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fix(tui): preserved bottom-anchored viewport during offscreen shrink

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- Added cursor remapping support to deferredMutation intents and emitted cursor positions when deferring offscreen mutations.
- Introduced planDeferredShrink to defer bottom-anchored offscreen deletions only when displayed rows were byte-identical, otherwise repainted the viewport.
- Added regression tests covering unknown-win32 offscreen middle-shrink behavior, including cursor-only moves and tail-content-change cases.
This commit is contained in:
can1357
2026-06-04 05:37:39 +02:00
parent b5c82a9274
commit 40ba8c19cf
2 changed files with 156 additions and 4 deletions
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packages/tui/src/tui.ts
+52 -4
View File
@@ -306,6 +306,11 @@ export class Container implements Component {
}
}
interface DeferredCursorUpdate {
position: { row: number; col: number } | null;
totalLines: number;
}
/**
* Render intent. `#planRender` decides which one a frame is, and the
* corresponding `#emit*` method owns the bytes written and the state update.
@@ -324,7 +329,10 @@ export class Container implements Component {
* native history. Keep row indices stable with blank tail padding, repaint
* only the viewport, and defer the real shorter replay to a checkpoint.
* - `deferredMutation`: a row-inserting edit would reindex native scrollback
* while the user is scrolled. Defer all bytes until a safe rebuild checkpoint.
* while the user is scrolled, or an offscreen-only shrink left the visible
* rows byte-identical (merely renumbered). Defer the content bytes until a
* safe rebuild checkpoint; a remapped cursor update may still be emitted so a
* caret-only move lands while the preserved rows stay put.
* - `shrink`: trailing rows were dropped — clear extras inline.
* - `diff`: differential repaint of visible rows / append new rows below.
*/
@@ -336,7 +344,7 @@ type RenderIntent =
| { kind: "overlayRebuild" }
| { kind: "viewportRepaint"; appendFrom?: number }
| { kind: "deferredShrink"; paddedLength: number }
| { kind: "deferredMutation" }
| { kind: "deferredMutation"; cursor?: DeferredCursorUpdate }
| { kind: "shrink" }
| { kind: "diff"; firstChanged: number; lastChanged: number; appendedLines: boolean };
@@ -1389,6 +1397,7 @@ export class TUI extends Container {
// 3. Classify intent.
const intent = this.#planRender(
lines,
cursorPos,
widthChanged,
heightChanged,
prevViewportTop,
@@ -1455,6 +1464,7 @@ export class TUI extends Container {
this.#emitViewportRepaint(lines, width, height, cursorPos);
return;
case "deferredMutation":
if (intent.cursor) this.#writeCursorPosition(intent.cursor.position, intent.cursor.totalLines);
return;
case "deferredShrink":
this.#emitViewportRepaint(
@@ -1483,6 +1493,43 @@ export class TUI extends Container {
}
}
/**
* Resolve a content shrink that re-exposes committed scrollback rows into the
* safe deferred intent. `deferredShrink` blank-pads the tail to keep the
* viewport's pre-shrink absolute indices — correct only when the rows above
* the change are unchanged (a pure trailing shrink). An offscreen *middle*
* deletion shifts every later row up, so that padded slice would draw
* post-shift content at the old viewport indices and hide the live rows. For
* an offscreen-only change, compare the new bottom-anchored viewport against
* the still-displayed window: when they match the visible set is merely
* renumbered, so a no-op preserves it (re-anchoring the cursor onto the
* displayed rows); when the visible tail truly changed, repaint it. A change
* landing at or inside the viewport keeps `deferredShrink`, whose blank-pad
* semantics are correct for visible drops/edits.
*/
#planDeferredShrink(
newLines: string[],
height: number,
paddedViewportTop: number,
firstChanged: number,
cursorPos: { row: number; col: number } | null,
): RenderIntent {
if (firstChanged < paddedViewportTop) {
const newViewportTop = Math.max(0, newLines.length - height);
for (let row = 0; row < height; row++) {
if ((newLines[newViewportTop + row] ?? "") !== (this.#previousLines[paddedViewportTop + row] ?? "")) {
return { kind: "viewportRepaint" };
}
}
const mappedCursor =
cursorPos === null
? null
: { row: paddedViewportTop + (cursorPos.row - newViewportTop), col: cursorPos.col };
return { kind: "deferredMutation", cursor: { position: mappedCursor, totalLines: this.#previousLines.length } };
}
return { kind: "deferredShrink", paddedLength: this.#previousLines.length };
}
/**
* Map the current frame onto a single render intent. Order matters: forced
* resets and session replacement short-circuit before any diff work. A real
@@ -1493,6 +1540,7 @@ export class TUI extends Container {
*/
#planRender(
newLines: string[],
cursorPos: { row: number; col: number } | null,
widthChanged: boolean,
heightChanged: boolean,
prevViewportTop: number,
@@ -1594,7 +1642,7 @@ export class TUI extends Container {
if (newLines.length <= paddedViewportTop) {
return { kind: "deferredMutation" };
}
return { kind: "deferredShrink", paddedLength: this.#previousLines.length };
return this.#planDeferredShrink(newLines, height, paddedViewportTop, diff.firstChanged, cursorPos);
}
// Non-ED3-risk POSIX with an unobservable viewport. If the shrink still
@@ -1607,7 +1655,7 @@ export class TUI extends Container {
return { kind: "historyRebuild" };
}
this.#markNativeScrollbackDirty();
return { kind: "deferredShrink", paddedLength: this.#previousLines.length };
return this.#planDeferredShrink(newLines, height, paddedViewportTop, diff.firstChanged, cursorPos);
}
// Multiplexer panes do not give us a safe native-history rebuild path, but
packages/tui/test/render-regressions.test.ts
+104
View File
@@ -2048,6 +2048,110 @@ describe("TUI terminal-state regressions", () => {
tui.stop();
}
});
it("preserves bottom-anchored viewport across an offscreen middle-shrink on unknown win32", async () => {
// Repro for #1809: `win32-unknown-small` blanked the visible window after a
// `deleteMiddle` far above the viewport. The shrink fell into the deferred
// fallback, which blank-pads the tail to keep pre-shrink absolute indices —
// correct only for trailing shrinks. An offscreen middle deletion shifts
// later rows up, so the padded slice at the old viewport indices showed
// post-shift content and dropped the live rows. The fix keeps the no-op
// when the new bottom-anchored window equals the displayed one.
