feat: enforce markdown formatting on save (#6969)

Fixes #6458

## 📝 Summary

Adds lint rule and codegen change that enforces markdown dedent.

Following front end convention, the following markdown is expected:

```python
mo.md(
    """
A multiline statement.
"""
)
```

```python
mo.md("A single liner (can also be triple)")
```

```python
mo.md(
    "A very very very very very very very very very very very very very long single liner (can also be triple)"
)
```

**note**: This is a noisy PR since examples are formatted. Look at
commits standalone:

[test: Add in tests for md
check](fba4a46)
[feat: Add markdown tidy rule and auto
formatting](b4a4360)
[tidy: refresh
examples](6985ebd)
[docs: update documentation
rules](6aaaa4a)

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Myles Scolnick <[email protected]>

Author: 3 people

.github/workflows/test_cli.yaml

@@ -166,8 +166,22 @@ jobs:
           uv add pytest pytest-asyncio
           uv pip install marimo*whl
 
-      - name: Check notebook quality with marimo check
+      - name: Check example quality with marimo check
         shell: bash
         run: |
           echo "Checking examples directory..."
           uv run marimo check --ignore-scripts --strict examples/**.py
+
+      - name: Check tutorial quality with marimo check
+        shell: bash
+        run: |
+          echo "Checking tutorials..."
+          uv run marimo check --ignore-scripts --fix \
+            marimo/_tutorials/**.py >> /dev/null \
+            || echo "Errors expected"
+          # Fail if there's a git diff
+          if [[ -n "$(git status --porcelain marimo/_tutorials)" ]]; then
+            echo "marimo check found issues in tutorials."
+            git --no-pager diff marimo/_tutorials
+            exit 1
+          fi

development_docs/adding_lint_rules.md

@@ -183,7 +183,7 @@ if __name__ == "__main__":
 
 #### b) Add snapshot test
 
-Add to `tests/_lint/test_runtime_errors_snapshot.py`:
+Add to `tests/_lint/test_snapshot.py`:
 
 ```python
 def test_your_rule_snapshot():
@@ -280,7 +280,7 @@ uv run hatch run test:test tests/_lint
 uv run hatch run test:test tests/_lint/test_your_rule.py
 
 # Update snapshots if needed
-uv run hatch run test:test tests/_lint/test_runtime_errors_snapshot.py --snapshot-update
+uv run hatch run test:test tests/_lint/test_snapshots.py --snapshot-update
 ```
 
