feat: support inferred types in conditionals

factory/parser.ts

@@ -22,6 +22,7 @@ import { FunctionNodeParser } from "../src/NodeParser/FunctionNodeParser";
 import { FunctionParser } from "../src/NodeParser/FunctionParser";
 import { HiddenNodeParser } from "../src/NodeParser/HiddenTypeNodeParser";
 import { IndexedAccessTypeNodeParser } from "../src/NodeParser/IndexedAccessTypeNodeParser";
+import { InferTypeNodeParser } from "../src/NodeParser/InferTypeNodeParser";
 import { InterfaceAndClassNodeParser } from "../src/NodeParser/InterfaceAndClassNodeParser";
 import { IntersectionNodeParser } from "../src/NodeParser/IntersectionNodeParser";
 import { IntrinsicNodeParser } from "../src/NodeParser/IntrinsicNodeParser";
@@ -122,6 +123,8 @@ export function createParser(program: ts.Program, config: Config, augmentor?: Pa
         .addNodeParser(new TypeReferenceNodeParser(typeChecker, chainNodeParser))
         .addNodeParser(new ExpressionWithTypeArgumentsNodeParser(typeChecker, chainNodeParser))
 
+        .addNodeParser(new InferTypeNodeParser(typeChecker, chainNodeParser))
+
         .addNodeParser(new IndexedAccessTypeNodeParser(chainNodeParser))
         .addNodeParser(new TypeofNodeParser(typeChecker, chainNodeParser))
         .addNodeParser(new MappedTypeNodeParser(chainNodeParser, mergedConfig.additionalProperties))

src/NodeParser/ConditionalTypeNodeParser.ts

@@ -6,6 +6,10 @@ import { isAssignableTo } from "../Utils/isAssignableTo";
 import { narrowType } from "../Utils/narrowType";
 import { UnionType } from "../Type/UnionType";
 
+class CheckType {
+    constructor(public parameterName: string, public type: BaseType | undefined) {}
+}
+
 export class ConditionalTypeNodeParser implements SubNodeParser {
     public constructor(protected typeChecker: ts.TypeChecker, protected childNodeParser: NodeParser) {}
 
@@ -18,22 +22,27 @@ export class ConditionalTypeNodeParser implements SubNodeParser {
         const extendsType = this.childNodeParser.createType(node.extendsType, context);
         const checkTypeParameterName = this.getTypeParameterName(node.checkType);
 
+        const inferMap = new Map();
+
         // If check-type is not a type parameter then condition is very simple, no type narrowing needed
         if (checkTypeParameterName == null) {
-            const result = isAssignableTo(extendsType, checkType);
-            return this.childNodeParser.createType(result ? node.trueType : node.falseType, context);
+            const result = isAssignableTo(extendsType, checkType, inferMap);
+            return this.childNodeParser.createType(
+                result ? node.trueType : node.falseType,
+                this.createSubContext(node, context, undefined, result ? inferMap : new Map())
+            );
         }
 
         // Narrow down check type for both condition branches
-        const trueCheckType = narrowType(checkType, (type) => isAssignableTo(extendsType, type));
+        const trueCheckType = narrowType(checkType, (type) => isAssignableTo(extendsType, type, inferMap));
         const falseCheckType = narrowType(checkType, (type) => !isAssignableTo(extendsType, type));
 
         // Follow the relevant branches and return the results from them
         const results: BaseType[] = [];
         if (trueCheckType !== undefined) {
             const result = this.childNodeParser.createType(
                 node.trueType,
-                this.createSubContext(node, checkTypeParameterName, trueCheckType, context)
+                this.createSubContext(node, context, new CheckType(checkTypeParameterName, trueCheckType), inferMap)
             );
             if (result) {
                 results.push(result);
@@ -42,7 +51,7 @@ export class ConditionalTypeNodeParser implements SubNodeParser {
         if (falseCheckType !== undefined) {
             const result = this.childNodeParser.createType(
                 node.falseType,
-                this.createSubContext(node, checkTypeParameterName, falseCheckType, context)
+                this.createSubContext(node, context, new CheckType(checkTypeParameterName, falseCheckType))
             );
             if (result) {
                 results.push(result);
@@ -72,25 +81,36 @@ export class ConditionalTypeNodeParser implements SubNodeParser {
      * the check-type is a type parameter which is then narrowed down by the extends-type.
      *
      * @param node                   - The reference node for the new context.
-     * @param checkTypeParameterName - The type parameter name of the check-type.
-     * @param narrowedCheckType      - The narrowed down check type to use for the type parameter in sub parsers.
+     * @param checkType              - An object containing the type parameter name of the check-type, and the narrowed
+     *                                 down check type to use for the type parameter in sub parsers.
+     * @param inferMap               - A map that links parameter names to their inferred types.
      * @return The created sub context.
      */
     protected createSubContext(
         node: ts.ConditionalTypeNode,
-        checkTypeParameterName: string,
-        narrowedCheckType: BaseType,
-        parentContext: Context
+        parentContext: Context,
+        checkType?: CheckType,
+        inferMap: Map<string, BaseType> = new Map()
     ): Context {
         const subContext = new Context(node);
 
