Go 1.19 is not yet released. These are work-in-progress release notes. Go 1.19 is expected to be released in August 2022.
There is only one small change to the language, a very small correction to the scope of type parameters in method declarations. Existing programs are unaffected.
The Go memory model has been revised to align Go with
the memory model used by C, C++, Java, JavaScript, Rust, and Swift.
Go only provides sequentially consistent atomics, not any of the more relaxed forms found in other languages.
Along with the memory model update,
Go 1.19 introduces new types in the sync/atomic package
that make it easier to use atomic values, such as
atomic.Int64
and
atomic.Pointer[T].
Go 1.19 adds support for the Loongson 64-bit architecture LoongArch
on Linux (GOOS=linux, GOARCH=loong64).
The riscv64 port now supports passing function arguments
and result using registers. Benchmarking shows typical performance
improvements of 10% or more on riscv64.
Go 1.19 adds support for links, lists, and clearer headings in doc comments.
As part of this change, gofmt
now reformats doc comments to make their rendered meaning clearer.
See “Go Doc Comments”
for syntax details and descriptions of common mistakes now highlighted by gofmt.
As another part of this change, the new package go/doc/comment
provides parsing and reformatting of doc comments
as well as support for rendering them to HTML, Markdown, and text.
unix build constraint
The build constraint unix is now recognized
in //go:build lines. The constraint is satisfied
if the target operating system, also known as GOOS, is
a Unix or Unix-like system. For the 1.19 release it is satisfied
if GOOS is one of
aix, android, darwin,
dragonfly, freebsd, hurd,
illumos, ios, linux,
netbsd, openbsd, or solaris.
In future releases the unix constraint may match
additional newly supported operating systems.
The -trimpath flag, if set, is now included in the build settings
stamped into Go binaries by go build, and can be
examined using
go version -m
or debug.ReadBuildInfo.
go generate now sets the GOROOT
environment variable explicitly in the generator's environment, so that
generators can locate the correct GOROOT even if built
with -trimpath.
go test and go generate now place
GOROOT/bin at the beginning of the PATH used for the
subprocess, so tests and generators that execute the go command
will resolve it to same GOROOT.
go env now quotes entries that contain spaces in
the CGO_CFLAGS, CGO_CPPFLAGS, CGO_CXXFLAGS, CGO_FFLAGS, CGO_LDFLAGS,
and GOGCCFLAGS variables it reports.
The go command now caches information necessary to load some modules,
which should result in a speed-up of some go list invocations.
The vet checker “errorsas” now reports when
errors.As is called
with a second argument of type *error,
a common mistake.
The runtime now includes support for a soft memory limit. This memory limit
includes the Go heap and all other memory managed by the runtime, and
excludes external memory sources such as mappings of the binary itself,
memory managed in other languages, and memory held by the operating system on
behalf of the Go program. This limit may be managed via
runtime/debug.SetMemoryLimit
or the equivalent
GOMEMLIMIT
environment variable. The limit works in conjunction with
runtime/debug.SetGCPercent
/ GOGC,
and will be respected even if GOGC=off, allowing Go programs to
always make maximal use of their memory limit, improving resource efficiency
in some cases. See the GC guide for
a detailed guide explaining the soft memory limit in more detail, as well as
a variety of common use-cases and scenarios. Please note that small memory
limits, on the order of tens of megabytes or less, are less likely to be
respected due to external latency factors, such as OS scheduling. See
issue 52433 for more details. Larger
memory limits, on the order of hundreds of megabytes or more, are stable and
production-ready.
In order to limit the effects of GC thrashing when the program's live heap
size approaches the soft memory limit, the Go runtime also attempts to limit
total GC CPU utilization to 50%, excluding idle time, choosing to use more
memory over preventing application progress. In practice, we expect this limit
to only play a role in exceptional cases, and the new
runtime metric
/gc/limiter/last-enabled:gc-cycle reports when this last
occurred.
The runtime now schedules many fewer GC worker goroutines on idle operating system threads when the application is idle enough to force a periodic GC cycle.
The runtime will now allocate initial goroutine stacks based on the historic average stack usage of goroutines. This avoids some of the early stack growth and copying needed in the average case in exchange for at most 2x wasted space on below-average goroutines.
