Merge pull request #21190 from storybookjs/shilman/csf-tools-fix-conf…

…igfile-named-export-scalars

Csf Tools: Fix overriding scalar named export values

code/lib/csf-tools/src/ConfigFile.test.ts

@@ -262,6 +262,17 @@ describe('ConfigFile', () => {
           };
         `);
       });
+      it('found top-level scalar', () => {
+        expect(
+          setField(
+            ['foo'],
+            'baz',
+            dedent`
+              export const foo = 'bar';
+            `
+          )
+        ).toMatchInlineSnapshot(`export const foo = 'baz';`);
+      });
       it('found object', () => {
         expect(
           setField(

code/lib/csf-tools/src/ConfigFile.ts

@@ -113,6 +113,11 @@ export class ConfigFile {
 
   _exports: Record<string, t.Expression> = {};
 
+  // FIXME: this is a hack. this is only used in the case where the user is
+  // modifying a named export that's a scalar. The _exports map is not suitable
+  // for that. But rather than refactor the whole thing, we just use this as a stopgap.
+  _exportDecls: Record<string, t.VariableDeclarator> = {};
+
   _exportsObject: t.ObjectExpression | undefined;
 
   _quotes: 'single' | 'double' | undefined;
@@ -172,6 +177,7 @@ export class ConfigFile {
                   exportVal = _findVarInitialization(exportVal.name, parent as t.Program) as any;
                 }
                 self._exports[exportName] = exportVal;
+                self._exportDecls[exportName] = decl;
               }
             });
           } else {
@@ -268,6 +274,9 @@ export class ConfigFile {
       this._exports[path[0]] = expr;
     } else if (exportNode && t.isObjectExpression(exportNode) && rest.length > 0) {
       _updateExportNode(rest, expr, exportNode);
+    } else if (exportNode && rest.length === 0 && this._exportDecls[path[0]]) {
+      const decl = this._exportDecls[path[0]];
+      decl.init = _makeObjectExpression([], expr);
     } else if (this.hasDefaultExport) {
       // This means the main.js of the user has a default export that is not an object expression, therefore we can't change the AST.
       throw new Error(