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

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.

--- a/mercurial/formatter.py	Thu Dec 21 22:05:30 2017 +0900
+++ b/mercurial/formatter.py	Thu Dec 21 22:17:39 2017 +0900
@@ -94,14 +94,14 @@
 
 >>> 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 @@
     and function"""
     return {
         'cache': {},  # for templatekw/funcs to store reusable data
+        'ctx': None,
         'repo': repo,
+        'revcache': None,  # per-ctx cache; set later
         'ui': ui,
     }
 

--- a/mercurial/templater.py	Thu Dec 21 22:05:30 2017 +0900
+++ b/mercurial/templater.py	Thu Dec 21 22:17:39 2017 +0900
@@ -1320,7 +1320,9 @@
 
     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 @@
     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):

--- a/tests/test-command-template.t	Thu Dec 21 22:05:30 2017 +0900
+++ b/tests/test-command-template.t	Thu Dec 21 22:17:39 2017 +0900
@@ -206,7 +206,13 @@
 
 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