-        // Set new narrowed type for check type parameter
-        subContext.pushParameter(checkTypeParameterName);
-        subContext.pushArgument(narrowedCheckType);
+        // Newly inferred types take precedence over check and parent types.
+        inferMap.forEach((value, key) => {
+            subContext.pushParameter(key);
+            subContext.pushArgument(value);
+        });
+
+        if (checkType !== undefined) {
+            // Set new narrowed type for check type parameter
+            if (!(checkType.parameterName in inferMap)) {
+                subContext.pushParameter(checkType.parameterName);
+                subContext.pushArgument(checkType.type);
+            }
+        }
 
         // Copy all other type parameters from parent context
         parentContext.getParameters().forEach((parentParameter) => {
-            if (parentParameter !== checkTypeParameterName) {
+            if (parentParameter !== checkType?.parameterName && !(parentParameter in inferMap)) {
                 subContext.pushParameter(parentParameter);
                 subContext.pushArgument(parentContext.getArgument(parentParameter));
             }

src/NodeParser/InferTypeNodeParser.ts

@@ -0,0 +1,17 @@
+import ts from "typescript";
+import { Context, NodeParser } from "../NodeParser";
+import { SubNodeParser } from "../SubNodeParser";
+import { BaseType } from "../Type/BaseType";
+import { InferType } from "../Type/InferType";
+
+export class InferTypeNodeParser implements SubNodeParser {
+    public constructor(protected typeChecker: ts.TypeChecker, protected childNodeParser: NodeParser) {}
+
+    public supportsNode(node: ts.InferTypeNode): boolean {
+        return node.kind === ts.SyntaxKind.InferType;
+    }
+
+    public createType(node: ts.InferTypeNode, _context: Context): BaseType | undefined {
+        return new InferType(node.typeParameter.name.escapedText.toString());
+    }
+}

src/NodeParser/MappedTypeNodeParser.ts

@@ -87,7 +87,7 @@ export class MappedTypeNodeParser implements SubNodeParser {
     protected getProperties(node: ts.MappedTypeNode, keyListType: UnionType, context: Context): ObjectProperty[] {
         return keyListType
             .getTypes()
-            .filter((type) => type instanceof LiteralType)
+            .filter((type): type is LiteralType => type instanceof LiteralType)
             .reduce((result: ObjectProperty[], key: LiteralType) => {
                 const namedKey = this.mapKey(node, key, context);
                 const propertyType = this.childNodeParser.createType(

src/NodeParser/RestTypeNodeParser.ts

@@ -3,14 +3,16 @@ import { Context, NodeParser } from "../NodeParser";
 import { SubNodeParser } from "../SubNodeParser";
 import { ArrayType } from "../Type/ArrayType";
 import { BaseType } from "../Type/BaseType";
+import { InferType } from "../Type/InferType";
 import { RestType } from "../Type/RestType";
+import { TupleType } from "../Type/TupleType";
 
 export class RestTypeNodeParser implements SubNodeParser {
     public constructor(protected childNodeParser: NodeParser) {}
     public supportsNode(node: ts.RestTypeNode): boolean {
         return node.kind === ts.SyntaxKind.RestType;
     }
     public createType(node: ts.RestTypeNode, context: Context): BaseType {
-        return new RestType(this.childNodeParser.createType(node.type, context) as ArrayType);
+        return new RestType(this.childNodeParser.createType(node.type, context) as ArrayType | InferType | TupleType);
     }
 }

src/Type/InferType.ts

@@ -0,0 +1,11 @@
+import { BaseType } from "./BaseType";
+
+export class InferType extends BaseType {
+    constructor(private id: string) {
+        super();
+    }
+
+    public getId(): string {
+        return this.id;
+    }
+}

src/Type/RestType.ts

@@ -1,8 +1,10 @@
 import { ArrayType } from "./ArrayType";
 import { BaseType } from "./BaseType";
+import { InferType } from "./InferType";
+import { TupleType } from "./TupleType";
 
 export class RestType extends BaseType {
-    public constructor(private item: ArrayType, private title: string | null = null) {
+    public constructor(private item: ArrayType | InferType | TupleType, private title: string | null = null) {
         super();
     }
 
