Intentional deviation from Ghostty 1.3.1 (DEVIANT_FIXES.md entry 10).
Two terminal inputs reach states that Zig handles only by assertion
(Debug/ReleaseSafe abort; ReleaseFast continues):
- Toggling mode 2027 around a BOM before a wide character hits
`assert(!b)` in print_grapheme. This repository's release profile
keeps debug assertions, so terminal output could crash a release
build. The assertion is removed and the path behaves like Zig
ReleaseFast.
- A grapheme (e.g. a Devanagari conjunct) at the right margin on the
bottom row with scrolling margins returned InvalidCoordinate and left
a grapheme flag without data, panicking later in the formatter. The
grapheme now moves from the cell that actually holds it and no cell is
flagged without data.
tools/difftest gains a Rust-only panic hunt (`difftest_fuzz panics`,
lenient driver): ~60k debug-build cases now run without any panic, and
3000 Zig differential cases show 0 divergences.
Test Plan:
- cargo test -p ghostty-terminal difftest_mode_2027_toggle_with_bom_does_not_panic
difftest_grapheme_wrap_scrolling_margins_keeps_grapheme
- cargo run -p difftest --bin difftest_fuzz -- panics
Adds tools/difftest: a Zig driver built against a copy of Ghostty
1.3.1's own src/terminal (Zig 0.15.2, set up under target/ by
tools/difftest/setup.sh) and a Rust twin on ghostty-terminal, both
printing a canonical dump of every scrollback/active row (cells,
graphemes, styles, hyperlinks, row flags), cursor, modes, regions,
tabstops and colors. A seeded generator produces escape-heavy streams
(UTF-8/wide/combining/emoji, C0, CSI with edge params, SGR, modes, ESC,
OSC, DCS, margins, insert/delete); `just difftest` runs it with Zig
assertions on (ReleaseSafe vs debug Rust) and off (ReleaseFast vs
production Rust), with minimizers and a triage script.
Divergences found and fixed in Rust (each with a regression test):
- ill-formed UTF-8 decoding follows the SIMD path a default Ghostty
build uses (not Zig's scalar fallback)
- PageList::erase_rows keeps Zig's row-flag behavior on regrow
- grapheme move on wrap with left/right margins uses the original cell
Upstream bugs found and deliberately NOT replicated (per the project
rule): a stale cell pointer after page growth in Terminal.zig:482/539
that drops a grapheme, plus several Zig assertion failures/segfaults;
documented with minimized repros in docs/rewrite/notes/difftest-DF.md.
Final run: 390k cases across many geometries, 0 divergences (Zig-abort
cases, ~0.1-0.5%, are not compared).
Test Plan:
- just difftest 20000 "1 2 3"
- cargo test -p ghostty-terminal (regression tests)
ddidderr