Charts: Ensure chart and legend combined height equals the specified height prop

[chihsuan]

Fixes CHARTS-30

Proposed changes:

When users set the height property for line/bar charts, they expect the chart and legend to be aligned with the container height, not just the chart height.

This PR dynamically measures the legend’s height and subtracts it from the chart area when rendering <XYChart />, so the total rendered height (chart + legend) matches the specified height prop.

The enhancement fixes layout issues that occur when charts are placed in fixed-height containers. For example, when a chart is placed in a container with a fixed height, the chart and legend may exceed the container height, causing the legend to be invisible.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Run pnpm --filter="@automattic/charts" storybook
• Go to http://localhost:50240/?path=/story/js-packages-charts-types-line-chart--with-legend
• Check that the total height of chart + legend matches the specified height prop (400px).
• Check that the vertical legend story displays correctly
• Check the bar chart legend stories display correctly

Before:

After:

Vertical legend:

I initially had concerns about potential layout shifts during chart rendering, but testing shows minimal impact. However, if layout shifts become problematic, we could consider adding an optional prop allowing consumers to specify an initial legend height to minimize any initial rendering adjustments.

Screen.Recording.2025-06-09.at.16.13.31.mov

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Review, ...).
  
• ✅ Add a "[Type]" label (Bug, Enhancement, Janitorial, Task).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

---

Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Make sure to test your changes on all platforms that it applies to. You're responsible for the quality of the code you ship.
3. You can use GitHub's Reviewers functionality to request a review.
4. When it's reviewed and merged, you will be pinged in Slack to deploy the changes to WordPress.com simple once the build is done.

If you have questions about anything, reach out in #jetpack-developers for guidance!

[jp-launch-control]

Code Coverage Summary

Coverage changed in 2 files.

File	Coverage	Δ%	Δ Uncovered
projects/js-packages/charts/src/components/bar-chart/bar-chart.tsx	22/25 (88.00%)	0.50%	0 💚
projects/js-packages/charts/src/components/line-chart/line-chart.tsx	54/66 (81.82%)	0.28%	0 💚

1 file is newly checked for coverage.

File	Coverage
projects/js-packages/charts/src/components/shared/use-element-height.ts	12/12 (100.00%) 💚

Full summary · JS report