Go 1.18 Release Notes - The Go Programming Language (original) (raw)

Introduction to Go 1.18

The latest Go release, version 1.18, is a significant release, including changes to the language, implementation of the toolchain, runtime, and libraries. Go 1.18 arrives seven months after Go 1.17. As always, the release maintains the Go 1 promise of compatibility. We expect almost all Go programs to continue to compile and run as before.

Changes to the language

Generics

Go 1.18 includes an implementation of generic features as described by theType Parameters Proposal. This includes major - but fully backward-compatible - changes to the language.

These new language changes required a large amount of new code that has not had significant testing in production settings. That will only happen as more people write and use generic code. We believe that this feature is well implemented and high quality. However, unlike most aspects of Go, we can’t back up that belief with real world experience. Therefore, while we encourage the use of generics where it makes sense, please use appropriate caution when deploying generic code in production.

While we believe that the new language features are well designed and clearly specified, it is possible that we have made mistakes. We want to stress that the Go 1 compatibility guarantee says “If it becomes necessary to address an inconsistency or incompleteness in the specification, resolving the issue could affect the meaning or legality of existing programs. We reserve the right to address such issues, including updating the implementations.” It also says “If a compiler or library has a bug that violates the specification, a program that depends on the buggy behavior may break if the bug is fixed. We reserve the right to fix such bugs.” In other words, it is possible that there will be code using generics that will work with the 1.18 release but break in later releases. We do not plan or expect to make any such change. However, breaking 1.18 programs in future releases may become necessary for reasons that we cannot today foresee. We will minimize any such breakage as much as possible, but we can’t guarantee that the breakage will be zero.

The following is a list of the most visible changes. For a more comprehensive overview, see theproposal. For details see the language spec.

The syntax forfunction andtype declarationsnow acceptstype parameters.
Parameterized functions and types can be instantiated by following them with a list of type arguments in square brackets.
The new token ~ has been added to the set ofoperators and punctuation.
The syntax forInterface typesnow permits the embedding of arbitrary types (not just type names of interfaces) as well as union and ~T type elements. Such interfaces may only be used as type constraints. An interface now defines a set of types as well as a set of methods.
The newpredeclared identifier any is an alias for the empty interface. It may be used instead ofinterface{}.
The newpredeclared identifier comparable is an interface that denotes the set of all types which can be compared using == or !=. It may only be used as (or embedded in) a type constraint.

There are three experimental packages using generics that may be useful. These packages are in x/exp repository; their API is not covered by the Go 1 guarantee and may change as we gain more experience with generics.

golang.org/x/exp/constraints

Constraints that are useful for generic code, such asconstraints.Ordered.

golang.org/x/exp/slices

A collection of generic functions that operate on slices of any element type.

golang.org/x/exp/maps

A collection of generic functions that operate on maps of any key or element type.

The current generics implementation has the following known limitations:

The Go compiler cannot handle type declarations inside generic functions or methods. We hope to provide support for this feature in a future release.
The Go compiler does not accept arguments of type parameter type with the predeclared functions real, imag, and complex. We hope to remove this restriction in a future release.
The Go compiler only supports calling a method m on a valuex of type parameter type P if m is explicitly declared by P’s constraint interface. Similarly, method values x.m and method expressionsP.m also are only supported if m is explicitly declared by P, even though m might be in the method set of P by virtue of the fact that all types in P implementm. We hope to remove this restriction in a future release.
The Go compiler does not support accessing a struct field x.fwhere x is of type parameter type even if all types in the type parameter’s type set have a field f. We may remove this restriction in a future release.
Embedding a type parameter, or a pointer to a type parameter, as an unnamed field in a struct type is not permitted. Similarly, embedding a type parameter in an interface type is not permitted. Whether these will ever be permitted is unclear at present.
A union element with more than one term may not contain an interface type with a non-empty method set. Whether this will ever be permitted is unclear at present.

Generics also represent a large change for the Go ecosystem. While we have updated several core tools with generics support, there is much more to do. It will take time for remaining tools, documentation, and libraries to catch up with these language changes.

Bug fixes

The Go 1.18 compiler now correctly reports declared but not used errors for variables that are set inside a function literal but are never used. Before Go 1.18, the compiler did not report an error in such cases. This fixes long-outstanding compiler issue #8560. As a result of this change, (possibly incorrect) programs may not compile anymore. The necessary fix is straightforward: fix the program if it was in fact incorrect, or use the offending variable, for instance by assigning it to the blank identifier _. Since go vet always pointed out this error, the number of affected programs is likely very small.

