Fix #438 Create Java .class files for javac in a temporary directory

ale_linters/java/javac.vim

@@ -9,8 +9,12 @@ function! ale_linters#java#javac#GetCommand(buffer) abort
     \   ?  '-cp ' . g:ale_java_javac_classpath
     \   : ''
 
+    " Create .class files in a temporary directory, which we will delete later.
+    let l:class_file_directory = ale#engine#CreateDirectory(a:buffer)
+
     return 'javac -Xlint '
     \ . l:cp_option
+    \ . ' -d ' . fnameescape(l:class_file_directory)
     \ . ' ' . g:ale_java_javac_options
     \ . ' %t'
 endfunction

autoload/ale/engine.vim

@@ -152,6 +152,17 @@ function! ale#engine#ManageDirectory(buffer, directory) abort
     call add(g:ale_buffer_info[a:buffer].temporary_directory_list, a:directory)
 endfunction
 
+" Create a new temporary directory and manage it in one go.
+function! ale#engine#CreateDirectory(buffer) abort
+    let l:temporary_directory = tempname()
+    " Create the temporary directory for the file, unreadable by 'other'
+    " users.
+    call mkdir(l:temporary_directory, '', 0750)
+    call ale#engine#ManageDirectory(a:buffer, l:temporary_directory)
+
+    return l:temporary_directory
+endfunction
+
 function! ale#engine#RemoveManagedFiles(buffer) abort
     if !has_key(g:ale_buffer_info, a:buffer)
         return

doc/ale.txt

@@ -637,6 +637,16 @@ ale#Queue(delay, [linting_flag])                                  *ale#Queue()*
   run. Linters with `lint_file` set to `1` are not run by default.
 
 
+ale#engine#CreateDirectory(buffer)               *ale#engine#CreateDirectory()*
+
+  Create a new temporary directory with a unique name, and manage that
+  directory with |ale#engine#ManageDirectory()|, so it will be removed as
+  soon as possible.
+
+  It is advised to only call this function from a callback function for
+  returning a linter command to run.
+
+
 ale#engine#EscapeCommandPart(command_part)     *ale#engine#EscapeCommandPart()*
 
   Given a |String|, return a |String| with all `%` characters replaced with

test/command_callback/test_javac_command_callback.vader

@@ -0,0 +1,33 @@
+Before:
+  runtime ale_linters/java/javac.vim
+  call ale#engine#InitBufferInfo(bufnr(''))
+
+After:
+  call ale#linter#Reset()
+  " We need to clean up the buffer to remove the temporary directories created
+  " for the command.
+  call ale#cleanup#Buffer(bufnr(''))
+  let g:ale_java_javac_options = ''
+  let g:ale_java_javac_classpath = ''
+
+Execute(The javac callback should return the correct default value):
+  let b:command = ale_linters#java#javac#GetCommand(bufnr(''))
+
+  Assert match(b:command, '\v^javac +-Xlint +-d +/tmp/[0-9a-zA-Z/]+ +\%t$') >= 0,
+  \ 'Invalid command string: ' . b:command
+
+Execute(The javac callback should use g:ale_java_javac_classpath correctly):
+  let g:ale_java_javac_classpath = 'foo.jar'
+
+  let b:command = ale_linters#java#javac#GetCommand(bufnr(''))
+
+  Assert match(b:command, '\v^javac +-Xlint -cp foo\.jar +-d +/tmp/[0-9a-zA-Z/]+ +\%t$') >= 0,
+  \ 'Invalid command string: ' . b:command
+
+Execute(The javac callback should use g:ale_java_javac_options correctly):
+  let g:ale_java_javac_options = '--anything --else'
+
+  let b:command = ale_linters#java#javac#GetCommand(bufnr(''))
+
+  Assert match(b:command, '\v^javac +-Xlint +-d +/tmp/[0-9a-zA-Z/]+ --anything --else +\%t$') >= 0,
+  \ 'Invalid command string: ' . b:command

test/test_temporary_file_management.vader

@@ -81,3 +81,23 @@ Execute(ALE should delete managed files when the buffer is removed):
   Assert !filereadable(g:filename), 'The tempoary file was not deleted'
   Assert !isdirectory(g:directory), 'The tempoary directory was not deleted'
   Assert isdirectory(g:preserved_directory), 'The tempoary directory was not kept'
+
+Execute(ALE should create and delete directories for ale#engine#CreateDirectory()):
+  call ale#engine#InitBufferInfo(bufnr('%'))
+
+  let b:dir = ale#engine#CreateDirectory(bufnr('%'))
+  let b:dir2 = ale#engine#CreateDirectory(bufnr('%'))
+
+  Assert isdirectory(b:dir), 'The directory was not created'
+
+  " We should get the correct file permissions.
+  " We want to ensure that the directory is not readable by 'other'
+  AssertEqual 'rwxr-x---', getfperm(b:dir)
+
+  " The two directories shouldn't be the same.
+  AssertNotEqual b:dir2, b:dir
+
+  call ale#cleanup#Buffer(bufnr('%'))
+
+  Assert !isdirectory(b:dir), 'The directory was not deleted'
+  Assert !isdirectory(b:dir2), 'The second directory was not deleted'