@@ -14,7 +16,7 @@ export class RestType extends BaseType {
         return this.title;
     }
 
-    public getType(): ArrayType {
+    public getType(): ArrayType | InferType | TupleType {
         return this.item;
     }
 }

src/Type/TupleType.ts

@@ -1,15 +1,40 @@
+import { derefType } from "../Utils/derefType";
+import { ArrayType } from "./ArrayType";
 import { BaseType } from "./BaseType";
+import { InferType } from "./InferType";
+import { RestType } from "./RestType";
+
+function normalize(types: Readonly<Array<BaseType | undefined>>): Array<BaseType | undefined> {
+    let normalized: Array<BaseType | undefined> = [];
+
+    for (const type of types) {
+        if (type instanceof RestType) {
+            const inner_type = derefType(type.getType()) as ArrayType | InferType | TupleType;
+            normalized = [
+                ...normalized,
+                ...(inner_type instanceof TupleType ? normalize(inner_type.getTypes()) : [type]),
+            ];
+        } else {
+            normalized.push(type);
+        }
+    }
+    return normalized;
+}
 
 export class TupleType extends BaseType {
-    public constructor(private types: readonly (BaseType | undefined)[]) {
+    private types: Readonly<Array<BaseType | undefined>>;
+
+    public constructor(types: Readonly<Array<BaseType | undefined>>) {
         super();
+
+        this.types = normalize(types);
     }
 
     public getId(): string {
         return `[${this.types.map((item) => item?.getId() ?? "never").join(",")}]`;
     }
 
-    public getTypes(): readonly (BaseType | undefined)[] {
+    public getTypes(): Readonly<Array<BaseType | undefined>> {
         return this.types;
     }
 }

src/TypeFormatter/TupleTypeFormatter.ts

@@ -1,5 +1,6 @@
 import { Definition } from "../Schema/Definition";
 import { SubTypeFormatter } from "../SubTypeFormatter";
+import { ArrayType } from "../Type/ArrayType";
 import { BaseType } from "../Type/BaseType";
 import { OptionalType } from "../Type/OptionalType";
 import { RestType } from "../Type/RestType";
@@ -8,6 +9,21 @@ import { TypeFormatter } from "../TypeFormatter";
 import { notUndefined } from "../Utils/notUndefined";
 import { uniqueArray } from "../Utils/uniqueArray";
 
+function uniformRestType(type: RestType, check_type: BaseType): boolean {
+    const inner = type.getType();
+    return (
+        (inner instanceof ArrayType && inner.getItem().getId() === check_type.getId()) ||
+        (inner instanceof TupleType &&
+            inner.getTypes().every((tuple_type) => {
+                if (tuple_type instanceof RestType) {
+                    return uniformRestType(tuple_type, check_type);
+                } else {
+                    return tuple_type?.getId() === check_type.getId();
+                }
+            }))
+    );
+}
+
 export class TupleTypeFormatter implements SubTypeFormatter {
     public constructor(protected childTypeFormatter: TypeFormatter) {}
 
@@ -20,6 +36,7 @@ export class TupleTypeFormatter implements SubTypeFormatter {
 
         const requiredElements = subTypes.filter((t) => !(t instanceof OptionalType) && !(t instanceof RestType));
         const optionalElements = subTypes.filter((t): t is OptionalType => t instanceof OptionalType);
+        // NOTE: A maximum of one rest type is assumed.
         const restType = subTypes.find((t): t is RestType => t instanceof RestType);
         const firstItemType = requiredElements.length > 0 ? requiredElements[0] : optionalElements[0]?.getType();
 
@@ -32,7 +49,7 @@ export class TupleTypeFormatter implements SubTypeFormatter {
             firstItemType &&
             requiredElements.every((item) => item.getId() === firstItemType.getId()) &&
             optionalElements.every((item) => item.getType().getId() === firstItemType.getId()) &&
-            (!restType || restType.getType().getItem().getId() === firstItemType.getId());
+            (!restType || uniformRestType(restType, firstItemType));
 
         // If so, generate a simple array with minItems (and possibly maxItems) instead.
         if (isUniformArray) {