The Go 1.18 compiler now reports an overflow when passing a rune constant expression such as '1' << 32 as an argument to the predeclared functionsprint and println, consistent with the behavior of user-defined functions. Before Go 1.18, the compiler did not report an error in such cases but silently accepted such constant arguments if they fit into anint64. As a result of this change, (possibly incorrect) programs may not compile anymore. The necessary fix is straightforward: fix the program if it was in fact incorrect, or explicitly convert the offending argument to the correct type. Since go vet always pointed out this error, the number of affected programs is likely very small.

Ports

AMD64

Go 1.18 introduces the new GOAMD64 environment variable, which selects at compile time a minimum target version of the AMD64 architecture. Allowed values are v1,v2, v3, or v4. Each higher level requires, and takes advantage of, additional processor features. A detailed description can be foundhere.

The GOAMD64 environment variable defaults to v1.

RISC-V

The 64-bit RISC-V architecture on Linux (the linux/riscv64 port) now supports the c-archive and c-shared build modes.

Linux

Go 1.18 requires Linux kernel version 2.6.32 or later.

Windows

The windows/arm and windows/arm64 ports now support non-cooperative preemption, bringing that capability to all four Windows ports, which should hopefully address subtle bugs encountered when calling into Win32 functions that block for extended periods of time.

iOS

On iOS (the ios/arm64 port) and iOS simulator running on AMD64-based macOS (the ios/amd64 port), Go 1.18 now requires iOS 12 or later; support for previous versions has been discontinued.

FreeBSD

Go 1.18 is the last release that is supported on FreeBSD 11.x, which has already reached end-of-life. Go 1.19 will require FreeBSD 12.2+ or FreeBSD 13.0+. FreeBSD 13.0+ will require a kernel with the COMPAT_FREEBSD12 option set (this is the default).

Fuzzing

Go 1.18 includes an implementation of fuzzing as described bythe fuzzing proposal.

See the fuzzing landing page to get started.

Please be aware that fuzzing can consume a lot of memory and may impact your machine’s performance while it runs. Also be aware that the fuzzing engine writes values that expand test coverage to a fuzz cache directory within$GOCACHE/fuzz while it runs. There is currently no limit to the number of files or total bytes that may be written to the fuzz cache, so it may occupy a large amount of storage (possibly several GBs).

Go command

`go` `get`

go get no longer builds or installs packages in module-aware mode. go get is now dedicated to adjusting dependencies in go.mod. Effectively, the-d flag is always enabled. To install the latest version of an executable outside the context of the current module, usego install example.com/cmd@latest. Anyversion querymay be used instead of latest. This form of go install was added in Go 1.16, so projects supporting older versions may need to provide install instructions for both go install and go get. go get now reports an error when used outside a module, since there is no go.mod file to update. In GOPATH mode (withGO111MODULE=off), go get still builds and installs packages, as before.

Automatic `go.mod` and `go.sum` updates

The go mod graph,go mod vendor,go mod verify, andgo mod why subcommands no longer automatically update the go.mod andgo.sum files. (Those files can be updated explicitly using go get,go mod tidy, orgo mod download.)

`go` `version`

The go command now embeds version control information in binaries. It includes the currently checked-out revision, commit time, and a flag indicating whether edited or untracked files are present. Version control information is embedded if the go command is invoked in a directory within a Git, Mercurial, Fossil, or Bazaar repository, and themain package and its containing main module are in the same repository. This information may be omitted using the flag-buildvcs=false.

Additionally, the go command embeds information about the build, including build and tool tags (set with -tags), compiler, assembler, and linker flags (like -gcflags), whether cgo was enabled, and if it was, the values of the cgo environment variables (like CGO_CFLAGS). Both VCS and build information may be read together with module information usinggo version -m file orruntime/debug.ReadBuildInfo (for the currently running binary) or the new debug/buildinfopackage.

The underlying data format of the embedded build information can change with new go releases, so an older version of go may not handle the build information produced with a newer version of go. To read the version information from a binary built with go 1.18, use the go version command and thedebug/buildinfo package from go 1.18+.

