Use can_render to only suggest .atom when supported by query

Will release as 0.6. Depends on Datasette 0.43. Closes #10.

See also simonw/datasette#770

datasette_atom/__init__.py

@@ -9,7 +9,7 @@
 
 @hookimpl
 def register_output_renderer():
-    return {"extension": "atom", "callback": render_atom}
+    return {"extension": "atom", "render": render_atom, "can_render": can_render_atom}
 
 
 def render_atom(args, data, view_name):
@@ -66,6 +66,10 @@ def render_atom(args, data, view_name):
     }
 
 
+def can_render_atom(columns):
+    return {"atom_id", "atom_title", "atom_updated"}.issubset(columns)
+
+
 def clean(html):
     cleaned = bleach.clean(
         html,

setup.py

@@ -1,7 +1,7 @@
 from setuptools import setup
 import os
 
-VERSION = "0.5"
+VERSION = "0.6"
 
 
 def get_long_description():
@@ -23,7 +23,7 @@ def get_long_description():
     version=VERSION,
     packages=["datasette_atom"],
     entry_points={"datasette": ["atom = datasette_atom"]},
-    install_requires=["datasette", "feedgen", "bleach"],
+    install_requires=["datasette~=0.43", "feedgen", "bleach"],
     extras_require={"test": ["pytest", "pytest-asyncio", "httpx"]},
     tests_require=["datasette-atom[test]"],
 )

tests/test_atom.py

@@ -180,3 +180,31 @@ async def test_atom_with_bad_html():
         EXPECTED_ATOM_WITH_HTML.format(version=datasette.__version__)
         == response.content.decode("utf-8").strip()
     )
+
+
+@pytest.mark.asyncio
+async def test_atom_link_only_shown_for_correct_queries():
+    sql = """
+    select
+        'atom-id' as atom_id,
+        'title' as atom_title,
+        '2019-10-23T21:32:12-07:00' as atom_updated,
+        'https://www.niche-museums.com/' as atom_link,
+        '<h2>blah</h2><script>alert("bad")</script>' as atom_content_html;
+    """
+    app = Datasette([], immutables=[], memory=True).app()
+    async with httpx.AsyncClient(app=app) as client:
+        response = await client.get(
+            "http://localhost/:memory:?" + urllib.parse.urlencode({"sql": sql})
+        )
+    assert 200 == response.status_code
+    assert "text/html; charset=utf-8" == response.headers["content-type"]
+    assert b'<a href="/:memory:.atom' in response.content
+    # But with a different query that link is not shown:
+    async with httpx.AsyncClient(app=app) as client:
+        response = await client.get(
+            "http://localhost/:memory:?"
+            + urllib.parse.urlencode({"sql": "select sqlite_version()"})
+        )
+    assert b'<a href="/:memory:.json' in response.content
+    assert b'<a href="/:memory:.atom' not in response.content