perf(runner): resolve a test's source location only when needed

.claude/rules/perf-fork-budget.md

@@ -191,7 +191,11 @@ them:
   that does used to cost five more forks per test (#1345), which is why that
   never showed up here. A census fixture only measures the path it exercises.
 - **Not the capture subshell.** A bare `$( )` costs ~0.46 ms here, about 6% of
-  the 7.8 ms. The rest is bash work in the per-test machinery.
+  the 7.8 ms. The rest is bash work in the per-test machinery. That 0.46 ms
+  predates arm64 and must not be reused for estimates: the same measurement on
+  macOS arm64 (bash 3.2.57) is 1.1-1.4 ms, and a subshell that also runs
+  `shopt`/`declare` in it, 1.08 ms (#1346). A subshell per test is worth
+  removing on that hardware even when this note says it is not the bottleneck.
 - **Not quadratic.** Per-test cost is 7.17 ms at 100 tests and 8.06 ms at 1000
   -- +12% over a 10x range, so the #830 fn-accumulation fix still holds. A
   regression there would show as per-test cost climbing with suite size.

CHANGELOG.md

@@ -3,6 +3,8 @@
 ## Unreleased
 
 ### Changed
+- Performance: a sequential run is about 0.7ms faster per test — a 500-test file went from 2.75s to 2.40s on macOS arm64, bash 3.2. Every test forked a subshell to read its own definition line, for a `<file>:<line>` that only a failure message and a report row ever use. It is resolved on demand now (#1346)
+- A standalone `bashunit assert <fn> …` no longer reports a source location belonging to another process. Launched from inside a test, it inherited that test's exported location and printed it as its own (#1346)
 - Performance: a test in a file that defines `set_up` or `tear_down` is about 2.6x faster, which brings it level with a hookless test (14.1ms to 5.4ms per test on macOS arm64, bash 3.2). Each hook minted its output file with `mktemp` and removed it with `rm`, and the ownership marker that left behind made the runner `rm -rf` the test's temp files at exit — five forks per test, even for a test that created no temp file of its own (#1345)
 
 ### Fixed

src/console/test_line.sh

@@ -46,6 +46,7 @@ function bashunit::console_results::print_successful_test() {
 # is unknown. Used to append source context to failure output.
 ##
 function bashunit::console_results::test_location_suffix() {
+  bashunit::runner::ensure_test_location
   local location=${_BASHUNIT_TEST_LOCATION:-}
   if [ -z "$location" ]; then
     return 0

src/reports/collect.sh

@@ -100,7 +100,10 @@ function bashunit::reports::add_test() {
 
   # Capture the line number from the current test location ("file:line"),
   # but only when it belongs to this test's file, so a stale location from a
-  # prior test never mislabels this entry.
+  # prior test never mislabels this entry. Resolved here rather than per test:
+  # reports are opt-in and this function has already returned when they are off
+  # (#1346).
+  bashunit::runner::ensure_test_location
   local line=""
   case "${_BASHUNIT_TEST_LOCATION:-}" in
     "$file":*) line="${_BASHUNIT_TEST_LOCATION##*:}" ;;

src/runner/context.sh

@@ -62,14 +62,50 @@ function bashunit::runner::export_test_identity() {
   local fn_name=$2
   bashunit::helper::generate_id "$fn_name"
   export BASHUNIT_CURRENT_TEST_ID="$_BASHUNIT_HELPER_ID_OUT"
-  bashunit::runner::resolve_test_location "$test_file" "$fn_name"
+  # Carry the inputs; do not resolve. Reading the definition line costs a
+  # subshell, and only a failure message and a report row ever ask for it
+  # (#1346). Cleared per test so a previous test's line cannot answer for this
+  # one.
+  #
+  # The inputs are deliberately NOT exported. Every consumer runs in a fork of
+  # this shell, which inherits them anyway, while an exec'd process gets a name
+  # its own shell never defined. That is how a standalone `bashunit -a` used to
+  # report the location of whichever test had launched it.
+  _BASHUNIT_TEST_LOCATION=""
+  _BASHUNIT_TEST_LOCATION_FILE=$test_file
+  _BASHUNIT_TEST_LOCATION_FN=$fn_name
   export _BASHUNIT_TEST_LOCATION
   if [ "${_BASHUNIT_COVERAGE_ON:-0}" = 1 ]; then
     export _BASHUNIT_COVERAGE_CURRENT_TEST_FILE="$test_file"
     export _BASHUNIT_COVERAGE_CURRENT_TEST_FN="$fn_name"
   fi
 }
 
