Allow export const in font loader (#40836)

Allow `export const font = Font()` syntax

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

packages/next-swc/crates/core/src/next_font_loaders/font_imports_generator.rs

@@ -68,7 +68,7 @@ impl<'a> FontImportsGenerator<'a> {
         None
     }
 
-    fn check_var_decl(&mut self, var_decl: &VarDecl) {
+    fn check_var_decl(&mut self, var_decl: &VarDecl) -> Option<Ident> {
         if let Some(decl) = var_decl.decls.get(0) {
             let ident = match &decl.name {
                 Pat::Ident(ident) => Ok(ident.id.clone()),
@@ -79,8 +79,6 @@ impl<'a> FontImportsGenerator<'a> {
                     let import_decl = self.check_call_expr(call_expr);
 
                     if let Some(mut import_decl) = import_decl {
-                        self.state.removeable_module_items.insert(var_decl.span.lo);
-
                         match var_decl.kind {
                             VarDeclKind::Const => {}
                             _ => {
@@ -100,12 +98,14 @@ impl<'a> FontImportsGenerator<'a> {
                                 import_decl.specifiers =
                                     vec![ImportSpecifier::Default(ImportDefaultSpecifier {
                                         span: DUMMY_SP,
-                                        local: ident,
+                                        local: ident.clone(),
                                     })];
 
                                 self.state
                                     .font_imports
                                     .push(ModuleItem::ModuleDecl(ModuleDecl::Import(import_decl)));
+
+                                return Some(ident);
                             }
                             Err(pattern) => {
                                 HANDLER.with(|handler| {
@@ -122,15 +122,45 @@ impl<'a> FontImportsGenerator<'a> {
                 }
             }
         }
+        None
     }
 }
 
 impl<'a> Visit for FontImportsGenerator<'a> {
     noop_visit_type!();
 
     fn visit_module_item(&mut self, item: &ModuleItem) {
-        if let ModuleItem::Stmt(Stmt::Decl(Decl::Var(var_decl))) = item {
-            self.check_var_decl(var_decl);
+        match item {
+            ModuleItem::Stmt(Stmt::Decl(Decl::Var(var_decl))) => {
+                if self.check_var_decl(var_decl).is_some() {
+                    self.state.removeable_module_items.insert(var_decl.span.lo);
+                }
+            }
+            ModuleItem::ModuleDecl(ModuleDecl::ExportDecl(export_decl)) => {
+                if let Decl::Var(var_decl) = &export_decl.decl {
+                    if let Some(ident) = self.check_var_decl(var_decl) {
+                        self.state
+                            .removeable_module_items
+                            .insert(export_decl.span.lo);
+
+                        self.state.font_exports.push(ModuleItem::ModuleDecl(
+                            ModuleDecl::ExportNamed(NamedExport {
+                                span: DUMMY_SP,
+                                specifiers: vec![ExportSpecifier::Named(ExportNamedSpecifier {
+                                    orig: ModuleExportName::Ident(ident),
+                                    span: DUMMY_SP,
+                                    exported: None,
+                                    is_type_only: false,
+                                })],
+                                src: None,
+                                type_only: false,
+                                asserts: None,
+                            }),
+                        ));
+                    }
+                }
+            }
+            _ => {}
         }
     }
 }

packages/next-swc/crates/core/src/next_font_loaders/mod.rs

@@ -39,6 +39,7 @@ pub struct State {
     font_functions: AHashMap<Id, FontFunction>,
     removeable_module_items: FxHashSet<BytePos>,
     font_imports: Vec<ModuleItem>,
+    font_exports: Vec<ModuleItem>,
     font_functions_in_allowed_scope: FxHashSet<BytePos>,
 }
 
@@ -76,10 +77,11 @@ impl VisitMut for NextFontLoaders {
             // Remove marked module items
             items.retain(|item| !self.state.removeable_module_items.contains(&item.span_lo()));
 
-            // Add font imports
+            // Add font imports and exports
             let mut new_items = Vec::new();
             new_items.append(&mut self.state.font_imports);
             new_items.append(items);
+            new_items.append(&mut self.state.font_exports);
             *items = new_items;
         }
     }

packages/next-swc/crates/core/tests/errors/next-font-loaders/export-let/input.js

@@ -0,0 +1,5 @@
+import React from 'react'
+import { Abel, Inter } from '@next/font/google'
+
+export let firaCode = Abel()
+export var inter = Inter()

packages/next-swc/crates/core/tests/errors/next-font-loaders/export-let/output.js

@@ -0,0 +1,5 @@
+import firaCode from "@next/font/google?pages/test.tsx;Abel";
+import inter from "@next/font/google?pages/test.tsx;Inter";
+import React from 'react';
+export { firaCode };
+export { inter };

packages/next-swc/crates/core/tests/errors/next-font-loaders/export-let/output.stderr

@@ -0,0 +1,12 @@
+
+  x Font loader calls must be assigned to a const
+   ,-[input.js:4:1]
+ 4 | export let firaCode = Abel()
+   :        ^^^^^^^^^^^^^^^^^^^^^
+   `----
+
+  x Font loader calls must be assigned to a const
+   ,-[input.js:5:1]
+ 5 | export var inter = Inter()
+   :        ^^^^^^^^^^^^^^^^^^^
+   `----

packages/next-swc/crates/core/tests/errors/next-font-loaders/not-ident/output.js

@@ -1 +1,7 @@
+const { a  } = Inter({
+    variant: '400'
+});
+const [b] = Inter({
+    variant: '400'
+});
 const { e  } = {};

packages/next-swc/crates/core/tests/fixture/next-font-loaders/export-const/input.js

@@ -0,0 +1,5 @@
+import React from 'react'
+import { Abel, Inter } from '@next/font/google'
+
+export const firaCode = Abel()
+export const inter = Inter()

packages/next-swc/crates/core/tests/fixture/next-font-loaders/export-const/output.js

@@ -0,0 +1,5 @@
+import firaCode from "@next/font/google?pages/test.tsx;Abel";
+import inter from "@next/font/google?pages/test.tsx;Inter";
+import React from 'react';
+export { firaCode };
+export { inter };

test/e2e/next-font/with-font-declarations-file/fonts.js

@@ -11,11 +11,11 @@ const openSans = Open_Sans()
 const sourceCodePro = Source_Code_Pro({ display: 'swap', preload: false })
 const abel = Abel({ variant: '400', display: 'optional', preload: false })
 
-const inter = Inter({ display: 'block', preload: true })
-const roboto = Roboto({ variant: '400' })
+export const inter = Inter({ display: 'block', preload: true })
+export const roboto = Roboto({ variant: '400' })
 
-const myLocalFont = localFont({
+export const myLocalFont = localFont({
   src: './my-font.woff2',
 })
 
-export { openSans, sourceCodePro, abel, inter, roboto, myLocalFont }
+export { openSans, sourceCodePro, abel }