fix(dts-generator): support rest parameters in functions in nested types (#507)

1.)
When no param and no return type is given, generate "Function" instead
of "()=>void" to allow passing parameters, just like it happens in
simple function types.

2.)
When api.json contains:
Object<string,function(...any)>|function

Then the d.ts file will contain:
Record<string, (...p1: any) => void> | Function;

Before this fix, the function had no parameter.

Author: akudev

packages/dts-generator/src/phases/dts-code-gen.ts

@@ -867,14 +867,25 @@ function genType(ast: Type, usage: string = "unknown"): string {
       return intersectionTypes.join(" & ");
     case "FunctionType":
       text = "";
-      if (ast.isConstructor) {
-        text += "new ";
-      }
-      if (!_.isEmpty(ast.typeParameters)) {
-        text += `<${_.map(ast.typeParameters, (param) => param.name).join(", ")}>`; // TODO defaults, constraints, expressions
+      if (
+        !ast.isConstructor &&
+        _.isEmpty(ast.typeParameters) &&
+        _.isEmpty(ast.parameters) &&
+        !ast.type
+      ) {
+        // for simple functions, generate "Function" type
+        text += "Function";
+      } else {
+        // generate arrow function type
+        if (ast.isConstructor) {
+          text += "new ";
+        }
+        if (!_.isEmpty(ast.typeParameters)) {
+          text += `<${_.map(ast.typeParameters, (param) => param.name).join(", ")}>`; // TODO defaults, constraints, expressions
+        }
+        text += `(${_.map(ast.parameters, (param) => `${param.repeatable ? "..." : ""}${param.name}${param.optional ? "?" : ""}: ${genType(param.type, "parameter")}`).join(", ")})`;
+        text += ` => ${ast.type ? genType(ast.type, "returnValue") : "void"}`;
       }
-      text += `(${_.map(ast.parameters, (param) => `${param.name}${param.optional ? "?" : ""}: ${genType(param.type, "parameter")}`).join(", ")})`;
-      text += ` => ${ast.type ? genType(ast.type, "returnValue") : "void"}`;
       return text;
     case "NativeTSTypeExpression":
       // native TS type expression, emit the 'type' string "as is"

packages/dts-generator/src/utils/ts-ast-type-builder.ts

@@ -115,6 +115,7 @@ export class TSASTTypeBuilder {
       name: "p" + (idx + 1), // JSDoc function types don't allow parameter names -> generate names
       type: param,
       optional: (param as any).optional,
+      repeatable: (param as any).repeatable,
     }));
     if (thisType != null) {
       // for TS, a 'this' type is specified as the first parameter type of a function

test-packages/openui5-snapshot-test/output-dts/sap.ui.core.d.ts

@@ -83938,11 +83938,11 @@ declare module "sap/ui/test/Opa5" {
      * whether a function is used as arrangement or action. Each function typically contains one or multiple
      * `waitFor` statements.
      */
-    actions?: Record<string, () => void> | Function;
+    actions?: Record<string, Function> | Function;
     /**
      * A map or a class of functions that can be used as assertions in Opa tests.
      */
-    assertions?: Record<string, () => void> | Function;
+    assertions?: Record<string, Function> | Function;
   };
 }