fix(theme): pre-populate parameter defaults in API explorer form

demo/examples/tests/paramDefaults.yaml

@@ -0,0 +1,111 @@
+openapi: 3.0.0
+info:
+  title: Parameter Defaults Demo API
+  version: 1.0.0
+  description: |
+    Validates that `schema.default` values are pre-populated in the API explorer
+    form for parameters in every location (header, query, path, cookie) and for
+    the common scalar/enum/boolean schema types.
+
+    Regression coverage for: https://github.com/PaloAltoNetworks/docusaurus-openapi-docs/issues/1226
+
+tags:
+  - name: defaults
+    description: Parameter default value tests
+
+paths:
+  /headers:
+    get:
+      tags:
+        - defaults
+      summary: Header parameter defaults
+      description: |
+        Each header below declares a `schema.default`. The right-hand request
+        form should render those defaults pre-filled and the generated code
+        snippets should include them.
+      parameters:
+        - name: X-Api-Version
+          in: header
+          description: Free-form string default.
+          required: true
+          schema:
+            type: string
+            default: "2025-01-01"
+        - name: X-Region
+          in: header
+          description: Enum default — should appear pre-selected in the dropdown.
+          schema:
+            type: string
+            enum:
+              - us-east-1
+              - us-west-2
+              - eu-central-1
+            default: us-west-2
+        - name: X-Trace-Enabled
+          in: header
+          description: Boolean default — should appear pre-selected as "true".
+          schema:
+            type: boolean
+            default: true
+      responses:
+        "200":
+          description: OK
+
+  /query:
+    get:
+      tags:
+        - defaults
+      summary: Query parameter defaults
+      parameters:
+        - name: limit
+          in: query
+          description: Integer default.
+          schema:
+            type: integer
+            default: 25
+        - name: sort
+          in: query
+          description: Enum default.
+          schema:
+            type: string
+            enum:
+              - asc
+              - desc
+            default: desc
+      responses:
+        "200":
+          description: OK
+
+  /items/{itemId}:
+    get:
+      tags:
+        - defaults
+      summary: Path parameter default
+      description: |
+        Path defaults are unusual but legal — confirm the form pre-fills the
+        value rather than leaving the URL placeholder unresolved.
+      parameters:
+        - name: itemId
+          in: path
+          required: true
+          schema:
+            type: string
+            default: sample-item
+      responses:
+        "200":
+          description: OK
+
+  /session:
+    get:
+      tags:
+        - defaults
+      summary: Cookie parameter default
+      parameters:
+        - name: session_id
+          in: cookie
+          schema:
+            type: string
+            default: anonymous
+      responses:
+        "200":
+          description: OK

packages/docusaurus-theme-openapi-docs/src/theme/ApiExplorer/ParamOptions/ParamFormItems/ParamBooleanFormItem.tsx

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  * ========================================================================== */
 
-import React from "react";
+import React, { useEffect } from "react";
 
 import { translate } from "@docusaurus/Translate";
 import { ErrorMessage } from "@hookform/error-message";
@@ -33,10 +33,26 @@ export default function ParamBooleanFormItem({
   const {
     control,
     formState: { errors },
+    setValue,
   } = useFormContext();
 
   const showErrorMessage = errors?.paramBoolean;
 
+  useEffect(() => {
+    if (param.value === undefined) return;
+    const initial =
+      typeof param.value === "boolean" ? String(param.value) : param.value;
+    if (initial === "true" || initial === "false") {
+      setValue("paramBoolean", initial);
+      // Boolean defaults arrive in redux as actual booleans; normalize to the
+      // string form the rest of the form uses.
+      if (typeof param.value === "boolean") {
+        dispatch(setParam({ ...param, value: initial }));
+      }
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
   return (
     <>
       <Controller
@@ -50,11 +66,12 @@ export default function ParamBooleanFormItem({
             : false,
         }}
         name="paramBoolean"
-        render={({ field: { onChange } }) => (
+        render={({ field: { onChange, value } }) => (
           <FormSelect
             label={label}
             type={type}
             required={required}
+            value={value ?? "---"}
             options={["---", "true", "false"]}
             onChange={(e: React.ChangeEvent<HTMLSelectElement>) => {
               const val = e.target.value;

packages/docusaurus-theme-openapi-docs/src/theme/ApiExplorer/ParamOptions/ParamFormItems/ParamSelectFormItem.tsx

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  * ========================================================================== */
 
-import React from "react";
+import React, { useEffect } from "react";
 
 import { translate } from "@docusaurus/Translate";
 import { ErrorMessage } from "@hookform/error-message";
@@ -32,6 +32,7 @@ export default function ParamSelectFormItem({
   const {
     control,
     formState: { errors },
+    setValue,
   } = useFormContext();
 
   const showErrorMessage = errors?.paramSelect;
@@ -40,6 +41,16 @@ export default function ParamSelectFormItem({
 
   const options = getSchemaEnum(param.schema) ?? [];
 
+  useEffect(() => {
+    if (
+      typeof param.value === "string" &&
+      (options as string[]).includes(param.value)
+    ) {
+      setValue("paramSelect", param.value);
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
   return (
     <>
       <Controller
@@ -53,11 +64,12 @@ export default function ParamSelectFormItem({
             : false,
         }}
         name="paramSelect"
-        render={({ field: { onChange } }) => (
+        render={({ field: { onChange, value } }) => (
           <FormSelect
             label={label}
             type={type}
             required={required}
+            value={value ?? "---"}
             options={["---", ...(options as string[])]}
             onChange={(e: React.ChangeEvent<HTMLSelectElement>) => {
               const val = e.target.value;

packages/docusaurus-theme-openapi-docs/src/theme/ApiExplorer/ParamOptions/ParamFormItems/ParamTextFormItem.tsx

@@ -5,11 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  * ========================================================================== */
 
-import React from "react";
+import React, { useEffect } from "react";
 
 import FormTextInput from "@theme/ApiExplorer/FormTextInput";
 import { Param, setParam } from "@theme/ApiExplorer/ParamOptions/slice";
 import { useTypedDispatch } from "@theme/ApiItem/hooks";
+import { useFormContext } from "react-hook-form";
 
 export interface ParamProps {
   param: Param;
@@ -25,6 +26,15 @@ export default function ParamTextFormItem({
   required,
 }: ParamProps) {
   const dispatch = useTypedDispatch();
+  const { setValue } = useFormContext();
+
+  useEffect(() => {
+    if (param.value !== undefined && !Array.isArray(param.value)) {
+      setValue(param.name, param.value);
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
   return (
     <FormTextInput
       label={label}

packages/docusaurus-theme-openapi-docs/src/theme/ApiItem/index.tsx

@@ -122,7 +122,12 @@ export default function ApiItem(props: Props): JSX.Element {
       (param: { in: "path" | "query" | "header" | "cookie" }) => {
         const paramType = param.in;
         const paramsArray: ParameterObject[] = params[paramType];
-        paramsArray?.push(param as ParameterObject);
+        const defaultValue = (param as any).schema?.default;
+        const initialized =
+          defaultValue !== undefined
+            ? ({ ...param, value: defaultValue } as unknown as ParameterObject)
+            : (param as ParameterObject);
+        paramsArray?.push(initialized);
       }
     );
     const auth = createAuth({