Fix ValueError crash when tab-set contains non-tab-item children (#258)

## Fix tab-set crash with invalid children

Fixes #243

### Summary

This PR fixes a `ValueError: not enough values to unpack (expected 2,
got 1)` crash that occurred when a `.. tab-set::` directive contained
invalid content (non-`tab-item` children).

### Changes Made

**1. Modified `TabSetDirective.run_with_defaults()` in
`sphinx_design/tabs.py` (lines 38-53):**
- Changed from `break` to `continue` to warn about ALL invalid children,
not just the first one
- Added filtering to remove invalid children from `tab_set.children`
- Valid `tab-item` directives are preserved in a new list and reassigned

**2. Added defensive validation in `TabSetHtmlTransform.run()` in
`sphinx_design/tabs.py` (lines 247-256):**
- Added check to skip non-`tab-item` children that may have slipped
through
- Added validation to ensure `tab-item` has exactly 2 children before
unpacking
- Logs appropriate warnings for malformed directives

**3. Added comprehensive test in `tests/test_misc.py`:**
- Tests that tab-set with invalid children does not crash
- Verifies warnings are properly logged
- Confirms valid tab items are still processed and rendered correctly

### Behavior After Fix

✅ **Before:** Sphinx-design crashed with `ValueError` when encountering
invalid content in a tab-set
✅ **After:** Sphinx-design logs warnings for each invalid child and
continues to render valid tab-items

**Example input with invalid content:**
```rst
.. tab-set::

   .. tab-item:: A
      A content

   foo  <-- Invalid content

   .. tab-item:: B
      B content
```

**Result:** Both valid tabs (A and B) render correctly, and a warning is
logged for the invalid "foo" content.

### Visual Verification

The fix was manually tested with a document containing invalid content
between tab items:

![Tab A rendered
correctly](https://github.com/user-attachments/assets/08e27cae-23d6-4f4b-be1c-48ae4bda7a43)
![Tab B rendered
correctly](https://github.com/user-attachments/assets/cf6b2e07-aeaf-4e0b-8101-095d15517968)

All three valid tab items render and function correctly despite invalid
content in the source.

### Tests

All 110 tests pass, including the new test specifically for this issue:
- ✅ `test_tab_set_with_invalid_children` - New test reproducing and
validating the fix
- ✅ All existing tests continue to pass
- ✅ All pre-commit hooks pass

### Checklist

- [x] Understand the issue and explore the codebase
- [x] Create tests to reproduce the ValueError bug
- [x] Fix `TabSetDirective.run_with_defaults()` to filter invalid
children
- [x] Add defensive validation in `TabSetHtmlTransform.run()`
- [x] Run tests to verify the fix (110/110 passed)
- [x] Verify build and lint pass
- [x] Manual verification with visual test
- [x] Fix pre-commit formatting issues

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> ## Issue
> Fixes #243
> 
> Sphinx-design crashes with a `ValueError: not enough values to unpack
(expected 2, got 1)` when a `.. tab-set::` directive contains something
other than `.. tab-item::` directives.
> 
> ### Reproduction
> ```rst
> Tab Test document
> =================
> 
> .. tab-set::
> 
>    .. tab-item:: A
> 
>       A content
> 
>    foo  <-- This line causes the crash
> 
>    .. tab-item:: B
> 
>       B content
> ```
> 
> ### Root Cause
> The problem is in `sphinx_design/tabs.py`:
> 
> 1. **In `TabSetDirective.run_with_defaults()` (lines 38-47):** When a
non-`tab-item` child is found, the code logs a warning but only `break`s
after the first invalid child. It does NOT remove the invalid children
from `tab_set.children`.
> 
> 2. **In `TabSetHtmlTransform.run()` (line 244):** The code assumes all
children are valid `tab-item` components with exactly 2 children:
>    ```python
>    tab_label, tab_content = tab_item.children
>    ```
> When an invalid child (like a text node) is encountered, it doesn't
have 2 children, causing the unpacking error.
> 
> ### Required Fix
> 
> **1. Modify `TabSetDirective.run_with_defaults()` in
`sphinx_design/tabs.py`:**
> 
> Change the loop that validates children to:
> - Use `continue` instead of `break` to warn about ALL invalid
children, not just the first
> - Filter out invalid children so only valid `tab-item` components
remain in `tab_set.children`
> 
> The current code:
> ```python
> for item in tab_set.children:
>     if not is_component(item, "tab-item"):
>         LOGGER.warning(
>             f"All children of a 'tab-set' "
>             f"should be 'tab-item' [{WARNING_TYPE}.tab]",
>             location=item,
>             type=WARNING_TYPE,
>             subtype="tab",
>         )
>         break
>     if "sync_id" in item.children[0]:
> item.children[0]["sync_group"] = self.options.get("sync-group", "tab")
> return [tab_set]
> ```
> 
> Should become:
> ```python
> valid_children = []
> for item in tab_set.children:
>     if not is_component(item, "tab-item"):
>         LOGGER.warning(
>             f"All children of a 'tab-set' "
>             f"should be 'tab-item' [{WARNING_TYPE}.tab]",
>             location=item,
>             type=WARNING_TYPE,
>             subtype="tab",
>         )
>         continue  # Skip invalid children instead of breaking
>     if "sync_id" in item.children[0]:
> item.children[0]["sync_group"] = self.options.get("sync-group", "tab")
>     valid_children.append(item)
> 
> tab_set.children = valid_children
> return [tab_set]
> ```
> 
> **2. Add defensive validation in `TabSetHtmlTransform.run()` in
`sphinx_design/tabs.py`:**
> 
> In the loop at line 242, add a check before unpacking to handle any
edge cases:
> ```python
> for idx, tab_item in enumerate(tab_set.children):
>     if not is_component(tab_item, "tab-item"):
>         continue  # Skip non tab-item children
>     if len(tab_item.children) != 2:
>         LOGGER.warning(
>             f"Malformed 'tab-item' directive [{WARNING_TYPE}.tab]",
>             location=tab_item,
>             type=WARNING_TYPE,
>             subtype="tab",
>         )
>         continue
>     tab_label, tab_content = tab_item.children
>     # ... rest of processing unchanged
> ```
> 
> Note: You'll need to import `is_component` at the top of the
`TabSetHtmlTransform.run()` method if it's not already available in that
scope (it should be available since it's imported from `.shared`).
> 
> ### Expected Behavior After Fix
> - Sphinx-design should NOT crash when invalid content is inside a
`tab-set`
> - A warning should be logged for each invalid child
> - Valid `tab-item` directives should still be processed and rendered
correctly
> - The warning should include accurate location information