`go` `mod` `download`

If the main module’s go.mod file specifies go 1.17or higher, go mod download without arguments now downloads source code for only the modules explicitly required in the main module’s go.mod file. (In a go 1.17 or higher module, that set already includes all dependencies needed to build the packages and tests in the main module.) To also download source code for transitive dependencies, usego mod download all.

`go` `mod` `vendor`

The go mod vendor subcommand now supports a -o flag to set the output directory. (Other go commands still read from the vendordirectory at the module root when loading packages with -mod=vendor, so the main use for this flag is for third-party tools that need to collect package source code.)

`go` `mod` `tidy`

The go mod tidy command now retains additional checksums in the go.sum file for modules whose source code is needed to verify that each imported package is provided by only one module in the build list. Because this condition is rare and failure to apply it results in a build error, this change is not conditioned on the go version in the main module’s go.mod file.

`go` `work`

The go command now supports a “Workspace” mode. If ago.work file is found in the working directory or a parent directory, or one is specified using the GOWORKenvironment variable, it will put the go command into workspace mode. In workspace mode, the go.work file will be used to determine the set of main modules used as the roots for module resolution, instead of using the normally-found go.modfile to specify the single main module. For more information see thego workdocumentation.

`go` `build` `-asan`

The go build command and related commands now support an -asan flag that enables interoperation with C (or C++) code compiled with the address sanitizer (C compiler option -fsanitize=address).

`go` `test`

The go command now supports additional command line options for the new fuzzing support described above:

go test supports-fuzz, -fuzztime, and-fuzzminimizetime options. For documentation on these seego help testflag.
go clean supports a -fuzzcacheoption. For documentation seego help clean.

`//go:build` lines

Go 1.17 introduced //go:build lines as a more readable way to write build constraints, instead of // +build lines. As of Go 1.17, gofmt adds //go:build lines to match existing +build lines and keeps them in sync, while go vet diagnoses when they are out of sync.

Since the release of Go 1.18 marks the end of support for Go 1.16, all supported versions of Go now understand //go:build lines. In Go 1.18, go fix now removes the now-obsolete// +build lines in modules declaringgo 1.18 or later in their go.mod files.

For more information, see go.dev/design/draft-gobuild.

Gofmt

gofmt now reads and formats input files concurrently, with a memory limit proportional to GOMAXPROCS. On a machine with multiple CPUs, gofmt should now be significantly faster.

Vet

Updates for Generics

The vet tool is updated to support generic code. In most cases, it reports an error in generic code whenever it would report an error in the equivalent non-generic code after substituting for type parameters with a type from theirtype set. For example, vet reports a format error in

func Print[T ~int|~string](t T) {
    fmt.Printf("%d", t)
}

because it would report a format error in the non-generic equivalent ofPrint[string]:

func PrintString(x string) {
    fmt.Printf("%d", x)
}

Precision improvements for existing checkers

The cmd/vet checkers copylock, printf,sortslice, testinggoroutine, and testshave all had moderate precision improvements to handle additional code patterns. This may lead to newly reported errors in existing packages. For example, theprintf checker now tracks formatting strings created by concatenating string constants. So vet will report an error in:

  // fmt.Printf formatting directive %d is being passed to Println.
  fmt.Println("%d"+` ≡ x (mod 2)`+"\n", x%2)

Runtime

The garbage collector now includes non-heap sources of garbage collector work (e.g., stack scanning) when determining how frequently to run. As a result, garbage collector overhead is more predictable when these sources are significant. For most applications these changes will be negligible; however, some Go applications may now use less memory and spend more time on garbage collection, or vice versa, than before. The intended workaround is to tweakGOGC where necessary.

The runtime now returns memory to the operating system more efficiently and has been tuned to work more aggressively as a result.

Go 1.17 generally improved the formatting of arguments in stack traces, but could print inaccurate values for arguments passed in registers. This is improved in Go 1.18 by printing a question mark (?) after each value that may be inaccurate.

The built-in function append now uses a slightly different formula when deciding how much to grow a slice when it must allocate a new underlying array. The new formula is less prone to sudden transitions in allocation behavior.

Compiler

Go 1.17 implemented a new way of passing function arguments and results using registers instead of the stack on 64-bit x86 architecture on selected operating systems. Go 1.18 expands the supported platforms to include 64-bit ARM (GOARCH=arm64), big- and little-endian 64-bit PowerPC (GOARCH=ppc64, ppc64le), as well as 64-bit x86 architecture (GOARCH=amd64) on all operating systems. On 64-bit ARM and 64-bit PowerPC systems, benchmarking shows typical performance improvements of 10% or more.

