[runtime/docs] Add custom lexer for shell sessions in runtime wiki.

This was missing from the previous wiki related commit.

TBR=aam@google.com

Change-Id: Ib68ead3bab2841bb8e02cb93fd71bce7515ff335
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134285
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>

runtime/tools/wiki/CustomShellSessionPygmentsLexer/custom_shell_session/__init__.py

@@ -0,0 +1,5 @@
+#
+# Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+#

runtime/tools/wiki/CustomShellSessionPygmentsLexer/custom_shell_session/lexer.py

@@ -0,0 +1,49 @@
+#
+# Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+#
+"""Simple lexer for shell sessions.
+
+Highlights command lines (lines starting with $ prompt) and comments starting
+with #. For example:
+
+    # This is a comment
+    $ this-is-a-command
+    This is output of the command
+
+    $ this-is-a-multiline-command with-some-arguments \
+      and more arguments \
+      and more arguments
+    And some output.
+
+"""
+
+from pygments.lexer import RegexLexer, words
+from pygments.token import Comment, Generic, Keyword
+
+_comment_style = Comment
+# Note: there is a slight inversion of styles to make it easier to read.
+# We highlight output with Prompt style and command as a normal text.
+_output_style = Generic.Prompt
+_command_style = Generic.Text
+_prompt_style = Keyword
+
+
+class CustomShellSessionLexer(RegexLexer):
+    name = 'CustomShellSession'
+    aliases = ['custom-shell-session']
+    filenames = ['*.log']
+    tokens = {
+        'root': [
+            (r'#.*\n', _comment_style),
+            (r'^\$', _prompt_style, 'command'),
+            (r'.', _output_style),
+        ],
+        'command': [
+            (r'\\\n', _command_style),  # Continue in 'command' state.
+            (r'$', _command_style, '#pop'),  # End of line without escape.
+            (r'.',
+             _command_style),  # Anything else continue in 'command' state.
+        ]
+    }

runtime/tools/wiki/CustomShellSessionPygmentsLexer/setup.py

@@ -0,0 +1,15 @@
+#
+# Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+#
+from setuptools import setup, find_packages
+
+setup(
+    name='custom-shell-session',
+    packages=find_packages(),
+    entry_points="""
+  [pygments.lexers]
+  custom-shell-session = custom_shell_session.lexer:CustomShellSessionLexer
+  """,
+)

runtime/tools/wiki/README.md

@@ -32,6 +32,11 @@ the given C++ symbol.
     ```console
     $ pip3 install coloredlogs jinja2 markdown aiohttp watchdog pymdown-extensions pygments
     ```
-2. Install SASS compiler (make sure that SASS binary is in your path).
-3. Generate `xref.json` file following instructions in
+2. Install the custom pygments lexer we use for shell session examples:
+    ```
+    $ cd runtime/tools/wiki/CustomShellSessionPygmentsLexer
+    $ python3 setup.py develop
+    ```
+3. Install SASS compiler (make sure that SASS binary is in your path).
+4. Generate `xref.json` file following instructions in
 `xref_extractor/README.md`.