+##
+# Resolves the running test's location, once, if anything asks for it.
+#
+# The lookup below forks a subshell, which measured 1.08ms per call on macOS
+# arm64 (bash 3.2.57) -- about 2.7s across this suite when every test paid it
+# up front. A passing test never reads the result, and reports are opt-in, so
+# the cost now falls only where the line is actually rendered (#1346).
+#
+# A caller inside `$( )` loses the assignment with its subshell, which only
+# means the next one resolves again: correct either way, and the failure path
+# is not hot.
+##
+function bashunit::runner::ensure_test_location() {
+  if [ -n "${_BASHUNIT_TEST_LOCATION:-}" ]; then
+    return 0
+  fi
+
+  if [ -z "${_BASHUNIT_TEST_LOCATION_FN:-}" ]; then
+    return 0
+  fi
+
+  bashunit::runner::resolve_test_location \
+    "${_BASHUNIT_TEST_LOCATION_FILE:-}" "$_BASHUNIT_TEST_LOCATION_FN"
+}
+
 ##
 # Resolves "<test_file>:<line>" for a test function and writes it into the
 # global _BASHUNIT_TEST_LOCATION, using `declare -F` under `extdebug` to read

tests/acceptance/snapshots/bashunit_direct_fn_call_advanced_test_sh.test_bashunit_direct_fn_call_failure.snapshot

@@ -1,4 +1,3 @@
 ✗ Failed: assert same
     Expected 'foo'
     but got  'bar'
-    at tests/acceptance/bashunit_direct_fn_call_advanced_test.sh:16

tests/unit/console/results_test.sh

@@ -798,16 +798,22 @@ function test_test_location_suffix_when_set() {
   export _BASHUNIT_TEST_LOCATION="$original"
 }
 
+# The suffix resolves the location on demand now (#1346), so "unknown" means
+# the inputs are gone too -- clearing only the cached value would just make it
+# resolve the test that is running.
 function test_test_location_suffix_empty_when_unset() {
   local original=${_BASHUNIT_TEST_LOCATION:-}
+  local original_fn=${_BASHUNIT_TEST_LOCATION_FN:-}
   unset _BASHUNIT_TEST_LOCATION
+  unset _BASHUNIT_TEST_LOCATION_FN
 
   local output
   output="$(bashunit::console_results::test_location_suffix)"
 
   assert_empty "$output"
 
   export _BASHUNIT_TEST_LOCATION="$original"
+  export _BASHUNIT_TEST_LOCATION_FN="$original_fn"
 }
 
