fix: a panic in prealloc when analyzing malformed or partially reco…

[Laisky]

Summary

This PR fixes a panic in prealloc when analyzing malformed or partially recovered AST nodes.

The panic happened because type inference assumed multi-value declarations/assignments always had at least one RHS expression, and accessed index 0 unconditionally.

Changes

• Add defensive checks in pkg/types.go:
  • inferValueType: return nil when len(value.Values) == 0
  • inferAssignType: return nil when len(assign.Rhs) == 0
• Add regression tests in pkg/types_test.go to ensure:
  • no panic for empty ValueSpec values
  • no panic for empty assignment RHS
  • no panic in end-to-end Check on malformed source

Compatibility

This is a backward-compatible hardening change:

• behavior for valid code is unchanged
• malformed/incomplete inputs now fail safely instead of panicking

[Copilot]

Pull request overview

Hardens prealloc’s internal type inference against malformed / partially recovered AST nodes to avoid panics during analysis.

Changes:

• Add defensive empty-slice checks in inferValueType and inferAssignType to avoid indexing into missing RHS/value lists.
• Add regression tests covering empty ValueSpec values, empty assignment RHS, and an end-to-end Check run on malformed parsed source.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/types.go	Adds guards returning nil when ValueSpec.Values / AssignStmt.Rhs are empty to prevent panics.
pkg/types_test.go	Introduces regression tests ensuring the analyzer doesn’t panic on malformed/partial AST shapes.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[alexkohler]

Thank you! 🚀