fix image reference clashes in rst (#89)

fixes #88 

If an image is set without a caption (e.g. `![](image.png)`), then pandoc will assign an iterative reference identifier to it:

```
|image0|

.. |image0| image:: image.png
```

However, this iterator restarts for each markdown cell, which can lead to reference clashes. Therefore we specifically assign the identifier here, as its url

```
|main_files/example1.png|

.. |main_files/example1.png| image:: main_files/example1.png
```

* flake8 fixes

ipypublish/filters_pandoc/format_label_elements.py

@@ -158,6 +158,17 @@ def format_image(image, doc):
         return pf.RawInline(latex, format="tex")
 
     elif doc.format in ("rst",):
+        if not image.content.list:
+            # If the container is empty, then pandoc will assign an iterative
+            # reference identifier to it (image0, image1).
+            # However, this iterator restarts for each markdown cell,
+            # which can lead to reference clashes.
+            # Therefore we specifically assign the identifier here, as its url
+            # TODO does this identifier need to be sanitized?
+            # (it works fine in the tests)
+            identifier = image.url
+            image.content = pf.ListContainer(pf.Str(str(identifier)))
+
         return image
         # TODO formatting and span identifier (convert width/height to %)
 

ipypublish/tests/test_convert_markdown_cells.py

@@ -26,3 +26,17 @@ def test_sphinx_rst(ipynb_app):
         raise AssertionError("pandoc version must be >= 2.6")
     ipynb_app.assert_converted_equals_expected(
         'sphinx_ipypublish_main.pandoc.2-6')
+
+
+@pytest.mark.ipynb('nb_with_mkdown_images')  # out_to_temp=False
+def test_sphinx_rst_with_mkdown_images(ipynb_app):
+    """ test a notebook with multiple images """
+    ipynb_app.run({
+        "conversion": "sphinx_ipypublish_main.run",
+        "log_to_file": True,
+        "default_pporder_kwargs": {"dump_files": True}})
+    ipynb_app.assert_converted_exists()
+    ipynb_app.assert_converted_equals_expected(
+        'sphinx_ipypublish_main')
+    assert ipynb_app.converted_path.joinpath(
+        "main_files/example.jpg").is_file()

ipypublish/tests/test_files/nb_with_mkdown_images/expected/sphinx_ipypublish_main.rst

@@ -0,0 +1,18 @@
+
+.. An html document created by ipypublish
+   outline: ipypublish.templates.outline_schemas/rst_outline.rst.j2
+   with segments:
+   - nbsphinx-ipypublish-content: ipypublish sphinx content
+
+Notebook to test markdown cells containing multiple images
+
+|main_files/example1.png|
+
+.. |main_files/example1.png| image:: main_files/example1.png
+
+|main_files/example.jpg|
+
+|main_files/example2.jpg|
+
+.. |main_files/example.jpg| image:: main_files/example.jpg
+.. |main_files/example2.jpg| image:: main_files/example2.jpg

ipypublish/tests/test_files/nb_with_mkdown_images/source/main.ipynb

@@ -0,0 +1,75 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Notebook to test markdown cells containing multiple images"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "![](media/example1.png)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "![](media/example.jpg)\n",
+    "\n",
+    "![](media/example2.jpg)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "celltoolbar": "Edit Metadata",
+  "hide_input": false,
+  "ipub": {
+   "pandoc": {
+    "use_numref": true
+   }
+  },
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.6.5"
+  },
+  "toc": {
+   "base_numbering": 1,
+   "nav_menu": {},
+   "number_sections": true,
+   "sideBar": true,
+   "skip_h1_title": false,
+   "title_cell": "Table of Contents",
+   "title_sidebar": "Contents",
+   "toc_cell": false,
+   "toc_position": {},
+   "toc_section_display": true,
+   "toc_window_display": false
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}