Move Tesseract options validation into plugin

src/ocrmypdf/_sync.py

@@ -323,8 +323,6 @@ def run_pipeline(options, *, plugin_manager, api=False):
             original_filename, start_input_file, work_folder / 'origin.pdf', options
         )
 
-        plugin_manager.hook.prepare(options=options)
-
         # Gather pdfinfo and create context
         pdfinfo = get_pdfinfo(
             origin_pdf,

src/ocrmypdf/_validation.py

@@ -123,18 +123,6 @@ def check_options_output(options):
         msg += f"Found Ghostscript {ghostscript.version()}"
         log.warning(msg)
 
-    # Decide on what renderer to use
-    if options.pdf_renderer == 'auto':
-        options.pdf_renderer = 'sandwich'
-
-    if options.pdf_renderer == 'sandwich' and not tesseract.has_textonly_pdf(
-        options.tesseract_env, languages
-    ):
-        raise MissingDependencyError(
-            "You are using an alpha version of Tesseract 4.0 that does not support "
-            "the textonly_pdf parameter. We don't support versions this old."
-        )
-
     if options.output_type == 'pdfa':
         options.output_type = 'pdfa-2'
 
@@ -277,18 +265,6 @@ def check_options_advanced(options):
             "--pdfa-image-compression argument has no effect when "
             "--output-type is not 'pdfa', 'pdfa-1', or 'pdfa-2'"
         )
-    if not tesseract.has_user_words(options.tesseract_env) and (
-        options.user_words or options.user_patterns
-    ):
-        log.warning(
-            "Tesseract 4.0 ignores --user-words and --user-patterns, so these "
-            "arguments have no effect."
-        )
-    if options.tesseract_pagesegmode in (0, 2):
-        log.warning(
-            "The --tesseract-pagesegmode argument you select will disable OCR. "
-            "This may cause processing to fail."
-        )
 
 
 def check_options_metadata(options):
@@ -322,6 +298,7 @@ def check_options(options, plugin_manager):
     check_options_advanced(options)
     check_options_pillow(options)
     check_dependency_versions(options)
+    plugin_manager.hook.check_options(options=options)
 
 
 def check_closed_streams(options):  # pragma: no cover
@@ -464,12 +441,6 @@ def report_output_file_size(options, input_file, output_file):
 
 
 def check_dependency_versions(options):
-    check_external_program(
-        program='tesseract',
-        package={'linux': 'tesseract-ocr'},
-        version_checker=tesseract.version,
-        need_version='4.0.0',  # using backport for Travis CI
-    )
     check_external_program(
         program='gs',
         package='ghostscript',

src/ocrmypdf/builtin_plugins/tesseract_ocr.py

@@ -15,11 +15,16 @@
 # You should have received a copy of the GNU General Public License
 # along with OCRmyPDF.  If not, see <http://www.gnu.org/licenses/>.
 
+import logging
+
 from ocrmypdf import hookimpl
 from ocrmypdf.cli import numeric
-from ocrmypdf.exec import tesseract
+from ocrmypdf.exceptions import MissingDependencyError
+from ocrmypdf.exec import check_external_program, tesseract
 from ocrmypdf.pluginspec import OcrEngine
 
+log = logging.getLogger(__name__)
+
 
 @hookimpl
 def add_options(parser):
@@ -76,6 +81,40 @@ def add_options(parser):
     )
 
 
+@hookimpl
+def check_options(options):
+    check_external_program(
+        program='tesseract',
+        package={'linux': 'tesseract-ocr'},
+        version_checker=tesseract.version,
+        need_version='4.0.0',  # using backport for Travis CI
+    )
+
+    # Decide on what renderer to use
+    if options.pdf_renderer == 'auto':
+        options.pdf_renderer = 'sandwich'
+
+    if options.pdf_renderer == 'sandwich' and not tesseract.has_textonly_pdf(
+        options.tesseract_env, set(options.language)
+    ):
+        raise MissingDependencyError(
+            "You are using an alpha version of Tesseract 4.0 that does not support "
+            "the textonly_pdf parameter. We don't support versions this old."
+        )
+    if not tesseract.has_user_words(options.tesseract_env) and (
+        options.user_words or options.user_patterns
+    ):
+        log.warning(
+            "Tesseract 4.0 ignores --user-words and --user-patterns, so these "
+            "arguments have no effect."
+        )
+    if options.tesseract_pagesegmode in (0, 2):
+        log.warning(
+            "The --tesseract-pagesegmode argument you select will disable OCR. "
+            "This may cause processing to fail."
+        )
+
+
 class TesseractOcrEngine(OcrEngine):
     @staticmethod
     def version():

src/ocrmypdf/pluginspec.py

@@ -39,7 +39,7 @@ def add_options(parser: ArgumentParser) -> None:
 
 
 @hookspec
-def prepare(options: Namespace) -> None:
+def check_options(options: Namespace) -> None:
     """Called to notify a plugin that a file will be processed.
 
 	The plugin may modify the *options*. All objects that are in options must