cwd: default to buffer's dir in stdin mode

This is necessary at least with flake8, which does not use
`--stdin-display-name` to find its configuration.

autoload/neomake.vim

@@ -345,17 +345,19 @@ function! s:MakeJob(make_id, options) abort
         \ 'buffer_output': a:options.maker.buffer_output,
         \ }, 'keep')
 
-    let [cd_error, cwd, cd_back_cmd] = s:cd_to_jobs_cwd(jobinfo)
-    if !empty(cd_error)
-        throw printf("Neomake: %s: could not change to maker's cwd (%s): %s.",
-                    \ maker.name, cwd, cd_error)
-    endif
-
+    let error = ''
+    let cd_back_cmd = ''
     try
-        let error = ''
         let jobinfo.argv = maker._get_argv(jobinfo)
-        call neomake#utils#hook('NeomakeJobInit', {'jobinfo': jobinfo})
 
+        " Change to job's cwd (after args, which may use uses_stdin to set it).
+        let [cd_error, cwd, cd_back_cmd] = s:cd_to_jobs_cwd(jobinfo)
+        if !empty(cd_error)
+            throw printf("Neomake: %s: could not change to maker's cwd (%s): %s.",
+                        \ maker.name, cwd, cd_error)
+        endif
+
+        call neomake#utils#hook('NeomakeJobInit', {'jobinfo': jobinfo})
         if s:async
             call neomake#utils#LoudMessage(printf('Starting async job: %s.', string(jobinfo.argv)), jobinfo)
         else
@@ -1702,12 +1704,15 @@ function! s:cd_to_jobs_cwd(jobinfo) abort
                 let cwd = expand(cwd, 1)
             endif
             let a:jobinfo.cwd = substitute(fnamemodify(cwd, ':p'), '[\/]$', '', '')
+        elseif get(a:jobinfo, 'uses_stdin', 0)
+            call neomake#utils#DebugMessage("Using buffer's directory for cwd with uses_stdin.", a:jobinfo)
+            let a:jobinfo.cwd = neomake#utils#fnamemodify(a:jobinfo.bufnr, ':h')
         else
             let a:jobinfo.cwd = s:make_info[a:jobinfo.make_id].cwd
         endif
     endif
     let cwd = a:jobinfo.cwd
-    if empty(cwd)
+    if empty(cwd) || cwd ==# '.'
         return ['', '', '']
     endif
     let cwd = substitute(fnamemodify(cwd, ':p'), '[\/]$', '', '')

doc/neomake.txt

@@ -367,7 +367,8 @@ You can specify the default for this via |g:neomake_remove_invalid_entries|.
 
                                                           *neomake-makers-cwd*
 The working directory of a maker defaults to the current working directory
-of the make run (|getcwd()|).
+of the make run (|getcwd()|), or the buffer's directory in case of using stdin
+(see |neomake-makers-supports_stdin|).
 The `cwd` property overrides this, and gets expanded in the context of the
 current buffer. Special buffers (like fugitive blobs) get handled for values
 starting with `%:` (typically used in this context), falling back to

tests/stdin.vader

@@ -8,10 +8,12 @@ Execute (stdin maker):
   normal! ifile1.test:line1
   normal! ofile1.test:line2
   call neomake#Make(1, [maker])
+  AssertNeomakeMessage "Using buffer's directory for cwd with uses_stdin.", 3
   if neomake#has_async_support()
     AssertNeomakeMessage "Starting async job: ['cat', '-'].", 2
     NeomakeTestsWaitForFinishedJobs
   endif
+  AssertNeomakeMessage 'cwd: .', 3
   AssertNeomakeMessage '\mstdout: unnamed_maker: [''file1.test:line1.*'
   AssertEqual map(getloclist(0), 'v:val.text'), ['line1', 'line2']
   bwipe!
@@ -167,3 +169,20 @@ Execute (stdin maker: uses neomake#utils#get_buffer_lines for buffer_lines):
   CallNeomake 1, [maker]
   AssertEqual map(getloclist(0), 'v:val.text'), ['', '']
   bwipe
+
+Execute (stdin maker: uses buffer's cwd by default):
+  let maker = {'exe': 'true', 'supports_stdin': 1}
+  let fname = tempname()
+  new
+  exe 'file '.fname
+
+  CallNeomake 1, [maker]
+  AssertNeomakeMessage printf('cwd: %s (changed).', fnamemodify(fname, ':h')), 3
+
+  CallNeomake 0, [extend(copy(maker), {'uses_filename': 1})]
+  AssertNeomakeMessage printf('cwd: %s (changed).', fnamemodify(fname, ':h')), 3
+
+  let maker.cwd = '.'
+  CallNeomake 1, [maker]
+  AssertNeomakeMessage printf('cwd: %s.', getcwd()), 3
+  bwipe