Improve declaration of untagged unions to allow for generator optimiz…

…ations

compiler/src/model/metamodel.ts

@@ -180,7 +180,7 @@ export abstract class BaseType {
   specLocation: string
 }
 
-export type Variants = ExternalTag | InternalTag | Container
+export type Variants = ExternalTag | InternalTag | Container | Untagged
 
 export class VariantBase {
   /**
@@ -207,6 +207,10 @@ export class Container extends VariantBase {
   kind: 'container'
 }
 
+export class Untagged extends VariantBase {
+  kind: 'untagged'
+}
+
 /**
  * Inherits clause (aka extends or implements) for an interface or request
  */
@@ -358,8 +362,11 @@ export class TypeAlias extends BaseType {
   type: ValueOf
   /** generic parameters: either concrete types or open parameters from the enclosing type */
   generics?: TypeName[]
-  /** Only applicable to `union_of` aliases: identify typed_key unions (external) and variant inventories (internal) */
-  variants?: InternalTag | ExternalTag
+  /** 
+   * Only applicable to `union_of` aliases: identify typed_key unions (external), variant inventories (internal) 
+   * and untagged variants
+   */
+  variants?: InternalTag | ExternalTag | Untagged
 }
 
 // ------------------------------------------------------------------------------------------------

compiler/src/model/utils.ts

@@ -496,8 +496,8 @@ export function modelTypeAlias (declaration: TypeAliasDeclaration): model.TypeAl
     if (variants != null) {
       assert(
         declaration.getJsDocs(),
-        variants.kind === 'internal_tag' || variants.kind === 'external_tag',
-        'Type Aliases can only have internal or external variants'
+        variants.kind === 'internal_tag' || variants.kind === 'external_tag' || variants.kind === 'untagged',
+        'Type Aliases can only have internal, external or untagged variants'
       )
       typeAlias.variants = variants
     }
@@ -1065,6 +1065,13 @@ export function parseVariantsTag (jsDoc: JSDoc[]): model.Variants | undefined {
     }
   }
 
+  if (type === 'untagged') {
+    return {
+      kind: 'untagged',
+      nonExhaustive: nonExhaustive
+    }
+  }
+
   assert(jsDoc, type === 'internal', `Bad variant type: ${type}`)
 
   const pairs = parseKeyValues(jsDoc, values, 'tag', 'default')

compiler/src/steps/validate-model.ts

@@ -575,7 +575,7 @@ export default async function validateModel (apiModel: model.Model, restSpec: Ma
     }
   }
 
-  function validateTaggedUnion (valueOf: model.UnionOf, variants: model.InternalTag | model.ExternalTag): void {
+  function validateTaggedUnion (valueOf: model.UnionOf, variants: model.InternalTag | model.ExternalTag | model.Untagged): void {
     if (variants.kind === 'external_tag') {
       // All items must have a 'variant' attribute
       const items = flattenUnionMembers(valueOf)
@@ -619,6 +619,55 @@ export default async function validateModel (apiModel: model.Model, restSpec: Ma
       }
 
       validateValueOf(valueOf, new Set())
+    } else  if (variants.kind === 'untagged') {
+      const items = flattenUnionMembers(valueOf)
+
+      const baseTypes = new Set<string>();
+
+      for (const item of items) {
+        if (item.kind !== 'instance_of') {
+          modelError('Items of type untagged unions must be type references')
+        } else {
+          validateTypeRef(item.type, undefined, new Set<string>())
+          const type = getTypeDef(item.type)
+          if (type == null) {
+            modelError(`Type ${fqn(item.type)} not found`)
+          } else {
+            if (type.kind !== 'interface') {
+              modelError(`Type ${fqn(item.type)} must be an interface to be used in an untagged union`)
+              continue
+            }
+
+            const intf = (type as model.Interface)
+
+            if (!intf.inherits) {
+              modelError(`Type ${fqn(item.type)} must derive from a base type to be used in an untagged union`)
+              continue
+            }
+
+            baseTypes.add(fqn(intf.inherits.type))
+
+            const baseType = getTypeDef(intf.inherits.type)
+            if (baseType === null) {
+              modelError(`Type ${fqn(intf.inherits.type)} not found`)
+              continue
+            }
+
+            if (baseType?.kind !== 'interface') {
+              modelError(`Type ${fqn(intf.inherits.type)} must be an interface to be used as the base class of another interface`)
+              continue
+            }
+
+            if (!intf.inherits.generics || intf.inherits.generics.length === 0) {
+              modelError('The common base type of an untagged union must accept at least one generic type argument')
+            }
+          }
+        }
+      }
+
+      if (baseTypes.size !== 1) {
+        modelError('All items of an untagged union must derive from the same common base type')
+      }
     }
   }
 

specification/_types/query_dsl/compound.ts

@@ -171,27 +171,35 @@ export class DecayPlacement<TOrigin, TScale> {
   origin?: TOrigin
 }
 
