templater: allow piping generator-type function output to filters Template functions use "yield"s assuming that the result will be combined into a string, which means both "f -> str" and "f -> generator" should behave in the same way. Before this patch, piping generator function resulted in a cryptic error. We had to insert "|stringify" in this case. $ hg log --template '{if(author, author)|user}\n' abort: template filter 'userfilter' is not compatible with keyword '[(<function runsymbol at 0x7f5af2e8d8c0>, 'author'), (<function runsymbol at 0x7f5af2e8d8c0>, 'author')]'