Add a Mistral lexer for pygments

This allows us to use the following code blocks in the Mistral documentation.

    .. code-block:: mistral

When we do that the code will then be highlighted in a way specific to
Mistral, rather than the generic YAML highlighting or none.

Change-Id: Ie25725b9f803e247d23f58c4b602be938c75cfbd

doc/source/main_features.rst

@@ -7,7 +7,7 @@ Task result / Data flow
 
 Mistral supports transferring data from one task to another. In other words,
 if *taskA* produces a value then *taskB* which follows *taskA* can use it.
-In order to use this data Mistral relies on a query language called `YAQL <https://github.com/openstack/yaql>`_. 
+In order to use this data Mistral relies on a query language called `YAQL <https://github.com/openstack/yaql>`_.
 YAQL is a powerful yet simple tool that allows the user to filter information,
 transform data and call functions. Find more information about it in the
 `YAQL official documentation <http://yaql.readthedocs.org>`_ . This mechanism
@@ -17,7 +17,7 @@ referred to as Data Flow.
 Below is a simple example of how Mistral Data Flow looks like from the DSL
 (workflow language) perspective:
 
-.. code-block:: yaml
+.. code-block:: mistral
 
  version: '2.0'
 

doc/source/quickstart.rst

@@ -37,7 +37,7 @@ Write a workflow
 
 For example, we have the following workflow.
 
-.. code-block:: yaml
+.. code-block:: mistral
 
     ---
     version: "2.0"

mistral/ext/pygmentplugin.py

@@ -0,0 +1,57 @@
+#    Licensed under the Apache License, Version 2.0 (the "License");
+#    you may not use this file except in compliance with the License.
+#    You may obtain a copy of the License at
+#
+#        http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS,
+#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#    See the License for the specific language governing permissions and
+#    limitations under the License.
+
+from pygments import lexer
+from pygments import token
+
+
+class MistralLexer(lexer.RegexLexer):
+
+    name = 'Mistral'
+    aliases = ['mistral']
+
+    tokens = {
+        "root": [
+            (r'^(\s)*(workflows|tasks|input|type)(\s)*:', token.Keyword),
+            (r'^(\s)*(version|name|description)(\s)*:', token.Keyword),
+            (r'^(\s)*(publish|timeout|retry|with\-items)(\s)*:',
+                token.Keyword),
+            (r'^(\s)*(on\-success|on\-error|on\-complete)(\s)*:',
+                token.Keyword),
+            (r'^(\s)*(action|workflow)(\s)*:', token.Keyword, 'call'),
+            (r'(\-|\:)(\s)*(fail|succeed|pause)(\s)+', token.Operator.Word),
+            (r'<%', token.Name.Entity, 'expression'),
+            (r'\{\{', token.Name.Entity, 'expression'),
+            (r'#.*$', token.Comment),
+            (r'(^|\s|\-)+\d+', token.Number),
+            lexer.include("generic"),
+        ],
+        "expression": [
+            (r'\$', token.Operator),
+            (r'\s(json_pp|task|tasks|execution|env|uuid)(?!\w)',
+                token.Name.Builtin),
+            lexer.include("generic"),
+            (r'%>', token.Name.Entity, '#pop'),
+            (r'}\\}', token.Name.Entity, '#pop'),
+        ],
+        "call": [
+            (r'(\s)*[\w\.]+($|\s)', token.Name.Function),
+            lexer.default('#pop'),
+        ],
+        "generic": [
+            (r'(\-|:|=|!|\[|\])', token.Operator),
+            (r'(null|None|True|False)', token.Name.Builtin),
+            (r'"(\\\\|\\"|[^"])*"', token.String.Double),
+            (r"'(\\\\|\\'|[^'])*'", token.String.Single),
+            (r'\w|\s|\(|\)|,|\.', token.Text),
+        ]
+    }

setup.cfg

@@ -89,3 +89,6 @@ mistral.auth =
 kombu_driver.executors =
     blocking = futurist:SynchronousExecutor
     threading = futurist:ThreadPoolExecutor
+
+pygments.lexers =
+    mistral = mistral.ext.pygmentplugin:MistralLexer