adjust imports on save

[bhcleek]

Introduce a new option, g:go_imports_autosave, to allow imports to be
adjusted even when g:go_fmt_command is not set to goimports.

Closes #2795

[orlangure]

I tested this option, and got some errors:

line    5:
E714: List required
Error detected while processing function go#auto#fmt_autosave[10]..go#fmt#Format[9]..go#lsp#Imports[18]..<SNR>114_await[3]..18:
line   13:
E171: Missing :endif
Error detected while processing function go#auto#fmt_autosave[10]..go#fmt#Format[9]..go#lsp#Imports[18]..<SNR>114_await:
line    3:
E170: Missing :endwhile
Error detected while processing function go#auto#fmt_autosave[10]..go#fmt#Format:
line    9:
E171: Missing :endif
Error detected while processing function go#auto#fmt_autosave:
line   10:
E171: Missing :endif
Press ENTER or type command to continue

My new config is:

  let g:go_fmt_autosave=0 " or 1 as well
  let g:go_imports_autosave=1
  let g:go_fmt_command='gopls'
  let g:go_imports_mode='gopls'

It happens if I try to save a file that does not exist yet.

With existing files, these options work, and imports are organized.

There is a weird issue when imports look like this:

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"
	"github.com/orlangure/gnomock"
)

In this case, a new line is added between stdlib imports and 3rd party imports, but it is added with trailing whitespace:

import (
	"encoding/json"
	"fmt"
	"net/http"
	"strings"
	"time"
	
	"github.com/orlangure/gnomock"
)

There is a tab on the blank line.

[bhcleek]

Thanks @orlangure

I don't intend to merge this until I've used it for a while; I fully expect to make changes before merging this.