pi-lens/rules/tree-sitter-queries/go/go-defer-in-loop.yml

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# Go Defer in Loop
# Detects defer statements inside loops (resource leak risk)
id: go-defer-in-loop
name: Defer Inside Loop
severity: warning
category: resource-management
defect_class: async-misuse
inline_tier: blocking
language: go

message: "defer in loop can cause resource exhaustion — move outside loop or use function"

description: |
  Using defer inside a loop defers cleanup until the function returns,
  not until the loop iteration ends. This can cause resource exhaustion.
  
  ✅ FIX: Move defer outside loop, or wrap loop body in a function.

query: |
  (for_statement
    body: (block
      (defer_statement) @DEFER))

metavars:
  - DEFER

has_fix: false

tags:
  - go
  - resource-leaks
  - performance

examples:
  bad: |
    for _, file := range files {
        f, _ := os.Open(file)
        defer f.Close()  // All closes deferred until function exit!
        process(f)
    }
  
  good: |
    for _, file := range files {
        func() {
            f, _ := os.Open(file)
            defer f.Close()  // Closes at end of anonymous function
            process(f)
        }()
    }