/bisect

Name

git:bisect

Synopsis

/git:bisect                       # Fully interactive - will ask for all inputs
/git:bisect [good-commit] [bad-commit]  # With commit references

Description

The git:bisect command is an interactive git bisect assistant that helps find the exact commit that introduced a specific change (bug, behavior change, feature, performance regression, etc.) using binary search.

What This Command Does:

1. Guides you through setup - Validates commits, checks for conflicts
2. Presents commits for evaluation - Shows relevant info about each commit
3. Learns from your decisions - Detects patterns in your choices
4. Can automate - If it understands your criterion, it can evaluate automatically (with your permission)
5. Reports the result - Shows the culprit commit with full details

Terminology

Git bisect uses confusing terms. This command uses clearer labels:

What You See	Git Term	Meaning
"Change IS in the code"	bad	The change you're looking for EXISTS in this commit
"Change is NOT in the code"	good	The change you're looking for does NOT exist yet

Never use "good" or "bad" alone - always explain what they mean in context.

Workflow

1. Provide (or select) reference commits
         ↓
2. Describe what change you're looking for
         ↓
3. [If criterion is clear] Confirm understanding → Choose manual/auto
         ↓
4. Evaluate commits (manually or automatically)
         ↓
5. Receive final report with culprit commit
         ↓
6. Clean up (git bisect reset)

Commands During Bisect

At any point during the bisect, you can:

• "show diff" or "more details" - See the full diff for the current commit
• "skip" - Skip a commit that cannot be tested (won't build, etc.)
• "abort" - Cancel the bisect and return to your original branch
• "automate" - Ask to enable automation (if pattern detected)

Tips

• You can test the current state by building/running your project between steps
• Use skip if a commit cannot be tested (build failure, unrelated issue)
• The process uses binary search: ~log₂(N) steps for N commits
• You can abort at any time; the session will be cleanly terminated

Implementation

Arguments provided: $ARGUMENTS

Parse arguments:

• If two arguments: first = commit where change is NOT present, second = commit where change IS present
• If one argument: ask which one it represents
• If no arguments: proceed to interactive mode

---

Critical Rules

Rule 1: Never decide without asking first

You may NEVER execute git bisect good or git bisect bad without explicit user confirmation. Even if you're 100% certain, you MUST ask first. No exceptions.

Rule 2: Early criterion detection (≥70% confidence)

If the user describes a criterion that you can verify programmatically (e.g., "when dependency X was updated to version > Y"), and you have ≥70% confidence you understand it correctly:

1. BEFORE evaluating any commit, present your understanding with maximum precision:

   "Based on your description, I believe you're looking for: [exact criterion with specific details]

   To verify this, I would check: [specific file/command/method]

   Is this correct?"

2. Wait for user response. Then:

   • If user confirms the criterion is correct, ask:

     "Would you like me to automatically evaluate commits based on this criterion? I will show each decision as I make it."

     • If user says yes → Enable automation mode
     • If user says no → Continue in manual mode (ask for each commit)

   • If user says the criterion is wrong:

     • Say: "I understand. Please clarify what you're looking for."
     • Reset your understanding completely
     • Enter manual mode
     • Continue learning from user responses

Rule 3: Learning from manual decisions

If you don't have ≥70% confidence initially, or after a criterion reset:

1. Present commit info and ask the user for their verdict
2. Analyze patterns in their decisions (files, authors, keywords)
3. When confidence reaches ≥70%, present your understanding and follow Rule 2

Rule 4: Automation flow

When automation is enabled (user explicitly said yes):

1. For each commit:
   • Show the commit being evaluated
   • Show your decision and the reasoning
   • Execute git bisect good or git bisect bad
2. If any commit doesn't clearly match the criterion, STOP and ask the user
3. Continue until bisect completes

---

Phase 1: Initialization

Step 1.1: Check for Existing Bisect Session

Run git bisect log to check if a bisect is in progress.

If bisect IS in progress:

1. Show the current state: how many steps done, current commit
2. Ask the user:
   • Continue: Resume the existing session
   • Abort: Run git bisect reset and optionally start fresh
   • View details: Show full bisect log before deciding

If NO bisect in progress: Continue to Step 1.2

Step 1.2: Check for Uncommitted Changes

Run git status --porcelain to check for uncommitted changes.

If there are uncommitted changes:

1. Warn: "You have uncommitted changes. Git bisect will checkout different commits which may conflict with your changes."
2. Offer options:
   • Stash changes: Run git stash push -m "Pre-bisect stash"
   • Proceed anyway: Continue (user accepts the risk)
   • Abort: Stop to handle manually

Step 1.3: Get Reference Commits

If commits were provided as arguments:

1. Validate using git rev-parse <commit>
2. Show what each commit represents (run git log -1 --format="%h %s" <commit>)
3. Confirm: "Commit X is where the change is NOT present, commit Y is where it IS present. Correct?"

If commits were NOT provided:

1. Show recent history: git log --oneline -20
2. Ask: "Which commit is known to NOT have the change you're looking for? (This will be the 'good' starting point)"
3. Ask: "Which commit IS known to have the change? (This will be the 'bad' starting point)"

Validate the relationship:

• The "good" commit (without change) should be an ancestor of the "bad" commit (with change)
• If they appear reversed, explain and offer to swap

Step 1.4: Understand the Search Criterion

Ask the user:

What change are you looking for?

Please describe:

• What behavior or code changed?
• How can you determine if a commit has or doesn't have this change?
• Is there a specific file, function, or behavior to check?

Store this description for analysis.

Step 1.5: Early Criterion Detection (CRITICAL)

After the user describes the change, analyze their response:

If you have ≥70% confidence that you understand a verifiable criterion:

1. Present your understanding with maximum precision:

   "Based on your description, I believe you're looking for: [exact criterion]

   To verify this, I would check: [specific method]

   Is this correct?"

2. WAIT for user response before proceeding.

3. If user confirms:

   "Would you like me to automatically evaluate commits based on this criterion? I will show each decision as I make it."

   • If yes → Set automation mode = true
   • If no → Set automation mode = false (manual mode)

4. If user says criterion is wrong:

   • Ask for clarification
   • Set automation mode = false
   • Proceed to bisect in manual mode

Only proceed to Step 1.6 after this interaction is complete.

Step 1.6: Start Bisect

Execute:

git bisect start
git bisect bad <commit-with-change>
git bisect good <commit-without-change>

Parse the output to show:

• Number of revisions to test
• Estimated number of steps (approximately log2 of revisions)
• The first commit to test

---

Phase 2: Evaluation Loop

Internal State to Track

Maintain a session log throughout the bisect:

## Session Log

**Search criterion**: [user's description]
**Detected pattern**: [none yet / description]
**Confidence level**: [0-100%]
**Automation enabled**: [no / yes]

| Step | Commit | Files Changed | Verdict | Observation |
|------|--------|---------------|---------|-------------|

For Each Commit

Step 2.1: Present Commit Information

Display:

═══════════════════════════════════════════════════════════
TESTING COMMIT [step X of ~Y estimated]
═══════════════════════════════════════════════════════════

Commit:  [short hash]
Author:  [author name]
Date:    [date]
Message: [subject line]

Files Changed:
[output of: git show --stat --format="" HEAD]

Summary: [X files changed, Y insertions(+), Z deletions(-)]
═══════════════════════════════════════════════════════════

Step 2.2: Evaluate Commit (depends on mode)

If AUTOMATION MODE is enabled:

1. Verify the criterion for this commit (run the check you described to user)
2. Show the result:

   Commit [hash]: Checking [criterion]...
   Result: [what you found]
   Decision: Change [IS / is NOT] in the code → marking as [bad/good]
   

3. Execute git bisect bad or git bisect good
4. If the result is unclear or doesn't match the criterion cleanly, STOP and ask user

If MANUAL MODE (automation not enabled):

Ask the user:

Is the change you're looking for present in this commit?

[1] Change IS in the code (will mark as 'bad')
[2] Change is NOT in the code (will mark as 'good')
[3] Cannot test this commit (skip)
[4] Show more details (diff, full message)
[5] Abort bisect

If in manual mode and confidence reaches ≥70%:

Before showing options, present your understanding:

I've noticed a pattern: [description of what you've observed]

Based on this, I believe the change [IS / is NOT] in this commit.

Is this the criterion you're using? If so, would you like me to automate?

