination, so such callers can then use the existing bytes always without copy. There are countless workarounds for this missing optimization, all not worth and all less readable: * https://bugs.ruby-lang.org/issues/19314 * https://github.com/ruby/net-protocol/pull/14 * Manual lazy substrings which track string + index + length * More but I don't remember all now, feel free to comment or link more urls/tickets. -- https://bugs.ruby-lang.org/

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[ruby-core:113430] [Ruby master Feature#19633] Allow passing block to `Kernel#autoload` as alternative to second `filename` argument
by shioyama (Chris Salzberg) 10 Jun '26

10 Jun '26

Issue #19633 has been reported by shioyama (Chris Salzberg). ---------------------------------------- Feature #19633: Allow passing block to `Kernel#autoload` as alternative to second `filename` argument https://bugs.ruby-lang.org/issues/19633 * Author: shioyama (Chris Salzberg) * Status: Open * Priority: Normal ---------------------------------------- `Kernel#autoload` takes two arguments, a symbol `module` representing the constant to be autoloaded, and a `filepath` to load the constant from (with `require`). Currently, Zeitwerk has to [monkeypatch `Kernel#require`](https://github.com/fxn/zeitwerk/blob/a7c4a983df0f4e4058f32c610dac1e8b99f687da/lib/zeitwerk/kernel.rb) to fetch the loader for the file being loaded, then run the original (aliased) `require`, then run autoload callbacks. In addition to the monkeypatch, this also requires a registry (`Zeitwerk::Registry`) to map file paths to loaders, to know which loader should be used for a given autoload-triggered `require`. In fact, Zeitwerk has to _assume_ that the monkey-patched `require` call came from an autoload trigger; there is no way to really be sure of the source. If Ruby allowed passing a block as an alternative to the explicit filepath, then I think this could be improved and would eliminate the need for a monkeypatch. So something like this: ```ruby autoload(:B) do require "lib/b" # trigger callback, etc end ``` I am implementing a gem called [Im](https://github.com/shioyama/im) which is a fork of Zeitwerk, and in the case of this gem, such a feature would be even more useful. Im implements autoloads on anonymous modules by registering an autoload and then "catching" the require and converting it into a `load`, passing the module as the second argument (see [here](https://github.com/shioyama/im/blob/44ce348639a1aae563a5be7a40602761e….) This is currently quite tricky because, again, it's hard to know _where_ a `require` came from. In addition to removing the monkeypatch (inherited from Zeitwerk), Im would further benefit from the block argument because then it could simply access the module via a closure, rather than pulling it from a registry: ```ruby mod.autoload(:Foo) do load "lib/foo.rb", mod end ``` I don't know how hard or easy this would be to implement, but if there is interest in this as a feature I'd be happy to look into implementing it. -- https://bugs.ruby-lang.org/

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[ruby-core:124888] [Ruby Bug#21927] Prism: misleading error message for forwarding in lambda argument
by nobu (Nobuyoshi Nakada) 07 Jun '26

07 Jun '26

Issue #21927 has been reported by nobu (Nobuyoshi Nakada). ---------------------------------------- Bug #21927: Prism: misleading error message for forwarding in lambda argument https://bugs.ruby-lang.org/issues/21927 * Author: nobu (Nobuyoshi Nakada) * Status: Open * Assignee: prism * ruby -v: d256629bf9 * Backport: 3.2: DONTNEED, 3.3: DONTNEED, 3.4: REQUIRED, 4.0: REQUIRED ---------------------------------------- Even in a forwarding method: ```console $ ruby --parser=prism -e 'def m(...) ->(...){}; end' -e: -e:1: syntax error found (SyntaxError) > 1 | def m(...) ->(...){}; end | ^~~ unexpected ... when the parent method is not forwarding ``` This message is proper for method arguments: ```console $ ruby --parser=prism -e 'def m() p(...); end' -e: -e:1: syntax error found (SyntaxError) > 1 | def m() p(...); end | ^~~ unexpected ... when the parent method is not forwarding ``` The message from parse.y is different; "unexpected ... in lambda argument": ```console $ ruby --parser=parse.y -e 'def m(...) ->(...){}; end' -e:1: unexpected ... in lambda argument def m(...) ->(...){}; end ruby: compile error (SyntaxError) ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124885] [Ruby Bug#21925] Prism misparses standalone "in" pattern matching in "case/in"
by knu (Akinori MUSHA) 07 Jun '26

