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.

5 files changed, 8 insertions, 1 deletions

diff --git a/CHANGES b/CHANGES
index 28e89863f..b61fdd58b 100644
--- a/CHANGES
+++ b/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
diff --git a/sphinx/transforms/post_transforms/images.py b/sphinx/transforms/post_transforms/images.py
index f9b78837f..c9ed572b8 100644
--- a/sphinx/transforms/post_transforms/images.py
+++ b/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:
diff --git a/tests/roots/test-ext-imgconverter/img.pdf b/tests/roots/test-ext-imgconverter/img.pdf
new file mode 100644
index 000000000..cacbd855d
--- /dev/null
+++ b/tests/roots/test-ext-imgconverter/img.pdf
diff --git a/tests/roots/test-ext-imgconverter/index.rst b/tests/roots/test-ext-imgconverter/index.rst
index 786c92e8d..f8ef1d6e2 100644
--- a/tests/roots/test-ext-imgconverter/index.rst
+++ b/tests/roots/test-ext-imgconverter/index.rst
@@ -2,3 +2,4 @@ test-ext-imgconverter
 =====================
 
 .. image:: svgimg.svg
+.. image:: img.pdf
diff --git a/tests/test_ext_imgconverter.py b/tests/test_ext_imgconverter.py
index 5f6f236cf..b4fd46d25 100644
--- a/tests/test_ext_imgconverter.py
+++ b/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()