Adding a less_css_library rule.

Requires npm install less.

anvil/rules/less_rules.py

@@ -0,0 +1,93 @@
+# Copyright 2012 Google Inc. All Rights Reserved.
+
+"""LESS stylesheets rules for the build system.
+
+Contains the following rules:
+less_css_library
+"""
+
+__author__ = 'benvanik@google.com (Ben Vanik)'
+
+
+import os
+
+from anvil.context import RuleContext
+from anvil.rule import Rule, build_rule
+from anvil.task import Task, NodeExecutableTask
+
+
+@build_rule('less_css_library')
+class LessCssLibraryRule(Rule):
+  """A LESS transformed file.
+  Uses the LESS compiler to process an input LESS file into a
+  single output CSS file.
+
+  Only the first source will be used as the root to less. The rest will be
+  treated as dependencies.
+
+  Inputs:
+    srcs: The root LESS file..
+    include_paths: Paths to search for include files.
+    compiler_flags: A list of string compiler flags.
+    out: Optional output name. If none is provided than the rule name will be
+        used.
+
+  Outputs:
+    A single compiled CSS file. If no out is specified a file with the name of
+    the rule will be created.
+  """
+
+  def __init__(self, name, include_paths=None,
+      compiler_flags=None, out=None, *args, **kwargs):
+    """Initializes a LESS CSS rule.
+
+    Args:
+      srcs: The root LESS file.
+      include_paths: Paths to search for include files.
+      compiler_flags: A list of string compiler flags.
+      out: Optional output name. If none is provided than the rule name will be
+          used.
+    """
+    super(LessCssLibraryRule, self).__init__(name, *args, **kwargs)
+
+    self.include_paths = []
+    if include_paths:
+        self.include_paths.extend(include_paths)
+    self._append_dependent_paths(self.include_paths)
+
+    self.compiler_flags = []
+    if compiler_flags:
+      self.compiler_flags.extend(compiler_flags)
+
+    self.out = out
+
+  class _Context(RuleContext):
+    def begin(self):
+      super(LessCssLibraryRule._Context, self).begin()
+
+      args = [
+        '--strict-imports'
+      ]
+      args.extend(self.rule.compiler_flags)
+
+      if len(self.rule.include_paths):
+        args.append('--include-path=%s' % (
+            ':'.join(self.rule.include_paths)))
+
+      output_path = self._get_out_path(name=self.rule.out, suffix='.css')
+      self._ensure_output_exists(os.path.dirname(output_path))
+      self._append_output_paths([output_path])
+
+      args.append(self.src_paths[0])
+      args.append(output_path)
+
+      # Skip if cache hit
+      if self._check_if_cached():
+        self._succeed()
+        return
+
+      d = self._run_task_async(NodeExecutableTask(
+          self.build_env, 'node_modules/less/bin/lessc', args))
+      # TODO(benvanik): pull out (stdout, stderr) from result and the exception
+      #     to get better error logging
+      self._chain(d)