[1] Yes, that's correct - please automate
[2] Yes, that's correct - but I'll decide manually
[3] No, that's not what I'm looking for
[4] Show more details first

If user chooses [1] → Enable automation mode If user chooses [2] → Stay in manual mode but show suggestions If user chooses [3] → Reset pattern analysis, continue manual

Step 2.3: Process Response

Based on user response:

Response	Action
Change IS in code	Run git bisect bad, record in log
Change NOT in code	Run git bisect good, record in log
Skip	Run git bisect skip, note why in log
Show details	Display requested info, ask again
Abort	Confirm, then run git bisect reset

Step 2.4: Update Session Log

After each decision, update the internal log with:

• Commit hash
• Key files changed
• User's verdict
• Any observations about patterns

Step 2.5: Pattern Analysis (Manual Mode Only)

When in manual mode, after each user decision:

1. Analyze correlations:

   • File patterns: Do "change present" commits touch specific files?
   • Author patterns: Is a specific author correlated?
   • Message patterns: Are there specific keywords?

2. Update confidence based on how well patterns predict user decisions

3. When confidence reaches ≥70%:

   • Present your understanding in Step 2.2 (as described above)
   • This may result in switching to automation mode if user accepts

---

Phase 3: Completion

Detecting Completion

Git bisect outputs "X is the first bad commit" when complete. Watch for this phrase.

Final Report

When bisect completes, present:

═══════════════════════════════════════════════════════════
BISECT COMPLETE - CULPRIT FOUND
═══════════════════════════════════════════════════════════

THE COMMIT THAT INTRODUCED THE CHANGE
─────────────────────────────────────

Commit:  [full hash]
Author:  [author name] <[email]>
Date:    [full date]

Message:
[full commit message]

Files Changed:
[git show --stat --format="" <hash>]

CHANGE SUMMARY
─────────────────────────────────────

Based on your search criterion: "[user's original description]"

This commit appears to have introduced the change by:
[Analysis of what changed in this commit that matches the criterion]

EVALUATION HISTORY
─────────────────────────────────────

| Step | Commit  | Verdict              | Key Files        |
|------|---------|----------------------|------------------|
| 1    | abc1234 | Change present       | src/main.rs      |
| 2    | def5678 | Change NOT present   | tests/test.rs    |
| ...  | ...     | ...                  | ...              |

SUGGESTED NEXT STEPS
─────────────────────────────────────

1. View full diff: git show [hash]
2. Compare with parent: git diff [hash]^..[hash]
3. Revert this commit: git revert [hash]
4. Blame specific file: git blame [file] | grep [hash]

═══════════════════════════════════════════════════════════

Cleanup

Ask:

"The bisect session is complete. Would you like me to run git bisect reset to return to your original branch?"

If yes, run git bisect reset and confirm the branch returned to.

---

Error Handling

Common Errors and Solutions

Error	Solution
"You need to start by 'git bisect start'"	Bisect was interrupted; restart the process
"Bad rev input: X"	Invalid commit reference; ask for correction and show recent commits
"Some good revs are not ancestors of the bad rev"	Commits are in wrong order; explain and offer to swap
Merge conflict during checkout	Suggest git bisect skip for this commit
"Cannot bisect on a detached HEAD"	This shouldn't happen normally; offer to reset

Abort Handling

If user requests abort at any point:

1. Confirm: "Are you sure you want to abort? The bisect progress will be lost."
2. If confirmed: Run git bisect reset
3. Show the branch/commit returned to
4. Optionally: Offer to save the bisect log first with git bisect log > bisect-log-$(date +%Y%m%d-%H%M%S).txt

Examples

1. Fully interactive - no arguments:

   /git:bisect
   

   Will show recent history and ask you to select commits.

2. With commit references:

   /git:bisect v1.28.0 HEAD
   

   Uses tag v1.28.0 as the "good" commit (change NOT present) and HEAD as the "bad" commit (change IS present).

3. With commit hashes:

   /git:bisect abc1234 def5678
   

4. Mixed references:

   /git:bisect v1.0.0 main
   

Return Value

• Final Report: A comprehensive report showing:

  • The culprit commit (full hash, author, date, message)
  • Files changed in that commit
  • Analysis of how the commit matches the search criterion
  • Evaluation history table
  • Suggested next steps (view diff, revert, blame)

• Session cleanup: Offers to run git bisect reset to return to original branch

Arguments

• $1 [good-commit] (optional): A commit reference (hash, tag, branch) where the change is NOT present. This is the older, "known good" state.
• $2 [bad-commit] (optional): A commit reference where the change IS present. This is the newer state that contains the change you're looking for.

Notes:

• If no arguments are provided, the command will show recent history and ask you to select commits
• If only one argument is provided, the command will ask which one it represents (good or bad)
• Commit references can be: hashes, tags, branch names, HEAD, HEAD~N, etc.