support tests/ with elm 0.19.0

With earlier elm versions, a separate package file is maintained for
tests, which when properly configured enabled the compiler to find what
it needed to compile the tests.  Under elm 0.19, test dependencies are
managed in the top-level package file, so `elm make` will fail on the
tests.  `elm-test make` is required in this case.

See https://github.com/elm-explorations/test/issues/64

ale_linters/elm/make.vim

@@ -137,9 +137,7 @@ function! ale_linters#elm#make#ParseMessageItem(item) abort
     endif
 endfunction
 
-" Return the command to execute the linter in the projects directory.
-" If it doesn't, then this will fail when imports are needed.
-function! ale_linters#elm#make#GetCommand(buffer) abort
+function! ale_linters#elm#make#GetPackageFile(buffer) abort
     let l:elm_json = ale#path#FindNearestFile(a:buffer, 'elm.json')
 
     if empty(l:elm_json)
@@ -147,10 +145,55 @@ function! ale_linters#elm#make#GetCommand(buffer) abort
         let l:elm_json = ale#path#FindNearestFile(a:buffer, 'elm-package.json')
     endif
 
+    return l:elm_json
+endfunction
+
+function! ale_linters#elm#make#IsVersionGte19(buffer) abort
+    let l:elm_json = ale_linters#elm#make#GetPackageFile(a:buffer)
+
+    if l:elm_json =~# '-package'
+        return 0
+    else
+        return 1
+    endif
+endfunction
+
+function! ale_linters#elm#make#GetRootDir(buffer) abort
+    let l:elm_json = ale_linters#elm#make#GetPackageFile(a:buffer)
+
     if empty(l:elm_json)
+        return ''
+    else
+        return fnamemodify(l:elm_json, ':p:h')
+    endif
+endfunction
+
+function! ale_linters#elm#make#IsTest(buffer) abort
+    let l:root_dir = ale_linters#elm#make#GetRootDir(a:buffer)
+
+    if empty(l:root_dir)
+        return 0
+    endif
+
+    let l:tests_dir = join([l:root_dir, 'tests', ''], has('win32') ? '\' : '/')
+
+    let l:buffer_path = fnamemodify(bufname(a:buffer), ':p')
+
+    if match(l:buffer_path, l:tests_dir) == 0
+        return 1
+    else
+        return 0
+    endif
+endfunction
+
+" Return the command to execute the linter in the projects directory.
+" If it doesn't, then this will fail when imports are needed.
+function! ale_linters#elm#make#GetCommand(buffer) abort
+    let l:root_dir = ale_linters#elm#make#GetRootDir(a:buffer)
+
+    if empty(l:root_dir)
         let l:dir_set_cmd = ''
     else
-        let l:root_dir = fnamemodify(l:elm_json, ':p:h')
         let l:dir_set_cmd = 'cd ' . ale#Escape(l:root_dir) . ' && '
     endif
 
@@ -161,11 +204,20 @@ function! ale_linters#elm#make#GetCommand(buffer) abort
     return l:dir_set_cmd . '%e make --report=json --output=/dev/null %t'
 endfunction
 
+function! ale_linters#elm#make#GetExecutable(buffer) abort
+    let l:is_test = ale_linters#elm#make#IsTest(a:buffer)
+    let l:is_v19 = ale_linters#elm#make#IsVersionGte19(a:buffer)
+
+    if l:is_test && l:is_v19
+        return ale#node#FindExecutable(a:buffer, 'elm_make', ['node_modules/.bin/elm-test'])
+    else
+        return ale#node#FindExecutable(a:buffer, 'elm_make', ['node_modules/.bin/elm'])
+    endif
+endfunction
+
 call ale#linter#Define('elm', {
 \   'name': 'make',
-\   'executable_callback': ale#node#FindExecutableFunc('elm_make', [
-\       'node_modules/.bin/elm',
-\   ]),
+\   'executable_callback': 'ale_linters#elm#make#GetExecutable',
 \   'output_stream': 'both',
 \   'command_callback': 'ale_linters#elm#make#GetCommand',
 \   'callback': 'ale_linters#elm#make#Handle'

test/command_callback/test_elm_make_command_callback.vader

@@ -7,29 +7,47 @@ After:
   call ale#assert#TearDownLinterTest()
 
 Execute(should get valid executable with default params):
-  call ale#test#SetFilename('../elm-test-files/app/testfile.elm')
+  call ale#test#SetFilename('../elm-test-files/newapp/src/Main.elm')
 
-  let g:executable = ale#path#Simplify(g:dir . '/../elm-test-files/app/node_modules/.bin/elm')
+  let g:executable = ale#path#Simplify(g:dir . '/../elm-test-files/newapp/node_modules/.bin/elm')
 
   AssertLinter g:executable,
-  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/app')) . ' && '
+  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/newapp')) . ' && '
+  \ . ale#Escape(g:executable) . ' make --report=json --output=/dev/null %t'
+
+Execute(should get elm-test executable for test code with elm >= 0.19):
+  call ale#test#SetFilename('../elm-test-files/newapp/tests/TestSuite.elm')
+
+  let g:executable = ale#path#Simplify(g:dir . '/../elm-test-files/newapp/node_modules/.bin/elm-test')
+
+  AssertLinter g:executable,
+  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/newapp')) . ' && '
+  \ . ale#Escape(g:executable) . ' make --report=json --output=/dev/null %t'
+
+Execute(should get plain elm executable for test code with elm < 0.19):
+  call ale#test#SetFilename('../elm-test-files/oldapp/tests/TestSuite.elm')
+
+  let g:executable = ale#path#Simplify(g:dir . '/../elm-test-files/oldapp/node_modules/.bin/elm')
+
+  AssertLinter g:executable,
+  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/oldapp')) . ' && '
   \ . ale#Escape(g:executable) . ' make --report=json --output=/dev/null %t'
 
 Execute(should get valid executable with 'use_global' params):
   let g:ale_elm_make_use_global = 1
 
-  call ale#test#SetFilename('../elm-test-files/app/testfile.elm')
+  call ale#test#SetFilename('../elm-test-files/newapp/src/Main.elm')
 
   AssertLinter 'elm',
-  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/app')) . ' && '
+  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/newapp')) . ' && '
   \ . ale#Escape('elm') . ' make --report=json --output=/dev/null %t'
 
 Execute(should get valid executable with 'use_global' and 'executable' params):
   let g:ale_elm_make_executable = 'other-elm'
   let g:ale_elm_make_use_global = 1
 
-  call ale#test#SetFilename('../elm-test-files/app/testfile.elm')
+  call ale#test#SetFilename('../elm-test-files/newapp/src/Main.elm')
 
   AssertLinter 'other-elm',
-  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/app')) . ' && '
+  \ 'cd ' . ale#Escape(ale#path#Simplify(g:dir . '/../elm-test-files/newapp')) . ' && '
   \ . ale#Escape('other-elm') . ' make --report=json --output=/dev/null %t'