// Any returned error will usually be of type [*ExitError].
// If c.Stderr was nil, Output populates [ExitError.Stderr].
func (c *Cmd) Output() ([]byte, error) {
	if c.Stdout != nil {
		return nil, errors.New("exec: Stdout already set")
	}
	var stdout bytes.Buffer
	c.Stdout = &stdout

	captureErr := c.Stderr == nil
	if captureErr {
		c.Stderr = &prefixSuffixSaver{N: 32 << 10}
	}

	err := c.Run()

				PrimaryIPFamily: v1.IPv6Protocol,
			},
			ssErr:   true,
			ssFatal: false,
			dsErr:   false,
		},
	}

	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			err, fatal := checkBadIPConfig(c.proxy, false)
			if err != nil && !c.ssErr {
				t.Errorf("unexpected error in single-stack case: %v", err)
			} else if err == nil && c.ssErr {

func writeSTSErrorResponse(ctx context.Context, w http.ResponseWriter, errCode STSErrorCode, err error) {
	stsErr := stsErrCodes.ToSTSErr(errCode)

	// Generate error response.
	stsErrorResponse := STSErrorResponse{}
	stsErrorResponse.Error.Code = stsErr.Code
	stsErrorResponse.RequestID = w.Header().Get(xhttp.AmzRequestID)
	stsErrorResponse.Error.Message = stsErr.Description
	if err != nil {
		stsErrorResponse.Error.Message = err.Error()
	}

stderr 'compile( |\.exe"?)'
stderr 'main.go:2.* can inline main' # from compiler
stderr 'link(\.exe"?)? -'
stderr '\d+ symbols' # from linker

# ... but not the second, even though it still prints the compiler and linker output.
go build -x -gcflags=-m -ldflags='-v -w' main.go
! stderr 'compile( |\.exe"?)'
stderr 'main.go:2.* can inline main' # from compiler
! stderr 'link(\.exe"?)? -'
stderr '\d+ symbols' # from linker

go get toolchain@go1.22.1
stderr '^go: added toolchain go1.22.1$'
! stderr '(added|removed|upgraded|downgraded) go'
grep 'toolchain go1.22.1' go.mod

go get toolchain@none
stderr '^go: removed toolchain go1.22.1$'
! stderr '(added|removed|upgraded|downgraded) go'
! grep toolchain go.mod

go get toolchain@go1.22.1
stderr '^go: added toolchain go1.22.1$'
! stderr '(added|removed|upgraded|downgraded) go'

go build -a -n -v -gcflags=-e z1 z2
stderr 'compile.* -p z1.* -e '
stderr 'compile.* -p z2.* -e '
stderr 'compile.* -p y'
! stderr 'compile.* -p [^z].* -e '

# -gcflags can specify package=flags, and can be repeated; last match wins
go build -a -n -v -gcflags=-e -gcflags=z1=-N z1 z2
stderr 'compile.* -p z1.* -N '
! stderr 'compile.* -p z1.* -e '
! stderr 'compile.* -p z2.* -N '
stderr 'compile.* -p z2.* -e '
stderr 'compile.* -p y'

stderr 'package command-line-arguments: invalid package directory .*uh-oh'

go run .
! stdout panic
! stderr panic
stderr '^ok$'

[cgo] go run main.go
[!cgo] go run main_nocgo.go
! stdout panic
! stderr panic
stderr '^ok$'

go test -v
! stdout panic
! stderr panic
stdout '^ok$'  # 'go test' combines the test's stdout into stderr

go test -v .
! stdout panic
! stderr panic

! stderr switching
stderr 'rsc.io/needgo122@v0.0.1 requires go >= 1.22'
stderr 'rsc.io/needgo123@v0.0.1 requires go >= 1.23'
stderr 'rsc.io/needall@v0.0.1 requires go >= 1.23'
stderr 'requires go >= 1.23'
! stderr 'requires go >= 1.21' # that's us!
cmp go.mod go.mod.new

# go get go@1.22 should resolve to the latest 1.22
env GOTOOLCHAIN=local
cp go.mod.new go.mod
! go get go@1.22

! go version
stderr 'go: downloading go1.20 '


# check for invalid GOTOOLCHAIN
env GOTOOLCHAIN=go1.14
go version
stdout 'go1.14'

env GOTOOLCHAIN=go1.20
! go version
stderr 'go: downloading go1.20 '

env GOTOOLCHAIN=go1.21
! go version
stderr 'go: invalid toolchain: go1.21 is a language version but not a toolchain version \(go1.21.x\)'

env GOTOOLCHAIN=go1.22
! go version

go vet -n -buildtags=false runtime
stderr '-buildtags=false'
! stderr '-unsafeptr=false'

# Issue 37030: "go vet <std package>" without other flags should disable the
# unsafeptr check by default.
go vet -n runtime
stderr '-unsafeptr=false'
! stderr '-unreachable=false'

# However, it should be enabled if requested explicitly.
go vet -n -unsafeptr runtime
stderr '-unsafeptr'
! stderr '-unsafeptr=false'