FileChangedShell autocmd blocks reload/prompt on file changes

[jcordasc]

What did you do? (required: The issue will be closed when not provided)

1. Open a go source file in vim w/ vim-go plugin loaded.
2. Update the file outside of vim.
3. Return to vim.

What did you expect to happen?

Expect either:

• you get prompted that the file has changed
• the file reloads if you have autoread set

What happened instead?

Nothing. No prompt or reload is triggered.

Configuration (MUST fill this out):

vim-go version: v1.20+

vimrc you used to reproduce (use a minimal vimrc with other plugins disabled; do not link to a 2,000 line vimrc):

vimrc

" no config needed

Vim version (first three lines from :version):

VIM - Vi IMproved 8.1 (2018 May 18, compiled Jun 26 2019 04:36:15)
macOS version
Included patches: 1-1600

Go version (go version):

go version go1.12.10 darwin/amd64

Go environment

go env Output:

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/user/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/user/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.12.10/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.12.10/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/21/8dfdmhv92pggrb64ccm2_y040000gp/T/go-build594152047=/tmp/go-build -gno-record-gcc-switches -fno-common"

Cause

Per the FileChangedShell and timestamp documentation, this is expected behavior when a FileChangedShell autocommand is registered that doesn't handle this itself, nor does it set v:fcs_choice.

Such an autocommand was introduced in this commit.

I'm also submitting a PR to change the autocommand to a FileChangedShellPost which will allow for vim's regular behavior on file changes and still call go#lsp#DidChange.