templater: add built-in filterby() function

Summary: This diff adds a built-in filterby() function to list the files that matches the given pattern.

Reviewed By: muirdm

Differential Revision: D81588900

fbshipit-source-id: 29315872b5b1e85135fb744c9e175c7338818b37

Author: zzl0

eden/scm/sapling/helptext.py

@@ -4311,6 +4311,10 @@
 
    $ @prog@ log -r 0 --template "pythonfiles: {join(files('**.py'), ', ')}\n"
 
+- Count the number of changed files ending with ".py"::
+
+   $ @prog@ log -r 0 -T "{filterby('**.py', files) | count}\n"
+
 - Separate non-empty arguments by a " "::
 
    $ @prog@ log -r 0 --template "{separate(' ', node, bookmarks, tags}\n"

eden/scm/sapling/templater.py

@@ -1345,6 +1345,21 @@ def startswith(context, mapping, args):
     return ""
 
 
+@templatefunc("filterby(pattern, files)")
+def filterby(context, mapping, args):
+    """Returns the files that match the given "pattern". See :prog:`help patterns`."""
+    if len(args) != 2:
+        raise error.ParseError(_("filterby expects two arguments"))
+
+    patn = evalstring(context, mapping, args[0])
+    texts = evalfuncarg(context, mapping, args[1])
+
+    ctx = mapping["ctx"]
+    m = ctx.match([patn])
+    texts = [t for t in texts if m.matchfn(t)]
+    return templatekw.showlist("text", texts, mapping)
+
+
 @templatefunc("truncate(text, maxlines, [suffix])")
 def truncate(context, mapping, args):
     """Truncate text to no more than "maxlines" in length. If "suffix" is

eden/scm/tests/test-command-template.t

@@ -3630,6 +3630,20 @@
   
   0
 
+# Test filterby function
+  $ hg log -T "{rev}\n{join(files, '\n')}\n"
+  2
+  aa
+  b
+  1
+  
+  0
+  a
+  $ hg log -r . -T "{filterby('path:aa', files)}\n"
+  aa
+  $ hg log -r . -T "{filterby('path:aa', files) | count}\n"
+  1
+
 # Test relpath function
 
   $ hg log -r0 -T '{files % "{file|relpath}\n"}'