hashicorp/terraform · error

length of keys and values should be equal

Error message

length of keys and values should be equal

What it means

Thrown by MatchkeysFunc.Impl when len(values) != len(keys). matchkeys pairs values[i] with keys[i] by index, so the two lists must be the same length; a mismatch is a logic error.

Source

Thrown at internal/lang/funcs/collection.go:365

		},
	},
	Type: func(args []cty.Value) (cty.Type, error) {
		ty, _ := convert.UnifyUnsafe([]cty.Type{args[1].Type(), args[2].Type()})
		if ty == cty.NilType {
			return cty.NilType, errors.New("keys and searchset must be of the same type")
		}

		// the return type is based on args[0] (values)
		return args[0].Type(), nil
	},
	RefineResult: refineNotNull,
	Impl: func(args []cty.Value, retType cty.Type) (ret cty.Value, err error) {
		if !args[0].IsKnown() {
			return cty.UnknownVal(cty.List(retType.ElementType())), nil
		}

		if args[0].LengthInt() != args[1].LengthInt() {
			return cty.ListValEmpty(retType.ElementType()), errors.New("length of keys and values should be equal")
		}

		output := make([]cty.Value, 0)
		values := args[0]

		// Keys and searchset must be the same type.
		// We can skip error checking here because we've already verified that
		// they can be unified in the Type function
		ty, _ := convert.UnifyUnsafe([]cty.Type{args[1].Type(), args[2].Type()})
		keys, _ := convert.Convert(args[1], ty)
		searchset, _ := convert.Convert(args[2], ty)

		// if searchset is empty, return an empty list.
		if searchset.LengthInt() == 0 {
			return cty.ListValEmpty(retType.ElementType()), nil
		}

		if !values.IsWhollyKnown() || !keys.IsWhollyKnown() {

View on GitHub (pinned to c9def3e214)

Solutions

1. Build values and keys together from a single source with a for expression so they stay aligned.
2. Add a precondition/guard: assert length(values) == length(keys).
3. Re-derive the shorter list from the same iteration as the longer one.

Example fix

# before
locals { m = matchkeys(var.names, var.ids, var.search_ids) }   # lengths differ
# after: derive both from one source
locals {
  pairs = [for x in var.items : { name = x.name, id = x.id }]
  m     = matchkeys([for p in local.pairs : p.name], [for p in local.pairs : p.id], var.search_ids)
}

# assert equal lengths before matchkeys
locals {
  ok = length(var.values) == length(var.keys)
  r  = local.ok ? matchkeys(var.values, var.keys, var.searchset) : []
}
check "align" {
  assert {
    condition     = length(var.values) == length(var.keys)
    error_message = "values and keys lists must have equal length"
  }
}

locals { r = try(matchkeys(var.values, var.keys, var.searchset), []) }

When it happens

Trigger: matchkeys(values, keys, searchset) where values and keys were built from different sources or filtered differently, producing unequal lengths.

Common situations: Two parallel lists that got out of sync; one list filtered while the other wasn't; copy-paste using the wrong variable.

Related errors

• no non-null, non-empty-string arguments
• cannot search an empty list
• item not found
• keys and searchset must be of the same type
• input must not contain null list

AI-assisted analysis of hashicorp/terraform@c9def3e214 (2026-08-07). Data as JSON: /api/errors/02785d499d6ada09. Report an issue: GitHub.