As mentioned in the Go 1.17 release notes, this change does not affect the functionality of any safe Go code and is designed to have no impact on most assembly code. See theGo 1.17 release notes for more details.

The compiler now can inline functions that contain range loops or labeled for loops.

The new -asan compiler option supports the new go command -asan option.

Because the compiler’s type checker was replaced in its entirety to support generics, some error messages now may use different wording than before. In some cases, pre-Go 1.18 error messages provided more detail or were phrased in a more helpful way. We intend to address these cases in Go 1.19.

Because of changes in the compiler related to supporting generics, the Go 1.18 compile speed can be roughly 15% slower than the Go 1.17 compile speed. The execution time of the compiled code is not affected. We intend to improve the speed of the compiler in future releases.

Linker

The linker emits far fewer relocations. As a result, most codebases will link faster, require less memory to link, and generate smaller binaries. Tools that process Go binaries should use Go 1.18’s debug/gosym package to transparently handle both old and new binaries.

The new -asan linker option supports the new go command -asan option.

Bootstrap

When building a Go release from source and GOROOT_BOOTSTRAPis not set, previous versions of Go looked for a Go 1.4 or later bootstrap toolchain in the directory $HOME/go1.4 (%HOMEDRIVE%%HOMEPATH%\go1.4 on Windows). Go now looks first for $HOME/go1.17 or $HOME/sdk/go1.17before falling back to $HOME/go1.4. We intend for Go 1.19 to require Go 1.17 or later for bootstrap, and this change should make the transition smoother. For more details, see go.dev/issue/44505.

Standard library

New `debug/buildinfo` package

The new debug/buildinfo package provides access to module versions, version control information, and build flags embedded in executable files built by the go command. The same information is also available viaruntime/debug.ReadBuildInfofor the currently running binary and via go version -m on the command line.

New `net/netip` package

The new net/netippackage defines a new IP address type, Addr. Compared to the existingnet.IP type, the netip.Addr type takes less memory, is immutable, and is comparable so it supports ==and can be used as a map key.

In addition to Addr, the package definesAddrPort, representing an IP and port, andPrefix, representing a network CIDR prefix.

The package also defines several functions to create and examine these new types:AddrFrom4,AddrFrom16,AddrFromSlice,AddrPortFrom,IPv4Unspecified,IPv6LinkLocalAllNodes,IPv6Unspecified,MustParseAddr,MustParseAddrPort,MustParsePrefix,ParseAddr,ParseAddrPort,ParsePrefix,PrefixFrom.

The net package includes new methods that parallel existing methods, but return netip.AddrPort instead of the heavier-weight net.IP or*net.UDPAddr types:Resolver.LookupNetIP,UDPConn.ReadFromUDPAddrPort,UDPConn.ReadMsgUDPAddrPort,UDPConn.WriteToUDPAddrPort,UDPConn.WriteMsgUDPAddrPort. The new UDPConn methods support allocation-free I/O.

The net package also now includes functions and methods to convert between the existingTCPAddr/UDPAddrtypes and netip.AddrPort:TCPAddrFromAddrPort,UDPAddrFromAddrPort,TCPAddr.AddrPort,UDPAddr.AddrPort.

TLS 1.0 and 1.1 disabled by default client-side

If Config.MinVersionis not set, it now defaults to TLS 1.2 for client connections. Any safely up-to-date server is expected to support TLS 1.2, and browsers have required it since 2020. TLS 1.0 and 1.1 are still supported by settingConfig.MinVersion to VersionTLS10. The server-side default is unchanged at TLS 1.0.

The default can be temporarily reverted to TLS 1.0 by setting theGODEBUG=tls10default=1 environment variable. This option will be removed in Go 1.19.

Rejecting SHA-1 certificates

crypto/x509 will now reject certificates signed with the SHA-1 hash function. This doesn’t apply to self-signed root certificates. Practical attacks against SHA-1have been demonstrated since 2017 and publicly trusted Certificate Authorities have not issued SHA-1 certificates since 2015.

This can be temporarily reverted by setting theGODEBUG=x509sha1=1 environment variable. This option will be removed in a future release.

