perf: skip escape scan for AsciiSafeStr in the char renderer#878
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The char render path (BaseCharRenderer.visitNonNullString) ran a CharSWAR.hasEscapeChar scan on every string, even for Val.AsciiSafeStr which is statically known to need no JSON escaping (chars 0x20-0x7e, no quote/backslash). The Native ByteRenderer already had this bypass; the char path did not. - Add BaseCharRenderer.visitAsciiSafeString: quote + bulk getChars + quote, correct even under escapeUnicode since all chars are <= 0x7e. - Route Val.AsciiSafeStr through it via a Materializer.visitStr helper at the three value-string sites; the ujson.Value AST path falls back to visitString. Result: - JMH render-only (string-heavy, 335 KB): 1.606 -> 1.441 ms/op (+10%). - Scala Native, isolated and interleaved: manifestJsonEx total_time 30.6 -> 29.5 ms (~+3.6%); kube-prometheus materialize_time neutral. Output byte-identical.
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## Motivation `std.manifestJson`, `std.manifestJsonMinified`, and `std.manifestJsonEx` routed through `java.io.StringWriter`, paying `StringBuffer` synchronization per `write`/`flush` on the hot manifestation path. Source-built jrsonnet comparisons showed sjsonnet trailing on object-heavy manifest workloads. ## Modification - Add `StringBuilderWriter`: an unsynchronized `Writer` over a `StringBuilder`. - Add package-private `FastMaterializeJsonRenderer` backed by `StringBuilderWriter`; route the three `std.manifestJson*` builtins through it. Public `MaterializeJsonRenderer` ABI/shape unchanged. - Use an in-place codepoint sort for `sortedVisibleKeyNames` / `maybeSortKeys` (avoids `.sorted` boxing). - Fix codepoint comparison for raw surrogate prefixes; `UnicodeHandlingTests` extended. ## Result Scala Native hyperfine on kube-prometheus, jrsonnet HEAD `2d7eed05`: | Workload (native) | Before | After | Δ | |---|---:|---:|---:| | kube-prometheus, sjsonnet | 158.4 ± 16.8 ms | 143.7 ± 3.2 ms | **−9.3%** | | `manifestJsonEx`, sjsonnet | — | 5.09 ± 1.01 ms | new | ## Test plan - [x] `./mill __.reformat` - [x] `./mill 'sjsonnet.jvm[3.3.7]'.test` — 518/518 pass This PR is the base for the stacked follow-ups #875 (TomlRenderer reuses `StringBuilderWriter`), and the independent #876/#877/#878.
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Motivation
The char render path (
BaseCharRenderer.visitNonNullString) ran aCharSWAR.hasEscapeCharscan on every string, even forVal.AsciiSafeStr— which is statically known to need no JSON escaping (chars0x20–0x7e, no"/\). The NativeByteRendereralready had this bypass; the char path did not.Modification
BaseCharRenderer.visitAsciiSafeString:"+ bulkgetChars+", correct even underescapeUnicodesince every char is<= 0x7e.Val.AsciiSafeStrthrough it via aMaterializer.visitStrhelper at the three value-string sites; theujson.ValueAST path falls back tovisitString.Result
manifestJsonExtotal_time 30.6 → 29.5 ms (~+3.6%); kube-prometheusmaterialize_timeneutral (no regression). Output byte-identical.Test plan
./mill __.reformat./mill 'sjsonnet.jvm[3.3.7]'.test— 518/518 pass