Fix: Error annotations fail when user functions contain "Handle" in their name

[rgeraskin]

Summary

• Fix error annotation when user functions contain the substring “handle” by making function-anchor detection precise.
• Ensures err2.Handle stack anchors are matched only for the err2 package (including versioned modules), not for user functions like FirstHandle or main.Handle.
• Closes issue #30.

Background

When using err2.Handle(&err) inside functions whose names contain “handle”, error annotations showed incorrect function names (e.g., main: main:). See Bug: Error annotations fail when user functions contain "Handle" in their name.

Changes

• Tightened isFuncAnchor logic in err2/internal/debug/debug.go:
  • Match only at a dot boundary.
  • Require the package token immediately before the dot to be exactly err2, or a version token vN preceded by err2 (supports .../err2/v2.Handle).
  • Single O(n) scan with strings.Index, no regex construction.
• Added helper isErr2BeforeDot to validate the package token.
• No changes to handler logic; only stack parsing is updated.

Why this approach

• Prevents substring collisions (e.g., “FirstHandle(”).
• Correctly identifies err2.Handle and versioned err2/vN.Handle.
• Avoids risky broad checks (like searching for /err2/ anywhere before).
• Maintains Go 1.18 compatibility (uses strings.LastIndex).

Tests

Added/extended cases in err2/internal/debug/debug_test.go to cover:

• Matches:
  • err2.Handle(...)
  • github.com/lainio/err2.Handle(...)
  • github.com/lainio/err2/v2.Handle(...)
  • github.com/lainio/err2/v10.Handle(...)
• Non-matches:
  • main.Handle(...)
  • mypackage.Handle(...)
  • main.FirstHandle(...)
  • github.com/myco/err2/mypackage.Handle(...)

Example

Before:

• Final error: main: main: my error

After:

• Final error: first handle: second handle: my error

Compatibility and Performance

• Backwards compatible with existing behavior for err2 stack parsing.
• O(n) per line; no new allocations beyond substring indexing.

Risks

• Low: Narrowed detection to dot boundaries and err2-scoped packages; tests cover edge cases.

Links

• Issue: #30

[lainio]

Thank you! I really appreciate your work. However, I'm a little confused with the fix, and that's why I have created a separate branch that fixes the bug just by changing one line in the file internal/handler/handler.go.

The complete fix can be seen in the branch fix-candidate-for-bug-30. I think we should continue the discussion here.

I apologize for not having had time to comment on this earlier.

[rgeraskin]

Thanks! I checked out your branch. In my opinion, your solution is much simpler and cleaner, and it resolves the issue. Also, I see that the same tests as for this PR pass for your branch. So I see no reason to accept this PR🙂

Looking forward to your fix being merged into master. Thanks!

[lainio]

Closing this. Fix done in #33.