Fix missing jbig2enc reported as error with -O3 instead of warning

Fixes #558

src/ocrmypdf/exec/__init__.py

@@ -233,10 +233,10 @@ def _error_trailer(program, package, **kwargs):
 
 
 def _error_missing_program(program, package, required_for, recommended):
-    if required_for:
+    if recommended:
+        log.warning(missing_recommend_program.format(**locals()))
+    elif required_for:
         log.error(missing_optional_program.format(**locals()))
-    elif recommended:
-        log.info(missing_recommend_program.format(**locals()))
     else:
         log.error(missing_program.format(**locals()))
     _error_trailer(**locals())
@@ -279,7 +279,7 @@ def check_external_program(
     found_version = remove_leading_v(found_version)
     need_version = remove_leading_v(need_version)
 
-    if LooseVersion(found_version) < LooseVersion(need_version):
+    if found_version and LooseVersion(found_version) < LooseVersion(need_version):
         _error_old_version(program, package, need_version, found_version, required_for)
         if not recommended:
             raise MissingDependencyError()

tests/test_validation.py

@@ -210,3 +210,24 @@ def test_version_comparison():
             version_checker=lambda: '1.0',
             need_version='2.0',
         )
+
+
+def test_optional_program_recommended(caplog):
+    caplog.clear()
+
+    def raiser():
+        raise FileNotFoundError('jbig2')
+
+    with caplog.at_level(logging.WARNING):
+        vd.check_external_program(
+            program="jbig2",
+            package="jbig2enc",
+            version_checker=raiser,
+            need_version='42',
+            required_for='this test case',
+            recommended=True,
+        )
+        assert any(
+            (loglevel == logging.WARNING and "recommended" in msg)
+            for _logger_name, loglevel, msg in caplog.record_tuples
+        )