Invalid var block formatting when g:go_gopls_gofumpt enabled

[moorereason]

What did you do?

With g:go_gopls_gofumpt = 1, save the following file:

package main

var (
        // foo
        b = 2
)

func main() {}

What did you expect to happen?

Expected the formatting of the var block to be reformatted as:

// foo
var b = 2

What happened instead?

Creates a syntactically invalid file:

package main

var (// foo
var b = 2

func main() {}

I'm unable to reproduce the issue with the gofumpt binary (see mvdan/gofumpt#119). This only appears to happen in vim-go with g:go_gopls_gofumpt enabled.

Configuration

vim-go version:

Occurs with v1.25 and HEAD (currently 8c883d7)

vimrc you used to reproduce:

vimrc

call plug#begin('~/.vim/plugged')
Plug 'fatih/vim-go'
call plug#end()

let g:go_gopls_gofumpt = 1

Vim version (first three lines from :version):

NVIM v0.4.4
Build type: Release
LuaJIT 2.0.5

Go version (go version):

go version go1.16.3 linux/amd64

Go environment

go env Output:

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/XXX/.cache/go-build"
GOENV="/home/XXX/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/XXX/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/XXX"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/XXX/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/XXX/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.3"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/XXX/src/mvdan.cc/gofumpt/go.mod"
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-build546098438=/tmp/go-build -gno-record-gcc-switches"

gopls version

gopls version Output:

golang.org/x/tools/gopls v0.6.11
    golang.org/x/tools/[email protected] h1:7S2k0xuVYc3secjy2uz0n+fGYxGJU6gXsLOmQ/r1HoI=

vim-go configuration:

vim-go configuration

g:go_loaded_install = 1
g:go_gopls_gofumpt = 1
g:go_jump_to_error = 1
g:go_loaded_gosnippets = 1

filetype detection configuration:

filetype detection

filetype detection:ON  plugin:ON  indent:ON

[bhcleek]

Thank you for the good report. I'll merge the fix tonight.