check-code: check for consistent usage of the websub filter in hgweb templates

The check-code tool now expects the "desc" keyword to be followed by the
"websub" filter, with the following exceptions:
a) It has no filters at all, e.g. a changeset description in the raw style
   templates or the repository description in the summary page.
b) It is followed by the "firstline" filter, e.g. the first line of the
   changeset description is displayed as a summary or title.

contrib/check-code.py

@@ -367,6 +367,16 b' inrevlogpats = ['
   []
 ]
 
+webtemplatefilters = []
+
+webtemplatepats = [
+  [],
+  [
+    (r'{desc(\|(?!websub|firstline)[^\|]*)+}',
+     'follow desc keyword with either firstline or websub'),
+  ]
+]
+
 checks = [
     ('python', r'.*\.(py|cgi)$', r'^#!.*python', pyfilters, pypats),
     ('test script', r'(.*/)?test-[^.~]*$', '', testfilters, testpats),
@@ -377,6 +387,8 b' checks = ['
     ('layering violation ui in util', r'mercurial/util\.py', '', pyfilters,
      inutilpats),
     ('txt', r'.*\.txt$', '', txtfilters, txtpats),
+    ('web template', r'mercurial/templates/.*\.tmpl', '',
+     webtemplatefilters, webtemplatepats),
 ]
 
 def _preparepats():

tests/test-check-code.t

@@ -284,3 +284,19 b''
    > print _(
    don't use % inside _()
   [1]
+
+web templates
+
+  $ mkdir -p mercurial/templates
+  $ cat > mercurial/templates/example.tmpl <<EOF
+  > {desc}
+  > {desc|escape}
+  > {desc|firstline}
+  > {desc|websub}
+  > EOF
+
+  $ "$check_code" --warnings mercurial/templates/example.tmpl
+  mercurial/templates/example.tmpl:2:
+   > {desc|escape}
+   warning: follow desc keyword with either firstline or websub
+  [1]