ComponentMetadata

type ComponentMetadata =
  | ComponentMetadataBase & {
  template?: undefined;
  templateUrl?: undefined;
}
  | ComponentMetadataBase & {
  template: string;
  templateUrl?: undefined;
}
  | ComponentMetadataBase & {
  template?: undefined;
  templateUrl: string;
};

Defined in: packages/analyzer/src/types.ts:68

XOR template source: at most ONE of template (inline) or templateUrl (external) may be set. Directives typically carry neither.

Both-set would be a producer bug (the analyzer should pick one); neither is legal for directives and for components the analyzer emits a diagnostic.