0.20.5

• Improved performance in String#index, String#rindex due to Rabin-Karp algorithm (thanks @makenowjust).
• Improved performance in Crypto::Bcrypt (see #3880, thanks @ysbaddaden).
• expect_raises returns raised exception (thanks @kostya).
• Line numbers debug information is always generated (see #3831, thanks @ysbaddaden).
• Added Zip::File, Zip::Reader and Zip::Writer. Native readers for zip files that delegate compression to existing zlib module.
• Added Hash#delete with block (see #3856, thanks @bmulvihill).
• Added String#[](char : Char) (see #3855, thanks @Sija).
• Added crystal tool expand to expand macro call in a given location (see #3732, thanks @makenowjust).
• Fixed crystal play is able to show compilation errors again.
• crystal doc recognizes crystal-lang/crystal in any remote (thanks @MaxLap).
• Some bug fixes

0.20.4

• (breaking change) A type that wants to convert itself to JSON now must override to_json(builder : JSON::Builder) instead of to_json(io : IO). The same is true for custom JSON converters. If you are using JSON.mapping then your code will continue to work without changes.
• (breaking change) Defining a finalize method on a struct now gives a compile error
• (breaking change) Default argument types now must match their restriction, if any (for example def foo(x : Int32 = nil) will now fail to compile if foo is invoked without arguments) (thanks @makenowjust)
• (breaking change) each methods now return Nil
• (breaking change) IO#skip(bytes) will now raise if there aren't at least the given amount of bytes in the IO (previously it would work well if there were less bytes, and it would hang if there were more)
• (breaking change) MemoryIO was removed (use IO::Memory instead)
• (breaking change) Number#step now requires named arguments, to and by, to avoid argument order confusion
• (breaking change) YAML::Emitter was renamed to YAML::Builder, and some of its methods were also renamed
• (breaking change) XML::Node#[] now always returns a String (previously it could also return Nil, which was incorrect)
• (breaking change) XML::Node#content now returns an empty String when no content is available
• HTTP::Client now automatically reconnects on a dropped keep-alive connection
• with ... yield now works well with method_missing
• Class variables can now be used in generic types (all generic instances share the same variable, and subclasses get their own copy, as usual)
• Added support for LLVM 4 (thanks @ysbaddaden)
• Added Enum.each and Enum#each (thanks @ysbaddaden)
• Added Hash#compact and Hash#compact! (thanks @makenowjust)
• Added IO#read_string(bytesize)
• Added IO#skip_to_end
• Added Iterator#flat_map (thanks @makenowjust)
• Added JSON.build and JSON::Builder
• Added NamedTuple#has_key?(String) (thanks @Sija)
• Added p(NamedTuple) (thanks @splattael)
• Added Regex::MatchData#== (thanks @makenowjust)
• Added String#sub(Regex, NamedTuple) (thanks @maiha)
• Added XML.build and XML::Builder
• Lots of improvements and applied consistencies to doc comments (thanks @Sija and @maiha)
• Some bug fixes

0.20.3

• (breaking change) IO#gets, IO#each_line, String#lines, String#each_line, etc. now chomp lines by default. You can pass chomp: false to prevent automatic chomping. Note that chomp is true by default for argless IO#gets (read line) but false if args are given.
• (breaking change) HTTP::Handler is now a module instead of a class (thanks @andrewhamon)
• (breaking change) Free variables now must be specified with forall, a single uppercase letter will not work anymore
• (breaking change) The libs directory is no longer in the default CRYSTAL_PATH, use lib (running crystal deps should fix this)
• Optimized compile times, specially on linux
• private can now be used with macros inside types (thanks @makenowjust)
• CLI: the -s/--stats option now also shows execution time (thanks @makenowjust)
• CLI: added -t/--time to show execution time (thanks @makenowjust)
• Socket now allows any family/type/protocol association, and many other improvements (thanks @ysbaddaden)
• YAML: an IO can now be passed to from_yaml (thanks @makenowjust)
• Added class_getter, class_setter, class_property, etc. (thanks @Sija)
• Added String#lchomp (thanks @Sija)
• Added IO#read_fully?
• Added Iterator#flatten (thanks @makenowjust)
• Added HTTP::WebSocket#ping, pong, on_ping, on_pong, and now a ping message is automatically replied with a pong message (thanks @Sija)
• Added File#empty? and Dir#empty? (thanks @dylandrop)
• Added Time::Span#/(Time::Span) (thanks @RX14)
• Added String#split versions that accept a block (thanks @splattael)
• Added URI#normalize and normalize! (thanks @taylorfinnell)
• Added reuse optional argument to many Array, Enumerable and Iterable methods that allow you to reuse the yielded/return array for better performance and less memory footprint
• The :debug flag is now present when compiled with --debug, useful for doing flag?(:debug) in macros (thanks @luislavena)
• Many bug fixes and performance improvements