On Unix operating systems, Go programs that import package
os now automatically increase the open file limit
(RLIMIT_NOFILE) to the maximum allowed value;
that is, they change the soft limit to match the hard limit.
This corrects artificially low limits set on some systems for compatibility with very old C programs using the
select system call.
Go programs are not helped by that limit, and instead even simple programs like gofmt
often ran out of file descriptors on such systems when processing many files in parallel.
One impact of this change is that Go programs that in turn execute very old C programs in child processes
may run those programs with too high a limit.
This can be corrected by setting the hard limit before invoking the Go program.
Unrecoverable fatal errors (such as concurrent map writes, or unlock of
unlocked mutexes) now print a simpler traceback excluding runtime metadata
(equivalent to a fatal panic) unless GOTRACEBACK=system or
crash. Runtime-internal fatal error tracebacks always include
full metadata regardless of the value of GOTRACEBACK
Support for debugger-injected function calls has been added on ARM64, enabling users to call functions from their binary in an interactive debugging session when using a debugger that is updated to make use of this functionality.
The address sanitizer support added in Go 1.18 now handles function arguments and global variables more precisely.
The compiler now uses
a jump
table to implement large integer and string switch statements.
Performance improvements for the switch statement vary but can be
on the order of 20% faster.
(GOARCH=amd64 and GOARCH=arm64 only)
The Go compiler now requires the -p=importpath flag to
build a linkable object file. This is already supplied by
the go command and by Bazel. Any other build systems
that invoke the Go compiler directly will need to make sure they
pass this flag as well.
Like the compiler, the assembler now requires the
-p=importpath flag to build a linkable object file.
This is already supplied by the go command. Any other
build systems that invoke the Go assembler directly will need to
make sure they pass this flag as well.
On ELF platforms, the linker now emits compressed DWARF sections in
the standard gABI format (SHF_COMPRESSED), instead of
the legacy .zdebug format.
The sync/atomic package defines new atomic types
Bool,
Int32,
Int64,
Uint32,
Uint64,
Uintptr, and
Pointer.
These types hide the underlying values so that all accesses are forced to use
the atomic APIs.
Pointer also avoids
the need to convert to
unsafe.Pointer at call sites.
Int64 and
Uint64 are
automatically aligned to 64-bit boundaries in structs and allocated data,
even on 32-bit systems.
Command and
LookPath no longer
allow results from a PATH search to be found relative to the current directory.
This removes a common source of security problems
but may also break existing programs that depend on using, say, exec.Command("prog")
to run a binary named prog (or, on Windows, prog.exe) in the current directory.
See the os/exec package documentation for
information about how best to update such programs.
On Windows, Command and LookPath now respect the
NoDefaultCurrentDirectoryInExePath
environment variable, making it possible to disable
the default implicit search of “.” in PATH lookups on Windows systems.
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind. There are also various performance improvements, not enumerated here.
Reader
now ignores non-ZIP data at the start of a ZIP file, matching most other implementations.
This is necessary to read some Java JAR files, among other uses.
Read no longer buffers
random data obtained from the operating system between calls.
On Plan 9, Read has been reimplemented, replacing the ANSI
X9.31 algorithm with fast key erasure.
The tls10default GODEBUG option has been
removed. It is still possible to enable TLS 1.0 client-side by setting
Config.MinVersion.
The TLS server and client now reject duplicate extensions in TLS handshakes, as required by RFC 5246, Section 7.4.1.4 and RFC 8446, Section 4.2.
CreateCertificate
no longer supports creating certificates with SignatureAlgorithm
set to MD5WithRSA.
CreateCertificate no longer accepts negative serial numbers.
ParseCertificate
and ParseCertificateRequest
now reject certificates and CSRs which contain duplicate extensions.
The new CertPool.Clone
and CertPool.Equal
methods allow cloning a CertPool and checking the equality of two
CertPools respectively.
The new function ParseRevocationList
provides a faster, safer to use CRL parser which returns a
RevocationList.
To support this addition, RevocationList adds new fields
RawIssuer, Signature,
AuthorityKeyId, and Extensions.
