Ensure skipped pages are explained in sidecars

ocrmypdf/pipeline.py

@@ -882,16 +882,25 @@ def merge_sidecars(
         log,
         context):
     options = context.get_options()
+    pdfinfo = context.get_pdfinfo()
 
-    txt_files = sorted(f for f in flatten_groups(input_files_groups)
-                       if f.endswith('.txt'))
+    txt_files = [None] * len(pdfinfo)
+
+    for infile in flatten_groups(input_files_groups):
+        if infile.endswith('.txt'):
+            idx = page_number(infile) - 1
+            txt_files[idx] = infile
 
     def write_pages(stream):
         for page_number, txt_file in enumerate(txt_files):
             if page_number != 0:
                 stream.write('\f')  # Form feed between pages
-            with open(txt_file, 'r') as in_:
-                stream.write(in_.read())
+            if txt_file:
+                with open(txt_file, 'r') as in_:
+                    stream.write(in_.read())
+            else:
+                stream.write('[OCR skipped on page {}]'.format(
+                        page_number + 1))
 
     if output_file == '-':
         write_pages(sys.stdout)

tests/test_main.py

@@ -970,4 +970,24 @@ def test_compression_changed(spoof_tesseract_noop, ocrmypdf_exec,
             "Colorspace changed"
     elif im.mode.startswith('L'):
         assert pdfimage['color'] == 'gray', \
-            "Colorspace changed"
+            "Colorspace changed"
+
+
+def test_sidecar_pagecount(spoof_tesseract_cache, resources, outpdf):
+    sidecar = outpdf + '.txt'
+    check_ocrmypdf(
+        resources / 'multipage.pdf', outpdf,
+        '--skip-text',
+        '--sidecar', sidecar,
+        env=spoof_tesseract_cache)
+
+    pdfinfo = pdf_get_all_pageinfo(str(resources / 'multipage.pdf'))
+    num_pages = len(pdfinfo)
+
+    with open(sidecar, 'r') as f:
+        ocr_text = f.read()
+
+    # There should a formfeed between each pair of pages, so the count of
+    # formfeeds is the page count less one
+    assert ocr_text.count('\f') == num_pages - 1, \
+        "Sidecar page count does not match PDF page count"