 ## Rule Implementation Guidelines
@@ -359,7 +359,7 @@ tests/_lint/
 ├── snapshots/            # Expected outputs
 │   └── your_rule_name_errors.txt
 ├── test_your_rule.py     # Unit tests
-└── test_runtime_errors_snapshot.py  # Snapshot tests
+└── test_snapshots.py  # Snapshot tests
 ```
 
 ## Documentation Requirements

docs/guides/lint_rules/index.md

@@ -53,6 +53,7 @@ These are style and formatting issues.
 | [MF004](rules/empty_cells.md) | empty-cells | Empty cells that can be safely removed. | ⚠️ |
 | [MF005](rules/sql_parse_error.md) | sql-parse-error | SQL parsing errors during dependency analysis | ❌ |
 | [MF006](rules/misc_log_capture.md) | misc-log-capture | Miscellaneous log messages during processing | ❌ |
+| [MF007](rules/markdown_indentation.md) | markdown-indentation | Markdown cells in `mo.md()` should be dedented. | 🛠️ |
 
 ## Legend
 

docs/guides/lint_rules/rules/markdown_dedent.md

@@ -0,0 +1,50 @@
+# MF007: markdown-indentation
+
+✨ **Formatting** 🛠️ Fixable
+
+MF007: Markdown strings in `mo.md()` should be dedented.
+
+## What it does
+
+Checks cells containing `mo.md()` calls to see if the markdown string
+content has unnecessary leading whitespace that should be removed.
+
+## Why is this bad?
+
+Indented markdown strings:
+
+- Are harder to read when viewing the source code
+- Produce larger diffs when making changes
+- Don't match the standard marimo formatting style
+- Can be confusing when the indentation doesn't reflect the markdown structure
+
+## Examples
+
+**Problematic:**
+
+```python
+mo.md(
+    r"""
+    # Title
+
+    Some content here.
+    """
+)
+```
+
+**Solution:**
+
+```python
+mo.md(r"""
+# Title
+
+Some content here.
+""")
+```
+
+**Note:** This fix is automatically applied with `marimo check --fix`.
+
+## References
+
+- [Understanding Errors](https://docs.marimo.io/guides/understanding_errors/)
+- [Best Practices](https://docs.marimo.io/guides/best_practices/)

docs/guides/lint_rules/rules/markdown_indentation.md

@@ -0,0 +1,48 @@
+# MF007: markdown-indentation
+
+✨ **Formatting** 🛠️ Fixable
+
+MF007: Markdown strings in `mo.md()` should be properly indented.
+
+## What it does
+
+Checks cells containing `mo.md()` calls to see if the markdown string
+content has unnecessary leading whitespace that should be removed.
+
+## Why is this bad?
+
+Indented markdown strings:
+- Are harder to read when viewing the source code
+- Produce larger diffs when making changes
+- Don't match the standard marimo formatting style
+- Can be confusing when the indentation doesn't reflect the markdown structure
+
+## Examples
+
+**Problematic:**
+```python
+mo.md(
+    r"""
+    # Title
+
+    Some content here.
+    """
+)
+```
+
+**Solution:**
+```python
+mo.md(r"""
+# Title
+
+Some content here.
+""")
+```
+
+**Note:** This fix is automatically applied with `marimo check --fix`.
+
+## References
+
+- [Understanding Errors](https://docs.marimo.io/guides/understanding_errors/)
+- [Best Practices](https://docs.marimo.io/guides/best_practices/)
+

examples/ai/chat/anthropic_example.py

@@ -8,7 +8,7 @@
 
 import marimo
 
-__generated_with = "0.15.5"
+__generated_with = "0.17.2"
 app = marimo.App(width="medium")
 
 
@@ -20,13 +20,11 @@ def _():
 
 @app.cell
 def _(mo):
-    mo.md(
-        r"""
+    mo.md(r"""
     # Using Anthropic
 
     This example shows how to use [`mo.ui.chat`](https://docs.marimo.io/api/inputs/chat.html#marimo.ui.chat) to make a chatbot backed by Anthropic.
-    """
-    )
+    """)
     return
 
 
@@ -76,7 +74,9 @@ def _(key, mo):
 
 @app.cell
 def _(mo):
-    mo.md("""Access the chatbot's historical messages with [`chatbot.value`](https://docs.marimo.io/api/inputs/chat.html#accessing-chat-history).""")
+    mo.md(
+        """Access the chatbot's historical messages with [`chatbot.value`](https://docs.marimo.io/api/inputs/chat.html#accessing-chat-history)."""
+    )
     return
 
 

examples/ai/chat/bedrock_example.py

@@ -9,7 +9,7 @@
 
 import marimo
 
-__generated_with = "0.15.5"