The new method RevocationList.CheckSignatureFrom
checks that the signature on a CRL is a valid signature from a
Certificate.
With the new CRL functionality, the existing functions
ParseCRL and
ParseDERCRL are deprecated.
Additionally the method Certificate.CheckCRLSignature
is deprecated.
When building paths, Certificate.Verify
now considers certificates to be equal when the subjects, public keys, and SANs
are all equal. Before, it required byte-for-byte equality.
The types CertificateList and
TBSCertificateList
have been deprecated. The new crypto/x509 CRL functionality
should be used instead.
The new EM_LONGARCH and R_LARCH_* constants
support the loong64 port.
The new File.COFFSymbolReadSectionDefAux
method, which returns a COFFSymbolAuxFormat5,
provides access to COMDAT information in PE file sections.
These are supported by new IMAGE_COMDAT_* and IMAGE_SCN_* constants.
The new interface
AppendByteOrder
provides efficient methods for appending a uint16, uint32, or uint64
to a byte slice.
BigEndian and
LittleEndian now implement this interface.
Similarly, the new functions
AppendUvarint and
AppendVarint
are efficient appending versions of
PutUvarint and
PutVarint.
The new method
Reader.InputOffset
reports the reader's current input position as a byte offset,
analogous to encoding/json's
Decoder.InputOffset.
The new method
Decoder.InputPos
reports the reader's current input position as a line and column,
analogous to encoding/csv's
Decoder.FieldPos.
The new function
TextVar
defines a flag with a value implementing
encoding.TextUnmarshaler,
allowing command-line flag variables to have types such as
big.Int,
netip.Addr, and
time.Time.
The parser now recognizes ~x as a unary expression with operator
token.TILDE,
allowing better error recovery when a type constraint such as ~int is used in an incorrect context.
The new methods Func.Origin
and Var.Origin return the
corresponding Object of the
generic type for synthetic Func
and Var objects created during type
instantiation.
It is no longer possible to produce an infinite number of distinct-but-identical
Named type instantiations via
recursive calls to
Named.Underlying or
Named.Method.
The new functions
Bytes
and
String
provide an efficient way hash a single byte slice or string.
They are equivalent to using the more general
Hash
with a single write, but they avoid setup overhead for small inputs.
The type FuncMap
is now an alias for
text/template's FuncMap
instead of its own named type.
This allows writing code that operates on a FuncMap from either setting.
Draw with the
Src operator preserves
non-premultiplied-alpha colors when destination and source images are
both image.NRGBA
or both image.NRGBA64.
This reverts a behavior change accidentally introduced by a Go 1.18
library optimization; the code now matches the behavior in Go 1.17 and earlier.
NopCloser's result now implements
WriterTo
whenever its input does.
MultiReader's result now implements
WriterTo unconditionally.
If any underlying reader does not implement WriterTo,
it is simulated appropriately.
On Windows only, the mime package now ignores a registry entry
recording that the extension .js should have MIME
type text/plain. This is a common unintentional
misconfiguration on Windows systems. The effect is
that .js will have the default MIME
type text/javascript; charset=utf-8.
Applications that expect text/plain on Windows must
now explicitly call
AddExtensionType.
The pure Go resolver will now use EDNS(0) to include a suggested
maximum reply packet length, permitting reply packets to contain
up to 1232 bytes (the previous maximum was 512).
In the unlikely event that this causes problems with a local DNS
resolver, setting the environment variable
GODEBUG=netdns=cgo to use the cgo-based resolver
should work.
Please report any such problems on the
issue tracker.
When a net package function or method returns an "I/O timeout"
error, the error will now satisfy errors.Is(err,
context.DeadlineExceeded). When a net package function
returns an "operation was canceled" error, the error will now
satisfy errors.Is(err, context.Canceled).
These changes are intended to make it easier for code to test
for cases in which a context cancellation or timeout causes a net
package function or method to return an error, while preserving
backward compatibility for error messages.
Resolver.PreferGo
is now implemented on Windows and Plan 9. It previously only worked on Unix
platforms. Combined with
Dialer.Resolver and
Resolver.Dial, it's now
possible to write portable programs and be in control of all DNS name lookups
when dialing.
