replace regex replacemend logic in iifefyFunctionFile and handle `_…

…ENTRIES` declarations

in `iifefyFunctionFile` replace the regex replacement code that was present to prepare the
file contents to be embedded in the iife with more proper AST code modding

as part of this change make also sure that `_ENTRIES` identifiers are not modified if they
were actually declared inside the function file (as it happens in older Vercel CLI releases)

packages/next-on-pages/package.json

@@ -65,7 +65,8 @@
 		"miniflare": "^3.20231218.1",
 		"package-manager-manager": "^0.2.0",
 		"pcre-to-regexp": "^1.1.0",
-		"semver": "^7.5.2"
+		"semver": "^7.5.2",
+		"recast": "^0.23.4"
 	},
 	"devDependencies": {
 		"@changesets/cli": "^2.26.0",

packages/next-on-pages/src/buildApplication/processVercelFunctions/dedupeEdgeFunctions.ts

@@ -23,6 +23,8 @@ import {
 } from '../../utils';
 import { copyAssetFile } from './prerenderFunctions';
 import { cliError } from '../../cli';
+import * as recast from 'recast';
+import * as recastParser from 'recast/parsers/babel';
 
 /**
  * Dedupes edge functions that were found in the build output.
@@ -253,7 +255,7 @@ async function buildFunctionFile(
 
 	fnInfo.outputPath = relative(workerJsDir, newFnPath);
 
-	const finalFileContents = iifefyFunctionFile(
+	const finalFileContents = await iifefyFunctionFile(
 		fileContents,
 		functionImports,
 		fnInfo,
@@ -286,24 +288,17 @@ type BuildFunctionFileOpts = {
  * @param chunksExportsMap a map containing getters and chunks identifiers being used by the function
  * @returns the updated/iifefied file content
  */
-function iifefyFunctionFile(
+async function iifefyFunctionFile(
 	fileContents: string,
 	functionImports: string[],
 	functionInfo: FunctionInfo,
 	chunksExportsMap: Map<string, Set<string>>,
-): string {
+): Promise<string> {
+	const preparedFileContents =
+		prepareFunctionFileContentForIifeConversion(fileContents);
+
 	const wrappedContent = `
-		export default ((self, globalThis, global) => {
-			${fileContents
-				// it looks like there can be direct references to _ENTRIES (i.e. `_ENTRIES` instead of `globalThis._ENTRIES` etc...)
-				// we have to update all such references otherwise our proxying won't take effect on those
-				// (note: older versions of the Vercel CLI (v31 and older) used to declare _ENTRIES as "let _ENTRIES = {};", so we do
-				// need to make sure that we don't add `globalThis.` in these cases (if we were to drop support for those older versions
-				// the below line to: ".replace(/([^.])_ENTRIES/g, '$1globalThis._ENTRIES')")
-				.replace(/(?<!(let)\s*)([^.]|^)_ENTRIES/g, '$2globalThis._ENTRIES')
-				// the default export needs to become the return value of the iife, which is then re-exported as default
-				.replace(/export\s+default\s+/g, 'return ')}
-		})(proxy, proxy, proxy);
+		export default ((self, globalThis, global) => {${preparedFileContents}})(proxy, proxy, proxy);
 	`;
 
 	const proxyCall = `const proxy = globalThis.__nextOnPagesRoutesIsolation.getProxyFor('${
@@ -330,6 +325,79 @@ function iifefyFunctionFile(
 	].join('\n');
 }
 
+/**
+ * iifefyFunctionFile converts a function file's content into an iife (so that we can apply global proxies to
+ * it), this function is used to prepare the file's content so that it is ready to be embedded into an iife
+ *
+ * @param fileContents the original file contents
+ * @returns the file contents updated and ready to be embedded into an iife
+ */
+function prepareFunctionFileContentForIifeConversion(fileContents: string) {
+	const ast = recast.parse(fileContents, {
+		parser: recastParser,
+	});
+
+	let containsEntriesDeclaration = false;
+
+	recast.visit(ast, {
+		visitVariableDeclaration: function (path) {
+			const declarations = (path.value.declarations ??
+				[]) as AST.VariableDeclaratorKind[];
+			const contains = declarations.some(d => {
+				return d.id.type === 'Identifier' && d.id.name === '_ENTRIES';
+			});
+			if (contains) {
+				containsEntriesDeclaration = true;
+				// we don't need to traverse the ast anymore, returning false informs react of this
+				return false;
+			}
+			return this.traverse(path);
+		},
+	});
+
+	recast.visit(ast, {
+		// it looks like there can be direct references to _ENTRIES (i.e. `_ENTRIES` instead of `globalThis._ENTRIES` etc...)
+		// we have to update all such references otherwise our proxying won't take effect on those
+		// (note: older versions of the Vercel CLI (v31 and older) used to declare _ENTRIES as a module scoped object, that is
+		// why only apply the logic below if we didn't find a declaration for `_ENTRIES` (because if there was an `_ENTRIES`
+		// declaration updating it would just be incorrect and would break the js)
+		visitIdentifier: containsEntriesDeclaration
+			? undefined
+			: function (path) {
+					const value = path.value as AST.IdentifierKind;
+					if (!value.name.startsWith('_ENTRIES')) {
+						// we're only interested in modifying _ENTRIES identifiers
+						return this.traverse(path);
+					}
+					if (path.name === 'property') {
+						// if _ENTRIES is already accessed as a property bail
+						// i.e. if we encounter X._ENTRIES we don't want to modify it
+						return this.traverse(path);
+					}
+					path.value.name = `globalThis.${path.value.name}`;
+					this.traverse(path);
+			  },
+		visitProgram: function (path) {
+			// function files export as their default a function (i.e. `export default (() => {...})`)
+			// since we're moving the function file's logic inside an iife we need to convert such
+			// export in a return statement (i.e. `return () => {...}`)
+			const body = path.value.body as AST.StatementKind[];
+			const defaultExportIndex = body.findIndex(
+				statement => statement.type === 'ExportDefaultDeclaration',
+			);
+			if (defaultExportIndex >= 0) {
+				path.value.body[defaultExportIndex] =
+					recast.types.builders.returnStatement(
+						path.value.body[defaultExportIndex].declaration,
+					);
+			}
+			this.traverse(path);
+		},
+	});
+
+	return recast.print(ast).code;
+}
+
 /**
  * Prepends Wasm imports to a code block's built file.
  *