Support $GO111MODULE with Go tooling

Allows the user to override $GO111MODULE environment variable through
ale options. This gives control over the default behavior of Go module
resolution.

Golang documentation:
https://github.com/golang/go/wiki/Modules#how-to-use-modules

Add `ale#Go#EnvString()` function to make it easy to add similar Go
environment variables in the future.

Use the new `EnvString` function in all available Go tools callbacks
& update tests

Also add test of linter command callback for `gofmt`

12 files changed, 34 insertions, 11 deletions

diff --git a/ale_linters/go/bingo.vim b/ale_linters/go/bingo.vim
index e446bdcc..1e43f8e4 100644
--- a/ale_linters/go/bingo.vim
+++ b/ale_linters/go/bingo.vim
@@ -5,11 +5,13 @@ call ale#Set('go_bingo_executable', 'bingo')
 call ale#Set('go_bingo_options', '--mode stdio')
 
 function! ale_linters#go#bingo#GetCommand(buffer) abort
-    return '%e' . ale#Pad(ale#Var(a:buffer, 'go_bingo_options'))
+    return ale#go#EnvString(a:buffer) . '%e' . ale#Pad(ale#Var(a:buffer, 'go_bingo_options'))
 endfunction
 
 function! ale_linters#go#bingo#FindProjectRoot(buffer) abort
-    let l:project_root = ale#path#FindNearestFile(a:buffer, 'go.mod')
+    let l:go_modules_off = ale#Var(a:buffer, 'go_go111module') is# 'off'
+    let l:project_root = l:go_modules_off ?
+    \ '' : ale#path#FindNearestFile(a:buffer, 'go.mod')
     let l:mods = ':h'
 
     if empty(l:project_root)
diff --git a/ale_linters/go/gobuild.vim b/ale_linters/go/gobuild.vim
index 374ded35..1dfb6daa 100644
--- a/ale_linters/go/gobuild.vim
+++ b/ale_linters/go/gobuild.vim
@@ -11,6 +11,7 @@ function! ale_linters#go#gobuild#GetCommand(buffer) abort
 
     " Run go test in local directory with relative path
     return ale#path#BufferCdString(a:buffer)
+    \   . ale#go#EnvString(a:buffer)
     \   . ale#Var(a:buffer, 'go_go_executable') . ' test'
     \   . (!empty(l:options) ? ' ' . l:options : '')
     \   . ' -c -o /dev/null ./'
diff --git a/ale_linters/go/gofmt.vim b/ale_linters/go/gofmt.vim
index 337deef8..a233b422 100644
--- a/ale_linters/go/gofmt.vim
+++ b/ale_linters/go/gofmt.vim
@@ -1,10 +1,16 @@
 " Author: neersighted <bjorn@neersighted.com>
 " Description: gofmt for Go files
 
+function! ale_linters#go#gofmt#GetCommand(buffer) abort
+    return ale#go#EnvString(a:buffer)
+    \   . '%e -e %t'
+endfunction
+
+
 call ale#linter#Define('go', {
 \   'name': 'gofmt',
 \   'output_stream': 'stderr',
 \   'executable': 'gofmt',
-\   'command': 'gofmt -e %t',
+\   'command': function('ale_linters#go#gofmt#GetCommand'),
 \   'callback': 'ale#handlers#unix#HandleAsError',
 \})
diff --git a/ale_linters/go/golangci_lint.vim b/ale_linters/go/golangci_lint.vim
index 357f7949..dd0e975a 100644
--- a/ale_linters/go/golangci_lint.vim
+++ b/ale_linters/go/golangci_lint.vim
@@ -10,13 +10,16 @@ function! ale_linters#go#golangci_lint#GetCommand(buffer) abort
     let l:options = ale#Var(a:buffer, 'go_golangci_lint_options')
     let l:lint_package = ale#Var(a:buffer, 'go_golangci_lint_package')
 
+
     if l:lint_package
         return ale#path#BufferCdString(a:buffer)
+        \   . ale#go#EnvString(a:buffer)
         \   . '%e run '
         \   .  l:options
     endif
 
     return ale#path#BufferCdString(a:buffer)
+    \   . ale#go#EnvString(a:buffer)
     \   . '%e run '
     \   . ale#Escape(l:filename)
     \   . ' ' . l:options
diff --git a/ale_linters/go/golint.vim b/ale_linters/go/golint.vim
index 765e1477..79bfaeb5 100644
--- a/ale_linters/go/golint.vim
+++ b/ale_linters/go/golint.vim
@@ -7,7 +7,7 @@ call ale#Set('go_golint_options', '')
 function! ale_linters#go#golint#GetCommand(buffer) abort
     let l:options = ale#Var(a:buffer, 'go_golint_options')
 
