title: Makefiles: How to properly use $wildcard to recursively descend?
body: <p>I have a folder of markdown files that are being converted to HTML files using a Makefile.  To figure out the source and dest, I use the following Makefile construct</p>
  
  <p><code>TARGETS_TO_BUILD := $(patsubst src/%.md, out/%.html, $(wildcard src/*.md src/**/*.md))</code></p>
  
  <p>If you echo out $(TARGETS_TO_BUILD) you get a list of paths <code>./out/index.html ./out/folder1/somepage.html</code> and so on.  Works fine.  </p>
  
  <p>However, if I start putting my source files into deeper and deeper folders, such that I end up with a deep tree, things stop working.  That wildcard (<code>src/**/*.md</code>) doesn't work. I have to start doing things like this:</p>
  
  <p><code>TARGETS_TO_BUILD := $(patsubst src/%.md, out/%.html, $(wildcard src/*.md src/**/*.md src/**/**/*.md src/**/**/**/*.md))</code>  </p>
  
  <p>I have to keep adding more and more of those.</p>
  
  <p>That glob string isn't working as expected.  I thought they would work with infinite depth. </p>