#289 Only use the --stdin-display-name flag if the flake8 version supports it

ale_linters/python/flake8.vim

@@ -7,18 +7,70 @@ let g:ale_python_flake8_executable =
 let g:ale_python_flake8_args =
 \   get(g:, 'ale_python_flake8_args', '')
 
+" A map from Python executable paths to semver strings parsed for those
+" executables, so we don't have to look up the version number constantly.
+let s:version_cache = {}
+
 function! ale_linters#python#flake8#GetExecutable(buffer) abort
     return g:ale_python_flake8_executable
 endfunction
 
-function! ale_linters#python#flake8#GetCommand(buffer) abort
+function! ale_linters#python#flake8#VersionCheck(buffer) abort
+    let l:executable = ale_linters#python#flake8#GetExecutable(a:buffer)
+
+    " If we have previously stored the version number in a cache, then
+    " don't look it up again.
+    if has_key(s:version_cache, l:executable)
+        " Returning an empty string skips this command.
+        return ''
+    endif
+
+    return ale_linters#python#flake8#GetExecutable(a:buffer) . ' --version'
+endfunction
+
+" Get the flake8 version from the output, or the cache.
+function! s:GetVersion(buffer, version_output) abort
+    let l:executable = ale_linters#python#flake8#GetExecutable(a:buffer)
+    let l:version = []
+
+    " Get the version from the cache.
+    if has_key(s:version_cache, l:executable)
+        return s:version_cache[l:executable]
+    endif
+
+    if !empty(a:version_output)
+        " Parse the version string, and store it in the cache.
+        let l:version = ale#semver#Parse(a:version_output[0])
+        let s:version_cache[l:executable] = l:version
+    endif
+
+    return l:version
+endfunction
+
+" flake8 versions 3 and up support the --stdin-display-name argument.
+function! s:SupportsDisplayName(version) abort
+    return !empty(a:version) && ale#semver#GreaterOrEqual(a:version, [3, 0, 0])
+endfunction
+
+function! ale_linters#python#flake8#GetCommand(buffer, version_output) abort
+    let l:version = s:GetVersion(a:buffer, a:version_output)
+
+    " Only include the --stdin-display-name argument if we can parse the
+    " flake8 version, and it is recent enough to support it.
+    let l:display_name_args = s:SupportsDisplayName(l:version)
+    \   ? '--stdin-display-name %s'
+    \   : ''
+
     return ale_linters#python#flake8#GetExecutable(a:buffer)
-    \   . ' ' . g:ale_python_flake8_args . ' --stdin-display-name %s -'
+    \   . ' ' . g:ale_python_flake8_args . ' ' . l:display_name_args . ' -'
 endfunction
 
 call ale#linter#Define('python', {
 \   'name': 'flake8',
 \   'executable_callback': 'ale_linters#python#flake8#GetExecutable',
-\   'command_callback': 'ale_linters#python#flake8#GetCommand',
+\   'command_chain': [
+\       {'callback': 'ale_linters#python#flake8#VersionCheck'},
+\       {'callback': 'ale_linters#python#flake8#GetCommand'},
+\   ],
 \   'callback': 'ale#handlers#HandlePEP8Format',
 \})

autoload/ale/semver.vim

@@ -0,0 +1,29 @@
+" Given some text, parse a semantic versioning string from the text
+" into a triple of integeers [major, minor, patch].
+"
+" If no match can be performed, then an empty List will be returned instead.
+function! ale#semver#Parse(text) abort
+    let l:match = matchlist(a:text, '^ *\(\d\+\)\.\(\d\+\)\.\(\d\+\)')
+
+    if empty(l:match)
+        return []
+    endif
+
+    return [l:match[1] + 0, l:match[2] + 0, l:match[3] + 0]
+endfunction
+
+" Given two triples of integers [major, minor, patch], compare the triples
+" and return 1 if the lhs is greater than or equal to the rhs.
+function! ale#semver#GreaterOrEqual(lhs, rhs) abort
+    if a:lhs[0] > a:rhs[0]
+        return 1
+    elseif a:lhs[0] == a:rhs[0]
+        if a:lhs[1] > a:rhs[1]
+            return 1
+        elseif a:lhs[1] == a:rhs[1]
+            return a:lhs[2] >= a:rhs[2]
+        endif
+    endif
+
+    return 0
+endfunction

test/test_semver_utils.vader

@@ -0,0 +1,16 @@
+Execute(ParseSemver should return the correct results):
+  " We should be able to parse the semver string from flake8
+  AssertEqual [3, 0, 4], ale#semver#Parse('3.0.4 (mccabe: 0.5.2, pyflakes: 1.2.3, pycodestyle: 2.0.0) CPython 2.7.12 on Linux')
+
+Execute(GreaterOrEqual should compare triples correctly):
+  Assert ale#semver#GreaterOrEqual([3, 0, 4], [3, 0, 0])
+  Assert ale#semver#GreaterOrEqual([3, 0, 0], [3, 0, 0])
+  Assert ale#semver#GreaterOrEqual([3, 0, 0], [2, 0, 0])
+  Assert ale#semver#GreaterOrEqual([3, 1, 0], [3, 1, 0])
+  Assert ale#semver#GreaterOrEqual([3, 2, 0], [3, 1, 0])
+  Assert ale#semver#GreaterOrEqual([3, 2, 2], [3, 1, 6])
+  Assert ale#semver#GreaterOrEqual([3, 2, 5], [3, 2, 5])
+  Assert ale#semver#GreaterOrEqual([3, 2, 6], [3, 2, 5])
+  Assert !ale#semver#GreaterOrEqual([2, 9, 1], [3, 0, 0])
+  Assert !ale#semver#GreaterOrEqual([3, 2, 3], [3, 3, 3])
+  Assert !ale#semver#GreaterOrEqual([3, 3, 2], [3, 3, 3])