[Codegen] Exclude unlinked libs from codegen (#47712)

packages/react-native/scripts/codegen/generate-artifacts-executor.js

@@ -152,6 +152,7 @@ function extractLibrariesFromJSON(configFile, dependencyPath) {
     const config = configFile.codegenConfig;
     return [
       {
+        libraryName: configFile.name,
         config,
         libraryPath: dependencyPath,
       },
@@ -251,19 +252,23 @@ function findExternalLibraries(pkgJson, projectRoot) {
   });
 }
 
-function findLibrariesFromReactNativeConfig(projectRoot) {
+function readRNConfigJSFile(projectRoot) {
   const rnConfigFileName = 'react-native.config.js';
 
-  console.log(
-    `\n\n[Codegen] >>>>> Searching for codegen-enabled libraries in ${rnConfigFileName}`,
-  );
-
   const rnConfigFilePath = path.resolve(projectRoot, rnConfigFileName);
 
   if (!fs.existsSync(rnConfigFilePath)) {
     return [];
   }
-  const rnConfig = require(rnConfigFilePath);
+  return require(rnConfigFilePath);
+}
+
+function findLibrariesFromReactNativeConfig(projectRoot) {
+  console.log(
+    `\n\n[Codegen] >>>>> Searching for codegen-enabled libraries in react-native.config.js`,
+  );
+
+  const rnConfig = readRNConfigJSFile(projectRoot);
 
   if (rnConfig.dependencies == null) {
     return [];
@@ -289,6 +294,33 @@ function findLibrariesFromReactNativeConfig(projectRoot) {
   });
 }
 
+// Function to look for libraries explicitly unlinked from the app
+// through the react-native.config.js file.
+// If this happens, it might be that the app does not need
+// to generate code for that library as it won't be used by that platform
+// @return { [libraryName: string]: [platform: string] }
+function findNotLinkedLibraries(projectRoot) {
+  const rnConfig = readRNConfigJSFile(projectRoot);
+
+  if (rnConfig.dependencies == null) {
+    return {};
+  }
+
+  let notLinkedLibraries = {};
+
+  Object.keys(rnConfig.dependencies).forEach(name => {
+    const dependency = rnConfig.dependencies[name];
+    let notLinkedPlatforms = [];
+    Object.keys(dependency.platforms).forEach(platform => {
+      if (dependency.platforms[platform] == null) {
+        notLinkedPlatforms.push(platform);
+      }
+    });
+    notLinkedLibraries[name] = notLinkedPlatforms
+  });
+  return notLinkedLibraries;
+}
+
 function findProjectRootLibraries(pkgJson, projectRoot) {
   console.log('[Codegen] Searching for codegen-enabled libraries in the app.');
 
@@ -694,6 +726,8 @@ function execute(projectRoot, targetPlatform, baseOutputPath) {
     let platforms =
       targetPlatform === 'all' ? supportedPlatforms : [targetPlatform];
 
+    const notLinkedLibraries = findNotLinkedLibraries(projectRoot);
+
     for (const platform of platforms) {
       const outputPath = computeOutputPath(
         projectRoot,
@@ -702,7 +736,15 @@ function execute(projectRoot, targetPlatform, baseOutputPath) {
         platform,
       );
 
-      const schemaInfos = generateSchemaInfos(libraries);
+      const schemaInfos = generateSchemaInfos(libraries.filter(library => {
+        const unlinkedPlatforms = notLinkedLibraries[library.libraryName];
+        if (unlinkedPlatforms && unlinkedPlatforms.includes(platform)) {
+          console.log(`[Codegen - ${library.libraryName}] Skipping Codegen on ${platform}`);
+          return false;
+        }
+        return true;
+      }));
+
       generateNativeCode(
         outputPath,
         schemaInfos.filter(schemaInfo =>