pi-lens/rules/ast-grep-rules/rule-tests/nil-map-assignment-test.yml

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id: nil-map-assignment
valid:
  - |
    // Properly initialized with make()
    m := make(map[string]int)
    m["key"] = 1
  - |
    // Map literal — initialized
    m := map[string]int{"a": 1}
    m["b"] = 2
  - |
    // Function parameter — caller passes initialized map
    func f(m map[string]int) {
      m["x"] = 1
    }
  - |
    // Struct field of named type
    type Cache struct{ data map[string]int }
    func (c *Cache) Put() { c.data["k"] = 1 }  // field map, no need to init
  - |
    // Inline init — Go initializes the map before any access
    var m map[string]int = make(map[string]int)
    m["k"] = 1
  - |
    // Multi-assign from function returning (map, error) — gorilla/mux pattern
    var headers map[string]string
    headers, r.err = mapFromPairsToString("k", "v")
    _ = headers
invalid:
  - |
    // Writing to uninitialized nil map — runtime panic
    var m map[string]int
    m["key"] = 1
  - |
    // Multi-type nil map
    var cache map[int]string
    cache[42] = "answer"
  - |
    // Nested uninitialized map
    var m map[string]map[int]bool
    m["x"][1] = true
  - |
    // gorilla/mux old_test.go:69 — declared, never initialized,
    // then written. Would panic if the test executed the write.
    func TestRoute(t *testing.T) {
      var headers map[string]string
      var resultVars map[bool]map[string]string
      _ = headers
      resultVars[true] = nil  // panics on nil map
    }