fix: emit a warning when no content is rendered (pypa#231)

* fix: emit a warning when no content is rendered

Fixes pypa#149

Signed-off-by: Mike Fiedler <[email protected]>

* feat: emit empty warning only if no warnings exist

This is a bit more gymnastics than I think is warranted,
but wanted to play out the example.

Needing to inspect the stream proved more complex than
originally expected, as each version confroms to a slightly
different interface.

- Updated the outpout string to be clearer
- Added test for empty RST file

Signed-off-by: Mike Fiedler <[email protected]>

* refactor: simplify now that distutils is gone

Signed-off-by: Mike Fiedler <[email protected]>

readme_renderer/rst.py

@@ -129,4 +129,7 @@ def render(
     if rendered:
         return clean(rendered)
     else:
+        # If the warnings stream is empty, docutils had none, so add ours.
+        if not stream.tell():
+            stream.write("No content rendered from RST source.")
         return None

tests/test_rst.py

@@ -53,3 +53,33 @@ def test_rst_raw():
 """, stream=warnings) is None
 
     assert '"raw" directive disabled' in warnings.getvalue()
+
+
+def test_rst_empty_file():
+    warnings = io.StringIO()
+    assert render("", stream=warnings) is None
+
+    assert "No content rendered from RST source." in warnings.getvalue()
+
+
+def test_rst_header_only():
+    warnings = io.StringIO()
+    assert render("""
+Header
+======
+""", stream=warnings) is None
+
+    assert "No content rendered from RST source." in warnings.getvalue()
+
+
+def test_header_and_malformed_emits_docutils_warning_only():
+    warnings = io.StringIO()
+    assert render("""
+Header
+======
+
+======
+""", stream=warnings) is None
+
+    assert len(warnings.getvalue().splitlines()) == 1
+    assert "No content rendered from RST source." not in warnings.getvalue()