0.20.1

• (breaking change) Set#merge as renamed to Set#merge!
• (breaking change) Slice.new(size) no longer works with non primitive integers and floats
• (breaking change) The macro method argify was renamed to splat
• Added pretty printing. The methods p and pp now use it. To get the old behaviour use puts obj.inspect
• Added ArrayLiteral#[]=, TypeNode#constant, TypeNode#overrides? and HashLiteral#double_splat in macros
• Added a finished macro hook that runs at the end of the program
• Added support for declaring the type of a local variable
• Added Slice.empty
• Flags enums now have a none? method
• IO::ByteFormat has now methods to encode/decode to/from a Slice
• Spec: the line number passed to run a specific it block can now be inside any line of that block
• The CallConvention attribute can now also be applied to a lib declaration, and all funs inside it will inherit it
• The method_missing hook can now define a method, useful for specifying block arguments
• Support double splat in macros ({{**...}})
• Some bug fixes

0.20.0

• (breaking change) Removed ifdef from the language
• (breaking change) Removed PointerIO
• (breaking change) The body property of HTTP::Request is now an IO? (previously it was String). Use request.body.try(&.gets_to_end) if you need the entire body as a String.
• (breaking change) MemoryIO has been renamed to IO::Memory. The old name can still be used but will produce a compile-time warning. MemoryIO will be removed immediately after 0.20.0.
• (breaking change) Char#digit? was split into Char#ascii_number? and Char#number?. The old name is still available and will produce a compile-time warning, but will be removed immediately after 0.20.0.
• (breaking change) Char#alpha? was split into Char#ascii_letter? and Char#letter?. The old name is still available and will produce a compile-time warning, but will be removed immediately after 0.20.0.
• (breaking change) The Iterable module is now generic
• Many String and Char methods are now unicode-aware, for example String#downcase, String#upcase, Char#downcase, Char#upcase, Char#whitespace?, etc.
• Added support for HTTP client and server streaming.
• Added support for ARM (thanks @ysbaddaden)
• Added support for AArch64 (thanks @ysbaddaden)
• Added support for LLVM 3.9 (thanks @ysbaddaden)
• Added __END_LINE__ magic constant in method default arguments: will be the last line of a call (if the call has a block, it will be the last line of that block)
• Added @def inside macros that takes the value of the current method
• API docs have a nicer style now, and notes like TODO and DEPRECATED are better highlighted (thanks @samueleaton)
• Slight improvement to debugging support (thanks @ggiraldez)
• Line numbers in backtraces (linux only for now) (thanks @ysbaddaden)
• Added iteration times to Benchmark.ips (thanks @RX14)
• Allow HTTP::Client block initializer to be used when passing an URI (thanks @philnash)
• JSON.mapping and YAML.mapping getter/setter generation can now be controlled (thanks @zatherz)
• Time is now serializable to JSON and YAML using ISO 8601 date-time format
• Added IO::MultiWriter (thanks @RX14)
• Added String#index(Regex) and String#rindex(Regex) (thanks @zatherz)
• Added String#partition and String#rpartition (thanks @johnjansen)
• Added FileUtils.cd, FileUtils.mkdir, FileUtils.mkdir_p, FileUtils.mv, FileUtils.pwd, FileUtils.rm, FileUtils.rm_r, FileUtils.rmdir (thanks @ghivert)
• Added JSON::Builder#raw_field (thanks @kostya)
• Added Enumerable#chunks and Iterator#chunk (thanks @kostya)
• Added Iterator#with_index
• Several enhancements to the Random module: now works for any integer type and avoids overflows (thanks @BlaXpirit)
• Optimized Array#sort by using introsort (thanks @c910335)
• Several bug fixes

0.19.4

• Added support for OpenBSD (thanks @wmoxam and @ysbaddaden)
• More iconv fixes for FreeBSD (thanks @ysbaddaden)
• Changed how require works for the upcoming shards release (this is backwards compatible). See #2788
• Added Atomic and exposed all LLVM atomic instructions to Crystal (needed to implemented multiple-thread support)
• Added Process.executable_path (thanks @kostya, @whereami and @ysbaddaden)
• Added HTML.unescape (thanks @dukex)
• Added Char#+(Int) and Char#-(Int)
• A few bug fixes

0.19.3

• crystal eval now accepts some flags like --stats, --release and --help
• Added File.chown and File.chmod (thanks @ysbaddaden)
• Added Time::Span.zero (useful for doing sum) (thanks @RX14)
• Added docs to OAuth and OAuth2
• Several bug fixes

0.19.2

• Generic type variables no longer need to be single-letter names (for example class Gen(Foo) is now possible)
• Added syntax to denote free variables: def foo(x : T) forall T. The old rule of single-letter name still applies but will be removed in the future.
• Removed the restriction that top-level types and constants can't have single-letter names
• Added @[Extern] attribute to mark regular Crystal structs as being able to be used in C bindings
• Faster Char#to_s when it's ASCII: this improves the performance of JSON and CSV parsing
• crystal spec: allow passing --release and other options
• crystal spec: allow running all specs in a given directory
• crystal playground: support custom workbook resources (thanks @bcardiff)
• crystal playground: standard output now understands ANSI colors (thanks @bcardiff)
• Added many more macro methods to traverse AST nodes (thanks @BlaXpirit)
• Error messages no longer include a type trace by default, pass --error-trace to show the full trace (the trace is often useless and makes it harder to understand error messages)
• Several bug fixes

0.19.1

• Types (class, module, etc.) can now be marked as private.
• Added WeakRef (thanks @bcardiff)
• Several bug fixes

0.19.0

• (breaking change) Added select keyword
• (breaking change) Removed $global variables. Use @@Class variables instead.
• (breaking change) Heredoc now ends when the matching identifier is found, either followed by a space or by a non-identifier
• (breaking change) Assignment to a local variable inside an assignment to that same variable is now an error
• (breaking change) Type names like T, T1, U, etc., are now disallowed at the top level, to avoid conflicts with free variables
• (breaking change) Type lookup (Foo::Bar::Baz) had some incorrect behaviour that now is fixed. This can break existing code that relied on this incorrect behaviour. The fix is to fully qualify types (::Foo::Bar::Baz)
• (breaking change) In relationships like class Bar < Foo(Baz) and include Moo(Baz), all of Foo, Moo and Baz must be defined before that point (this was not always the case in previous versions)
• (breaking change) Removed the deprecated syntax x as T
• (breaking change) Removed block form of String#match
• (breaking change) Removed IO#read_nonblock
• (breaking change) Int#/ now performs floored division. Use Int#tdiv for truncated division (see their docs to learn the difference)
• Added support for LLVM 3.8 (thanks @omarroth)
• || now does type filtering
• Generic inheritance should now work well, and (instantiated) generic modules can now be used as the type of instance variables
• NamedTuple can now be accessed with strings too (thanks @jhass)
• Base64 can now encode and decode directly to an IO (thanks @kostya)
• BigInt now uses GMP implementation of gcd and lcm (thanks @endSly)
• ECR now supports removing leading and trailing whitespace (<%-, -%>)
• HTTP::Request#path now never returns nil: it fallbacks to "/" (thanks @jhass)
• String#tr(..., "") is now the same as String#delete
• tool hierarchy now supports --format json (thanks @bmulvihill)
• Added Char#ascii?
• Added Class#nilable? and Union#nilable?
• Added Hash#has_value? (thanks @kachick)
• Added IO::Sized and IO::Delimited (thanks @RX14)
• Added IO::Hexdump (thanks @ysbaddaden)
• Added IO#noecho and IO#noecho! (thanks @jhass)
• Added Logger.new(nil) to create a null logger
• Added OptionParser#missing_option and OptionParser#invalid_option (thanks @jhass)
• Added Process.exists?, Process#exists? and Process#terminated? (thanks @jhass)
• Added Process.exec (thanks @jhass)
• Added Slice#copy_to, Slice#copy_from, Slice#move_to and Slice#move_from (thanks @RX14)
• Added URI#== and URI#hash (thanks @timcraft)
• Added YAML#parse(IO)
• Added Indexable module that Array, Slice, Tuple and StaticArray include
• Added indent parameter to to_pretty_json
• Added lazy form of getter and property macros
• Added macro methods to access an ASTNode's location
• Unified String and Char to integer/float conversion API (thanks @jhass)
• Lots of bug fixes