Allow usage of pylint via stdin

Mimics flake8 stdin usage.
This makes it possible for pylint to run on unsaved files
works on pylint>=2.5.0

I didn't notice a performance degradation in terms of running pylint itself.
Of course, there *is* a performance hit overall, as pylint will be run on every
change, and it can be fairly slow

Author: mpanarin

pyls/plugins/pylint_lint.py

@@ -3,6 +3,8 @@
 import collections
 import logging
 import sys
+import re
+from subprocess import Popen, PIPE
 
 from pylint.epylint import py_run
 from pyls import hookimpl, lsp
@@ -154,12 +156,149 @@ def _build_pylint_flags(settings):
 def pyls_settings():
     # Default pylint to disabled because it requires a config
     # file to be useful.
-    return {'plugins': {'pylint': {'enabled': False, 'args': []}}}
+    return {'plugins': {'pylint': {
+        'enabled': False,
+        'args': [],
+        # disabled by default as it can slow down the workflow
+        'executable': None,
+    }}}
 
 
 @hookimpl
 def pyls_lint(config, document, is_saved):
+    """Run pylint linter."""
     settings = config.plugin_settings('pylint')
     log.debug("Got pylint settings: %s", settings)
+    # pylint >= 2.5.0 is required for working through stdin and only
+    # available with python3
+    if settings.get('executable') and sys.version_info[0] >= 3:
+        flags = build_args_stdio(settings)
+        pylint_executable = settings.get('executable', 'pylint')
+        return pylint_lint_stdin(pylint_executable, document, flags)
     flags = _build_pylint_flags(settings)
     return PylintLinter.lint(document, is_saved, flags=flags)
+
+
+def build_args_stdio(settings):
+    """Build arguments for calling pylint.
+
+    :param settings: client settings
+    :type settings: dict
+
+    :return: arguments to path to pylint
+    :rtype: list
+    """
+    pylint_args = settings.get('args')
+    if pylint_args is None:
+        return []
+    return pylint_args
+
+
+def pylint_lint_stdin(pylint_executable, document, flags):
+    """Run pylint linter from stdin.
+
+    This runs pylint in a subprocess with popen.
+    This allows passing the file from stdin and as a result
+    run pylint on unsaved files. Can slowdown the workflow.
+
+    :param pylint_executable: path to pylint executable
+    :type pylint_executable: string
+    :param document: document to run pylint on
+    :type document: pyls.workspace.Document
+    :param flags: arguments to path to pylint
+    :type flags: list
+
+    :return: linting diagnostics
+    :rtype: list
+    """
+    pylint_result = _run_pylint_stdio(pylint_executable, document, flags)
+    return _parse_pylint_stdio_result(document, pylint_result)
+
+
+def _run_pylint_stdio(pylint_executable, document, flags):
+    """Run pylint in popen.
+
+    :param pylint_executable: path to pylint executable
+    :type pylint_executable: string
+    :param document: document to run pylint on
+    :type document: pyls.workspace.Document
+    :param flags: arguments to path to pylint
+    :type flags: list
+
+    :return: result of calling pylint
+    :rtype: string
+    """
+    log.debug("Calling %s with args: '%s'", pylint_executable, flags)
+    try:
+        cmd = [pylint_executable]
+        cmd.extend(flags)
+        cmd.extend(['--from-stdin', document.path])
+        p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)
+    except IOError:
+        log.debug("Can't execute %s. Trying with 'python -m pylint'", pylint_executable)
+        cmd = ['python', '-m', 'pylint']
+        cmd.extend(flags)
+        cmd.extend(['--from-stdin', document.path])
+        p = Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)
+    (stdout, stderr) = p.communicate(document.source.encode())
+    if stderr:
+        log.error("Error while running pylint '%s'", stderr.decode())
+    return stdout.decode()
+
+
+def _parse_pylint_stdio_result(document, stdout):
+    """Parse pylint results.
+
+    :param document: document to run pylint on
+    :type document: pyls.workspace.Document
+    :param stdout: pylint results to parse
+    :type stdout: string
+
+    :return: linting diagnostics
+    :rtype: list
+    """
+    diagnostics = []
+    lines = stdout.splitlines()
+    for raw_line in lines:
+        parsed_line = re.match(r'(.*):(\d*):(\d*): (\w*): (.*)', raw_line)
+        if not parsed_line:
+            log.debug("Pylint output parser can't parse line '%s'", raw_line)
+            continue
+
+        parsed_line = parsed_line.groups()
+        if len(parsed_line) != 5:
+            log.debug("Pylint output parser can't parse line '%s'", raw_line)
+            continue
+
+        _, line, character, code, msg = parsed_line
+        line = int(line) - 1
+        character = int(character)
+        severity_map = {
+            'C': lsp.DiagnosticSeverity.Information,
+            'E': lsp.DiagnosticSeverity.Error,
+            'F': lsp.DiagnosticSeverity.Error,
+            'R': lsp.DiagnosticSeverity.Hint,
+            'W': lsp.DiagnosticSeverity.Warning,
+        }
+        severity = severity_map[code[0]]
+        diagnostics.append(
+            {
+                'source': 'pylint',
+                'code': code,
+                'range': {
+                    'start': {
+                        'line': line,
+                        'character': character
+                    },
+                    'end': {
+                        'line': line,
+                        # no way to determine the column
+                        'character': len(document.lines[line]) - 1
+                    }
+                },
+                'message': msg,
+                'severity': severity,
+            }
+        )
+
+    return diagnostics

setup.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+import sys
 from setuptools import find_packages, setup
 import versioneer
 
@@ -53,7 +54,9 @@
             'pycodestyle>=2.6.0,<2.7.0',
             'pydocstyle>=2.0.0',
             'pyflakes>=2.2.0,<2.3.0',
-            'pylint',
+            # pylint >= 2.5.0 is required for working through stdin and only
+            # available with python3
+            'pylint>=2.5.0' if sys.version_info.major >= 3 else 'pylint',
             'rope>=0.10.5',
             'yapf',
         ],
@@ -63,12 +66,14 @@
         'pycodestyle': ['pycodestyle>=2.6.0,<2.7.0'],
         'pydocstyle': ['pydocstyle>=2.0.0'],
         'pyflakes': ['pyflakes>=2.2.0,<2.3.0'],
-        'pylint': ['pylint'],
+        'pylint': [
+            'pylint>=2.5.0' if sys.version_info.major >= 3 else 'pylint'],
         'rope': ['rope>0.10.5'],
         'yapf': ['yapf'],
-        'test': ['versioneer', 'pylint', 'pytest', 'mock', 'pytest-cov',
-                 'coverage', 'numpy', 'pandas', 'matplotlib',
-                 'pyqt5;python_version>="3"', 'flaky'],
+        'test': ['versioneer',
+                 'pylint>=2.5.0' if sys.version_info.major >= 3 else 'pylint',
+                 'pytest', 'mock', 'pytest-cov', 'coverage', 'numpy', 'pandas',
+                 'matplotlib', 'pyqt5;python_version>="3"', 'flaky'],
     },
 
     # To provide executable scripts, use entry points in preference to the

test/plugins/test_pylint_lint.py

@@ -3,7 +3,7 @@
 import os
 import tempfile
 
-from test import py2_only, py3_only
+from test import py2_only, py3_only, IS_PY3
 from pyls import lsp, uris
 from pyls.workspace import Document
 from pyls.plugins import pylint_lint
@@ -49,6 +49,20 @@ def test_pylint(config, workspace):
         assert unused_import['range']['start'] == {'line': 0, 'character': 0}
         assert unused_import['severity'] == lsp.DiagnosticSeverity.Warning
 
+        if IS_PY3:
+            # test running pylint in stdin
+            config.plugin_settings('pylint')['executable'] = 'pylint'
+            diags = pylint_lint.pyls_lint(config, doc, True)
+
+            msg = 'Unused import sys (unused-import)'
+            unused_import = [d for d in diags if d['message'] == msg][0]
+
+            assert unused_import['range']['start'] == {
+                'line': 0,
+                'character': 0,
+            }
+            assert unused_import['severity'] == lsp.DiagnosticSeverity.Warning
+
 
 @py3_only
 def test_syntax_error_pylint_py3(config, workspace):
@@ -60,6 +74,15 @@ def test_syntax_error_pylint_py3(config, workspace):
         assert diag['range']['start'] == {'line': 0, 'character': 12}
         assert diag['severity'] == lsp.DiagnosticSeverity.Error
 
+        # test running pylint in stdin
+        config.plugin_settings('pylint')['executable'] = 'pylint'
+        diag = pylint_lint.pyls_lint(config, doc, True)[0]
+
+        assert diag['message'].startswith('invalid syntax')
+        # Pylint doesn't give column numbers for invalid syntax.
+        assert diag['range']['start'] == {'line': 0, 'character': 12}
+        assert diag['severity'] == lsp.DiagnosticSeverity.Error
+
 
 @py2_only
 def test_syntax_error_pylint_py2(config, workspace):

vscode-client/package.json

@@ -259,6 +259,11 @@
                     "uniqueItems": false,
                     "description": "Arguments to pass to pylint."
                 },
+                "pyls.plugins.pylint.executable": {
+                  "type": "string",
+                  "default": null,
+                  "description": "Executable to run pylint with. Enabling this will run pylint on unsaved files via stdin. Can slow down workflow. Only works with python3."
+                },
                 "pyls.plugins.rope_completion.enabled": {
                     "type": "boolean",
                     "default": true,