`BASH_SOURCE[0]` is empty when running `bash /path/script.sh`

[chaliy]

Summary

When executing a script via bash /path/script.sh, BASH_SOURCE[0] is empty. In real bash, BASH_SOURCE[0] equals the script file path.

Reproduction

# FAIL — BASH_SOURCE empty in bash /script
echo 'echo "source: ${BASH_SOURCE[0]}"' > /tmp/test_source.sh
bash /tmp/test_source.sh
# expected: source: /tmp/test_source.sh
# actual:   source:

# FAIL — dirname pattern breaks
echo 'DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"; echo "dir: $DIR"' > /tmp/test_dir.sh
bash /tmp/test_dir.sh
# expected: dir: /tmp
# actual:   (error or empty — dirname of empty string)

# PASS — source (.) does populate BASH_SOURCE
echo 'echo "source: ${BASH_SOURCE[0]}"' > /tmp/test_sourced.sh
source /tmp/test_sourced.sh
# expected: source: /tmp/test_sourced.sh

Spec tests to add

Add to crates/bashkit/tests/spec_cases/bash/:

### bash_source_in_executed_script
# BASH_SOURCE[0] should equal script path when run via bash
echo 'echo "${BASH_SOURCE[0]}"' > /tmp/bsrc_test.sh
bash /tmp/bsrc_test.sh
### expect
/tmp/bsrc_test.sh
### end

### bash_source_dirname_pattern
# Common pattern: find script's own directory
echo 'echo "$(dirname "${BASH_SOURCE[0]}")"' > /tmp/bsrc_dir.sh
bash /tmp/bsrc_dir.sh
### expect
/tmp
### end

### bash_source_in_sourced_script
# BASH_SOURCE[0] in sourced scripts (verify no regression)
echo 'echo "${BASH_SOURCE[0]}"' > /tmp/bsrc_sourced.sh
source /tmp/bsrc_sourced.sh
### expect
/tmp/bsrc_sourced.sh
### end

Where to fix

execute_shell() in crates/bashkit/src/interpreter/mod.rs (around lines 2559-2673). When a script file path is provided, push it onto bash_source_stack (or call update_bash_source()) before executing the script content. Pop it after execution completes.

Search for existing bash_source handling in the source builtin implementation for reference — it already does this correctly.

Real-world impact

Scripts that use BASH_SOURCE[0] to find their own location (a very common pattern) will break. The wedow/harness uses this in bin/harness line 6 to discover HARNESS_ROOT, and in spec/run to locate test files.