Reproduce and fix Rmd issue in 1.3rc1

jupytext/cell_reader.py

@@ -276,8 +276,10 @@ def __init__(self, fmt=None, default_language=None):
         self.split_at_heading = (fmt or {}).get('split_at_heading', False)
         self.in_region = False
         self.in_raw = False
-        if self.format_version in ['1.0', '1.1']:
+        if self.format_version in ['1.0', '1.1'] and self.ext != '.Rmd':
+            # Restore the pattern used in Markdown <= 1.1
             self.start_code_re = re.compile(r"^```(.*)")
+            self.non_jupyter_code_re = re.compile(r"^```\{")
 
     def metadata_and_language_from_option_line(self, line):
         match_region = self.start_region_re.match(line)

tests/test_read_simple_rmd.py

@@ -1,5 +1,5 @@
 import re
-from nbformat.v4.nbbase import new_markdown_cell, new_notebook
+from nbformat.v4.nbbase import new_notebook, new_markdown_cell, new_code_cell
 from jupytext.compare import compare, compare_notebooks
 import jupytext
 from .utils import skip_if_dict_is_not_ordered
@@ -81,3 +81,21 @@ def test_two_markdown_cell_with_code_works(nb=new_notebook(cells=[
     text = jupytext.writes(nb, 'Rmd')
     nb2 = jupytext.reads(text, 'Rmd')
     compare_notebooks(nb2, nb)
+
+
+def test_tags_in_rmd(rmd='''---
+jupyter:
+  jupytext:
+    text_representation:
+      extension: .Rmd
+      format_name: rmarkdown
+      format_version: '1.1'
+      jupytext_version: 1.2.3
+---
+
+```{python tags=c("parameters")}
+p = 1
+```
+''', nb=new_notebook(cells=[new_code_cell('p = 1', metadata={'tags': ['parameters']})])):
+    nb2 = jupytext.reads(rmd, 'Rmd')
+    compare_notebooks(nb2, nb)