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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854

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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
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enhancementNew feature or request

Description

@Chemaclass
Chemaclass
opened on Jul 24, 2026

🎯 Goal (SPIKE + ADR — not a straight merge)

Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.

📍 Current mechanism

  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).

💡 Hypothesis

set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.

Sketch:

exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set

🔬 What the spike must answer

  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.

📦 Deliverables

  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.

✅ Definition of done (for the spike)

  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.

⛓️ Constraints

  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).

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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
Assignees
Chemaclass
Labels
enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
Skip to content
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
Closed
Closed
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
Assignees
Chemaclass
Labels
enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
Metadata
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
Skip to content
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
Closed
Closed
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
Assignees
Chemaclass
Labels
enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
Metadata
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enhancementNew feature or request
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
Skip to content
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
Closed
Closed
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
Assignees
Chemaclass
Labels
enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
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enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
Metadata
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    Done
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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
Skip to content
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
Closed
Closed
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
Assignees
Chemaclass
Labels
enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
Metadata
Metadata
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enhancementNew feature or request
Type
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Projects
  • bashunit
    Status
    Done
Milestone
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Issue actions

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spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) · Issue #854 · TypedDevs/bashunit · GitHub
Skip to content
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR) #854
Closed
Closed
spike(coverage): benchmark BASH_XTRACEFD tracing vs the per-line DEBUG trap (ADR)#854
Assignees
Chemaclass
Labels
enhancementNew feature or request
Description
@Chemaclass
Chemaclass
opened on Jul 24, 2026
🎯 Goal (SPIKE + ADR — not a straight merge)
Prototype and benchmark replacing the per-line DEBUG-trap coverage mechanism with set -x / BASH_XTRACEFD tracing to a dedicated file descriptor + offline parse. Decide, with numbers, whether it can make --coverage fast enough to run on every CI job (gating) instead of nightly-only.
📍 Current mechanism
  • DEBUG trap → bashunit::coverage::record_line "$BASH_SOURCE" "$LINENO" on every executed line (src/coverage.sh:126, enable at :115-127). This invokes a full shell function per line — that dispatch is the dominant cost and the reason coverage is nightly/non-gating (.github/workflows/coverage.yml).
💡 Hypothesis
set -x with a controlled PS4 writes one trace line per executed command at C level to BASH_XTRACEFD, with no per-line shell-function call. Parsing that trace once after the run could be an order of magnitude cheaper than the DEBUG-trap callback. This is the mechanism bashcov/kcov-style tooling leans on.
Sketch:
exec {cov_fd}>coverage.trace # NB: {var}>… is Bash 4.1+; on 3.x use a fixed high FDexport PS4='@@COV@@${BASH_SOURCE}:${LINENO}@@ '
BASH_XTRACEFD=$cov_fdset -x
# … run test body …set +x
# offline: grep '^@@COV@@' coverage.trace, strip, sort -u → covered file:line set
🔬 What the spike must answer
  1. Speed: wall-time of the unit suite under --coverage via xtrace vs. the current DEBUG trap, on Bash 3.2 (macOS) and Bash 5 (Linux). Include parse time. This is the whole point — quantify it.
  2. Bash 3.0 floor:BASH_XTRACEFD exists (Bash 4.1+). On Bash 3.x it does not — xtrace goes to stderr, which collides with test output. Determine the fallback: (a) fixed high FD redirect that works on 3.x, (b) DEBUG-trap retained as the 3.x path with xtrace as a 4.1+ fast path, or (c) xtrace-only with a documented Bash-4.1 floor for --coverage (core stays 3.0). Recommend one.
  3. Correctness: can PS4+trace reconstruct the same covered-line set as the DEBUG trap? Handle: multi-line statements (the DEBUG trap's attribution quirk, src/coverage.sh:668), subshells/pipes, functions, sourced files, and the framework's own lines (must be excluded — the trace will include bashunit internals).
  4. Per-test attribution: DEBUG-trap fills the hits buffer with file:line|testfile:testfn (src/coverage.sh:299). Reproduce by emitting a marker into the trace at each start_test and partitioning the trace by marker.
  5. Interference: tests that run set -x / set their own PS4 / read $BASH_XTRACEFD; spies/mocks; --parallel workers (each needs its own trace FD/file). Enumerate the collisions and whether they're containable.
  6. Noise/size: trace files can be huge and expansion-noisy (quoting, command args). Measure size and parse robustness.
📦 Deliverables
  • A branch with a working prototype (behind an env flag, e.g. BASHUNIT_COVERAGE_ENGINE=xtrace|trap) — enough to benchmark, not necessarily production-complete.
  • Benchmark numbers (table: engine × bash version × suite → wall + parse time + trace size).
  • adrs/adr-009-coverage-tracing-engine.md recording the decision (adopt / adopt-as-fast-path / reject) with the evidence. Follow adrs/TEMPLATE.md; reference ADR-007 (branch MVP) and ADR-008.
  • If ADR = adopt: a follow-up implementation issue with the migration + fallback plan.
✅ Definition of done (for the spike)
  • ADR merged with a clear recommendation backed by measured numbers on both bash versions.
  • No change to the shipped default engine unless the ADR explicitly approves it and the full gate (./bashunit tests/, --parallel --simple --strict, make sa, make lint) is green with per-test attribution + --parallel merge preserved.
⛓️ Constraints
  • Do not break the Bash 3.0 floor for the framework core. --coverage may adopt a higher floor only if the ADR justifies it and the trap path remains as the 3.x fallback, or the raised floor is explicitly accepted.
  • Depends on / composes with the per-line dedup issue (that reduces trap-path cost; the spike compares against the improved trap baseline).
Metadata
Metadata
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enhancementNew feature or request
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  • bashunit
    Status
    Done
Milestone
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