Issue 4488 - Add support for JSON page front matter

cms/utils.py

Index: cms/utils.py
===================================================================
--- a/cms/utils.py
+++ b/cms/utils.py
@@ -14,6 +14,7 @@
 # along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
 
 import re
+import json
 
 __all__ = [
     'get_page_params',
@@ -65,21 +66,33 @@
         Metadata of the page, remaining source text without metadata.
 
     """
-    metadata = {}
-    lines = source.splitlines(True)
-    for i, line in enumerate(lines):
-        if line.strip() in {'<!--', '-->'}:
-            lines[i] = ''
-            continue
-        if not re.search(r'^\s*[\w\-]+\s*=', line):
-            break
-        name, value = line.split('=', 1)
-        value = value.strip()
-        if value.startswith('[') and value.endswith(']'):
-            value = [element.strip() for element in value[1:-1].split(',')]
-        lines[i] = '\n'
-        metadata[name.strip()] = value
-    return metadata, ''.join(lines)
+    m = re.search(r'^\s*<!--\s*(.*?)-->', source, re.S)
+    text = m.group(1) if m else source
+
+    decoder = json.JSONDecoder()
+    try:
+        metadata, length = decoder.raw_decode(text)
+    except ValueError:
+        metadata = None
+
+    if not isinstance(metadata, dict):
+        metadata = {}
+        length = 0
+        for line in text.splitlines(True):
+            if not re.search(r'^\s*[\w\-]+\s*=', line):
+                break
+            name, value = line.split('=', 1)
+            value = value.strip()
+            if value.startswith('[') and value.endswith(']'):
+                value = [element.strip() for element in value[1:-1].split(',')]
+            metadata[name.strip()] = value
+            length += len(line)
+
+    # Need to preserve line numbers for jinja2 tracebacks

[Sebastian Noack, 2018/03/31 22:07:36]

This comment is slightly out of place here. Perhaps move it inside the block.
Otherwise it looks like that the check in the next line is related to preserving
line numbers too (which it is not).

[rosie, 2018/04/18 02:35:32]

Done.

+    if length > 0:
+        cutoff = m.end() if m else length
+        source = '\n' * source.count('\n', 0, cutoff) + source[cutoff:]
+    return metadata, source
 
 
 def get_page_params(source, locale, page, format=None, site_url_override=None,