fix: preserve cursor position when updating cell code in watch mode or auto-formatting #6792
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…r auto-formatting Fixes #6788 When using `marimo edit --watch` or auto-formatting, the cursor would jump to the top of a cell on save (or auto-save). This occurred because file watching would detect changes, send an `update-cell-codes` message to the frontend, and the frontend would replace the entire editor content without preserving the cursor position. This also fixes an old issue where the cursor would jump to the top of a cell after auto-formatting (regardless of whether it was on watch mode or not). ## Solution Created a new `replaceEditorContent()` utility that: - Checks if the editor has focus before replacing content - When focused, uses **line-based cursor preservation**: - Keeps the cursor on the same line number - Maintains the same column position within that line - If the line shrinks, clamps the cursor to the end of the line - If the line no longer exists, moves the cursor to the end of the last line - Prevents the cursor from jumping during external updates (like from file watching or auto-formatting)
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Light2Dark
previously approved these changes
Oct 15, 2025
## 📝 Summary <!-- Provide a concise summary of what this pull request is addressing. If this PR fixes any issues, list them here by number (e.g., Fixes #123). --> was curious on some of these behaviours, added tests ## 🔍 Description of Changes <!-- Detail the specific changes made in this pull request. Explain the problem addressed and how it was resolved. If applicable, provide before and after comparisons, screenshots, or any relevant details to help reviewers understand the changes easily. --> ## 📋 Checklist - [x] I have read the [contributor guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md). - [ ] For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on [Discord](https://marimo.io/discord?ref=pr), or the community [discussions](https://github.com/marimo-team/marimo/discussions) (Please provide a link if applicable). - [x] I have added tests for the changes made. - [x] I have run the code and verified that it works as expected.
Light2Dark
approved these changes
Oct 15, 2025
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Fixes #6788
When using
marimo edit --watchor auto-formatting, the cursor would jump to the top of a cell on save (or auto-save). This occurred because file watching would detect changes, send anupdate-cell-codesmessage to the frontend, and the frontend would replace the entire editor content without preserving the cursor position.This also fixes an old issue where the cursor would jump to the top of a cell after auto-formatting (regardless of whether it was on watch mode or not).
Solution
Created a new
replaceEditorContent()utility that: