[vogella]

Full-screen CLIs such as Codex in --no-alt-screen mode render through DECSTBM scroll regions anchored at the top of the screen and scroll by emitting newlines at the region bottom. The emulator scrolled such a region in place and discarded the displaced top line, so no scroll-back history was created and the output could not be scrolled backwards.

Like xterm and VTE, a newline at the bottom of a scroll region whose top margin is the top of the screen now moves the displaced top line into the scroll-back history, while the lines below the region keep their position on the screen. Regions with a lower top margin still scroll in place, guarded by the characterization tests from #2701; the test documenting the old top-anchored behavior is flipped to assert the history is created.

This addresses the missing backward scrolling reported in #2680.

[github-actions]

Test Results

    54 files  ±0      54 suites  ±0   37m 53s ⏱️ -40s
 5 007 tests +3   4 985 ✅ +3   22 💤 ±0  0 ❌ ±0 
12 912 runs  +9  12 758 ✅ +9  154 💤 ±0  0 ❌ ±0 

Results for commit 9c5d82b. ± Comparison against base commit bc125e3.

This pull request removes 1 and adds 4 tests. Note that renamed tests count towards both.

org.eclipse.terminal.internal.emulator.VT100EmulatorBackendTest ‑ testNewlineInTopAnchoredScrollRegionCurrentlyDiscardsTopLine

org.eclipse.terminal.internal.emulator.VT100EmulatorBackendTest ‑ testNewlineInTopAnchoredScrollRegionCoveringWholeScreen
org.eclipse.terminal.internal.emulator.VT100EmulatorBackendTest ‑ testNewlineInTopAnchoredScrollRegionMovesTopLineToHistory
org.eclipse.terminal.internal.emulator.VT100EmulatorBackendTest ‑ testNewlineInTopAnchoredScrollRegionWithFullHistoryDropsOldestLine
org.eclipse.terminal.internal.emulator.VT100EmulatorBackendTest ‑ testNewlineInTopAnchoredScrollRegionWithFullHistoryNotifiesScrollToSnapshots

♻️ This comment has been updated with latest results.

[stefano-1973]

It seems to work:

[Copilot]

🟡 Changes recommended

When history is full and a footer is present, footer scrolling discards the upward-scroll notification, causing selections to be cleared even though the selected text survives.

1 open issue

• Preserve selections when scrolling a full history with a footer · New

What changed in this PR

This PR updates the terminal emulator to preserve scroll-back history for top-anchored scroll regions, addressing the missing backward scrolling reported in #2680.

Changes:

• Retains displaced top lines in history while keeping footer lines fixed.
• Updates the characterization test from #2701 and adds coverage for full history and whole-screen regions.

File	Description
terminal/​tests/​org.eclipse.terminal.test/​src/​org/​eclipse/​terminal/​internal/​emulator/​VT100EmulatorBackendTest.java	Verifies history retention, capacity limits, footer stability, and cursor position.
terminal/​bundles/​org.eclipse.terminal.control/​src/​org/​eclipse/​terminal/​internal/​emulator/​VT100EmulatorBackend.java	Routes top-anchored newline scrolling into history and restores footer positioning.

_{Review effort: Balanced}

[akurtakov]

My test which this PR fixes:
In a terminal in the runtime Eclipse, run clear and then vim -u NONE -N --cmd 'set t_ti= t_te=' /etc/services. The --cmd 'set t_ti= t_te=' keeps Vim off the alternate screen, and it has to be --cmd, because with -c Vim has already switched. Hold j (or press Ctrl-E repeatedly) well past the bottom of the screen, then quit with :q and scroll up. Vim scrolls each line with a scroll region over every row except its status line and a newline at the bottom of that region, so on master those lines are thrown away and the history is empty. With #2764 they go into the history, and you'll see /etc/services from its first line (# /etc/services:) onward, above the prompt.

[Copilot]

🟡 Changes recommended

The scroll optimization leaves stale text in unused ring slots that addLine() later exposes, causing incorrect content when the terminal grows after scrolling.

1 open issue

• Restrict scroll rotation to a full ring · New

1 resolved since last review

• Preserve selections when scrolling a full history with a footer

_{Review effort: Balanced}

[vogella]

My test which this PR fixes: In a terminal in the runtime Eclipse, run clear and then vim -u NONE -N --cmd 'set t_ti= t_te=' /etc/services. The --cmd 'set t_ti= t_te=' keeps Vim off the alternate screen, and it has to be --cmd, because with -c Vim has already switched. Hold j (or press Ctrl-E repeatedly) well past the bottom of the screen, then quit with :q and scroll up. Vim scrolls each line with a scroll region over every row except its status line and a newline at the bottom of that region, so on master those lines are thrown away and the history is empty. With #2764 they go into the history, and you'll see /etc/services from its first line (# /etc/services:) onward, above the prompt.

This statement is hard for me to read, but I think this desribes a positive result of testing the PR.

Planning to merge tomorrow, please clarify in case my understanding of the above it not correct.