templater: look up symbols/resources as if they were separated (issue5699)

It wouldn't be easy to split the mapping dict into (symbols, resources). This
patch instead rejects invalid lookup taking resources.keys() as source of
truth.

The doctest is updated since mapping['repo'] is now reserved for a repo
object.

mercurial/formatter.py

@@ -94,14 +94,14 b' Nested example:'
 
 >>> def subrepos(ui, fm):
 ...     fm.startitem()
-...     fm.write(b'repo', b'[%s]\\n', b'baz')
+...     fm.write(b'reponame', b'[%s]\\n', b'baz')
 ...     files(ui, fm.nested(b'files'))
 ...     fm.end()
 >>> show(subrepos)
 [baz]
 foo
 bar
->>> show(subrepos, template=b'{repo}: {join(files % "{path}", ", ")}\\n')
+>>> show(subrepos, template=b'{reponame}: {join(files % "{path}", ", ")}\\n')
 baz: foo, bar
 """
 
@@ -491,7 +491,9 b' def templateresources(ui, repo=None):'
     and function"""
     return {
         'cache': {},  # for templatekw/funcs to store reusable data
+        'ctx': None,
         'repo': repo,
+        'revcache': None,  # per-ctx cache; set later
         'ui': ui,
     }
 

mercurial/templater.py

@@ -1320,7 +1320,9 b' class engine(object):'
 
     def symbol(self, mapping, key):
         """Resolve symbol to value or function; None if nothing found"""
-        v = mapping.get(key)
+        v = None
+        if key not in self._resources:
+            v = mapping.get(key)
         if v is None:
             v = self._defaults.get(key)
         return v
@@ -1328,11 +1330,13 b' class engine(object):'
     def resource(self, mapping, key):
         """Return internal data (e.g. cache) used for keyword/function
         evaluation"""
-        v = mapping.get(key)
+        v = None
+        if key in self._resources:
+            v = mapping.get(key)
         if v is None:
             v = self._resources.get(key)
         if v is None:
-            raise KeyError
+            raise error.Abort(_('template resource not available: %s') % key)
         return v
 
     def _load(self, t):

tests/test-command-template.t

@@ -206,7 +206,13 b' never cause crash:'
 
 Internal resources shouldn't be exposed (issue5699):
 
-  $ hg log -r. -T '{cache}{repo}{templ}{ui}'
+  $ hg log -r. -T '{cache}{ctx}{repo}{revcache}{templ}{ui}'
+
+Never crash on internal resource not available:
+
+  $ hg --cwd .. debugtemplate '{"c0bebeef"|shortest}\n'
+  abort: template resource not available: ctx
+  [255]
 
 Quoting for ui.logtemplate