Minor changes to the library

As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibilityin mind.

bufio

The new Writer.AvailableBuffermethod returns an empty buffer with a possibly non-empty capacity for use with append-like APIs. After appending, the buffer can be provided to a succeeding Write call and possibly avoid any copying.

The Reader.Reset andWriter.Reset methods now use the default buffer size when called on objects with anil buffer.

bytes

The new Cut function slices a []byte around a separator. It can replace and simplify many common uses ofIndex,IndexByte,IndexRune, and SplitN.

Trim, TrimLeft, and TrimRight are now allocation free and, especially for small ASCII cutsets, up to 10 times faster.

The Title function is now deprecated. It doesn’t handle Unicode punctuation and language-specific capitalization rules, and is superseded by thegolang.org/x/text/cases package.

crypto/elliptic

The P224,P384, andP521 curve implementations are now all backed by code generated by theaddchain andfiat-cryptoprojects, the latter of which is based on a formally-verified model of the arithmetic operations. They now use safer complete formulas and internal APIs. P-224 and P-384 are now approximately four times faster. All specific curve implementations are now constant-time.

Operating on invalid curve points (those for which theIsOnCurve method returns false, and which are never returned by Unmarshal or a Curve method operating on a valid point) has always been undefined behavior, can lead to key recovery attacks, and is now unsupported by the new backend. If an invalid point is supplied to aP224, P384, or P521 method, that method will now return a random point. The behavior might change to an explicit panic in a future release.

crypto/tls

The new Conn.NetConnmethod allows access to the underlyingnet.Conn.

crypto/x509

Certificate.Verifynow uses platform APIs to verify certificate validity on macOS and iOS when it is called with a nilVerifyOpts.Rootsor when using the root pool returned fromSystemCertPool.

SystemCertPoolis now available on Windows.

On Windows, macOS, and iOS, when aCertPool returned bySystemCertPoolhas additional certificates added to it,Certificate.Verifywill do two verifications: one using the platform verifier APIs and the system roots, and one using the Go verifier and the additional roots. Chains returned by the platform verifier APIs will be prioritized.

CertPool.Subjectsis deprecated. On Windows, macOS, and iOS theCertPool returned bySystemCertPoolwill return a pool which does not include system roots in the slice returned by Subjects, as a static list can’t appropriately represent the platform policies and might not be available at all from the platform APIs.

Support for signing certificates using signature algorithms that depend on the MD5 hash (MD5WithRSA) may be removed in Go 1.19.

debug/dwarf

The StructFieldand BasicTypestructs both now have a DataBitOffset field, which holds the value of the DW_AT_data_bit_offsetattribute if present.

debug/elf

The R_PPC64_RELATIVEconstant has been added.

debug/plan9obj

The File.Symbolsmethod now returns the new exported error value ErrNoSymbolsif the file has no symbol section.

embed

A go:embeddirective may now start with all: to include files whose names start with dot or underscore.

go/ast

Per the proposalAdditions to go/ast and go/token to support parameterized functions and typesthe following additions are made to the go/ast package:

the FuncTypeand TypeSpecnodes have a new field TypeParams to hold type parameters, if any.
The new expression node IndexListExprrepresents index expressions with multiple indices, used for function and type instantiations with more than one explicit type argument.

go/constant

The new Kind.Stringmethod returns a human-readable name for the receiver kind.

go/token

The new constant TILDErepresents the ~ token per the proposalAdditions to go/ast and go/token to support parameterized functions and types.

go/types

The new Config.GoVersionfield sets the accepted Go language version.

Per the proposalAdditions to go/types to support type parametersthe following additions are made to the go/types package:

The new typeTypeParam, factory functionNewTypeParam, and associated methods are added to represent a type parameter.
The new typeTypeParamList holds a list of type parameters.
The new typeTypeList holds a list of types.
The new factory functionNewSignatureType allocates aSignature with (receiver or function) type parameters. To access those type parameters, the Signature type has two new methodsSignature.RecvTypeParams andSignature.TypeParams.
Named types have four new methods:Named.Origin to get the original parameterized types of instantiated types,Named.TypeArgs andNamed.TypeParams to get the type arguments or type parameters of an instantiated or parameterized type, andNamed.SetTypeParams to set the type parameters (for instance, when importing a named type where allocation of the named type and setting of type parameters cannot be done simultaneously due to possible cycles).
The Interface type has four new methods:Interface.IsComparable andInterface.IsMethodSet to query properties of the type set defined by the interface, andInterface.MarkImplicit andInterface.IsImplicit to set and test whether the interface is an implicit interface around a type constraint literal.
The new typesUnion andTerm, factory functionsNewUnion andNewTerm, and associated methods are added to represent type sets in interfaces.
The new functionInstantiateinstantiates a parameterized type.
The new Info.Instancesmap records function and type instantiations through the newInstance type.
The new type ArgumentErrorand associated methods are added to represent an error related to a type argument.
The new type Context and factory functionNewContextare added to facilitate sharing of identical type instances across type-checked packages, via the newConfig.Contextfield.

