Broaden anchor-window clamp to CUP-park on empty trailing row (#157)#159
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Broaden anchor-window clamp to CUP-park on empty trailing row (#157)#159
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Pull request overview
This PR fixes a regression variant of the anchor-window scroll/clamp behavior (#157) by expanding the clamp guard beyond pending-wrap to also handle TUIs that CUP-position the cursor onto an empty trailing row, which can otherwise leave pt == point-max and trigger redisplay to scroll window-start.
Changes:
- Add a native render helper (
render.isRowEmptyAt) and new exported module predicateghostel--cursor-on-empty-row-p. - Broaden
ghostel--anchor-window’s clamp condition to(or pending-wrap cursor-on-empty-row). - Add ERT coverage for the new predicate and for the #157 clamp/no-clamp scenarios; bump module/package version to 0.16.3.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
ghostel.el |
Expands the clamp condition in ghostel--anchor-window and updates module version/min-version + function declaration. |
src/render.zig |
Implements isRowEmptyAt to detect rows that would render as empty buffer lines. |
src/module.zig |
Exports ghostel--cursor-on-empty-row-p and bumps native module version. |
src/ghostty.zig |
Adds DATA_CURSOR_Y constant binding used by the new predicate. |
test/ghostel-test.el |
Adds unit/regression tests for empty-row predicate and anchor-window clamp behavior. |
build.zig.zon |
Bumps package version to 0.16.3. |
evil-ghostel.el |
Bumps package version to 0.16.3. |
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dakra
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Addresses Copilot review on #159. `isRowEmptyAt' iterates the render state's viewport row iterator, so `cy' should come from the same coordinate space. `DATA_CURSOR_Y' is active-area-relative and happens to match viewport Y in the common case (viewport pinned to bottom by redraw), but the render-state pair exposes a `HAS_VALUE' flag that correctly returns nil when the cursor isn't visible in the current viewport — which is also the safe answer for the anchor-window clamp. Move `render_state_update' to `fnCursorOnEmptyRow' and drop the redundant call inside `isRowEmptyAt'; update the helper docstring to state the caller contract. Remove the now-unused `DATA_CURSOR_Y' constant.
ad8536e narrowed the `ghostel--anchor-window' clamp to fire only when libghostty reports pending-wrap, which fixed the #146 regression but reopened a variant of #138 for TUIs that move their cursor to the bottom of the screen via absolute positioning (CUP) rather than via writing-then-wrapping. In that case `pt' equals `point-max' and the cursor sits on the last viewport row, but pending-wrap is nil — so the clamp doesn't fire and Emacs shifts `window-start' by one row to make `pt' "visible," fighting the viewport pin. Expose a second terminal-side predicate `ghostel--cursor-on-empty-row-p' backed by a new `render.isRowEmptyAt' helper, and widen the clamp guard to `(or pending-wrap cursor-on-empty-row)'. The predicate returns t iff the row containing the cursor has no written cells and no cells with non-default styling — exactly the condition under which `buildRowContent' produces `byte_len == 0'. Wide-spacer-tail cells are skipped to mirror `buildRowContent' (defensive — in practice spacer tails always follow a wide grapheme). Source `cy' from `RS_DATA_CURSOR_VIEWPORT_Y' gated by `...HAS_VALUE' so the coordinate space matches the viewport row iterator that `isRowEmptyAt' walks, and the predicate returns nil when the cursor isn't visible in the current viewport. Caller owns the `ghostty_render_state_update' refresh so it only happens once per call. An earlier draft (#158) tried `pos-visible-in-window-p' but it reflects the previous redisplay rather than the just-pinned `window-start', and breaks in batch. The terminal-side predicate answers the real question — is there anything on this row to anchor `pt' to? — without consulting Emacs redisplay state. Bump module version to 0.16.3 (new exported function). Test changes: - `ghostel-test-cursor-on-empty-row-p' covers the predicate across fresh-terminal / post-write / post-CRLF / post-CUP cursor positions. - `ghostel-test-anchor-window-clamps-on-empty-row' is the #157 regression test: feeds "foo\r\nbar\r\n" to park the cursor on an empty last row, asserts PT lands at `point-max', pending-wrap is nil, empty-row is t, and the clamp fires. - `ghostel-test-anchor-window-no-clamp-on-populated-last-row' complements #146: cursor at `point-max' on a last row that does have content (e.g. a shell prompt) must NOT be clamped regardless of which predicate is consulted. Closes #157.
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Summary
Fixes the #157 variant of #138: TUIs that CUP-park their cursor onto an empty trailing row (e.g. Claude Code on focus loss per the reporter's evidence) hit the same `pt = point-max` / window-start-shift symptom that #138 fixed, but without pending-wrap — so the `ad8536e` clamp narrowing lets them through.
Adds a second terminal-side predicate `ghostel--cursor-on-empty-row-p` (backed by a new `render.isRowEmptyAt` helper) and broadens the `ghostel--anchor-window` clamp guard to `(or pending-wrap cursor-on-empty-row)`. Predicate returns t iff the cursor's row has no written cells and no non-default styling — exactly when `buildRowContent` produces `byte_len == 0`.
Why not `pos-visible-in-window-p` (the approach in the now-closed #158): it reflects the previous redisplay, not the `window-start` we just pinned under `inhibit-redisplay`, and returns nil in batch — breaks existing tests. Terminal-side predicate answers the question without needing redisplay state.
Module version bumped 0.16.2 → 0.16.3 (new exported function).
Test plan