+__generated_with = "0.17.2"
 app = marimo.App(width="medium")
 
 
@@ -21,17 +21,15 @@ def _():
 
 @app.cell(hide_code=True)
 def _(mo):
-    mo.md(
-        r"""
+    mo.md(r"""
     # AWS Bedrock Chat Example
 
     This example demonstrates using AWS Bedrock with marimo's chat interface.
 
     AWS Bedrock provides access to foundation models from leading AI companies like Anthropic, Meta, and others.
 
     ⚠️ **Note:** You'll need an AWS account with access to the AWS Bedrock service and the specific model you want to use.
-    """
-    )
+    """)
     return
 
 
@@ -227,8 +225,7 @@ def create_chat(config_form):
 
 @app.cell
 def _(mo):
-    mo.md(
-        r"""
+    mo.md(r"""
     ## Notes on AWS Bedrock Usage
 
     1. **Model Access**: You need to request access to the specific models you want to use in the AWS Bedrock console.
@@ -243,8 +240,7 @@ def _(mo):
     - That your AWS credentials are configured correctly
     - That you have requested model access in the AWS Bedrock console
     - That you're using a region where the selected model is available
-    """
-    )
+    """)
     return
 
 

examples/ai/chat/custom.py

@@ -7,7 +7,7 @@
 
 import marimo
 
-__generated_with = "0.15.5"
+__generated_with = "0.17.2"
 app = marimo.App(width="medium")
 
 
@@ -19,15 +19,13 @@ def _():
 
 @app.cell(hide_code=True)
 def _(mo):
-    mo.md(
-        """
-        # Custom chatbot
-
-        This example shows how to make a custom chatbot: just supply a function that takes two arguments,
-        `messages` and `config`, and returns the chatbot's response. This response can be any object; it
-        doesn't have to be a string!
-        """
-    )
+    mo.md("""
+    # Custom chatbot
+
+    This example shows how to make a custom chatbot: just supply a function that takes two arguments,
+    `messages` and `config`, and returns the chatbot's response. This response can be any object; it
+    doesn't have to be a string!
+    """)
     return
 
 

examples/ai/chat/dagger_code_interpreter.py

@@ -11,7 +11,7 @@
 
 import marimo
 
-__generated_with = "0.15.5"
+__generated_with = "0.17.2"
 app = marimo.App(width="medium")
 
 
@@ -25,15 +25,13 @@ def _():
 
 @app.cell(hide_code=True)
 def _(mo):
-    mo.md(
-        """
-        # Chatbot code-interpreter with [Dagger](https://dagger.io/)
+    mo.md("""
+    # Chatbot code-interpreter with [Dagger](https://dagger.io/)
 
-        This example shows how to create a code-interpreter that executes code using [Dagger](https://dagger.io/) so the code is run in an isolated container.
+    This example shows how to create a code-interpreter that executes code using [Dagger](https://dagger.io/) so the code is run in an isolated container.
 
-        This example requires Docker running on your computer.
-        """
-    )
+    This example requires Docker running on your computer.
+    """)
     return
 
 

examples/ai/chat/deepseek_example.py

@@ -8,7 +8,7 @@
 
 import marimo
 
-__generated_with = "0.15.5"
+__generated_with = "0.17.2"
 app = marimo.App(width="medium")
 
 
@@ -20,13 +20,11 @@ def _():
 
 @app.cell(hide_code=True)
 def _(mo):
-    mo.md(
-        r"""
-        # Using DeepSeek
+    mo.md(r"""
+    # Using DeepSeek
 
-        This example shows how to use [`mo.ui.chat`](https://docs.marimo.io/api/inputs/chat/?h=mo.ui.chat) to make a chatbot backed by [Deepseek](https://deepseek.com/).
-        """
-    )
+    This example shows how to use [`mo.ui.chat`](https://docs.marimo.io/api/inputs/chat/?h=mo.ui.chat) to make a chatbot backed by [Deepseek](https://deepseek.com/).
+    """)
     return
 
 
@@ -88,7 +86,9 @@ def _(key, mo):
 
 @app.cell(hide_code=True)
 def _(mo):
-    mo.md("""Access the chatbot's historical messages with [`chatbot.value`](https://docs.marimo.io/api/inputs/chat.html#accessing-chat-history).""")
+    mo.md(
+        """Access the chatbot's historical messages with [`chatbot.value`](https://docs.marimo.io/api/inputs/chat.html#accessing-chat-history)."""
+    )
     return