feat(compiler): emit browser api bindings only where the client calls them

packages/compiler/src/client-codegen.ts

@@ -308,15 +308,51 @@ function _functionEntry(
 }
 
 /**
- * Client-mode api blocks become members of an `api` object in client scope.
+ * Block names the page's client functions actually call.
+ *
+ * A block's response and error bodies are page code. Emitting one the browser
+ * never calls would ship a server-only transform to every visitor and grow the
+ * bundle for nothing.
+ */
+function clientCalledApiNames(ast: PageAst): Set<string> {
+  const called = new Set<string>();
+  const bodies = ast.runtimeFunctions
+    .filter((fn) => ["client", "shared"].includes(fn.runtime))
+    .map((fn) => fn.body)
+    .join("\n");
+
+  for (const match of bodies.matchAll(/\bapi\s*\.\s*([A-Za-z_$][A-Za-z0-9_$]*)/g)) {
+    called.add(match[1]!);
+  }
+
+  return called;
+}
+
+/**
+ * A block is emitted into the browser module when it is authored as
+ * client-only, or when it is mode "any" and a client function actually calls
+ * it. `hasClientApi` below must use this exact predicate so the `api`
+ * reserved-binding exclusion and the emitted object can never disagree.
+ */
+function isClientEmittedApiBlock(block: PageAst["dataApis"][number], called: Set<string>): boolean {
+  return (
+    Boolean(block.sections) &&
+    (block.mode === "client" || (block.mode === "any" && called.has(block.name)))
+  );
+}
+
+/**
+ * Client-mode and client-called any-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 called = clientCalledApiNames(ast);
   const members = ast.dataApis
-    .filter((block) => block.mode === "client" && block.sections)
+    .filter((block) => isClientEmittedApiBlock(block, called))
     .map((block) => {
       const sections = block.sections!;
       const response = eraseFunctionTypes(sections.response).trim() || "return data;";
@@ -345,7 +381,9 @@ export function generateBrowserModule(ast: PageAst): string {
   // `state api` without any client api blocks must keep reading/writing that
   // state as before, so only exclude the "api" name from destructuring when
   // there is a real `api` binding to shadow it.
-  const hasClientApi = ast.dataApis.some((block) => block.mode === "client" && block.sections);
+  const hasClientApi = ast.dataApis.some((block) =>
+    isClientEmittedApiBlock(block, clientCalledApiNames(ast)),
+  );
   const localRuntimeBindings = hasClientApi
     ? RUNTIME_BINDINGS
     : new Set([...RUNTIME_BINDINGS].filter((name) => name !== "api"));