fix: make GTR_DEBUG actually report the failing location

[helizaga]

Description

GTR_DEBUG=1 has never produced any output. bin/git-gtr installs an ERR trap when the variable is set, but the script runs under set -e alone. An ERR trap is inherited by functions, command substitutions and subshells only under set -E, and every command in this CLI runs inside main() and then a cmd_* handler, so the trap never fired. The comment above it promised behavior the code did not deliver.

This changes the option line to set -eE and adds the regression test the feature never had.

Motivation

The debug aid is documented in the code as showing file:line:function on set -e failures, and is the first thing a contributor or agent would reach for when diagnosing an unexpected failure. As written it silently does nothing, so time spent on it is wasted.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring (no functional changes)

Why the default path is unaffected

set -E only controls ERR trap inheritance, and the trap is installed solely when GTR_DEBUG is set. Confirmed with a four-way matrix on the same script:

Configuration	Trap output	Exit
set -e, no trap (today's default)	silent	1
set -eE, no trap (default after this change)	silent	1
set -e + trap (today's GTR_DEBUG=1)	silent	1
set -eE + trap (this change, GTR_DEBUG=1)	TRAP p2.sh:6 inner()	1

Rows one and two are identical, so the non-debug path behaves exactly as before.

Debug mode does not become noisy

ERR follows the same suppression rules as set -e, so guarded failures do not fire it: || true, if cmd; then, and guarded command substitutions all produce nothing. Against the real binary, six ordinary invocations including handled error paths (go, rm, editor, run on a missing branch, plus list and doctor) emitted zero trap lines.

What it does report is the case it was written for:

ERROR at /path/to/lib/config.sh:272 in cfg_set()

That is cfg_set calling git config unguarded, reached by making that write fail.

Testing

tests/debug_trap.bats runs the real binary as a subprocess, which no existing test did, so the option line in bin/git-gtr is actually exercised:

• an unguarded failure reports file, line and function;
• nothing is reported when GTR_DEBUG is unset;
• nothing is reported for a successful command;
• nothing is reported for a handled error path.

It is a genuine regression guard: reverting the option line to set -e makes the first case fail, and restoring it makes it pass.

Tested on:

• macOS (26.6.2, git 2.54.0, bash 5.3.15)
• Linux
• Windows (Git Bash)

Linux coverage comes from the CI Tests job on this PR.

Automated gates

• bats tests/ — 558 of 559 pass. The one failure, cmd_clean --merged uses nested registered worktree path, is pre-existing and environment-specific: it fails identically three times out of three on unmodified main in a clean checkout, the CI Tests job passes on that same commit, and the test calls cmd_clean directly without ever invoking bin/git-gtr. Its failing assertion is a path comparison that differs on macOS.
• shellcheck bin/gtr bin/git-gtr lib/*.sh lib/commands/*.sh adapters/editor/*.sh adapters/ai/*.sh — clean.
• ./scripts/generate-completions.sh --check — up to date.

Core functionality

Commands were exercised through the debug probes above (go, rm, editor, run, list, doctor, config set) plus the full BATS suite. No command behavior changes when GTR_DEBUG is unset, which is the default.

Breaking Changes

• This PR introduces breaking changes

None. With no ERR trap installed, set -E has no observable effect.

Checklist

• I have read CONTRIBUTING.md
• My code follows the project's style guidelines
• I have performed manual testing on at least one platform
• I have updated documentation if needed (see note below)
• My changes work on multiple platforms (or I've noted platform-specific behavior)
• I have added/updated shell completions (not applicable; no commands or flags changed, and --check passes)
• I have tested with both git gtr and ./bin/gtr
• No new external dependencies are introduced
• All existing functionality still works

Additional Context

set -o pipefail was considered and deliberately left out; it is a broader behavior change that deserves its own evaluation.

Open PRs #197 and #198 currently document this limitation rather than claiming the flag works. If this merges, those notes should be updated to describe the fixed behavior. All three branches add a ## [Unreleased] changelog entry, so whichever merges later needs a trivial rebase of that hunk.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Improved diagnostic output when debug mode is enabled, including the file, line, and function associated with unexpected failures.
  • Debug information now also appears for failures within nested command execution.

• Bug Fixes

  • Unexpected failures are now reported more consistently during debugging.
  • Normal operation remains unchanged when debugging is disabled.

• Documentation

  • Added an unreleased changelog entry describing the improved debug diagnostics.

• Tests

  • Added coverage for successful commands, handled failures, disabled debugging, and unexpected failures.

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Walkthrough

The CLI now uses set -eE so GTR_DEBUG reports failing locations inside nested shell contexts. New Bats tests verify diagnostic output and suppression rules. The changelog documents the fix.

Changes

Debug diagnostics

Layer / File(s)	Summary
ERR trap inheritance bin/git-gtr, CHANGELOG.md	bin/git-gtr changes set -e to set -eE. The changelog records the resulting GTR_DEBUG file, line, and function details.
Debug trap regression coverage tests/debug_trap.bats	Integration tests cover isolated failures, disabled debugging, successful commands, handled errors, and failures in cmd_run subshells.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: natoboram

Merge Risk: ⚪ Minimal · up to 08de4

The change preserves non-debug failure behavior and adds diagnostics for the exercised nested paths; no concrete issue requiring a merge block is established.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: correcting GTR_DEBUG so it reports the failing location.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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---

_{A rabbit found a hidden trail
Where error clues no longer fail
File and line now clearly gleam
Nested shells reveal the seam
Tests guard the debug light
And quiet paths stay quiet at night}

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Actionable comments posted: 1

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Inline comments:
In `@tests/debug_trap.bats`:
- Around line 31-62: Extend the GTR_DEBUG regression coverage in
tests/debug_trap.bats to trigger unguarded failures inside a function, command
substitution, and subshell, asserting each produces the expected “ERROR at”
diagnostic with location context. Keep the existing silent-success and
handled-error tests intact, and ensure the cases would fail if ERR trap
inheritance is enabled only for functions but not the other nested contexts.

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• bin/git-gtr
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