The predicatesAssignableTo,ConvertibleTo,Implements,Identical,IdenticalIgnoreTags, andAssertableTonow also work with arguments that are or contain generalized interfaces, i.e. interfaces that may only be used as type constraints in Go code. Note that the behavior of AssignableTo,ConvertibleTo, Implements, andAssertableTo is undefined with arguments that are uninstantiated generic types, and AssertableTo is undefined if the first argument is a generalized interface.

html/template

Within a range pipeline the new{{break}} command will end the loop early and the new {{continue}} command will immediately start the next loop iteration.

The and function no longer always evaluates all arguments; it stops evaluating arguments after the first argument that evaluates to false. Similarly, the or function now stops evaluating arguments after the first argument that evaluates to true. This makes a difference if any of the arguments is a function call.

image/draw

The Draw and DrawMask fallback implementations (used when the arguments are not the most common image types) are now faster when those arguments implement the optionaldraw.RGBA64Imageand image.RGBA64Imageinterfaces that were added in Go 1.17.

net

net.Error.Temporary has been deprecated.

net/http

On WebAssembly targets, the Dial, DialContext,DialTLS and DialTLSContext method fields inTransportwill now be correctly used, if specified, for making HTTP requests.

The newCookie.Validmethod reports whether the cookie is valid.

The newMaxBytesHandlerfunction creates a Handler that wraps itsResponseWriter and Request.Body with aMaxBytesReader.

When looking up a domain name containing non-ASCII characters, the Unicode-to-ASCII conversion is now done in accordance with Nontransitional Processing as defined in theUnicode IDNA Compatibility Processing standard (UTS #46). The interpretation of four distinct runes are changed: ß, ς, zero-width joiner U+200D, and zero-width non-joiner U+200C. Nontransitional Processing is consistent with most applications and web browsers.

os/user

User.GroupIdsnow uses a Go native implementation when cgo is not available.

reflect

The newValue.SetIterKeyand Value.SetIterValuemethods set a Value using a map iterator as the source. They are equivalent toValue.Set(iter.Key()) and Value.Set(iter.Value()), but do fewer allocations.

The newValue.UnsafePointermethod returns the Value’s value as an unsafe.Pointer. This allows callers to migrate from Value.UnsafeAddrand Value.Pointerto eliminate the need to perform uintptr to unsafe.Pointer conversions at the callsite (as unsafe.Pointer rules require).

The newMapIter.Resetmethod changes its receiver to iterate over a different map. The use ofMapIter.Resetallows allocation-free iteration over many maps.

A number of methods (Value.CanInt,Value.CanUint,Value.CanFloat,Value.CanComplex) have been added toValueto test if a conversion is safe.

Value.FieldByIndexErrhas been added to avoid the panic that occurs inValue.FieldByIndexwhen stepping through a nil pointer to an embedded struct.

reflect.Ptr andreflect.PtrTohave been renamed toreflect.Pointer andreflect.PointerTo, respectively, for consistency with the rest of the reflect package. The old names will continue to work, but will be deprecated in a future Go release.

regexp

regexpnow treats each invalid byte of a UTF-8 string as U+FFFD.

runtime/debug

The BuildInfostruct has two new fields, containing additional information about how the binary was built:

GoVersionholds the version of Go used to build the binary.
Settingsis a slice ofBuildSettingsstructs holding key/value pairs describing the build.

runtime/pprof

The CPU profiler now uses per-thread timers on Linux. This increases the maximum CPU usage that a profile can observe, and reduces some forms of bias.

strconv

strconv.Unquotenow rejects Unicode surrogate halves.

strings

The new Cut function slices a string around a separator. It can replace and simplify many common uses ofIndex,IndexByte,IndexRune, and SplitN.

The new Clone function copies the inputstring without the returned cloned string referencing the input string’s memory.