What's new in Go 1.12?

28 January 2019

Time flies

Go 1.10 is already 11 months old!

Go 1.11 was released on August 24th, 2018.

On November 5th, 2018 we entered the release freeze for Go 1.12.

Go 1.12

Is Go 1.12 out yet?

import "golang.org/x/build/maintner/maintnerd/apipb"

// PrintGoReleases uses the provided maintner client
// to print the latest supported Go releases.
func PrintGoReleases(mc apipb.MaintnerServiceClient) error {
    resp, err := mc.ListGoReleases(context.Background(), &apipb.ListGoReleasesRequest{})
    if err != nil {
        return err
    }
    for _, r := range resp.Releases {
        fmt.Println(r.TagName)
    }
    return nil
}

Go 1.12

Is Go 1.12 out yet?

$ go run golang.org/x/build/maintner/maintq list-releases
major:1 minor:11 patch:5 tag_name:"go1.11.5" tag_commit:"35bb62e60a7779ff82c3067903b3306ff8666471" branch_name:"release-branch.go1.11" branch_commit:"f8e8303f566652fc74125e50a23eab612e8fc749"
major:1 minor:10 patch:8 tag_name:"go1.10.8" tag_commit:"b0cb374daf646454998bac7b393f3236a2ab6aca" branch_name:"release-branch.go1.10" branch_commit:"bd0449f8d16a5ac1b1962c7ea07d764a7f18eca7"
$

Go 1.12 Beta 2

Source: twitter.com/golang/status/1083529360798302210

Go 1.12 Beta 2

Source: twitter.com/bradfitz/status/1083558450129395712

Go release cycle

Source: golang.org/s/release

Go 1.12 release notes

Source: tip.golang.org/doc/go1.12

Agenda

Changes since Go 1.11:

• The Language
• The Ports
• The Tooling
• The Runtime
• The Standard Library

Sources:

tip.golang.org/doc/go1.12

github.com/golang/go/issues?q=is:closed+is:issue+milestone:Go1.12

dev.golang.org/release#Go1.12

Changes to the language

Language

Language

Language

Things are happening:

• blog.golang.org/toward-go2 (July 2017)

• blog.golang.org/go2draft (August 2018)

• blog.golang.org/go2-here-we-come (November 2018)

• golang.org/wiki/Go2GenericsFeedback

• Etc.

Ports

Ports

New ports:

• windows/arm! Supports running Go on Windows 10 IoT Core on 32-bit ARM chips such as the Raspberry Pi 3.

• aix/ppc64! AIX 7.2 and later on POWER8 architectures (external linking, cgo, pprof, and race detector aren't yet supported).

Reserved for future:

• hurd is now a recognized value for GOOS, reserved for the GNU/Hurd system for use with gccgo.

Ports

Improvements:

• Race detector now supported on linux/arm64.

• cgo now supported on linux/ppc64.

• Various enhancements to WebAssembly port.

• libSystem is used when making syscalls on macOS and iOS. Can't use syscall.Getdirentries on iOS.

Ports

Last release to support:

• FreeBSD 10.x (EOLed). Go 1.13 will require FreeBSD 11.2+ or FreeBSD 12.0+.

• macOS 10.10 Yosemite. Go 1.13 will require macOS 10.11 El Capitan or later.

Tooling

Tooling

go tool vet is no longer supported.

If you're currently doing:

go tool vet .

May replace with:

go vet ./...

Tooling

godoc and go doc:

• godoc no longer has a CLI and is only a web server. Use go doc for CLI.

$ godoc -help
usage: godoc
  ...
  -http string
        HTTP service address (default "localhost:6060")
  ...

• go doc gets a new -all flag to print all exported APIs like godoc used to.

$ go doc -help
Usage of [go] doc:
    go doc
    go doc <pkg>
    go doc <sym>[.<method>]
    go doc [<pkg>].<sym>[.<method>]
    go doc <pkg> <sym>[.<method>]

Tooling

Modules:

• go command supports module-aware operations outside of a module directory with GO111MODULE=on.

Only those that don't need current working directory or explicit go.mod editing. E.g., go get, go list, and go mod download behave as if in empty module. go env GOMOD reports system's null device (/dev/null).

• go commands that download and extract modules are now safe to invoke concurrently.

The module cache (GOPATH/pkg/mod) must reside in a filesystem that supports file locking.

• New go directive in go.mod files indicates language version. E.g., go 1.12.

Tooling

Build cache requirement:

• The build cache is now required. A step toward eliminating $GOPATH/pkg.

• Setting the environment variable GOCACHE=off will cause go commands that write to the cache to fail.

Tooling

Binary-only packages:

• Go 1.12 is the last release that will support binary-only packages.

Tooling

Cgo:

• C type EGLDisplay will be translated to the Go type uintptr.

• Mangled C names are no longer accepted in packages that use cgo. For example, use the documented cgo name C.char rather than the mangled name _Ctype_char.

Tooling

Compiler toolchain:

• More functions are eligible for inlining by default, including functions that do nothing but call another function. Use runtime.CallersFrames instead of iterating over the result of runtime.Callers directly.

• Live variable analysis has improved. Finalizers may run sooner, use runtime.KeepAlive if needed.

• Many improvements to the DWARF debug information produced by the compiler.

• The obsolete "safe" compiler mode (enabled by the -u gcflag) has been removed.

