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`

test/command_callback/test_bingo_command_callback.vader

@@ -9,6 +9,7 @@ After:
   endif
 
   unlet! b:ale_completion_enabled
+  unlet! b:ale_go_go111module
 
   call ale#assert#TearDownLinterTest()
 
@@ -34,6 +35,14 @@ Execute(should set bingo options):
   AssertLinter 'bingo',
   \ ale#Escape('bingo') . ' --mode stdio --trace'
 
+Execute(should support Go environment variables):
+  call ale#test#SetFilename('go_paths/go1/prj1/file.go')
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'bingo',
+  \ ale#Env('GO111MODULE', 'on') . ale#Escape('bingo') . ' --mode stdio'
+
+
 Execute(Should return directory for 'go.mod' if found in parent directory):
   call ale#test#SetFilename('../go_files/test.go')
 
@@ -44,3 +53,20 @@ Execute(Should return nearest directory with '.git' if found in parent directory
   call mkdir(g:dir . '/.git')
 
   AssertLSPProject g:dir
+
+Execute(Should ignore 'go.mod' and return '.git' dir if modules off):
+  call ale#test#SetFilename('../go_files/test.go')
+
+  let b:ale_go_go111module = 'off'
+  let b:parent_dir = ale#path#Simplify(g:dir . '/..')
+  let b:git_dir = b:parent_dir . '/.git'
+
+  if !isdirectory(b:git_dir)
+    call mkdir(b:git_dir)
+  endif
+
+  AssertLSPProject b:parent_dir
+
+  call delete(b:git_dir, 'd')
+  unlet! b:parent_dir
+  unlet! b:git_dir

test/command_callback/test_gobuild_command_callback.vader

@@ -14,6 +14,16 @@ Execute(The default commands should be correct):
   \ ale#path#CdString(expand('%:p:h'))
   \   . 'go test -c -o /dev/null ./'
 
+Execute(Go environment variables should be supported):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'go',
+  \ ale#path#CdString(expand('%:p:h'))
+  \   . ale#Env('GO111MODULE', 'on')
+  \   . 'go test -c -o /dev/null ./'
+
+  unlet! b:ale_go_go111module
+
 Execute(Extra options should be supported):
   let g:ale_go_gobuild_options = '--foo-bar'
 

test/command_callback/test_gofmt_command_callback.vader

@@ -0,0 +1,19 @@
+Before:
+  call ale#assert#SetUpLinterTest('go', 'gofmt')
+  call ale#test#SetFilename('../go_files/testfile2.go')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(The default gofmt command should be correct):
+  AssertLinter 'gofmt',
+  \ ale#Escape('gofmt') . ' -e %t'
+
+Execute(The gofmt command should support Go environment variables):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'gofmt',
+  \ ale#Env('GO111MODULE', 'on')
+  \ . ale#Escape('gofmt') . ' -e %t'
+
+  unlet! b:ale_go_go111module

test/command_callback/test_golangci_lint_command_callback.vader

@@ -30,6 +30,18 @@ Execute(The golangci-lint callback should use configured options):
   \   . ' run ' . ale#Escape(expand('%' . ':t'))
   \   . ' --foobar'
 
+Execute(The golangci-lint callback should support environment variables):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'golangci-lint',
+  \ ale#path#CdString(expand('%:p:h'))
+  \   . ale#Env('GO111MODULE', 'on')
+  \   . ale#Escape('golangci-lint')
+  \   . ' run ' . ale#Escape(expand('%' . ':t'))
+  \   . ' --enable-all'
+
+  unlet! b:ale_go_go111module
+
 Execute(The golangci-lint `lint_package` option should use the correct command):
   let b:ale_go_golangci_lint_package = 1
 

test/command_callback/test_golangserver_command_callback.vader

@@ -14,6 +14,7 @@ After:
   Restore
 
   unlet! b:ale_completion_enabled
+  unlet! b:ale_go_go111module
   unlet! g:sep
 
   call ale#assert#TearDownLinterTest()
@@ -52,6 +53,12 @@ Execute(should ignore go-langserver -gocodecompletion option):
 
   AssertLinter 'go-langserver', ale#Escape('go-langserver') . ' -trace'
 
+Execute(should support Go environment variables):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'go-langserver',
+  \ ale#Env('GO111MODULE', 'on') . ale#Escape('go-langserver')
+
 Execute(should set go-langserver for go app1):
   call ale#test#SetFilename('go_paths/go1/prj1/file.go')
 

test/command_callback/test_golint_command_callbacks.vader

@@ -16,3 +16,11 @@ Execute(The golint options should be configurable):
   let b:ale_go_golint_options = '--foo'
 
   AssertLinter 'golint', ale#Escape('golint') . ' --foo %t'
+
+Execute(The golint command should support Go environment variables):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'golint',
+  \ ale#Env('GO111MODULE', 'on') . ale#Escape('golint') . ' %t'
+
+  unlet! b:ale_go_go111module

test/command_callback/test_gometalinter_command_callback.vader

@@ -30,6 +30,16 @@ Execute(The gometalinter callback should use configured options):
   \   . ' --include=' . ale#Escape(ale#util#EscapePCRE(expand('%' . ':t')))
   \   . ' --foobar' . ' .'
 
