test-template-engine: deduplicate methods of custom template engine

tests/test-template-engine.t

@@ -1,74 +1,63 b''
 
   $ cat > engine.py << EOF
   > 
   > from mercurial import (
   >     templater,
   >     templateutil,
   > )
   > 
-  > class mytemplater(object):
-  >     def __init__(self, loader, filters, defaults, resources, aliases):
-  >         self.loader = loader
-  >         self._defaults = defaults
-  >         self._resources = resources
-  > 
-  >     def symbol(self, mapping, key):
-  >         return mapping[key]
-  > 
-  >     def resource(self, mapping, key):
-  >         v = self._resources[key]
-  >         if v is None:
-  >             v = mapping[key]
-  >         return v
+  > class mytemplater(templater.engine):
+  >     def _load(self, t):
+  >         return self._loader(t)
   > 
   >     def process(self, t, map):
-  >         tmpl = self.loader(t)
+  >         tmpl = self._load(t)
   >         props = self._defaults.copy()
   >         props.update(map)
   >         for k, v in props.items():
   >             if k in ('templ', 'ctx', 'repo', 'revcache', 'cache', 'troubles'):
   >                 continue
   >             if callable(v) and getattr(v, '_requires', None) is None:
   >                 props = self._resources.copy()
   >                 props.update(map)
   >                 v = v(**props)
   >             elif callable(v):
   >                 v = v(self, props)
   >             v = templateutil.stringify(v)
   >             tmpl = tmpl.replace('{{%s}}' % k, v)
   >         yield tmpl
   > 
   > templater.engines['my'] = mytemplater
   > EOF
   $ hg init test
   $ echo '[extensions]' > test/.hg/hgrc
   $ echo "engine = `pwd`/engine.py" >> test/.hg/hgrc
   $ cd test
   $ cat > mymap << EOF
   > changeset = my:changeset.txt
   > EOF
   $ cat > changeset.txt << EOF
   > {{rev}} {{node}} {{author}}
   > EOF
   $ hg ci -Ama
   adding changeset.txt
   adding mymap
   $ hg log --style=./mymap
   0 97e5f848f0936960273bbf75be6388cd0350a32b test
 
   $ cat > changeset.txt << EOF
   > {{p1rev}} {{p1node}} {{p2rev}} {{p2node}}
   > EOF
   $ hg ci -Ama
   $ hg log --style=./mymap
   0 97e5f848f0936960273bbf75be6388cd0350a32b -1 0000000000000000000000000000000000000000
   -1 0000000000000000000000000000000000000000 -1 0000000000000000000000000000000000000000
 
 invalid engine type:
 
   $ echo 'changeset = unknown:changeset.txt' > unknownenginemap
   $ hg log --style=./unknownenginemap
   abort: invalid template engine: unknown
   [255]
 
   $ cd ..