template: provide a termwidth keyword (issue5395)

We want to provide terminal-sized output. As a starting point, expose the
terminal width to the templater for use in things like fill.

mercurial/templatekw.py

@@ -589,5 +589,10 b' def loadkeyword(ui, extname, registrarob'
     for name, func in registrarobj._table.iteritems():
         keywords[name] = func
 
+@templatekeyword('termwidth')
+def termwidth(repo, ctx, templ, **args):
+    """Integer. The width of the current terminal."""
+    return repo.ui.termwidth()
+
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = keywords.values()

tests/test-command-template.t

@@ -3214,6 +3214,11 b' Test recursive evaluation:'
   hg: parse error: fill expects an integer width
   [255]
 
+  $ COLUMNS=25 hg log -l1 --template '{fill(desc, termwidth, "{node|short}:", "termwidth.{rev}:")}'
+  bcc7ff960b8e:desc to be
+  termwidth.1:wrapped desc
+  termwidth.1:to be wrapped (no-eol)
+
   $ hg log -l 1 --template '{sub(r"[0-9]", "-", author)}'
   {node|short} (no-eol)
   $ hg log -l 1 --template '{sub(r"[0-9]", "-", "{node|short}")}'