+Execute(The gometalinter should use configured environment variables):
+  let b:ale_go_go111module = 'off'
+  AssertLinter 'gometalinter',
+  \ ale#path#CdString(expand('%:p:h'))
+  \   . ale#Env('GO111MODULE', 'off')
+  \   . ale#Escape('gometalinter')
+  \   . ' --include=' . ale#Escape(ale#util#EscapePCRE(expand('%' . ':t')))
+  \   . ' .'
+  unlet! b:ale_go_go111module
+
 Execute(The gometalinter `lint_package` option should use the correct command):
   let b:ale_go_gometalinter_lint_package = 1
 

test/command_callback/test_gopls_command_callback.vader

@@ -8,6 +8,7 @@ After:
     call delete(g:dir . '/.git', 'd')
   endif
 
+  unlet! b:ale_go_go111module
   unlet! b:ale_completion_enabled
 
   call ale#assert#TearDownLinterTest()
@@ -34,6 +35,12 @@ Execute(should set gopls options):
   AssertLinter 'gopls',
   \ ale#Escape('gopls') . ' --mode stdio --trace'
 
+Execute(should support go environment variables):
+  let b:ale_go_go111module = 'off'
+
+  AssertLinter 'gopls',
+  \ ale#Env('GO111MODULE', 'off') . ale#Escape('gopls') . ' --mode stdio'
+
 Execute(Should return directory for 'go.mod' if found in parent directory):
   call ale#test#SetFilename('../go_files/test.go')
 
@@ -44,3 +51,20 @@ Execute(Should return nearest directory with '.git' if found in parent directory
   call mkdir(g:dir . '/.git')
 
   AssertLSPProject g:dir
+
+Execute(Should ignore 'go.mod' and return '.git' dir if modules off):
+  call ale#test#SetFilename('../go_files/test.go')
+
+  let b:ale_go_go111module = 'off'
+  let b:parent_dir = ale#path#Simplify(g:dir . '/..')
+  let b:git_dir = b:parent_dir . '/.git'
+
+  if !isdirectory(b:git_dir)
+    call mkdir(b:git_dir)
+  endif
+
+  AssertLSPProject b:parent_dir
+
+  call delete(b:git_dir, 'd')
+  unlet! b:parent_dir
+  unlet! b:git_dir

test/command_callback/test_gosimple_command_callback.vader

@@ -8,3 +8,12 @@ After:
 Execute(The default gosimple command should be correct):
   AssertLinter 'gosimple',
   \ ale#path#CdString(expand('%:p:h')) . ' gosimple .'
+
+Execute(The gosimple command should support Go environment variables):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'gosimple',
+  \ ale#path#CdString(expand('%:p:h')) . ' '
+  \ . ale#Env('GO111MODULE', 'on') . 'gosimple .'
+
+  unlet! b:ale_go_go111module

test/command_callback/test_gotype_command_callback.vader

@@ -13,3 +13,13 @@ Execute(The gotype callback should ignore test files):
   call ale#test#SetFilename('bla_test.go')
 
   AssertLinter 'gotype', ''
+
+Execute(The gotype callback should support Go environment variables):
+  let b:ale_go_go111module = 'on'
+
+  AssertLinter 'gotype',
+  \ ale#path#CdString(expand('%:p:h')) . ' '
+  \ . ale#Env('GO111MODULE', 'on')
+  \ . 'gotype -e .'
+
+  unlet! b:ale_go_go111module

test/command_callback/test_govet_command_callback.vader

@@ -17,3 +17,11 @@ Execute(Extra options should be supported):
 Execute(The executable should be configurable):
   let g:ale_go_go_executable = 'foobar'
   AssertLinter 'foobar', ale#path#CdString(expand('%:p:h')) . ' foobar vet  .'
+
+Execute(Go environment variables should be supported):
+  let b:ale_go_go111module = 'on'
+  AssertLinter 'go',
+  \ ale#path#CdString(expand('%:p:h')) . ' '
+  \ . ale#Env('GO111MODULE', 'on')
+  \ . 'go vet  .'
+  unlet! b:ale_go_go111module

test/command_callback/test_staticcheck_command_callback.vader

@@ -24,3 +24,20 @@ Execute(The staticcheck `lint_package` option should use the correct command):
 
   AssertLinter 'staticcheck',
   \ ale#path#CdString(expand('%:p:h')) . 'staticcheck .',
+
+Execute(The staticcheck callback should use the `GO111MODULE` option if set):
+  let b:ale_go_go111module = 'off'
+
+  AssertLinter 'staticcheck',
+  \ ale#path#CdString(expand('%:p:h'))
+  \   . ale#Env('GO111MODULE', 'off')
+  \   . 'staticcheck '
+  \   . ale#Escape(expand('%' . ':t'))
+
+  " Test with lint_package option set
+  let b:ale_go_staticcheck_lint_package = 1
+  AssertLinter 'staticcheck',
+  \ ale#path#CdString(expand('%:p:h'))
+  \   . ale#Env('GO111MODULE', 'off')
+  \   . 'staticcheck .'
+  unlet! b:ale_go_go111module