<div dir="ltr"><p>minimal code for reproducing the issue</p>
<div class="gmail-highlight gmail-highlight-source-erlang"><pre>-<span class="gmail-pl-k">module</span>(<span class="gmail-pl-en">a</span>).
-<span class="gmail-pl-k">export</span>([<span class="gmail-pl-en">test</span>/<span class="gmail-pl-c1">0</span>]).
-<span class="gmail-pl-k">include_lib</span>(<span class="gmail-pl-s"><span class="gmail-pl-pds">"</span>syntax_tools/include/merl.hrl<span class="gmail-pl-pds">"</span></span>).

<span class="gmail-pl-en">test</span>() <span class="gmail-pl-k">-></span> 
        <span class="gmail-pl-smi">Str</span> <span class="gmail-pl-k">=</span> <span class="gmail-pl-s"><span class="gmail-pl-pds">"</span>a_string<span class="gmail-pl-pds">"</span></span>,
        <span class="gmail-pl-k">?</span><span class="gmail-pl-en">Q</span>(<span class="gmail-pl-s"><span class="gmail-pl-pds">"</span>_@Str@ -> 1<span class="gmail-pl-pds">"</span></span>).</pre></div>
<p>Result in OTP 19:</p>
<pre><code>{tree,clause,
      {attr,7,[],none},
      {clause,[{tree,string,{attr,0,[],none},"a_string"}],
              none,
              [{integer,7,1}]}}
</code></pre>
<p>in OTP 21</p>
<pre><code>{tree,clause,
      {attr,7,[],none},
      {clause,[{tree,class_qualifier,
                     {attr,0,[],none},
                     {class_qualifier,{atom,7,throw},
                                      {tree,string,{attr,0,[],none},"a_string"},
                                      {var,7,'_'}}}],
              none,
              [{integer,7,1}]}}

</code></pre><br></div>