-export class DecayFunctionBase {
+export class DecayFunctionBase<TOrigin, TScale> 
+  implements AdditionalProperty<Field, DecayPlacement<TOrigin, TScale>>
+{
   /**
    * Determines how the distance is calculated when a field used for computing the decay contains multiple values.
    * @server_default min
    */
   multi_value_mode?: MultiValueMode
 }
 
-export class NumericDecayFunction
-  extends DecayFunctionBase
-  implements AdditionalProperty<Field, DecayPlacement<double, double>> {}
+export class NumericDecayFunction extends DecayFunctionBase<
+  double, 
+  double
+> {}
 
-export class DateDecayFunction
-  extends DecayFunctionBase
-  implements AdditionalProperty<Field, DecayPlacement<DateMath, Duration>> {}
+export class DateDecayFunction extends DecayFunctionBase<
+  DateMath, 
+  Duration
+> {}
 
-export class GeoDecayFunction
-  extends DecayFunctionBase
-  implements AdditionalProperty<Field, DecayPlacement<GeoLocation, Distance>> {}
+export class GeoDecayFunction extends DecayFunctionBase<
+  GeoLocation, 
+  Distance
+> {}
 
-/** @codegen_names date, numeric, geo */
+/**
+ * @codegen_names date, numeric, geo
+ * @variants untagged
+ */
 // Note: deserialization depends on value types
 export type DecayFunction =
   | DateDecayFunction

specification/_types/query_dsl/specialized.ts

@@ -69,7 +69,10 @@ export class DateDistanceFeatureQuery extends DistanceFeatureQueryBase<
   Duration
 > {}
 
-/** @codegen_names geo, date */
+/**
+ * @codegen_names geo, date
+ * @variants untagged
+ */
 // Note: deserialization depends on value types
 export type DistanceFeatureQuery =
   | GeoDistanceFeatureQuery

specification/_types/query_dsl/term.ts

@@ -105,33 +105,30 @@ export class PrefixQuery extends QueryBase {
   case_insensitive?: boolean
 }
 
-export class RangeQueryBase extends QueryBase {
+export class RangeQueryBase<T> extends QueryBase {
   /**
    * Indicates how the range query matches values for `range` fields.
    * @server_default intersects
    */
   relation?: RangeRelation
-}
-
-export class DateRangeQuery extends RangeQueryBase {
   /**
    * Greater than.
    */
-  gt?: DateMath
+  gt?: T
   /**
    * Greater than or equal to.
    */
-  gte?: DateMath
+  gte?: T
   /**
    * Less than.
    */
-  lt?: DateMath
+  lt?: T
   /**
    * Less than or equal to.
    */
-  lte?: DateMath
-  from?: DateMath | null
-  to?: DateMath | null
+  lte?: T
+  from?: T | null
+  to?: T | null
   /**
    * Date format used to convert `date` values in the query.
    */
@@ -142,51 +139,24 @@ export class DateRangeQuery extends RangeQueryBase {
   time_zone?: TimeZone
 }
 
-export class NumberRangeQuery extends RangeQueryBase {
-  /**
-   * Greater than.
-   */
-  gt?: double
-  /**
-   * Greater than or equal to.
-   */
-  gte?: double
-  /**
-   * Less than.
-   */
-  lt?: double
-  /**
-   * Less than or equal to.
-   */
-  lte?: double
-  from?: double | null
-  to?: double | null
-}
+export class DateRangeQuery extends RangeQueryBase<
+  DateMath
+> {}
 
-export class TermsRangeQuery extends RangeQueryBase {
-  /**
-   * Greater than.
-   */
-  gt?: string
-  /**
-   * Greater than or equal to.
-   */
-  gte?: string
-  /**
-   * Less than.
-   */
-  lt?: string
-  /**
-   * Less than or equal to.
-   */
-  lte?: string
-  from?: string | null
-  to?: string | null
-}
+export class NumberRangeQuery extends RangeQueryBase<
+  double
+> {}
 
-/** @codegen_names date, number, terms */
+export class TermRangeQuery extends RangeQueryBase<
+  string
+> {}
+
+/**
+ * @codegen_names date, number, term
+ * @variants untagged
+ */
 // Note: deserialization depends on value types
-export type RangeQuery = DateRangeQuery | NumberRangeQuery | TermsRangeQuery
+export type RangeQuery = DateRangeQuery | NumberRangeQuery | TermRangeQuery
 
 export enum RangeRelation {
   /**