fix: whitespace discrepancies on round trip conversions (#6521)

## 📝 Summary

Fixes slight discrepancies between frontend provided serialization and
markdown -> marimo serialization

Unblocks mwouts/jupytext#1431

Author: dmadisetti

frontend/src/core/codemirror/language/languages/markdown.ts

@@ -103,6 +103,9 @@ export class MarkdownLanguageAdapter
     code: string,
     metadata: MarkdownLanguageAdapterMetadata,
   ): [string, number] {
+    // NB. Must be kept consistent with marimo/_convert/utils.py
+    // ::markdown_to_marimo
+
     // Empty string
     if (code === "") {
       // Need at least a space, otherwise the output will be 6 quotes

marimo/_convert/markdown/markdown.py

@@ -247,7 +247,7 @@ def _tree_to_ir(root: Element) -> SafeWrap[NotebookSerializationV1]:
     header = root.get("header", None)
     pyproject = root.get("pyproject", None)
     if pyproject and not header:
-        header = "\n# ".join(["# ///script", *pyproject.splitlines(), "///"])
+        header = "\n# ".join(["# /// script", *pyproject.splitlines(), "///"])
     notebook = NotebookSerializationV1(
         app=AppInstantiation(options=app_config),
         cells=[

marimo/_convert/utils.py

@@ -5,14 +5,25 @@
 
 
 def markdown_to_marimo(source: str) -> str:
+    # NB. This should be kept in sync with the logic in
+    # frontend/src/core/codemirror/language/languages/markdown.ts
+    # ::transformOut
     source = source.replace('"""', '\\"\\"\\"')
+
+    # 6 quotes in a row breaks
+    if not source:
+        source = " "
+
+    if "\n" not in source:
+        return f'mo.md(r"""{source}""")'
+
     return "\n".join(
         [
             "mo.md(",
             # r-string: a backslash is just a backslash!
             codegen.indent_text('r"""'),
-            codegen.indent_text(source),
-            codegen.indent_text('"""'),
+            source,
+            '"""',
             ")",
         ]
     )

marimo/_server/export/exporter.py

@@ -291,7 +291,7 @@ def export_as_md(
                 metadata["header"] = header.strip()
         else:
             header_file = previous if previous else filename
-            if header_file:
+            if header_file and Path(header_file).exists():
                 with open(header_file, encoding="utf-8") as f:
                     _metadata, _ = extract_frontmatter(f.read())
                 metadata.update(_metadata)

tests/_cli/snapshots/markdown_to_marimo.txt

@@ -8,10 +8,10 @@ app = marimo.App()
 def _(mo):
     mo.md(
         r"""
-        # Test Markdown
+    # Test Markdown
 
-        print('Hello from Markdown!')
-        """
+    print('Hello from Markdown!')
+    """
     )
     return
 

tests/_cli/snapshots/remote_markdown_to_marimo.txt

@@ -8,12 +8,12 @@ app = marimo.App()
 def _(mo):
     mo.md(
         r"""
-        # Remote Markdown Test
+    # Remote Markdown Test
 
-        ```python
-        print('Hello from Remote Markdown!')
-        ```
-        """
+    ```python
+    print('Hello from Remote Markdown!')
+    ```
+    """
     )
     return
 

tests/_convert/snapshots/basic_marimo_example.py.txt

@@ -0,0 +1,33 @@
+import marimo
+
+__generated_with = "0.15.2"
+app = marimo.App(width="medium")
+
+
+@app.cell(hide_code=True)
+def _(mo):
+    mo.md(r"""This is a simple marimo notebook""")
+    return
+
+
+@app.cell
+def _():
+    x = 1
+    return (x,)
+
+
+@app.cell
+def _(x):
+    y = x+1
+    y
+    return
+
+
+@app.cell
+def _():
+    import marimo as mo
+    return (mo,)
+
+
+if __name__ == "__main__":
+    app.run()

tests/_convert/snapshots/basic_marimo_example_roundtrip.py.txt

@@ -0,0 +1,33 @@
+import marimo
+
+__generated_with = "0.0.0"
+app = marimo.App(width="medium", app_title="Test Notebook")
+
+
+@app.cell(hide_code=True)
+def _(mo):
+    mo.md(r"""This is a simple marimo notebook""")
+    return
+
+
+@app.cell
+def _():
+    x = 1
+    return (x,)
+
+
+@app.cell
+def _(x):
+    y = x+1
+    y
+    return
+
+
+@app.cell
+def _():
+    import marimo as mo
+    return (mo,)
+
+
+if __name__ == "__main__":
+    app.run()

tests/_convert/snapshots/basic_marimo_example_to_md.txt

@@ -0,0 +1,20 @@
+---
+title: Test Notebook
+marimo-version: 0.0.0
+width: medium
+---
+
+This is a simple marimo notebook
+
+```python {.marimo}
+x = 1
+```
+
+```python {.marimo}
+y = x+1
+y
+```
+
+```python {.marimo}
+import marimo as mo
+```

tests/_convert/snapshots/convert_hides_markdown_cells.py.txt

@@ -5,33 +5,21 @@ app = marimo.App()
 
 @app.cell(hide_code=True)
 def _(mo):
-    mo.md(
-        r"""
-        A markdown cell.
-        """
-    )
+    mo.md(r"""A markdown cell.""")
     return
 
 
 @app.cell(hide_code=True)
 def _(mo):
     # Cell tags: blah
-    mo.md(
-        r"""
-        A markdown cell with tags: ['blah'].
-        """
-    )
+    mo.md(r"""A markdown cell with tags: ['blah'].""")
     return
 
 
 @app.cell(hide_code=True)
 def _(mo):
     # Cell tags: blah
-    mo.md(
-        r"""
-        A markdown cell with tags: ['blah', 'hide-cell'].
-        """
-    )
+    mo.md(r"""A markdown cell with tags: ['blah', 'hide-cell'].""")
     return