0029. The folder tree can list files

Date: 2026-10-25

Status

Accepted. The user asked for Programmer, a new IDE, to show its projects in Patina's tree. The shape of the option below is my design.

Context

tree::FolderTree came from UnAmp (ADR-0001), where a sidebar picks a folder of music, so it lists only folders. Programmer opens a project folder in each tab, as Notebook does, and its sidebar has to show the source files in it. Notebook has a tree of its own that lists its notes, which reads the whole workspace on the window's thread when it opens. A large source tree (a target/ or node_modules/ folder) would freeze the window doing that, which FolderTree's lazy, threaded listing already avoids.

We considered:

• A second tree component for files. It would copy the lazy listing, the reveal and the layout, and the two would drift (ADR-0001).
• A filter callback choosing which entries to show. More general, but no app needs more than "folders" or "folders and files" yet.

Decision

• FolderTree::files(true) lists each folder's files after its subfolders, both sorted case-insensitively, hidden ones still skipped. Off by default, so UnAmp's tree is unchanged.
• Files are leaves lined up with the folders' names. show returns a clicked file as it returns a clicked folder, and current can be a file, shown selected. reveal opens the folders leading to a file and scrolls it into view.

Consequences

• Programmer, and Notebook if it moves to it, get a sidebar that never blocks on a big folder.
• Every file is listed; there's no way yet to hide target/ or what .gitignore names. An app that needs that is the trigger for a filter.
• The app tells files from folders by the path it gets back, which costs a stat on click.