• Stack frame pointers now maintained on linux/arm64 for the benefit of profiling tools like perf.

• Compiler accepts a -lang flag to set the Go language version to use. For example, -lang=go1.8 causes the compiler to error on type aliases.

Runtime

Runtime

• Timer and deadline code is faster and scales better with higher numbers of CPUs, improving performance of manipulating network connection deadlines.

• Significantly improved performance of sweeping when a large fraction of the heap remains live, reducing allocation latency right after a GC.

• Releases memory back to OS more aggressively, especially after large allocations that can't reuse existing heap space.

Runtime

• On Linux, uses MADV_FREE advice to release unused memory; more efficient but may result in higher reported RSS.

• cpu.extension=off for GODEBUG to disable the use of optional CPU instruction set extensions in the standard library and runtime.

• Stopped overcounting large heap allocations, resulting in improved accuracy of memory profiles.

Standard library

Standard library

Let's begin with the most visible change:

• crypto/tls gains TLS 1.3 support! 🔐

(A few moments later...)

TLS 1.3 (RFC 8446) support in crypto/tls

• Go programs will automatically negotiate TLS 1.3 if available, as long as didn't set explicit MaxVersion in Config.

• All TLS 1.2 features except TLSUnique in ConnectionState and renegotiation are available in TLS 1.3 and provide equivalent or better security and performance.

• TLS 1.3 cipher suites are not configurable. All supported cipher suites are safe.

• Early data (also called "0-RTT mode") is not currently supported as a client or server. Additionally, a Go 1.12 server does not support skipping unexpected early data if a client sends it. Considerations for load-balancing.

• Errors on the client will be returned by the first Read, not Handshake. E.g., if the server rejects the client certificate.

Standard library

Minor changes and updates with Go 1 promise of compatibility in mind:

• fmt
• net/...
• crypto/...
• bytes, strings
• database/sql
• expvar
• go/...
• image/...
• math/...
• More!

Standard library

fmt

• Maps are now printed in key-sorted order to ease testing.

For example, fmt.Print ing this map:

map[uint8]string{7: "bar", 3: "foo"}

With Go 1.11:

map[7:bar 3:foo]
// or
map[3:foo 7:bar]

With Go 1.12:

map[3:foo 7:bar]

• Non-reflexive map key values like NaN were previously displayed as <nil>, now fixed.

Standard library

os

• New ProcessState.ExitCode method returns the process's exit code.

• New function UserHomeDir returns the current user's home directory.

• RemoveAll supports paths longer than 4096 characters on most Unix systems.

Standard library

net/http/httputil

• ReverseProxy now automatically proxies WebSocket requests.

Standard library

net/http

• Misdirected HTTP requests to HTTPS servers rejected with a plaintext "400 Bad Request" response.

• Transport no longer rejects HTTP responses which declare HTTP Trailers but don't use chunked encoding. Instead, declared trailers are ignored.

• Transport no longer handles MAX_CONCURRENT_STREAMS values advertised from HTTP/2 servers as strictly as it did during Go 1.10 and Go 1.11. Instead, default behavior is more like Go 1.9, new TCP connections are created as needed.

• New Client.CloseIdleConnections method is short for Client.Transport.CloseIdleConnections.

Standard library

net

• Fast Fallback ("Happy Eyeballs") is enabled by default; Dialer.DualStack is ignored and deprecated. Can be disabled.

• TCP keep-alives enabled by default if Dialer.KeepAlive is zero. Can be disabled.

• On Linux, the splice system call is used when copying from a UnixConn to a TCPConn.

Standard library

io

• New StringWriter interface:

// StringWriter is the interface that wraps the WriteString method.
type StringWriter interface {
    WriteString(s string) (n int, err error)
}

Standard library

reflect

• A new MapIter type is an iterator for ranging over a map, follows same iteration semantics as a range statement.

Standard library

bytes, strings

• New ReplaceAll returns a copy of a byte slice/string with all non-overlapping instances of a value replaced by another.

• new(Reader) is now functionally equivalent to NewReader(nil).

Standard library

syscall/js

• Callbacks now get executed synchronously, which is necessary for APIs of many JavaScript libraries.

• New Wrapper interface is used by ValueOf.

• New Value.Truthy method reports the JavaScript "truthiness".

• Zero Value now represents the JavaScript undefined value, not number zero.

• Callback renamed to Func, NewCallback renamed to FuncOf.

Standard library

crypto/rc4

• Removed optimized assembly implementations. RC4 is insecure and should only be used for compatibility with legacy systems.

Standard library

image

• RegisterFormat is now safe for concurrent use.

image/png

• Paletted images with fewer than 16 colors encode to smaller output.

Standard library

time

• Time zone database in GOROOT/lib/time/zoneinfo.zip has been updated to version 2018i. Only used if a time zone database is not provided by OS.

Standard library

math

• Sin, Cos, Tan, and Sincos apply Payne-Hanek range reduction to huge arguments for more accurate answers.

math/bits

• New extended precision operations Add, Sub, Mul, and Div are available in uint, uint32, and uint64 versions.

Standard library

syscall

• New Syscall18 added for Windows, allowing for calls with up to 18 arguments.

Standard library

testing

• -benchtime flag now supports setting an explicit iteration count with "x". For example, -benchtime=100x.

Standard library

Your favorite change missing here or in the Go 1.12 release notes?

Let me know!

Thank you