Fix #8720: viewcode: module pages are generated for epub on incremental build

The module pages should be generated for epub only if enabled via
configuration.  But they are generated after the build for other
viewcode-supported builders.  This checks the current builder on
generating module pages.

CHANGES

@@ -65,6 +65,7 @@ Bugs fixed
   availability of the same URL twice
 * #8094: texinfo: image files on the different directory with document are not
   copied
+* #8720: viewcode: module pages are generated for epub on incremental build
 * #8671: :confval:`highlight_options` is not working
 * #8341: C, fix intersphinx lookup types for names in declarations.
 * C, C++: in general fix intersphinx and role lookup types.

sphinx/ext/viewcode.py

@@ -182,6 +182,10 @@ def collect_pages(app: Sphinx) -> Generator[Tuple[str, Dict[str, Any], str], Non
     env = app.builder.env
     if not hasattr(env, '_viewcode_modules'):
         return
+    if app.builder.name == "singlehtml":
+        return
+    if app.builder.name.startswith("epub") and not env.config.viewcode_enable_epub:
+        return
     highlighter = app.builder.highlighter  # type: ignore
     urito = app.builder.get_relative_uri
 

tests/test_ext_viewcode.py

@@ -49,6 +49,21 @@ def test_viewcode(app, status, warning):
             '<span>    &quot;&quot;&quot;</span></div>\n') in result
 
 
+@pytest.mark.sphinx('epub', testroot='ext-viewcode')
+def test_viewcode_epub_default(app, status, warning):
+    app.builder.build_all()
+
+    assert not (app.outdir / '_modules/spam/mod1.xhtml').exists()
+
+
+@pytest.mark.sphinx('epub', testroot='ext-viewcode',
+                    confoverrides={'viewcode_enable_epub': True})
+def test_viewcode_epub_enabled(app, status, warning):
+    app.builder.build_all()
+
+    assert (app.outdir / '_modules/spam/mod1.xhtml').exists()
+
+
 @pytest.mark.sphinx(testroot='ext-viewcode', tags=['test_linkcode'])
 def test_linkcode(app, status, warning):
     app.builder.build(['objects'])