umputun / revdiff / 33195480393

90%

master: 91%

Pull #337

github

fix(ui): bound horizontal scroll to the widest rendered line

Holding the right arrow scrolled scrollX past the widest line without limit.
Once past every line applyHorizontalScroll takes its plain-cut branch with
both overflow flags false, so every row cuts to nothing and the diff pane
goes blank with no « indicator to explain it — recoverable only by scrolling
all the way back or switching files.

Every nonzero write to scrollX now goes through setScrollX, bounded by the
widest row the pane currently renders, so a runaway offset can no longer cut
the whole document away. This does not promise every viewport shows content
at every legal offset: a wide row further down the file owns the bound, so
short rows on screen can still cut to empty. That per-line behavior lives in
applyHorizontalScroll and is pinned as deliberate by
TestModel_ApplyHorizontalScrollNoLeftIndicatorWhenScrolledPastContent.

The bound reads the rendered document rather than the loaded one: collapsed
mode hides removed lines, so a wide hidden removal must not widen it, and
expanding a hunk reveals those lines again. Delete-only placeholders are
measured from their own synthetic text.

Per-line widths are cached at load, parallel to file.lines, so the bound
costs an integer scan rather than re-measuring strings on every keypress.
The walk uses a moving hunk index rather than hunkStartFor, which rescans
the whole hunk slice per line.

Layout changes that widen the pane lower the bound without a horizontal
keypress of their own. All four — resize, tree hide, line-number and blame
toggles — already render through syncViewportToCursor, so the clamp lives
there; the two collapsed mutations render directly and clamp locally.

Related to #334, which surfaced this while asking for mouse horizontal
scroll. The mouse gesture is a separate question and stays open.

66 of 68 new or added lines in 3 files covered. (97.06%)

11608 of 12876 relevant lines covered (90.15%)

3469.07 hits per line