-    return '%e'
+    return ale#go#EnvString(a:buffer) . '%e'
     \   . (!empty(l:options) ? ' ' . l:options : '')
     \   . ' %t'
 endfunction
diff --git a/ale_linters/go/gometalinter.vim b/ale_linters/go/gometalinter.vim
index 19d70a81..eed9550a 100644
--- a/ale_linters/go/gometalinter.vim
+++ b/ale_linters/go/gometalinter.vim
@@ -14,11 +14,13 @@ function! ale_linters#go#gometalinter#GetCommand(buffer) abort
     " be calculated to absolute paths in the Handler
     if l:lint_package
         return ale#path#BufferCdString(a:buffer)
+        \   . ale#go#EnvString(a:buffer)
         \   . '%e'
         \   . (!empty(l:options) ? ' ' . l:options : '') . ' .'
     endif
 
     return ale#path#BufferCdString(a:buffer)
+    \   . ale#go#EnvString(a:buffer)
     \   . '%e'
     \   . ' --include=' . ale#Escape(ale#util#EscapePCRE(l:filename))
     \   . (!empty(l:options) ? ' ' . l:options : '') . ' .'
diff --git a/ale_linters/go/gopls.vim b/ale_linters/go/gopls.vim
index c411dc2b..dcff5ec7 100644
--- a/ale_linters/go/gopls.vim
+++ b/ale_linters/go/gopls.vim
@@ -6,11 +6,15 @@ call ale#Set('go_gopls_executable', 'gopls')
 call ale#Set('go_gopls_options', '--mode stdio')
 
 function! ale_linters#go#gopls#GetCommand(buffer) abort
-    return '%e' . ale#Pad(ale#Var(a:buffer, 'go_gopls_options'))
+    return ale#go#EnvString(a:buffer)
+    \   . '%e'
+    \   . ale#Pad(ale#Var(a:buffer, 'go_gopls_options'))
 endfunction
 
 function! ale_linters#go#gopls#FindProjectRoot(buffer) abort
-    let l:project_root = ale#path#FindNearestFile(a:buffer, 'go.mod')
+    let l:go_modules_off = ale#Var(a:buffer, 'go_go111module') is# 'off'
+    let l:project_root = l:go_modules_off ?
+    \ '' : ale#path#FindNearestFile(a:buffer, 'go.mod')
     let l:mods = ':h'
 
     if empty(l:project_root)
diff --git a/ale_linters/go/gosimple.vim b/ale_linters/go/gosimple.vim
index 281a0e53..ad52c621 100644
--- a/ale_linters/go/gosimple.vim
+++ b/ale_linters/go/gosimple.vim
@@ -2,7 +2,8 @@
 " Description: gosimple for Go files
 
 function! ale_linters#go#gosimple#GetCommand(buffer) abort
-    return ale#path#BufferCdString(a:buffer) . ' gosimple .'
+    return ale#path#BufferCdString(a:buffer) . ' '
+    \   . ale#go#EnvString(a:buffer) . 'gosimple .'
 endfunction
 
 call ale#linter#Define('go', {
diff --git a/ale_linters/go/gotype.vim b/ale_linters/go/gotype.vim
index d5d563aa..6a5149ca 100644
--- a/ale_linters/go/gotype.vim
+++ b/ale_linters/go/gotype.vim
@@ -6,7 +6,8 @@ function! ale_linters#go#gotype#GetCommand(buffer) abort
         return ''
     endif
 
-    return ale#path#BufferCdString(a:buffer) . ' gotype -e .'
+    return ale#path#BufferCdString(a:buffer) . ' '
+    \   . ale#go#EnvString(a:buffer) . 'gotype -e .'
 endfunction
 
 call ale#linter#Define('go', {
diff --git a/ale_linters/go/govet.vim b/ale_linters/go/govet.vim
index bb81d5d0..dddafe17 100644
--- a/ale_linters/go/govet.vim
+++ b/ale_linters/go/govet.vim
@@ -11,6 +11,7 @@ function! ale_linters#go#govet#GetCommand(buffer) abort
     let l:options = ale#Var(a:buffer, 'go_govet_options')
 
     return ale#path#BufferCdString(a:buffer) . ' '
+    \   . ale#go#EnvString(a:buffer)
     \   . ale#Var(a:buffer, 'go_go_executable') . ' vet '
     \   . (!empty(l:options) ? ' ' . l:options : '')
     \   . ' .'
diff --git a/ale_linters/go/langserver.vim b/ale_linters/go/langserver.vim
index 776186c7..7130db40 100644
--- a/ale_linters/go/langserver.vim
+++ b/ale_linters/go/langserver.vim
@@ -15,8 +15,9 @@ function! ale_linters#go#langserver#GetCommand(buffer) abort
     endif
 
     let l:options = uniq(sort(l:options))
+    let l:env = ale#go#EnvString(a:buffer)
 
-    return join(extend(l:executable, l:options), ' ')
+    return l:env . join(extend(l:executable, l:options), ' ')
 endfunction
 
 call ale#linter#Define('go', {
diff --git a/ale_linters/go/staticcheck.vim b/ale_linters/go/staticcheck.vim
index 26fe0193..ed40c6c2 100644
--- a/ale_linters/go/staticcheck.vim
+++ b/ale_linters/go/staticcheck.vim
@@ -8,17 +8,18 @@ function! ale_linters#go#staticcheck#GetCommand(buffer) abort
     let l:filename = expand('#' . a:buffer . ':t')
     let l:options = ale#Var(a:buffer, 'go_staticcheck_options')
     let l:lint_package = ale#Var(a:buffer, 'go_staticcheck_lint_package')
+    let l:env = ale#go#EnvString(a:buffer)
 
     " BufferCdString is used so that we can be sure the paths output from
     " staticcheck can be calculated to absolute paths in the Handler
     if l:lint_package
         return ale#path#BufferCdString(a:buffer)
-        \   . 'staticcheck'
+        \   . l:env . 'staticcheck'
         \   . (!empty(l:options) ? ' ' . l:options : '') . ' .'
     endif
 
     return ale#path#BufferCdString(a:buffer)
-    \   . 'staticcheck'
+    \   . l:env . 'staticcheck'
     \   . (!empty(l:options) ? ' ' . l:options : '')
     \   . ' ' . ale#Escape(l:filename)
 endfunction