Crystal

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{
  "source": "crystal.releases",
  "vendor": "Crystal",
  "id": "tag:github.com,2008:Repository/6887813/1.21.0",
  "published_at": "2026-07-16T16:13:01.000Z",
  "title": "1.21.0",
  "url": "https://github.com/crystal-lang/crystal/releases/tag/1.21.0",
  "summary": "Breaking changes stdlib (runtime) Release: Execution Contexts ( #17100 , #17104 , thanks @ysbaddaden ) (text) Disable automatic fallback to legacy PCRE ( #16924 , thanks @straight-shoota ) Features lang Add %W percent string array literals with interpolation ( #16919 , thanks @straight-shoota ) (macros) Add TypeNode#all_methods that includes the type's ancestor's methods ( #16902 , thanks @Blacksmoke16 ) stdlib (cli) Align long-only options in OptionParser help ( #16914 , thanks @kojix2 ) (collection) Make Channel(T) an Iterator(T) ( #16916 , thanks @jgaskins ) (crypto) Add support for OpenSSL 4.0 ( #16839 , thanks @straight-shoota ) (crypto) Support OpenSSL 4.x DLLs on Windows MSVC ( #17116 , thanks @HertzDevil ) (networking) [experimental] Add Socket#sendfile (and Crystal::EventLoop::Socket#sendfile ) ( #16665 , #17133 , thanks @ysbaddaden , @straight-shoota ) (networking) Add HTTP::WebSocket#receive as a synchronous call ( #16689 , thanks @jgaskins ) (runtime) Add Crystal::EventLoop::FileDescriptor#pread ( #17068 , thanks @ysbaddaden ) (runtime) Add without_main flag ( #17074 , thanks @kojix2 ) (runtime) OpenBSD: use kqueue event loop by default ( #17123 , thanks @ysbaddaden ) (serialization) Support nested root properties in JSON::Field ( #17016 , thanks @tcoatswo ) (serialization) Add URI::Params::Field(ignore:) , ignore_serialize , ignore_deserialize ( #17029 , thanks @trypsynth ) (specs) Allow chaining #should , #should_not expectations ( #17020 , thanks @straight-shoota ) (system) Expose Path#kind ( #16917 , thanks @Sija ) (system) Add splat overloads for Process.capture , .run and .new ( #16975 , thanks @straight-shoota ) (system) Add Process::Status.[] constructor ( #17003 , thanks @straight-shoota ) (text) Add String#present? ( #16930 , thanks @Sija ) (text) Add UUID.v6 and .v8 generators ( #17010 , thanks @trypsynth ) compiler (cli) Classify compiler exit reasons ( #17028 , thanks @straight-shoota ) (debugger) Improve proc debug metadata ( #16830 , thanks @skuznetsov ) (debugger) Emit debug metadata for constants and class vars ( #16831 , thanks @skuznetsov ) (debugger) Improve LLDB collection formatters ( #16832 , thanks @skuznetsov ) (parser) Add ASTNode#inspect ( #16699 , thanks @straight-shoota ) (parser) Parse MacroVar with empty expressions: %var{} ( #16772 , thanks @straight-shoota ) (semantic) Split branches on when Bar, Baz ( #17072 , thanks @straight-shoota ) tools (docs-generator) Improve wording in warning about doc generator without LibXML2 ( #16926 , thanks @kojix2 ) Bugfixes stdlib (cli) Fix summary wrapping condition in OptionParser ( #16915 , thanks @kojix2 ) (cli) Avoid Process.exec on Windows and explicitly spawn subprocess ( #17049 , thanks @straight-shoota ) (collection) Fix Iterator#compact_map with EmptyIterator ( #16928 , thanks @straight-shoota ) (collection) Fix Iterator#compact_map with non-nilable compactor proc ( #16927 , thanks @straight-shoota ) (concurrency) Fix swapped atomic orderings in Sync::MU fast paths ( #17063 , thanks @stevegeek ) (llvm) Fix use line 0 for unknown debug location ( #17013 , thanks @straight-shoota ) (networking) Fix HTTP::Request.form_params? to recognize Content-Type and charset ( #16934 , #16971 , thanks @swsch , @straight-shoota ) (networking) Fix HTTP::Client to retry for connection recovery only ( #16981 , thanks @straight-shoota ) (networking) Disable transport read-ahead for Kernel TLS sockets ( #17053 , thanks @jage ) (runtime) Fiber::ExecutionContext::Monitor compat with old Crystal releases ( #17007 , thanks @ysbaddaden ) (runtime) EventLoop::IoUring#open musn't set O_NONBLOCK when blocking ( #17035 , thanks @ysbaddaden ) (runtime) underperforming unlock conditions in Sync::MU ( #17070 , thanks @ysbaddaden ) (runtime) fdlock#try_close? must release ref after yielding to the block ( #17089 , thanks @ysbaddaden ) (runtime) Fiber::ExecutionContext.current? ( #17092 , thanks @ysbaddaden ) (runtime) Refactor Win32 iocp evloop ( #17101 , thanks @ysbaddaden ) (serialization) memory leak in XML::Node#each_namespace ( #17038 , thanks @ysbaddaden ) (system) skip Windows registry MIME entries with an invalid Content Type ( #17106 , thanks @SAY-5 ) (text) Fix IO::Encoder#write when operating on long strings ( #16797 , thanks @jgaskins ) compiler (cli) Remedy short-flag conflict for crystal spec -p ( #17062 , thanks @straight-shoota ) (codegen) Fix codegen treating distinct lib type aliases as the same type ( #16961 , thanks @stakach ) (interpreter) Add interpreter upcast_distinct for Pointer to Pointer ( #16962 , thanks @stakach ) (interpreter:repl) Fix auto-indentation in the REPL when typing classes. ( #16910 , thanks @I3oris ) (interpreter:repl) Fix interpreter multidispatch cache collision ( #16958 , thanks @stakach ) (parser) Fix lexing MacroVar syntax in literal ( #16779 , thanks @straight-shoota ) (parser) Fix parsing macro var without exps followed by macro expression ( #16879 , thanks @straight-shoota ) (parser) Fix parse parenthesized expression in block arg assignment ( #16894 , thanks @straight-shoota ) (parser) Do not merge nested Expression and ExceptionHandler ( #16852 , thanks @straight-shoota ) (parser) Fix parser silently ignoring &(...) , &[...] , &{...} in assignment ( #16960 , thanks @stakach ) (parser) Fix parser allow / and // immediately after self , nil , true , false ( #16942 , thanks @stakach ) (parser) Fix short block setter call end location ( #17039 , thanks @Sija ) (semantic) Fix freeze type of variable declared with out ( #16870 , thanks @straight-shoota ) (semantic) Fix lookup_matches_in_type to reject partial matches ( #16867 , thanks @straight-shoota ) (semantic) Fix location of double splat named tuple typenode entry locations ( #16889 , thanks @Blacksmoke16 ) (semantic) Fix sizeof , offsetof as generic type argument in inferred ivar type ( #16811 , thanks @kojix2 ) (semantic) Fix macro argument errors for path receiver calls ( #16923 , thanks @kojix2 ) (semantic) Detect uninitialized ancestor ivars through macro_def initializers ( #16959 , thanks @stakach ) (semantic) Preserve nil_if_read? across while cond filters ( #16963 , thanks @stakach ) (semantic) Keep wider subclass observer when call owner narrows ( #16947 ) ( #16990 , thanks @stakach ) (semantic) Symmetric common_descendent for two generic class types ( #10831 ) ( #16999 , thanks @stakach ) tools (formatter) Fix format empty then with trailing comment ( #16878 , thanks @straight-shoota ) (formatter) Fix formatting whitespace in ternary if with trailing comments ( #16880 , thanks @straight-shoota ) (formatter) Fix formatter on empty string literal continuation ( #16817 , thanks @straight-shoota ) (formatter) Fix format annotations of splat parameter ( #16987 , thanks @straight-shoota ) (formatter) Fix formatter strip empty lines in heredoc ( #17034 , thanks @straight-shoota ) Chores stdlib (cli) [deprecation] Deprecate Colorize.on_tty_only! ( #16859 , thanks @straight-shoota ) (concurrency) [deprecation] Deprecate spawn(same_thread:) ( #17097 , thanks @ysbaddaden ) (files) [deprecation] Rename parameter to writable in IO::Memory.new ( #16858 , #16883 , thanks @straight-shoota ) (system) [deprecation] Hide platform-specific Process::Status constructor ( #16997 , thanks @straight-shoota ) Performance stdlib (collection) Preallocate correct size for hash in Hash.zip ( #17054 , thanks @carlhoerberg ) Refactor stdlib (cli) Split error helper for compiler CLI into independent methods ( #16984 , thanks @straight-shoota ) (cli) Refactor compiler code to raise CompilerError instead of abort ( #16995 , thanks @straight-shoota ) (concurrency) simplify read console (windows) ( #17098 , thanks @ysbaddaden ) (concurrency) Process#wait on Windows ( #17099 , thanks @ysbaddaden ) (networking) Refactor bubbling exceptions from user code in HTTP::Client#exec(&) ( #16969 , thanks @straight-shoota ) (runtime) Internalize IO::Evented into Crystal::EventLoop::Wasi ( #17030 , thanks @ysbaddaden ) (runtime) Fix: thread safety of the libevent event loop ( #17031 , thanks @ysbaddaden ) (runtime) Drop unused IO::Evented and Crystal::ThreadLocalValue ( #17032 , thanks @ysbaddaden ) (runtime) Consolidate #overlapped_connect and #overlapped_accept into EventLoop::IOCP ( #17090 , thanks @ysbaddaden ) (runtime) OpenBSD now supports EVFILT_USER ( #17121 , thanks @ysbaddaden ) (system) Refactor Dir::Globber to a struct with instance methods ( #16899 , thanks @straight-shoota ) (system) Refactor internal Process constructor to receive Crystal::System::Process ( #16933 , thanks @straight-shoota ) (system) dont parse but mmap ELF, Mach-O, PE files and some DWARF sections ( #16939 , #17134 , thanks @ysbaddaden ) compiler Replace backticks with Process.capture ( #17012 , #17122 , thanks @straight-shoota , @ysbaddaden ) (codegen) Set optsize and minsize fun attributes for the -Os and -Oz optimization modes ( #16983 , thanks @ysbaddaden ) (parser) Parse parens in type grammar into Union#parens ( #16744 , #16908 , thanks @straight-shoota ) (parser) Refactor whitespace branch in Lexer#next_macro_token [follow-up #16771 ] ( #16776 , thanks @straight-shoota ) (parser) Refactor formatter, remove internal delimited_pair(advance) ( #17023 , thanks @straight-shoota ) tools (formatter) [breaking] Standardize parsing of symbol and string array literals ( #16748 , thanks @straight-shoota ) (formatter) Drop format_binary parameter alternative ( #16912 , thanks @straight-shoota ) other Fix violations reported by ameba 1.7 ( #17021 , thanks @straight-shoota ) Documentation stdlib (cli) Add missing_option to OptionParser example ( #17112 , thanks @LaskaIDK ) (macros) Improve docs for ::delegate ( #16854 , thanks @straight-shoota ) (text) Document null-termination on String#to_unsafe ( #16869 , thanks @mvanhorn ) (text) Document String is not inheritable ( #17000 , thanks @LaskaIDK ) other Fix typo writable in documentation ( #16848 , thanks @straight-shoota ) Format asciidoc ( #16992 , thanks @straight-shoota ) rumdl: Fix MD077: Continuation