 # --- print_tap_line -----------------------------------------------------------

tests/unit/runner/context_test.sh

@@ -69,3 +69,83 @@ function test_restore_workdir_aborts_loudly_when_the_directory_is_gone() {
   assert_contains "cannot restore the working directory" "$output"
   assert_contains "$gone" "$output"
 }
+
+# --- test location ------------------------------------------------------------
+
+# Resolving "<file>:<line>" reads the definition line with
+# `$(shopt -s extdebug; declare -F …)`, a subshell that costs 1.08ms on macOS
+# arm64 — ~2.7s over this suite. Only a failure message and a report row ever
+# read it, so the identity carries the inputs and nothing resolves up front
+# (#1346).
+function test_export_test_identity_leaves_the_location_unresolved() {
+  local orig_id=${BASHUNIT_CURRENT_TEST_ID:-}
+  local orig_location=${_BASHUNIT_TEST_LOCATION:-}
+  local orig_file=${_BASHUNIT_TEST_LOCATION_FILE:-}
+  local orig_fn=${_BASHUNIT_TEST_LOCATION_FN:-}
+
+  bashunit::runner::export_test_identity "some_test.sh" "test_not_defined_here"
+
+  assert_empty "$_BASHUNIT_TEST_LOCATION"
+  assert_same "some_test.sh" "$_BASHUNIT_TEST_LOCATION_FILE"
+  assert_same "test_not_defined_here" "$_BASHUNIT_TEST_LOCATION_FN"
+
+  export BASHUNIT_CURRENT_TEST_ID="$orig_id"
+  export _BASHUNIT_TEST_LOCATION="$orig_location"
+  export _BASHUNIT_TEST_LOCATION_FILE="$orig_file"
+  export _BASHUNIT_TEST_LOCATION_FN="$orig_fn"
+}
+
+function test_ensure_test_location_resolves_on_demand() {
+  local orig_location=${_BASHUNIT_TEST_LOCATION:-}
+  local orig_file=${_BASHUNIT_TEST_LOCATION_FILE:-}
+  local orig_fn=${_BASHUNIT_TEST_LOCATION_FN:-}
+  _BASHUNIT_TEST_LOCATION=""
+  _BASHUNIT_TEST_LOCATION_FILE="mine.sh"
+  _BASHUNIT_TEST_LOCATION_FN="test_ensure_test_location_resolves_on_demand"
+
+  bashunit::runner::ensure_test_location
+
+  assert_matches "^mine\.sh:[0-9]+$" "$_BASHUNIT_TEST_LOCATION"
+
+  export _BASHUNIT_TEST_LOCATION="$orig_location"
+  export _BASHUNIT_TEST_LOCATION_FILE="$orig_file"
+  export _BASHUNIT_TEST_LOCATION_FN="$orig_fn"
+}
+
+# Resolved once per test: the failure path renders the suffix up to three
+# times, and each would otherwise pay the subshell again.
+function test_ensure_test_location_keeps_an_already_resolved_location() {
+  local orig_location=${_BASHUNIT_TEST_LOCATION:-}
+  local orig_file=${_BASHUNIT_TEST_LOCATION_FILE:-}
+  local orig_fn=${_BASHUNIT_TEST_LOCATION_FN:-}
+  _BASHUNIT_TEST_LOCATION="already/resolved.sh:7"
+  _BASHUNIT_TEST_LOCATION_FILE="mine.sh"
+  _BASHUNIT_TEST_LOCATION_FN="test_ensure_test_location_keeps_an_already_resolved_location"
+
+  bashunit::runner::ensure_test_location
+
+  assert_same "already/resolved.sh:7" "$_BASHUNIT_TEST_LOCATION"
+
+  export _BASHUNIT_TEST_LOCATION="$orig_location"
+  export _BASHUNIT_TEST_LOCATION_FILE="$orig_file"
+  export _BASHUNIT_TEST_LOCATION_FN="$orig_fn"
+}
+
+# Nothing to resolve from, so nothing is claimed: an empty location renders no
+# "at …" suffix at all.
+function test_ensure_test_location_stays_empty_without_a_function_name() {
+  local orig_location=${_BASHUNIT_TEST_LOCATION:-}
+  local orig_file=${_BASHUNIT_TEST_LOCATION_FILE:-}
+  local orig_fn=${_BASHUNIT_TEST_LOCATION_FN:-}
+  _BASHUNIT_TEST_LOCATION=""
+  _BASHUNIT_TEST_LOCATION_FILE=""
+  _BASHUNIT_TEST_LOCATION_FN=""
+
+  bashunit::runner::ensure_test_location
+
+  assert_empty "$_BASHUNIT_TEST_LOCATION"
+
+  export _BASHUNIT_TEST_LOCATION="$orig_location"
+  export _BASHUNIT_TEST_LOCATION_FILE="$orig_file"
+  export _BASHUNIT_TEST_LOCATION_FN="$orig_fn"
+}