07 Jun '26

Issue #21925 has been reported by knu (Akinori MUSHA). ---------------------------------------- Bug #21925: Prism misparses standalone "in" pattern matching in "case/in" https://bugs.ruby-lang.org/issues/21925 * Author: knu (Akinori MUSHA) * Status: Open * Target version: 4.1 * ruby -v: ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [arm64-darwin23] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- Prism misparses standalone `in` pattern matching in `case/in` when the left-hand side is a method call with a dot receiver ## Summary When a standalone `expr in pattern` one-line pattern match appears inside a `case/in` branch, and `expr` is a method call with a dot receiver (for example, `obj.method`), Prism incorrectly parses `in pattern` as a new branch of the outer `case/in` instead of treating it as a `MatchPredicateNode`. The parse.y parser handles this case correctly. ## Reproduction ``` $ ruby -v ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [arm64-darwin23] ``` It also reproduces on Ruby 3.4.8 (2025-12-17 revision 995b59f666) +PRISM [arm64-darwin25]. ### Minimal script ```ruby x = "x" case x in Integer nil in String p :before x.itself in String p :after end ``` ### Command output ``` $ ruby -e ' x = "x" case x in Integer nil in String p :before x.itself in String p :after end ' :before $ ruby --parser=parse.y -e ' x = "x" case x in Integer nil in String p :before x.itself in String p :after end ' :before :after ``` ### Expected behavior (parse.y) Both `:before` and `:after` are printed. `x.itself in String` is parsed as a standalone pattern match (predicate) inside the `in String` branch. ### Actual behavior (Prism) Only `:before` is printed; `p :after` is never executed. ## Analysis Prism splits `x.itself in String` at the `in` keyword, treating `x.itself` as the last statement of the `in String` branch and `in String` as a third branch of the outer `case/in`. The following script shows how each parser interprets the `case/in` branches: ```ruby code = <<~RUBY x = "x" case x in Integer nil in String x.itself in String p :after end RUBY # Prism require "prism" ast = Prism.parse(code).value.statements.body[1] puts "Prism: conditions: #{ast.conditions.length}" ast.conditions.each_with_index do |c, i| pat = c.pattern name = pat.respond_to?(:name) ? pat.name : pat.class stmts = c.statements&.body&.map { |s| s.class.name.split("::").last } || [] puts " in[#{i}]: pattern=#{name}, body=#{stmts}" end # parse.y (Ripper) require "ripper" sexp = Ripper.sexp(code) case_node = sexp[1][1] def count_in_branches(node) return [] unless node.is_a?(Array) && node[0] == :in pattern_node = node[1] body = node[2] || [] name = pattern_node.is_a?(Array) && pattern_node[1].is_a?(Array) ? pattern_node[1][1] : pattern_node[1] stmts = body.map { |s| s[0].to_s } [{ pattern: name, body: stmts }] + count_in_branches(node[3]) end branches = count_in_branches(case_node[2]) puts "\nparse.y (Ripper): conditions: #{branches.length}" branches.each_with_index do |b, i| puts " in[#{i}]: pattern=#{b[:pattern]}, body=#{b[:body]}" end ``` Output (run with `ruby --parser=parse.y` so Ripper uses parse.y): ``` Prism: conditions: 3 in[0]: pattern=Integer, body=["NilNode"] in[1]: pattern=String, body=["CallNode"] in[2]: pattern=String, body=["CallNode"] parse.y (Ripper): conditions: 2 in[0]: pattern=Integer, body=["var_ref"] in[1]: pattern=String, body=["case", "command"] ``` Prism reports 3 branches, while parse.y reports 2. In the parse.y result, `in[1]` correctly contains both the inner expression (`x.itself in String` parsed as a standalone pattern match) and the `command` (`p :after`). In the Prism result, `x.itself` becomes the sole body of `in[1]`, and `in String` is misinterpreted as a new `in[2]` branch of the outer `case`. ## Consideration From experimentation, the issue appears to be triggered only when all of the following are true: 1. The outer `case/in` has at least two `in` branches before the affected branch. 2. The standalone `in` expression uses a dot-receiver method call as its left-hand side, such as `obj.method in Pattern`. Conditions where this behavior is not observed: - If the expression is a receiver-less call, such as `f(x) in Pattern`, the parser keeps it as a standalone pattern match. - If the receiver expression is parenthesized, such as `(obj.method) in Pattern`, the parser keeps it as a standalone pattern match. - If you assign first, such as `y = obj.method; y in Pattern`, the parser keeps it as a standalone pattern match. -- https://bugs.ruby-lang.org/

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[ruby-core:123731] [Ruby Bug#21674] Possible regression in return case in statement
by jandudulski (Jan Dudulski) 07 Jun '26

07 Jun '26

Issue #21674 has been reported by jandudulski (Jan Dudulski). ---------------------------------------- Bug #21674: Possible regression in return case in statement https://bugs.ruby-lang.org/issues/21674 * Author: jandudulski (Jan Dudulski) * Status: Open * ruby -v: 3.4.6 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Suddenly my code started failing in Ruby 3.4.6 and 3.4.7. Shortest code example: ``` ruby args = [:increased] context = Data.define(:event).new(:decreased) case args in [event] context.event in ^event end ``` In Ruby prior to 3.4.6 in returns `false` (as expected) but in 3.4.6 and 3.4.7 it returns `:decreased`. `context.event in ^event` still returns `false`. -- https://bugs.ruby-lang.org/

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[ruby-core:124474] [Ruby Bug#21831] Prism doesn't count underscores in the fraction part of rational float
by nobu (Nobuyoshi Nakada) 07 Jun '26

