mapsize/rust/README.md

mapsize — Rust port

A port of the Go implementation (repo root) to Rust, with the same CLI, TUI, keys, themes and snapshot format. .msz snapshots are byte-compatible in both directions. The code is Linux/Unix only; the Windows code paths were not ported.

cd rust
cargo build --release          # target/release/mapsize
cargo test --release           # 69 tests (ported from the Go suites, fuzz tests excepted)

Module layout mirrors internal/: inventory, scan, platform, treemap, filter, snapshot (+ compare), duplicate, export, config, textutil, tui, app. The tree is shared as Arc<RwLock<Tree>> with the same single-writer invariants as ARCHITECTURE.md; cancel::Cancel replaces context.Context; crossterm replaces Bubble Tea as the event loop (the canvas renderer is ported as-is, plus line-diffed frame output).

Known differences from Go

• --log/--log-level are accepted but there is no debug log yet.
• A scanner thread panic restores the terminal and aborts the process instead of returning an "internal error" message.
• The colour profile is detected from NO_COLOR/TERM/COLORTERM only (no terminal query); --color still overrides.
• JSON export does not HTML-escape <>&; started is written in UTC.
• The filter lexer no longer hangs on queries containing bytes Go treats as white space but never skips (e.g. voilà, whose UTF-8 contains 0xA0).
• Huge sizes saturate rather than wrap in filters and snapshot comparison.

Benchmarks

Machine: Intel Core i7-7700 (4C/8T), 32 GiB, ext4 on md RAID over 7200 rpm HDDs. Go 1.27.1, Rust 1.91.1 (lto, codegen-units = 1). The host was shared and heavily loaded during the runs (load average 30–50 on 8 threads), so absolute times are inflated 2–4× compared with PERFORMANCE.md. To keep the comparison fair, Go and Rust runs were interleaved and the tables report best-of (micro) or median and best (end-to-end). Re-run on an idle machine before quoting absolute numbers:

go test -c -o /tmp/tui.test ./internal/tui && go test -c -o /tmp/treemap.test ./internal/treemap
(cd rust && cargo build --release --example bench)
rust/bench/micro.py /tmp/tui.test /tmp/treemap.test rust/target/release/examples/bench 5
rust/bench/compare.py bin/mapsize rust/target/release/mapsize ~/go/pkg/mod 7

In-process (Go go test -bench suite vs examples/bench.rs)

The tree is 1,008,201 synthetic nodes, rendered at 200×60.

benchmark	Go	Rust	speed-up
treemap/Squarify(300)	299.3 µs	22.2 µs	13.48×
treemap/Neighbour(300)	5.0 µs	2.8 µs	1.76×
tui/BigColdFrame	86.88 ms	29.32 ms	2.96×
tui/BigResize	7.15 ms	4.76 ms	1.50×
tui/BigFlatDirCold	86.33 ms	22.90 ms	3.77×
tui/BigNavigate	4.85 ms	4.07 ms	1.19×
tui/BigFilter/size > 1MB	78.62 ms	59.51 ms	1.32×
tui/BigFilter/*.dat AND size > 500k	302.03 ms	154.90 ms	1.95×
tui/BigFilter/path contains sub3	337.79 ms	136.85 ms	2.47×

End to end (~/go/pkg/mod: 388k files + 65k dirs, warm cache)

scenario	Go median	Rust median	Go best	Rust best	Go RSS	Rust RSS	speed-up
scan, 1 workers	4.68 s	5.51 s	4.34 s	4.86 s	114 MB	75 MB	0.85×
scan, 8 workers	2.03 s	2.03 s	1.61 s	1.42 s	113 MB	78 MB	1.00×
scan, 32 workers	3.09 s	2.59 s	2.85 s	2.07 s	116 MB	89 MB	1.19×
scan + save snapshot	4.69 s	3.60 s	4.02 s	3.29 s	117 MB	80 MB	1.30×
load own snapshot	1.20 s	0.71 s	0.71 s	0.48 s	85 MB	78 MB	1.69×
load Go snapshot	1.03 s	1.14 s	0.84 s	0.48 s	85 MB	78 MB	0.90×
scan + JSON export	6.10 s	4.74 s	5.44 s	4.16 s	152 MB	79 MB	1.29×
scan + top 50 largest files	4.49 s	4.31 s	3.62 s	3.65 s	117 MB	79 MB	1.04×

Reading the numbers:

• Scanning is syscall-bound (statx/getdents were about 60% of Go's profile), so wall time is roughly at parity. Rust edges ahead at high worker counts. The single-worker case is about 15% slower, but that run was the noisiest of the set.
• Memory: peak RSS is 30–48% lower (78 MB vs 113 MB while scanning 458k nodes). The JSON export streams without Go's per-node allocations (79 MB vs 152 MB).
• Snapshots: loading is about 1.7× faster on the median. The two binaries load each other's files.
• UI: cold frames are 3–3.8× faster, and squarified layout is about 13× faster. Navigation and resize gain less (1.2–1.5×) because they mostly reuse cached layout.
• Filters: 1.3–2.5× faster. This required caching lower-cased directory paths in a Vec with reused buffers, and a *.ext fast path in the filepath.Match port.