x/tools/cmd/goimports doesn't reorder standard library imports if they're already in separate blocks

[DylanSpOddball]

What version of Go are you using (go version)?

$ go version
go version go1.17.5 linux/amd64

Does this issue reproduce with the latest release?

Yes (1.17.5 is the latest release, as of filing this issue)

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/dylan/.cache/go-build"
GOENV="/home/dylan/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/dylan/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/dylan/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.5"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3462334434=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Use goimports to reorder imports, expecting to see standard library dependencies placed above other dependencies.

main.go:

import (
    _ "github.com/google/uuid"

    _ "time"
)

Command run: goimports main.go

What did you expect to see?

I expected to see

import (
    _ "time"

    _ "github.com/google/uuid"
)

following the convention that standard library imports are placed first. (This convention is followed by goimports when stdlib dependencies are mixed in with another block, as well as being mentioned on GitHub at https://github.com/golang/go/wiki/CodeReviewComments#imports)

What did you see instead?

No changes:

$ goimports main.go
import (
        _ "github.com/google/uuid"

        _ "time"
)

Other notes

• The last comment on x/tools/cmd/goimports: -local adds local packages before external packages #31646 mentions running into this same issue.
• It's not clear what goimports is supposed to do from the documentation. If this is working as designed, it'd be helpful to note that in the docs.

[seankhliao]

Duplicate of #20818