[PATCH] templater: add intersperse() template function

[Martin von Zweigbergk]

# HG changeset patch
# User Martin von Zweigbergk <martinvonz at google.com>
# Date 1462294194 25200
#      Tue May 03 09:49:54 2016 -0700
# Branch stable
# Node ID d88e385e84ca345474c177932e605c79a487a8d4
# Parent  61463b8fcef871ff3efff53945df4671c71c4e31
templater: add intersperse() template function

A pretty common pattern in templates is adding conditional separators
like so:

  {node}{if(bookmarks, " {bookmarks}")}{if(tags, " {tags}")}

With this patch, the above can be simplified to:

  {intersperse(" ", node, bookmarks, tags)}

diff -r 61463b8fcef8 -r d88e385e84ca mercurial/templater.py
--- a/mercurial/templater.py	Sun May 01 14:36:12 2016 -0500
+++ b/mercurial/templater.py	Tue May 03 09:49:54 2016 -0700
@@ -621,6 +621,26 @@
             yield joiner
         yield x
 
+ at templatefunc('intersperse(sep, args)')
+def intersperse(context, mapping, args):
+    """Add a separator between non-empty arguments."""
+    if not args:
+        # i18n: "intersperse" is a keyword
+        raise error.ParseError(_("intersperse expects at least one argument"))
+
+    joiner = evalstring(context, mapping, args[0])
+
+    first = True
+    for x in args[1:]:
+        argstr = evalstring(context, mapping, x)
+        if not argstr:
+            continue
+        if first:
+            first = False
+        else:
+            yield joiner
+        yield argstr
+
 @templatefunc('label(label, expr)')
 def label(context, mapping, args):
     """Apply a label to generated content. Content with
diff -r 61463b8fcef8 -r d88e385e84ca tests/test-command-template.t
--- a/tests/test-command-template.t	Sun May 01 14:36:12 2016 -0500
+++ b/tests/test-command-template.t	Tue May 03 09:49:54 2016 -0700
@@ -3320,6 +3320,15 @@
   hg: parse error: pad() expects an integer width
   [255]
 
+Test intersperse function
+
+  $ hg log -r 0 -T '{intersperse("-", "", "a", "b", "", "", "c", "")}\n'
+  a-b-c
+  $ hg log -r 0 -T '{intersperse(" ", "{rev}:{node|short}", author|user, branch)}\n'
+  0:f7769ec2ab97 test default
+  $ hg log -r 0 --color=always -T '{intersperse(" ", "a", label(red, "b"), "c", label(red, ""), "d")}\n'
+  a \x1b[0;31mb\x1b[0m c d (esc)
+
 Test ifcontains function
 
   $ hg log --template '{rev} {ifcontains(rev, "2 two 0", "is in the string", "is not")}\n'