fix: strip type exports upon DCE

fixes #6480

Author: schiller-manuel

packages/router-plugin/package.json

@@ -114,7 +114,6 @@
     "@tanstack/router-generator": "workspace:*",
     "@tanstack/router-utils": "workspace:*",
     "@tanstack/virtual-file-routes": "workspace:*",
-    "babel-dead-code-elimination": "^1.0.11",
     "chokidar": "^3.6.0",
     "unplugin": "^2.1.2",
     "zod": "^3.24.2"

packages/router-plugin/src/core/code-splitter/compilers.ts

@@ -2,10 +2,11 @@ import * as t from '@babel/types'
 import babel from '@babel/core'
 import * as template from '@babel/template'
 import {
+  generateFromAst,
+  parseAst,
   deadCodeElimination,
   findReferencedIdentifiers,
-} from 'babel-dead-code-elimination'
-import { generateFromAst, parseAst } from '@tanstack/router-utils'
+} from '@tanstack/router-utils'
 import { tsrSplit } from '../constants'
 import { routeHmrStatement } from '../route-hmr-statement'
 import { createIdentifier } from './path-ids'
@@ -430,6 +431,7 @@ export function compileCodeSplitReferenceRoute(
   if (!modified) {
     return null
   }
+
   deadCodeElimination(ast, refIdents)
 
   // if there are exported identifiers, then we need to add a warning

packages/router-utils/package.json

@@ -66,13 +66,14 @@
     "@babel/core": "^7.28.5",
     "@babel/generator": "^7.28.5",
     "@babel/parser": "^7.28.5",
+    "@babel/types": "^7.28.5",
     "ansis": "^4.1.0",
+    "babel-dead-code-elimination": "^1.0.11",
     "diff": "^8.0.2",
     "pathe": "^2.0.3",
     "tinyglobby": "^0.2.15"
   },
   "devDependencies": {
-    "@babel/types": "^7.28.5",
     "@types/babel__core": "^7.20.5",
     "@types/babel__generator": "^7.27.0",
     "@types/diff": "^7.0.2"

packages/router-utils/src/ast.ts

@@ -1,5 +1,10 @@
 import { parse } from '@babel/parser'
 import _generate from '@babel/generator'
+import * as t from '@babel/types'
+import {
+  deadCodeElimination as _deadCodeElimination,
+  findReferencedIdentifiers,
+} from 'babel-dead-code-elimination'
 import type { GeneratorOptions, GeneratorResult } from '@babel/generator'
 import type { ParseResult, ParserOptions } from '@babel/parser'
 import type * as _babel_types from '@babel/types'
@@ -36,3 +41,119 @@ export function generateFromAst(
   )
 }
 export type { GeneratorResult } from '@babel/generator'
+
+/**
+ * Strips TypeScript type-only exports and imports from an AST.
+ *
+ * This is necessary because babel-dead-code-elimination doesn't handle
+ * TypeScript type exports/imports. When a type export references an import
+ * that pulls in server-only code, the dead code elimination won't remove
+ * that import because it sees the type as still referencing it.
+ *
+ * This function removes:
+ * - `export type Foo = ...`
+ * - `export interface Foo { ... }`
+ * - `export type { Foo } from './module'`
+ * - Type specifiers in mixed exports: `export { value, type Foo }` -> `export { value }`
+ * - `import type { Foo } from './module'`
+ * - Type specifiers in mixed imports: `import { value, type Foo } from './module'` -> `import { value }`
+ * - Top-level `type Foo = ...` declarations (non-exported)
+ * - Top-level `interface Foo { ... }` declarations (non-exported)
+ *
+ * @param ast - The Babel AST (or ParseResult) to mutate
+ */
+export function stripTypeExports(ast: ParseResult<_babel_types.File>): void {
+  // Filter the program body to remove type-only nodes
+  ast.program.body = ast.program.body.filter((node) => {
+    // Remove top-level type alias declarations: `type Foo = string`
+    if (t.isTSTypeAliasDeclaration(node)) {
+      return false
+    }
+
+    // Remove top-level interface declarations: `interface Foo { ... }`
+    if (t.isTSInterfaceDeclaration(node)) {
+      return false
+    }
+
+    // Handle export declarations
+    if (t.isExportNamedDeclaration(node)) {
+      // Remove entire export if it's a type-only export
+      // e.g., `export type Foo = string`, `export interface Bar {}`, `export type { X } from './y'`
+      if (node.exportKind === 'type') {
+        return false
+      }
+
+      // For value exports with mixed specifiers, filter out type-only specifiers
+      // e.g., `export { value, type TypeOnly }` -> `export { value }`
+      if (node.specifiers.length > 0) {
+        node.specifiers = node.specifiers.filter((specifier) => {
+          if (t.isExportSpecifier(specifier)) {
+            return specifier.exportKind !== 'type'
+          }
+          return true
+        })
+
+        // If all specifiers were removed, remove the entire export declaration
+        // (unless it has a declaration like `export const x = 1`)
+        if (node.specifiers.length === 0 && !node.declaration) {
+          return false
+        }
+      }
+    }
+
+    // Handle import declarations
+    if (t.isImportDeclaration(node)) {
+      // Remove entire import if it's a type-only import
+      // e.g., `import type { Foo } from './module'`
+      if (node.importKind === 'type') {
+        return false
+      }
+
+      // For value imports with mixed specifiers, filter out type-only specifiers
+      // e.g., `import { value, type TypeOnly } from './module'` -> `import { value }`
+      if (node.specifiers.length > 0) {
+        node.specifiers = node.specifiers.filter((specifier) => {
+          if (t.isImportSpecifier(specifier)) {
+            return specifier.importKind !== 'type'
+          }
+          return true
+        })
+
+        // If all specifiers were removed, remove the entire import declaration
+        if (node.specifiers.length === 0) {
+          return false
+        }
+      }
+    }
+
+    return true
+  })
+}
+
+// Re-export findReferencedIdentifiers from babel-dead-code-elimination
+export { findReferencedIdentifiers }
+
+/**
+ * Performs dead code elimination on the AST, with TypeScript type stripping.
+ *
+ * This is a wrapper around babel-dead-code-elimination that first strips
+ * TypeScript type-only exports and imports. This is necessary because
+ * babel-dead-code-elimination doesn't handle type exports, which can cause
+ * imports to be retained when they're only referenced by type exports.
+ *
+ * @param ast - The Babel AST to mutate
+ * @param candidates - Optional set of identifier paths to consider for removal.
+ *                     If provided, only these identifiers will be candidates for removal.
+ *                     This should be the result of `findReferencedIdentifiers(ast)` called
+ *                     before any AST transformations.
+ */
+export function deadCodeElimination(
+  ast: ParseResult<_babel_types.File>,
+  candidates?: Set<any>,
+): void {
+  // First strip TypeScript type-only exports and imports
+  stripTypeExports(ast)
+
+  // Then run the original dead code elimination
+  _deadCodeElimination(ast, candidates)
+}

packages/router-utils/src/index.ts

@@ -1,4 +1,10 @@
-export { parseAst, generateFromAst } from './ast'
+export {
+  parseAst,
+  generateFromAst,
+  deadCodeElimination,
+  findReferencedIdentifiers,
+  stripTypeExports,
+} from './ast'
 export type { ParseAstOptions, ParseAstResult, GeneratorResult } from './ast'
 export { logDiff } from './logger'