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fix(arithmetic): bound nested dollar expansion - #2668
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Negative indices need bash 4.3+; macOS ships bash 3.2 while Linux CI
has bash 5.x, so ${a[-1]} makes the assertion environment-dependent.
${a[i-0]} still exercises arithmetic inside the subscript everywhere.
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## What changed Nested arithmetic dollar expansion (`$((...))` inside `$((...))`) no longer escapes the shared evaluation budget. Each nested expansion now charges fuel and borrows the parent budget instead of starting fresh, so hostile nesting aborts with a bounded error instead of exhausting the stack. ## Why Finding arter-y7s8: textual expansion ran before the shared depth/fuel checks, and every recursive `$((...))` got a brand-new budget, so the 8-deep / 1024-byte limits never engaged across nesting levels. ## Before / After Sensor (`echo \$((1+\` x 5000 + `1\` + `))\` x 5000`): - Before: never returns (stack exhaustion, unbounded diagnostics). - After: exits 1 in ~2.7s, 327-byte stderr ending in `expression recursion level exceeded`. Tests: 7 regression tests in `arithmetic_resource_tests.rs` (recursion aborts, valid nesting keeps working, bash parity within limits); 40/40 arithmetic integration tests pass. `cargo fmt`, `clippy --all-targets`, `cargo vet`, capability/OKF/doc-link/workflow/changelog checks all green. Note (macOS-local only, unrelated paths, Linux CI is the gate): `blackbox depth_50 cmd-subst` test needs a bigger thread stack locally (passes with `RUST_MIN_STACK=16777216`); `scripts/tests` python suite needs Python 3.11+ (local python is 3.9). ## Risk - Low: only the arithmetic evaluation path; valid expressions (nesting <= 8, subscripts, namerefs) verified unchanged against real bash. - What can break: scripts relying on >8-deep arithmetic nesting now get an error instead of a hang. ## Checklist - [x] Tests added or updated - [x] Backward compatibility considered (internal code, no compat needed) Produced by [yolop](https://everruns.com/yolop)
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What changed
Nested arithmetic dollar expansion (
$((...))inside$((...))) no longer escapes the shared evaluation budget. Each nested expansion now charges fuel and borrows the parent budget instead of starting fresh, so hostile nesting aborts with a bounded error instead of exhausting the stack.Why
Finding arter-y7s8: textual expansion ran before the shared depth/fuel checks, and every recursive
$((...))got a brand-new budget, so the 8-deep / 1024-byte limits never engaged across nesting levels.Before / After
Sensor (
echo \$((1+\x 5000 +1\+))\x 5000`):expression recursion level exceeded.Tests: 7 regression tests in
arithmetic_resource_tests.rs(recursion aborts, valid nesting keeps working, bash parity within limits); 40/40 arithmetic integration tests pass.cargo fmt,clippy --all-targets,cargo vet, capability/OKF/doc-link/workflow/changelog checks all green.Note (macOS-local only, unrelated paths, Linux CI is the gate):
blackbox depth_50 cmd-substtest needs a bigger thread stack locally (passes withRUST_MIN_STACK=16777216);scripts/testspython suite needs Python 3.11+ (local python is 3.9).Risk
Checklist
Produced by yolop