core: portable shell scanner takes quadratic time in the argument count #59165

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1. opencode-agent commented on Oct 26, 2026

   

   opencode-agentBot

   on Oct 26, 2026 – with OpenCode Agent

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   Thanks for the clear report and numbers. I could reproduce this by calling ShellScan.scan(..., "bash") directly on v2.1.4, and it still happens on the latest dev (c54677bece).

   When the argument count doubles, the scan takes about four times as long. Timings at 2000 / 8000 / 16000 args on v2.1.4:

   • printf a a ...: 65 / 665 / 2517 ms
   • set a a ...: 27 / 309 / 1663 ms
   • declare -a -a ...: 53 / 819 / 3329 ms
   • command command ... ls: 37 / 523 ms
   • echo a a ... (control): 1 / 6 / 8 ms

   Latest dev gives nearly the same numbers (e.g. printf 2504 ms and declare 3163 ms at 16000 args). That is well past the 500 ms budget the existing bounded-time tests use. The cause matches your description: for every word, bashWordEvaluation re-walks the precommand chain in bashBuiltinIndex and copies all earlier words with state.words.slice(name + 1).

   The script below reproduces it; pass it the path to an OpenCode checkout. Your PR #59163 addresses this and is still open.

   Reproduction script (scan-timing.ts)

   // Usage: bun /workspace/repro/scan-timing.ts <path-to-opencode-checkout>
   const repo = process.argv[2] ?? "/workspace/repo"
   const { ShellScan } = await import(`${repo}/packages/core/src/shell/scan.ts`)
   const cases: Record<string, (n: number) => string> = {
     "printf a a ...": (n) => "printf " + "a ".repeat(n),
     "set a a ...": (n) => "set " + "a ".repeat(n),
     "declare -a -a ...": (n) => "declare " + "-a ".repeat(n),
     "command command ... ls": (n) => "command ".repeat(n) + "ls",
     "echo a a ... (control)": (n) => "echo " + "a ".repeat(n),
   }
   for (const [name, build] of Object.entries(cases)) {
     const row: string[] = []
     for (const n of [2000, 8000, 16000]) {
       const input = build(n)
       const t = performance.now()
       ShellScan.scan(input, "bash")
       row.push(`${n}: ${(performance.now() - t).toFixed(0)} ms`)
     }
     console.log(name.padEnd(26), row.join("  "))
   }

   Run it: bun scan-timing.ts
2. opencode-agent

   added

   reproduced

   on Oct 26, 2026