gh-75733: Show IDLE's trees in a ttk.Treeview

[serhiy-storchaka]

idlelib.tree drew every row on a canvas: hardcoded pixel sizes that fit neither every font nor every monitor, an icon on every row whether it helped or not, and its own bindings for clicks and scrolling. This replaces the drawing with a ttk.Treeview, which takes its row height from the configured font and its indicators, colours and keys from ttk and the theme. That is the fix for the HiDPI clipping in this issue, and it removes the two blockers you listed: rows no longer need an icon, and a click no longer has to be handled by the tree itself.

The module keeps its name — idlelib/tree.py is now ScrolledTreeview (a ttk.Treeview with scrollbars, coloured from the configuration) and TreeWidget (a tree of TreeItems on top of it, asking an item for its children only when its row is opened). test_tree.py holds the tests for it.

Converted, in one commit because they share the widget: the Module and Path browsers, Debug ▸ Stack Viewer, the object browser, the remote stack viewer the Shell opens for a subprocess exception, and the stack, Locals and Globals panes of the Debug Control window. The stack pane was a ScrolledList listbox with its own scrollbar, popup menu and key bindings, all of which ttk provides.

The item protocol gains two methods and loses two:

• GetValues() fills the columns after the tree column, so the stack views show a frame as module, function, line and source rather than one glued string, and the Locals/Globals panes are name/value tables.
• GetTags() says what kind of row an item is, and the tree that shows it decides what a kind looks like. The Path Browser uses it to mark directories, packages and modules with the icons already in Icons/ (so a package row no longer needs ": package"); the Module Browser marks nothing.
• GetIconName() and GetSelectedIconName() go: the canvas drew an image on every row and these chose which, while a Treeview draws none unless asked. plusnode.gif and minusnode.gif go with them, as ttk draws the indicators itself.

Also closed by this, since they cannot be done separately once the drawing changes:

• IDLE: disable edits of debugger local/global vars that are not propagated. #69184 — the Locals and Globals panes are read-only tables. Editing those entries never reached the objects, which live in the user process; the panes are also sized in rows now, not in a guess at the pixel height of an entry.
• IDLE: Remove noisy icons from module browser #69277 — the Module Browser puts no icon on any line; the text of a row already says whether it is a class or a function.

The debugger's stack pane marks the frame it stopped in with an arrow and a bold row instead of prefixing the text with "> ", so rows no longer shift by two characters and the marker survives selecting another row. The arrow is drawn in code rather than read from a file, so it follows the configured font size and the theme's foreground — a shipped bitmap would be black on IDLE Dark.

• Issue: IDLE: Convert browsers to use ttk.Treeview #75733

[serhiy-storchaka]

Trying it by hand. Each module runs its unit tests and then opens its window:

./python -m idlelib.tree          # the widget itself, on the attributes of sys
./python -m idlelib.stackviewer   # Stack Viewer: exception, frames, namespaces
./python -m idlelib.pathbrowser   # Path Browser: the icons
./python -m idlelib.browser       # Module Browser
./python -m idlelib.debugobj      # object browser: Name | Value

./python -m idlelib.idle_test.htest walks all of them with instructions in the master window.

In a running IDLE (./python -m idlelib): File ▸ Module Browser (Alt-C) and File ▸ Path Browser; Debug ▸ Stack Viewer after an exception in the Shell. The Debug Control panes have no htest — the # TODO: htest? at the end of debugger.py — so for those use Debug ▸ Debugger, enter

def inner(n): return 1/n
def outer(n): return inner(n)
outer(0)

and press Step until you are inside inner.

Worth looking at:

• Keyboard: Up/Down move, Left/Right collapse and expand, Return opens a file at its line — none of which the canvas tree did.
• Stack Viewer: Name | Line | Value; a frame fills all three, an exception and a namespace only the first, a variable the first and last.
• Debug Control: Module | Function | Line | Source; the frame the debugger stopped in is bold with an arrow, and stays marked when you select another row. Locals and Globals are read-only tables, at most 15 rows tall, and a long value scrolls in its column rather than stretching the pane.
• Path Browser: closed folder for a directory, open folder for a package, Python icon for a module; expand a module and its def/class rows have no icon.
• Fonts and themes: change them in Options ▸ Configure IDLE and reopen a window — row height, colours and the debugger's arrow follow. Windows already open do not restyle themselves; that was true before as well.