Adding line-length-linter to build

.pylintrc

@@ -1,11 +1,12 @@
 [MASTER]
 
-# Load the DocStringChecker plugin.
-load-plugins=lint
+# Load the DocStringChecker and line_length_linter plugins.
+load-plugins=lint,line_length_lint
 
 # We actually want to disable all standard pylint checkers, enable
-# DocStringChecker, then disable specific checks in DocStringChecker, but there
-# does not seem to be a way of doing that. Instead, we disable everything aside
-# from the whitelist of DocStringChecker checks that we want.
+# DocStringChecker and line_length_linter, then disable specific checks in the
+# plugins, but there does not seem to be a way of doing that. Instead, we
+# disable everything aside from the whitelist of DocStringChecker checks that
+# we want.
 disable=all
-enable=docstring-trailing-whitespace,docstring-leading-whitespace,docstring-cuddled-quotes,docstring-section-newline,docstring-section-name,docstring-section-order,docstring-first-line,docstring-missing-args,docstring-misnamed-args,docstring-arg-spacing,docstring-too-many-newlines,docstring-second-line-blank,docstring-section-indent
+enable=docstring-trailing-whitespace,docstring-leading-whitespace,docstring-cuddled-quotes,docstring-section-newline,docstring-section-name,docstring-section-order,docstring-first-line,docstring-missing-args,docstring-misnamed-args,docstring-arg-spacing,docstring-too-many-newlines,docstring-second-line-blank,docstring-section-indent,line-length

build

@@ -26,6 +26,8 @@ yapf --diff --recursive --style google ./ --exclude=./third_party/*
 # Run static analysis for Python bugs/cruft.
 pyflakes "${SOURCE_DIR}/" "${TEST_DIR}/"
 
-# Check docstrings for style consistency.
-PYTHONPATH=$PYTHONPATH:$(pwd)/third_party/docstringchecker \
+# Run custom linters.
+LINTER_PATHS="$(pwd)/third_party/docstringchecker"
+LINTER_PATHS+=":$(pwd)/third_party/line_length_linter"
+PYTHONPATH="${PYTHONPATH}:${LINTER_PATHS}" \
   pylint --reports=n --rcfile=.pylintrc "$SOURCE_DIR" "$TEST_DIR"

third_party/line_length_linter/line_length_lint.py

@@ -0,0 +1,145 @@
+import re
+import sys
+
+from pylint import checkers
+from pylint import interfaces
+
+# Maximum number of characters that should be in a line.
+_LINE_LENGTH_MAX = 80
+# Matches URLs that start with http or https, like https://ketohub.io.
+_URL_PATTERN = re.compile(
+    r'https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)'
+)
+# Matches triple single or double quotes.
+_TRIPLE_QUOTE_PATTERN = re.compile(r'(\'\'\'|\"\"\")')
+# Matches a line containing a string.
+_STRING_PATTERN = re.compile(r'(\'.+\')|(\".+\")')
+# Matches a comment line.
+_COMMENT_PATTERN = re.compile(r'(^|\s)#')
+# Matches raw strings, for example r'whatever'.
+_RAW_STRING_PATTERN = re.compile(r'(r\'.+\')')
+
+
+class LineLengthChecker(checkers.BaseChecker):
+    """PyLint AST based checker to verify line length requirements.
+
+    Line lengths are verified using the following rules:
+        - Generally, lines should not exceed _LINE_LENGTH_MAX.
+        - It is always okay to exceed this limit if the line contains a URL.
+        - Raw strings can exceed the limit.
+        - Lines that are within a triple-quoted string may also exceed the limit
+          if the triple-quoted string is not a docstring.
+        - Only comments, docstrings, or lines containing a string are
+            checked.
+    """
+    __implements__ = interfaces.IAstroidChecker
+
+    class _MessageC0001(object):
+        pass
+
+    name = 'line-length'
+    priority = -1
+    msgs = {
+        'C0001':
+        ('Lines should not be longer than %d characters.' % _LINE_LENGTH_MAX,
+         ('line-over-max-length'), _MessageC0001)
+    }
+
+    options = ()
+
+    def visit_function(self, node):
+        self._check_docstring(node)
+
+    def visit_class(self, node):
+        self._check_docstring(node)
+
+    def visit_module(self, node):
+        self._check_docstring(node)
+
+    def leave_module(self, node):
+        """Called after all of the nodes within a module have been visited."""
+        self._process_module(node)
+
+    def _check_docstring(self, node):
+        doc = node.doc
+        if not doc:
+            return
+        lines = node.doc.split('\n')
+        for line_offset, line in enumerate(lines):
+            self._check_line_length(line, node.fromlineno + line_offset, node)
+
+    def _process_module(self, node):
+        """Check the line length of all lines of interest within a module.
+
+        Iterates through all the lines in a module, checking that all lines of
+        interest do not exceed the line length max unless a URL is present.
+        Handles the module's content as a stream instead of as AST nodes.
+
+        Lines of interest include comments and lines that contain strings.
+
+        Args:
+            node: AST node object for the module.
+        """
+        with node.stream() as stream:
+            for line_number, line in enumerate(stream):
+                if _is_line_of_interest(line):
+                    self._check_line_length(line, line_number, node)
+
+    def _check_line_length(self, line, line_number, node):
+        """Check if length of line is valid.
+
+        Args:
+            line: String of line that we're verifying.
+            line_number: Zero-indexed line number of line.
+            node: AST node that the line belongs to.
+        """
+        if not _over_line_length(line):
+            return
+        if _contains_url(line):
+            return
+        if _contains_a_raw_string(line):
+            return
+        if not _is_one_line_triple_quote(line):
+            # We add 1 to the line number because arrays are 0 indexed
+            # but line numbers are not.
+            self.add_message('C0001', node=node, line=line_number + 1)
+
+
+def _is_line_of_interest(line):
+    """Checks if line is a comment or contains a string."""
+    return any([_contains_a_string(line), _is_a_comment_line(line)])
+
+
+def _is_one_line_triple_quote(line):
+    return len(_TRIPLE_QUOTE_PATTERN.findall(line)) == 2
+
+
+def _contains_a_raw_string(line):
+    return _RAW_STRING_PATTERN.search(line)
+
+
+def _contains_a_string(line):
+    return _STRING_PATTERN.search(line)
+
+
+def _is_a_comment_line(line):
+    return _COMMENT_PATTERN.search(line)
+
+
+def _contains_url(line):
+    return _URL_PATTERN.search(line)
+
+
+def _over_line_length(line):
+    return len(line) > _LINE_LENGTH_MAX + 1
+
+
+def register(linter):
+    """Pylint will call this func to register all checkers in this module."""
+    this_module = sys.modules[__name__]
+    for member in dir(this_module):
+        if (not member.endswith('Checker') or
+                member in ('BaseChecker', 'IAstroidChecker')):
+            continue
+        cls = getattr(this_module, member)
+        linter.register_checker(cls(linter))

third_party/line_length_linter/update.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+# Downloads the latest copy of the line_length_linter plugin.
+
+set -x
+
+REMOTE_URL="https://raw.githubusercontent.com/mtlynch/line-length-linter/master/line_length_linter/line_length_lint.py"
+OUTPUT_DIR=$(dirname "$0")
+OUTPUT_FILE="${OUTPUT_DIR}/line_length_lint.py"
+
+curl "$REMOTE_URL" > "$OUTPUT_FILE"