source-loader parse-helpers.js 6.4.9 regression (vs. 6.4.0)

[mgcrea]

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used patch-package to patch @storybook/source-loader@6.4.9 for the project I'm working on.

Here is the diff that solved my problem:

diff --git a/node_modules/@storybook/source-loader/dist/cjs/abstract-syntax-tree/parse-helpers.js b/node_modules/@storybook/source-loader/dist/cjs/abstract-syntax-tree/parse-helpers.js
index 1a9a63b..5040657 100644
--- a/node_modules/@storybook/source-loader/dist/cjs/abstract-syntax-tree/parse-helpers.js
+++ b/node_modules/@storybook/source-loader/dist/cjs/abstract-syntax-tree/parse-helpers.js
@@ -83,7 +83,7 @@ function findTemplate(templateName, program) {
 
     if (node.type === 'VariableDeclaration') {
       declarations = node.declarations;
-    } else if (node.type === 'ExportNamedDeclaration' && node.declaration.type === 'VariableDeclaration') {
+    } else if (node.type === 'ExportNamedDeclaration' && node.declaration?.type === 'VariableDeclaration') {
       declarations = node.declaration.declarations;
     }
 

This issue body was partially generated by patch-package.

Not sure why but bumping from 6.4.0 to 6.4.9 leads to some node element (inside program.body) that have a node.declaration set to null:

{
  node: {
    type: 'ExportNamedDeclaration',
    source: null,
    specifiers: [
      {
        type: 'ExportSpecifier',
        local: {
          type: 'Identifier',
          name: 'Button',
          range: [ 266, 272 ],
          loc: {
            start: { line: 5, column: 8 },
            end: { line: 5, column: 14 }
          },
          start: 266,
          end: 272
        },
        exported: {
          type: 'Identifier',
          name: 'Button',
          range: [ 266, 272 ],
          loc: {
            start: { line: 5, column: 8 },
            end: { line: 5, column: 14 }
          },
          start: 266,
          end: 272
        },
        exportKind: 'value',
        range: [ 266, 272 ],
        loc: { start: { line: 5, column: 8 }, end: { line: 5, column: 14 } },
        start: 266,
        end: 272
      }
    ],
    exportKind: 'value',
    declaration: null,
    assertions: [],
    range: [ 258, 274 ],
    loc: { start: { line: 5, column: 0 }, end: { line: 5, column: 16 } },
    start: 258,
    end: 274
  }
}

And breaks storybook.

[shilman]

@mgcrea Do you mind creating a PR with the change? I think we can merge this as is. Thanks!

[mgcrea]

@shilman done :) #17027

[shilman]

Shiver me timbers!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.5.0-alpha.4 containing PR #17027 that references this issue. Upgrade today to the @next NPM tag to try it out!

npx sb upgrade --prerelease

[shilman]

Hurrah!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.4.10 containing PR #17027 that references this issue. Upgrade today to the @latest NPM tag to try it out!

npx sb upgrade