Backport blacklist of Ghostscript 9.24

src/ocrmypdf/__main__.py

@@ -863,6 +863,14 @@ def run_pipeline():
             "security vulnerabilities with certain malformed PDFs. Consider "
             "upgrading to version 7.0.0 or newer.".format(qpdf.version()))
 
+    if ghostscript.version() == '9.24':
+        complain(
+            "Ghostscript 9.24 contains serious regressions and is not "
+            "supported. Please upgrade to Ghostscript 9.25 or use an older "
+            "version."
+        )
+        return ExitCode.missing_dependency
+
     # Any changes to options will not take effect for options that are already
     # bound to function parameters in the pipeline. (For example
     # options.input_file, options.pdf_renderer are already bound.)

src/ocrmypdf/exec/ghostscript.py

@@ -43,7 +43,8 @@ def jpeg_passthrough_available():
     https://bugs.ghostscript.com/show_bug.cgi?id=699216
 
     The issue was fixed for 9.24, hence that is the first version we consider
-    the feature available.
+    the feature available. (However, we don't use 9.24 at all, so the first
+    version that allows JPEG passthrough is 9.25.
 
     Regardless, in ocrmypdf 6.x we are ignoring this new feature entirely to
     avoid new behavior.

src/ocrmypdf/pipeline.py

@@ -935,8 +935,8 @@ def generate_postscript_stub(
                 v.encode('ascii', errors='strict')
         except UnicodeEncodeError:
             log.warning(
-                "Ghostscript 9.24 does not support Unicode strings in metadata."
-                " These will be converted to ASCII if possible."
+                "Ghostscript 9.24+ does not support Unicode strings in "
+                " metadata. These will be converted to ASCII if possible."
             )
 
     generate_pdfa_ps(output_file, pdfmark, ascii_docinfo=ascii_docinfo)