diff mercurial/templatekw.py @ 34330:89aec1834a86

templatekw: add new-style template expansion to {manifest}

The goal is to allow us to easily access to nested data. The dot operator
will be introduced later so we can write '{p1.files}' instead of
'{revset("p1()") % "{files}"}' for example.

In the example above, 'p1' needs to carry a mapping dict along with its
string representation. If it were a list or a dict, it could be wrapped
semi-transparently with the _hybrid class, but for non-list/dict types,
it would be difficult to proxy all necessary functions to underlying value
type because several core operations may conflict with the ones of the
underlying value:

 - hash(value) should be different from hash(wrapped(value)), which means
   dict[wrapped(value)] would be invalid
 - 'value == wrapped(value)' would be false, breaks 'ifcontains'
 - len(wrapped(value)) may be either len(value) or len(iter(wrapped(value)))

So the wrapper has no proxy functions and its scope designed to be minimal.
It's unwrapped at eval*() functions so we don't have to care for a wrapped
object unless it's really needed:

  # most template functions just call evalfuncarg()
  unwrapped_value = evalfuncarg(context, mapping, args[n])
  # if wrapped value is needed, use evalrawexp()
  maybe_wrapped_value = evalrawexp(context, mapping, args[n])

Another idea was to wrap every template variable with a tagging class, but
which seemed uneasy without a static type checker.

This patch updates {manifest} to a mappable as an example.

--- a/mercurial/templatekw.py	Mon Apr 24 21:37:11 2017 +0900
+++ b/mercurial/templatekw.py	Sun Apr 24 18:41:23 2016 +0900
@@ -70,6 +70,28 @@
             raise AttributeError(name)
         return getattr(self._values, name)
 
+class _mappable(object):
+    """Wrapper for non-list/dict object to support map operation
+
+    This class allows us to handle both:
+    - "{manifest}"
+    - "{manifest % '{rev}:{node}'}"
+
+    Unlike a _hybrid, this does not simulate the behavior of the underling
+    value. Use unwrapvalue() or unwraphybrid() to obtain the inner object.
+    """
+
+    def __init__(self, gen, value, makemap):
+        self.gen = gen
+        self._value = value  # may be generator of strings
+        self._makemap = makemap
+
+    def tomap(self):
+        return self._makemap()
+
+    def itermaps(self):
+        yield self.tomap()
+
 def hybriddict(data, key='key', value='value', fmt='%s=%s', gen=None):
     """Wrap data to support both dict-like and string-like operations"""
     return _hybrid(gen, data, lambda k: {key: k, value: data[k]},
@@ -86,6 +108,12 @@
         return thing
     return thing.gen
 
+def unwrapvalue(thing):
+    """Move the inner value object out of the wrapper"""
+    if not util.safehasattr(thing, '_value'):
+        return thing
+    return thing._value
+
 def showdict(name, data, mapping, plural=None, key='key', value='value',
              fmt='%s=%s', separator=' '):
     c = [{key: k, value: v} for k, v in data.iteritems()]
@@ -543,10 +571,14 @@
     if mnode is None:
         # just avoid crash, we might want to use the 'ff...' hash in future
         return
+    mrev = repo.manifestlog._revlog.rev(mnode)
+    mhex = hex(mnode)
     args = args.copy()
-    args.update({r'rev': repo.manifestlog._revlog.rev(mnode),
-                 r'node': hex(mnode)})
-    return templ('manifest', **args)
+    args.update({r'rev': mrev, r'node': mhex})
+    f = templ('manifest', **args)
+    # TODO: perhaps 'ctx' should be dropped from mapping because manifest
+    # rev and node are completely different from changeset's.
+    return _mappable(f, f, lambda: {'rev': mrev, 'node': mhex})
 
 def shownames(namespace, **args):
     """helper method to generate a template keyword for a namespace"""