07 Jun '26

Issue #21831 has been reported by nobu (Nobuyoshi Nakada). ---------------------------------------- Bug #21831: Prism doesn't count underscores in the fraction part of rational float https://bugs.ruby-lang.org/issues/21831 * Author: nobu (Nobuyoshi Nakada) * Status: Open * Backport: 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED, 4.0: REQUIRED ---------------------------------------- Good. ```console $ ruby3.3 -e 'p 0.1_2r.to_f' 0.12 $ ruby3.4 --parser=parse.y -e 'p 0.1_2r.to_f' 0.12 ``` Wrong. ```console $ ruby3.4 -e 'p 0.1_2r.to_f' 0.012 ``` -- https://bugs.ruby-lang.org/

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[ruby-core:124887] [Ruby Bug#21926] Thread#value on popen3 wait thread hangs in finalizer
by stevecrozz (Stephen Crosby) 23 May '26

23 May '26

Issue #21926 has been reported by stevecrozz (Stephen Crosby). ---------------------------------------- Bug #21926: Thread#value on popen3 wait thread hangs in finalizer https://bugs.ruby-lang.org/issues/21926 * Author: stevecrozz (Stephen Crosby) * Status: Open * ruby -v: 3.3.7 * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- Calling Thread#value on an Open3.popen3 wait thread from a finalizer completes in Ruby 3.2 but hangs in Ruby 3.3+. See repro.rb below. When the Ruby process hangs in these conditions, it no longer responds to signals and it seems to be unable to run any other threads. This affects the schmooze gem (and potentially other code using Open3.popen3 with finalizers), causing test suites to hang intermittently. ``` ruby # repro.rb require 'open3' class ProcessWrapper def initialize @stdin, @stdout, @stderr, @wait_thread = Open3.popen3("cat") ObjectSpace.define_finalizer(self, self.class.make_finalizer(@stdin, @stdout, @stderr, @wait_thread)) end def self.make_finalizer(stdin, stdout, stderr, wait_thread) proc do stdin.close rescue nil stdout.close rescue nil stderr.close rescue nil wait_thread.value # Hangs here in Ruby 3.3+ end end end 100.times { ProcessWrapper.new } GC.stress = true 1000.times { Object.new } puts "done" ``` ## Environment - Linux x86_64 - Tested on Ruby 3.2.7, 3.3.7, 3.4.8 -- https://bugs.ruby-lang.org/

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[ruby-core:124594] [Ruby Bug#21844] Inconsistent ArgumentError message for Data::define.new
by jnchito (Junichi Ito) 20 May '26

20 May '26

Issue #21844 has been reported by jnchito (Junichi Ito). ---------------------------------------- Bug #21844: Inconsistent ArgumentError message for Data::define.new https://bugs.ruby-lang.org/issues/21844 * Author: jnchito (Junichi Ito) * Status: Open * ruby -v: ruby 4.0.1 (2026-01-13 revision e04267a14b) +PRISM [arm64-darwin25] * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- The code below shows `Data::define.new` treats symbol and string keys equivalently: ``` ruby C = Data.define(:a, :b) C.new(a: 1, b: 1) #=> #<data C a=1, b=1> C.new('a' => 1, 'b' => 1) #=> #<data C a=1, b=1> ``` But it acts differently when detecting missing keywords: ```ruby C.new(a: 1) #=> 'Data#initialize': missing keyword: :b (ArgumentError) C.new('a' => 1) #=> 'Data#initialize': missing keywords: :a, :b (ArgumentError) ``` I feel it should work like this: ```ruby C.new('a' => 1) #=> 'Data#initialize': missing keyword: :b (ArgumentError) ``` I created a PR to fix it: https://github.com/ruby/ruby/pull/15910 -- https://bugs.ruby-lang.org/

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[ruby-core:124286] [Ruby Bug#21789] `IO#flush` doesn't invoke fiber scheduler io_write hook
by noteflakes (Sharon Rosner) 16 May '26

16 May '26

Issue #21789 has been reported by noteflakes (Sharon Rosner). ---------------------------------------- Bug #21789: `IO#flush` doesn't invoke fiber scheduler io_write hook https://bugs.ruby-lang.org/issues/21789 * Author: noteflakes (Sharon Rosner) * Status: Open * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- When calling `IO#flush` or closing an IO with unflushed writes, the flushing is done by calling `rb_io_blocking_region_wait` and eventually doing a `write` system call. When done in a non-blocking fiber with an active fiber scheduler, this will invoke the `#blocking_operation_wait` fiber scheduler hook, which will run the system call in a worker thread, and therefore the flushing bypasses the async I/O capabilities of the fiber scheduler. The proposed fix is to test for the presence of a fiber scheduler in `io_flush_buffer_async` and invoke the `#io_write` fiber scheduler hook with the unflushed part of the IO's write buffer. Associated PR here: https://github.com/ruby/ruby/pull/15609 -- https://bugs.ruby-lang.org/

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