</details>



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*This pull request was created from Copilot chat.*
>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: chrisjsewell <[email protected]>
Co-authored-by: Chris Sewell <[email protected]>

Author: Copilot

sphinx_design/tabs.py

@@ -35,6 +35,7 @@ def run_with_defaults(self) -> list[nodes.Node]:
         )
         self.set_source_info(tab_set)
         self.state.nested_parse(self.content, self.content_offset, tab_set)
+        valid_children = []
         for item in tab_set.children:
             if not is_component(item, "tab-item"):
                 LOGGER.warning(
@@ -44,9 +45,12 @@ def run_with_defaults(self) -> list[nodes.Node]:
                     type=WARNING_TYPE,
                     subtype="tab",
                 )
-                break
+                continue  # Skip invalid children instead of breaking
             if "sync_id" in item.children[0]:
                 item.children[0]["sync_group"] = self.options.get("sync-group", "tab")
+            valid_children.append(item)
+
+        tab_set.children = valid_children
         return [tab_set]
 
 
@@ -240,10 +244,17 @@ def run(self) -> None:
             selected_idx = 0 if selected_idx is None else selected_idx
 
             for idx, tab_item in enumerate(tab_set.children):
-                try:
-                    tab_label, tab_content = tab_item.children
-                except ValueError:
-                    raise
+                if not is_component(tab_item, "tab-item"):
+                    continue  # Skip non tab-item children
+                if len(tab_item.children) != 2:
+                    LOGGER.warning(
+                        f"Malformed 'tab-item' directive [{WARNING_TYPE}.tab]",
+                        location=tab_item,
+                        type=WARNING_TYPE,
+                        subtype="tab",
+                    )
+                    continue
+                tab_label, tab_content = tab_item.children
                 tab_item_identity = tab_item_id_base + str(tab_item_id_num)
                 tab_item_id_num += 1
 

tests/test_misc.py

@@ -30,3 +30,45 @@ def test_material(style, file_regression):
     for name in sorted(data):
         content += f"{name}: {','.join(data[name]['heights'])}\n"
     file_regression.check(content)
+
+
+def test_tab_set_with_invalid_children(
+    sphinx_builder, file_regression, normalize_doctree_xml
+):
+    """Test that tab-set with invalid children does not crash.
+
+    This reproduces the issue from https://github.com/executablebooks/sphinx-design/issues/243
+    where a ValueError was raised when a tab-set contained non-tab-item children.
+    """
+    builder = sphinx_builder(conf_kwargs={"extensions": ["sphinx_design"]})
+    builder.src_path.joinpath("index.rst").write_text(
+        """
+Tab Test document
+=================
+
+.. tab-set::
+
+   .. tab-item:: A
+
+      A content
+
+   foo
+
+   .. tab-item:: B
+
+      B content
+""",
+        encoding="utf8",
+    )
+    # Build should not crash, but should produce a warning
+    builder.build(assert_pass=False)
+    assert "All children of a 'tab-set' should be 'tab-item'" in builder.warnings
+
+    # Valid tab items should still be processed
+    doctree = builder.get_doctree("index", post_transforms=True)
+    doctree.attributes.pop("translation_progress", None)
+    file_regression.check(
+        normalize_doctree_xml(doctree.pformat()),
+        extension=".xml",
+        encoding="utf8",
+    )

tests/test_misc/test_tab_set_with_invalid_children.xml

@@ -0,0 +1,17 @@
+<document source="index">
+    <section ids="tab-test-document" names="tab\ test\ document">
+        <title>
+            Tab Test document
+        <container classes="sd-tab-set" design_component="tab-set" is_div="True">
+            <sd_tab_input checked="True" id="sd-tab-item-0" set_id="sd-tab-set-0" type="radio">
+            <sd_tab_label classes="sd-tab-label" input_id="sd-tab-item-0">
+                A
+            <container classes="sd-tab-content" design_component="tab-content" is_div="True">
+                <paragraph>
+                    A content
+            <sd_tab_input checked="False" id="sd-tab-item-1" set_id="sd-tab-set-0" type="radio">
+            <sd_tab_label classes="sd-tab-label" input_id="sd-tab-item-1">
+                B
+            <container classes="sd-tab-content" design_component="tab-content" is_div="True">
+                <paragraph>
+                    B content