const originalPlatform = process.platform;
Object.defineProperty(process, "platform", { configurable: true, value: "win32" });
const term = new UnknownViewportTerminal(32, 6);
const tui = new TUI(term);
const initial = rows("line-", 30);
const component = new MutableLinesComponent(initial);
tui.addChild(component);
try {
tui.start();
await settle(term);
expect(visible(term).map(l => l.trim())).toEqual(["line-24", "line-25", "line-26", "line-27", "line-28", "line-29"]);
// Delete one offscreen row (index 5): the last six rows are unchanged,
// only their absolute indices shift.
component.setLines([...initial.slice(0, 5), ...initial.slice(6)]);
tui.requestRender(true, { allowUnknownViewportMutation: true });
await settle(term);
expect(visible(term).map(l => l.trim())).toEqual(["line-24", "line-25", "line-26", "line-27", "line-28", "line-29"]);
} finally {
Object.defineProperty(process, "platform", { configurable: true, value: originalPlatform });
tui.stop();
}
});
it("repaints the viewport when an offscreen shrink also changes the visible tail", async () => {
const originalPlatform = process.platform;
Object.defineProperty(process, "platform", { configurable: true, value: "win32" });
const term = new UnknownViewportTerminal(32, 6);
const tui = new TUI(term);
const initial = rows("line-", 30);
const component = new MutableLinesComponent(initial);
tui.addChild(component);
try {
tui.start();
await settle(term);
// Offscreen deletion AND a visible tail change: the no-op would freeze
// the stale tail, so the renderer must repaint the true bottom.
component.setLines([...initial.slice(0, 5), ...initial.slice(6, -1), "prompt-updated"]);
tui.requestRender(true, { allowUnknownViewportMutation: true });
await settle(term);
expect(visible(term).map(l => l.trim())).toEqual(["line-24", "line-25", "line-26", "line-27", "line-28", "prompt-updated"]);
} finally {
Object.defineProperty(process, "platform", { configurable: true, value: originalPlatform });
tui.stop();
}
});
it("preserves a cursor-only tail move while deferring an offscreen shrink on unknown win32", async () => {
const originalPlatform = process.platform;
Object.defineProperty(process, "platform", { configurable: true, value: "win32" });
const term = new UnknownViewportTerminal(32, 6);
const tui = new TUI(term);
const initial = [...rows("line-", 29), `prompt>a${CURSOR_MARKER}b`];
const component = new MutableLinesComponent(initial);
tui.addChild(component);
try {
tui.start();
await settle(term);
expect(term.getCursor()).toEqual({ row: 5, col: "prompt>a".length });
// Offscreen deletion; the visible rows are byte-identical after stripping
// CURSOR_MARKER, but the caret moves to the end. The deferred no-op must
// still emit the remapped cursor.
component.setLines([...initial.slice(0, 5), ...initial.slice(6, -1), `prompt>ab${CURSOR_MARKER}`]);
tui.requestRender(true, { allowUnknownViewportMutation: true });
await settle(term);
expect(visible(term).map(l => l.trim())).toEqual(["line-24", "line-25", "line-26", "line-27", "line-28", "prompt>ab"]);
expect(term.getCursor()).toEqual({ row: 5, col: "prompt>ab".length });
} finally {
Object.defineProperty(process, "platform", { configurable: true, value: originalPlatform });
tui.stop();
}
});
it("preserves bottom-anchored viewport across an offscreen middle-shrink on unknown ED3 eager-off", async () => {
// The same guard covers the ED3-risk eager-off deferredShrink site (the
// non-forced path, where the viewport probe is unobservable and the user
// may be following the live tail). An offscreen-only delete must keep the
// visible rows, not blank-pad shifted content.
await withTerminalRisk(true, async () => {
const term = new UnknownViewportTerminal(32, 6);
const tui = new TUI(term);
const initial = rows("line-", 30);
const component = new MutableLinesComponent(initial);
tui.addChild(component);
try {
tui.start();
await settle(term);
component.setLines([...initial.slice(0, 5), ...initial.slice(6)]);
tui.requestRender();
await settle(term);
expect(visible(term).map(l => l.trim())).toEqual(["line-24", "line-25", "line-26", "line-27", "line-28", "line-29"]);
} finally {
tui.stop();
}
});
});
it("defers bottom-anchored shrink when POSIX viewport state is unknown", async () => {
// Repro for #1566 follow-up (kitty/Linux): a bottom-anchored shrink across the
// viewport boundary used to fall through to `viewportRepaint`, which redrew the