The net package now has initial support for the netgo
build tag on Windows. When used, the package uses the Go DNS client (as used
by Resolver.PreferGo) instead of asking Windows for
DNS results. The upstream DNS server it discovers from Windows
may not yet be correct with complex system network configurations, however.
ResponseWriter.WriteHeader
now supports sending user-defined 1xx informational headers.
The io.ReadCloser returned by
MaxBytesReader
will now return the defined error type
MaxBytesError
when its read limit is exceeded.
The HTTP client will handle a 3xx response without a
Location header by returning it to the caller,
rather than treating it as an error.
The new
JoinPath
function and
URL.JoinPath
method create a new URL by joining a list of path
elements.
The URL type now distinguishes between URLs with no
authority and URLs with an empty authority. For example,
http:///path has an empty authority (host),
while http:/path has none.
The new URL field
OmitHost is set to true when a
URL has an empty authority.
A Cmd with a non-empty Dir field
and nil Env now implicitly sets the PWD environment
variable for the subprocess to match Dir.
The new method Cmd.Environ reports the
environment that would be used to run the command, including the
implicitly set PWD variable.
The method Value.Bytes
now accepts addressable arrays in addition to slices.
The methods Value.Len
and Value.Cap
now successfully operate on a pointer to an array and return the length of that array,
to match what the builtin
len and cap functions do.
Go 1.18 release candidate 1, Go 1.17.8, and Go 1.16.15 included a security fix
to the regular expression parser, making it reject very deeply nested expressions.
Because Go patch releases do not introduce new API,
the parser returned syntax.ErrInternalError in this case.
Go 1.19 adds a more specific error, syntax.ErrNestingDepth,
which the parser now returns instead.
The GOROOT function now returns the empty string
(instead of "go") when the binary was built with
the -trimpath flag set and the GOROOT
variable is not set in the process environment.
The new /sched/gomaxprocs:threads
metric reports
the current
runtime.GOMAXPROCS
value.
The new /cgo/go-to-c-calls:calls
metric
reports the total number of calls made from Go to C. This metric is
identical to the
runtime.NumCgoCall
function.
The new /gc/limiter/last-enabled:gc-cycle
metric
reports the last GC cycle when the GC CPU limiter was enabled. See the
runtime notes for details about the GC CPU limiter.
Stop-the-world pause times have been significantly reduced when collecting goroutine profiles, reducing the overall latency impact to the application.
MaxRSS is now reported in heap profiles for all Unix
operating systems (it was previously only reported for
GOOS=android, darwin, ios, and
linux).
The race detector has been upgraded to use thread sanitizer
version v3 on all supported platforms
except windows/amd64
and openbsd/amd64, which remain on v2.
Compared to v2, it is now typically 1.5x to 2x faster, uses half
as much memory, and it supports an unlimited number of
goroutines.
The race detector is now supported on GOARCH=s390x.
Race detector support for openbsd/amd64 has been
removed from thread sanitizer upstream, so it is unlikely to
ever be updated from v2.
When tracing and the CPU profiler are enabled simultaneously, the execution trace includes CPU profile samples as instantaneous events.
The sorting algorithm has been rewritten to use pattern-defeating quicksort, which is faster for several common scenarios.
The new function Find is like Search but often easier to use: it returns an additional boolean reporting whether an equal value was found.
Quote
and related functions now quote the rune U+007F as \x7f,
not \u007f,
for consistency with other ASCII values.
On PowerPC (GOARCH=ppc64, ppc64le),
Syscall,
Syscall6,
RawSyscall, and
RawSyscall6
now always return 0 for return value r2 instead of an
undefined value.
On AIX and Solaris, Getrusage is now defined.
The new method
Duration.Abs
provides a convenient and safe way to take the absolute value of a duration,
converting −2⁶³ to 2⁶³−1.
(This boundary case can happen as the result of subtracting a recent time from the zero time.)
The new method
Time.ZoneBounds
returns the start and end times of the time zone in effect at a given time.
It can be used in a loop to enumerate all the known time zone transitions at a given location.