[bindings] Add custom field to enable writing one-off C++ in the zig class

src/bun.js/scripts/generate-classes.ts

@@ -447,7 +447,7 @@ function generateConstructorHeader(typeName) {
     `;
 }
 
-function generateConstructorImpl(typeName, obj) {
+function generateConstructorImpl(typeName, obj: ClassDefinition) {
   const name = constructorName(typeName);
   const { klass: fields } = obj;
   const hashTable =
@@ -890,6 +890,7 @@ JSC_DEFINE_CUSTOM_SETTER(${symbolName(
   return rows.join("\n");
 }
 
+var extraIncludes = [];
 function generateClassHeader(typeName, obj: ClassDefinition) {
   var { klass, proto, JSType = "ObjectType", values = [] } = obj;
   const name = className(typeName);
@@ -1003,6 +1004,21 @@ function generateClassHeader(typeName, obj: ClassDefinition) {
     
         void finishCreation(JSC::VM&);
 
+        ${Object.entries(obj.custom ?? {})
+          .map(([fieldName, field]) => {
+            if (field.extraHeaderIncludes?.length ?? 0) {
+              extraIncludes.push(...field.extraHeaderIncludes);
+            }
+
+            var str = "";
+            if (field.header) {
+              str += `#include "${field.header}";` + "\n";
+            }
+            str += `${field.type} ${fieldName};`;
+            return str;
+          })
+          .join("\n")}
+
         ${weakOwner}
 
         ${DECLARE_VISIT_CHILDREN}
@@ -1089,11 +1105,19 @@ void ${name}::visitOutputConstraintsImpl(JSCell *cell, Visitor& visitor)
 
 DEFINE_VISIT_OUTPUT_CONSTRAINTS(${name});
 
+
+
         `.trim();
   }
 
   var output = ``;
 
+  for (let { impl } of Object.values(obj.custom ?? {})) {
+    if (impl) {
+      output += `#include "${impl}";` + "\n";
+    }
+  }
+
   if (hasPendingActivity) {
     output += `
     extern "C" bool ${symbolName(typeName, "hasPendingActivity")}(void* ptr);
@@ -1291,7 +1315,6 @@ function generateZig(
       symbolName(typeName, "hasPendingActivity"),
     );
   }
-
   Object.values(klass).map((a) =>
     appendSymbols(exports, (name) => classSymbolName(typeName, name), a),
   );
@@ -1649,7 +1672,8 @@ function generateLazyClassStructureImpl(
       `.trim();
 }
 
-const GENERATED_CLASSES_HEADER = `
+const GENERATED_CLASSES_HEADER = [
+  `
 // GENERATED CODE - DO NOT MODIFY BY HAND
 // Generated by make codegen
 #pragma once
@@ -1661,12 +1685,16 @@ namespace Zig {
 
 #include "JSDOMWrapper.h"
 #include <wtf/NeverDestroyed.h>
+`,
+
+  `
 
 namespace WebCore {
 using namespace Zig;
 using namespace JSC;
 
-`;
+`,
+];
 
 const GENERATED_CLASSES_FOOTER = `
 }
@@ -1746,6 +1774,21 @@ void GlobalObject::visitGeneratedLazyClasses(GlobalObject *thisObject, Visitor&
 }
 
 const ZIG_GENERATED_CLASSES_HEADER = `
+/// Generated code! To regenerate, run:
+///
+///    make codegen
+///
+/// This file is generated by:
+///  1. \`bun src/bun.js/scripts/generate-classes.ts\`
+///  2. Scan for **/*.classes.ts files in src/bun.js/src
+///  3. Generate a JS wrapper for each class in:
+///        - Zig: generated_classes.zig
+///        - C++: ZigGeneratedClasses.h, ZigGeneratedClasses.cpp
+///  4. For the Zig code to successfully compile:
+///        - Add it to generated_classes_list.zig
+///        - pub usingnamespace JSC.Codegen.JSMyClassName;
+///  5. make clean-bindings && make bindings -j10
+///  
 const JSC = @import("bun").JSC;
 const Classes = @import("./generated_classes_list.zig").Classes;
 const Environment = @import("../../env.zig");
@@ -1799,9 +1842,12 @@ comptime {
   
   `,
 ]);
+const allHeaders = classes.map((a) => generateHeader(a.name, a));
 await writeAndUnlink(`${import.meta.dir}/../bindings/ZigGeneratedClasses.h`, [
-  GENERATED_CLASSES_HEADER,
-  ...classes.map((a) => generateHeader(a.name, a)),
+  GENERATED_CLASSES_HEADER[0],
+  ...[...new Set(extraIncludes.map((a) => `#include "${a}";` + "\n"))],
+  GENERATED_CLASSES_HEADER[1],
+  ...allHeaders,
   GENERATED_CLASSES_FOOTER,
 ]);
 await writeAndUnlink(`${import.meta.dir}/../bindings/ZigGeneratedClasses.cpp`, [