From bd2f6ac5e3087f1445ad1d66fb43aba1994c1d0f Mon Sep 17 00:00:00 2001
From: Ajay Ghanwat <ghanwat.ajay@workroot.in>
Date: Wed, 19 Aug 2026 15:41:13 +0530
Subject: [PATCH] feat(compiler): compile client api blocks into the browser
 module

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
---
 packages/compiler/src/client-codegen.ts       | 27 ++++++
 .../compiler/test/api-block-codegen.test.ts   | 82 +++++++++++++++++++
 2 files changed, 109 insertions(+)
 create mode 100644 packages/compiler/test/api-block-codegen.test.ts

diff --git a/packages/compiler/src/client-codegen.ts b/packages/compiler/src/client-codegen.ts
index 7292ba27..066b7b5d 100644
--- a/packages/compiler/src/client-codegen.ts
+++ b/packages/compiler/src/client-codegen.ts
@@ -308,6 +308,32 @@ function _functionEntry(
   }`;
 }
 
+/**
+ * Client-mode api blocks become members of an `api` object in client scope.
+ *
+ * Only the response and error bodies are emitted; the declared field types are
+ * type-only and are consumed by the types generator instead. Anything
+ * TypeScript reaching this module would be a syntax error in the .mjs artifact.
+ */
+function apiBindings(ast: PageAst): string {
+  const members = ast.dataApis
+    .filter((block) => block.mode === "client" && block.sections)
+    .map((block) => {
+      const sections = block.sections!;
+      const response = sections.response.trim() || "return data;";
+      const error = sections.error.trim();
+      const failure = error
+        ? `(error) => { const status = error.status; const message = error.message; const data = error.data; ${error} }`
+        : `(error) => { throw error; }`;
+
+      return `    ${JSON.stringify(block.name)}: async (input) => context.callApi(${JSON.stringify(
+        block.path,
+      )}, ${JSON.stringify(block.method)}, input).then((data) => { ${response} }).catch(${failure})`;
+    });
+
+  return members.length ? `const api = {\n${members.join(",\n")}\n  };` : "";
+}
+
 export function generateBrowserModule(ast: PageAst): string {
   const functions = ast.runtimeFunctions.filter((fn) =>
     ["legacy", "client", "shared"].includes(fn.runtime),
@@ -365,6 +391,7 @@ function __wrnexusCreateClientFunctions(context) {
   const server = context.server;
   const props = context.props;
   const refs = context.refs;
+  ${apiBindings(ast)}
   const __wrnexusCommit = () => { ${sharedCommit} };
   const __wrnexusRestore = () => { ${sharedRestore} };
   ${!hasAuthoredCommit ? "const commit = __wrnexusCommit;" : ""}
diff --git a/packages/compiler/test/api-block-codegen.test.ts b/packages/compiler/test/api-block-codegen.test.ts
new file mode 100644
index 00000000..d1f07da2
--- /dev/null
+++ b/packages/compiler/test/api-block-codegen.test.ts
@@ -0,0 +1,82 @@
+import { expect, test } from "bun:test";
+import { parse } from "@wrnexus/syntax";
+import { generateTargets } from "../src/targets.ts";
+
+function browserModule(inner: string): string {
+  return generateTargets(
+    parse(`page Repro {
+  client {
+${inner}
+  }
+
+  functions {
+    client async function run(): Promise<void> {
+      const users = await api.searchUsers({ name: "Ajay" })
+      console.log(users)
+    }
+  }
+
+  view { <main><button @click="run()">go</button></main> }
+}
+`),
+  ).browser;
+}
+
+const BLOCK = `    api searchUsers POST /api/users {
+      request {
+        body {
+          name?: string
+          age?: number
+        }
+      }
+
+      response {
+        return data.users
+      }
+
+      error {
+        return []
+      }
+    }`;
+
+test("emits an api member that calls the transport with the block's path and method", () => {
+  const generated = browserModule(BLOCK);
+
+  expect(generated).toContain("const api =");
+  expect(generated).toContain("searchUsers");
+  expect(generated).toContain('"/api/users"');
+  expect(generated).toContain('"POST"');
+});
+
+test("declared field types never reach the browser module", () => {
+  // The artifact is written as .mjs and parsed as JavaScript.
+  const generated = browserModule(BLOCK);
+
+  expect(generated).not.toContain("name?: string");
+  expect(generated).not.toContain("age?: number");
+});
+
+test("the emitted module is valid JavaScript", () => {
+  const generated = browserModule(BLOCK);
+
+  expect(() => {
+    new Function(generated.replace(/^\s*import[^\n]*$/gm, "").replace(/\bexport\s+/g, ""));
+  }).not.toThrow();
+});
+
+test("a block without an error section still emits its response body", () => {
+  const generated = browserModule(`    api plainUsers GET /api/users {
+      request {
+        parameters {
+          team: string
+        }
+      }
+
+      response {
+        return data.users
+      }
+    }`);
+
+  expect(generated).toContain("plainUsers");
+  expect(generated).toContain("data.users");
+});