line over-indented ( #17085 , thanks @straight-shoota ) Specs stdlib (cli) Refactor run_git spec helper to use Process.capture_result? ( #17079 , thanks @straight-shoota ) (collection) Add specs for Iterator.empty ( #17014 , thanks @straight-shoota ) (concurrency) Fix: Crystal 1.0.0 is confused by file private types ( #17067 , thanks @ysbaddaden ) (networking) Extract spec helpers close_connection and client_for for HTTP client specs ( #16968 , thanks @straight-shoota ) (text) Add specs for range accessor with open ended exclusive range ( #16849 , thanks @straight-shoota ) compiler (cli) Add compiler-cli test suite ( #17033 , thanks @straight-shoota ) (debugger) Fix lldb-check expectations in debug tests for compatibility with modern LLDB ( #16860 , thanks @straight-shoota ) other Remove unnecessary not_nil! in spec suite ( #16865 , thanks @straight-shoota ) Replace not_nil! with should_not(be_nil) in spec suite ( #16906 , thanks @straight-shoota ) Infrastructure Changelog for 1.21.0 ( #17095 , thanks @straight-shoota ) Update previous Crystal release 1.20.0 ( #16844 , thanks @ysbaddaden ) Update previous Crystal release 1.20.1 ( #16901 , thanks @straight-shoota ) Merge release/1.19 @ 1.19.2 into master ( #16905 , thanks @straight-shoota ) Merge release/1.20 @ 1.20.1 into master ( #16900 , thanks @straight-shoota ) Update devenv.lock ( #16819 , #16935 , #17006 , #17075 , #17084 , thanks @github-actions, @crysbot ) Update changelog script ( #16946 , thanks @straight-shoota ) Extract CRYSTAL_BOOTSTRAP_VERSION in bin/ci ( #16966 , thanks @straight-shoota ) Update previous Crystal release 1.20.2 ( #16954 , thanks @straight-shoota ) Makefile: Split install target into subcomponents ( #16980 , thanks @straight-shoota ) Update release-update script ( #16977 , thanks @straight-shoota ) Makefile: Build manpages for install target ( #16991 , thanks @straight-shoota ) Apply shfmt ( #17015 , thanks @straight-shoota ) Apply mbake formatter for Makefile ( #17024 , thanks @straight-shoota ) infra: devenv input for git-hooks follows nixpkgs ( #17064 , thanks @straight-shoota ) Replace markdownlint with rumdl ( #17069 , thanks @straight-shoota ) Replace .markdownlint.yaml with rumdl.toml ( #17078 , thanks @straight-shoota ) (ci) Fix -Devloop=io_uring flag in Linux CI ( #16843 , thanks @straight-shoota ) (ci) Use PAT from GHA environments for backport job ( #16864 , thanks @straight-shoota ) (ci) Use AWS credentials from GHA environments for deploy_api_docs job ( #16863 , thanks @straight-shoota ) (ci) Update GH Actions ( #16836 , #16944 , #17011 , #17042 , [ #17117 ], thanks @renovate ) (ci) Use Crysbot token in update-devenv workflow to trigger CI ( #16938 , thanks @straight-shoota ) (ci) Fix tags for nightly docker images ( #16973 , thanks @straight-shoota ) (ci) Drop separate aarch64 workflow ( #16965 , thanks @straight-shoota ) (ci) Update crate-ci/typos action to v1.46.2 ( #16986 , thanks @renovate ) (ci) Update macos-15 runners to macos-26 ( #17022 , thanks @straight-shoota ) (ci) Upgrade library dependencies for Windows CI ( #17025 , thanks @straight-shoota ) (ci) Upgrade windows runners to VS 2026 ( #17043 , thanks @straight-shoota ) (ci) Upgrade nixpkgs 26.05 in Lint workflow ( #17066 , thanks @straight-shoota ) (ci) Update previous Crystal release 1.20.3 ( #17114 , thanks @ysbaddaden )",
  "tags": [
    "Crystal",
    "crystal.releases",
    "programming-language",
    "crystal",
    "compiled"
  ]
}