<p dir="auto">Under <strong>What do I need?</strong> click should also be listed.</p>
<p dir="auto">This is a major backwards-compat breaking change, but I suspect not the intended design and hopefully easy to fix.</p>
<p dir="auto">The issue is related to PR <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="296333921" data-permission-text="Title is private" data-url="https://github.com/pallets/flask/issues/2629" data-hovercard-type="pull_request" data-hovercard-url="/pallets/flask/pull/2629/hovercard" href="https://github.com/pallets/flask/pull/2629">#2629</a>, and this example follows from that:</p>
<p dir="auto">Given blueprint <code class="notranslate">bp</code> and app <code class="notranslate">app</code>:</p>
<div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="@bp.route('b/')
def tmp():
    return &quot;URI should be '/a/b/&quot;

app.register_blueprint(bp, url_prefix='/a/')"><pre class="notranslate"><span class="pl-en">@<span class="pl-s1">bp</span>.<span class="pl-en">route</span>(<span class="pl-s">'b/'</span>)</span>
<span class="pl-k">def</span> <span class="pl-en">tmp</span>():
    <span class="pl-k">return</span> <span class="pl-s">"URI should be '/a/b/"</span>

<span class="pl-s1">app</span>.<span class="pl-en">register_blueprint</span>(<span class="pl-s1">bp</span>, <span class="pl-s1">url_prefix</span><span class="pl-c1">=</span><span class="pl-s">'/a/'</span>)</pre></div>
<p dir="auto">In Flask 0.12 the URL is correctly <code class="notranslate">/a/b</code>, but in Flask 1.0 it's <code class="notranslate">/ab</code>.</p>
<p dir="auto">Since issue <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="296333921" data-permission-text="Title is private" data-url="https://github.com/pallets/flask/issues/2629" data-hovercard-type="pull_request" data-hovercard-url="/pallets/flask/pull/2629/hovercard" href="https://github.com/pallets/flask/pull/2629">#2629</a> relates to resolve double-slashes, I imagine this is a bug (and not a design decision) - and the correct solution would be to remove a slash only when there are two.</p>