avoid_missing_enum_constant_in_map

v0.8.0 Warning Collection Type

This rule flags a map literal whose key type is an enum but whose entries do not cover every constant of that enum.

Why use this rule

A map keyed by an enum is almost always intended as a total lookup table — labels, icons, colors, route names. When a constant is missing, map[value] returns null rather than failing, so the gap travels: it becomes a null-check crash, an empty label, or a ! that throws somewhere unrelated.

The bigger risk is drift. A switch over an enum is checked for exhaustiveness by the compiler, so adding a constant produces errors at every site that must change. A map gets no such check — add a constant and every lookup table in the codebase is quietly incomplete.

See also: Dart enums

Don’t

enum Status { active, inactive, pending }

const statusLabels = <Status, String>{
  Status.active: 'Active',
  Status.inactive: 'Inactive',
  // pending is missing — lookups return null
};

Do

enum Status { active, inactive, pending }

const statusLabels = <Status, String>{
  Status.active: 'Active',
  Status.inactive: 'Inactive',
  Status.pending: 'Pending',
};

When a total map is not what you want, make the fallback explicit at the lookup instead:

final label = statusLabels[status] ?? 'Unknown';

Known limitations

The rule only reports when the map’s contents can be enumerated statically. It stays silent when the literal contains a spread (...other), an if or for element, or a key that is not a plain enum constant reference — in those cases the final key set is not knowable at analysis time.

An empty map literal is also skipped, since that is a deliberate starting point rather than an oversight.

Configuration

This rule is in the opinionated preset, so it is on with preset: opinionated, or by name:

many_lints.yaml

rules:
  avoid_missing_enum_constant_in_map: true

To turn it off again:

many_lints.yaml

rules:
  avoid_missing_enum_constant_in_map: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• prefer_enums_by_name — Use .byName() instead of .firstWhere() to look up enum values by name.
• enum_constants_ordering — Keep enum constants in a configured order.
• avoid_accessing_collections_by_constant_index — Avoid accessing a collection by a constant index inside a loop.
• avoid_map_keys_contains — Use containsKey() instead of .keys.contains() for better performance.