Fix #9103: LaTeX: imgconverter: conversion runs even if not needed

The imgconverter unexpectedly goes to convert even if the given image
is supported by the target builder when the image globbing is not used.
This enables format guess-ing on not globbed.

CHANGES

@@ -16,6 +16,7 @@ Deprecated
 Features added
 --------------
 
+* #9103: LaTeX: imgconverter: conversion runs even if not needed
 * #9023: More CSS classes on domain descriptions, see :ref:`nodes` for details.
 
 Bugs fixed

sphinx/transforms/post_transforms/images.py

@@ -197,7 +197,7 @@ class ImageConverter(BaseImageConverter):
     def match(self, node: nodes.image) -> bool:
         if not self.app.builder.supported_image_types:
             return False
-        elif set(node['candidates']) & set(self.app.builder.supported_image_types):
+        elif set(self.guess_mimetypes(node)) & set(self.app.builder.supported_image_types):
             # builder supports the image; no need to convert
             return False
         elif self.available is None:

tests/roots/test-ext-imgconverter/index.rst

@@ -2,3 +2,4 @@ test-ext-imgconverter
 =====================
 
 .. image:: svgimg.svg
+.. image:: img.pdf

tests/test_ext_imgconverter.py

@@ -19,6 +19,11 @@ def test_ext_imgconverter(app, status, warning):
     app.builder.build_all()
 
     content = (app.outdir / 'python.tex').read_text()
+
+    # supported image (not converted)
+    assert '\\sphinxincludegraphics{{img}.pdf}' in content
+
+    # non supported image (converted)
     assert '\\sphinxincludegraphics{{svgimg}.png}' in content
     assert not (app.outdir / 'svgimg.svg').exists()
     assert (app.outdir / 'svgimg.png').exists()