templater: add dict() constructor

It's troublesome to build JSON by template, so let's add programmatic way.

mercurial/templater.py

@@ -532,6 +532,14 b' def date(context, mapping, args):'
         # i18n: "date" is a keyword
         raise error.ParseError(_("date expects a date information"))
 
+@templatefunc('dict([key=value...])', argspec='**kwargs')
+def dict_(context, mapping, args):
+    """Construct a dict from key-value pairs."""
+    data = util.sortdict()
+    data.update((k, evalfuncarg(context, mapping, v))
+                for k, v in args['kwargs'].iteritems())
+    return templatekw.hybriddict(data)
+
 @templatefunc('diff([includepattern [, excludepattern]])')
 def diff(context, mapping, args):
     """Show a diff, optionally

tests/test-command-template.t

@@ -3404,6 +3404,22 b' Test branches inside if statement:'
   $ hg log -r 0 --template '{if(branches, "yes", "no")}\n'
   no
 
+Test dict constructor:
+
+  $ hg log -r 0 -T '{dict(y=node|short, x=rev)}\n'
+  y=f7769ec2ab97 x=0
+  $ hg log -r 0 -T '{dict(x=rev, y=node|short) % "{key}={value}\n"}'
+  x=0
+  y=f7769ec2ab97
+  $ hg log -r 0 -T '{dict(x=rev, y=node|short)|json}\n'
+  {"x": 0, "y": "f7769ec2ab97"}
+  $ hg log -r 0 -T '{dict()|json}\n'
+  {}
+
+  $ hg log -r 0 -T '{dict(x=rev, x=node)}'
+  hg: parse error: dict got multiple values for keyword argument 'x'
+  [255]
+
 Test get function:
 
   $ hg log -r 0 --template '{get(extras, "branch")}\n'