React Native: Package subpath './package.json' is not defined by "exports"

[brianlenz]

When using domutils v3 in a React Native project, you'll get a warning when building:

warn Package domutils has been ignored because it contains invalid configuration. Reason: Package subpath './package.json' is not defined by "exports" in $PATH/node_modules/domutils/package.json

This is something that has been reported for multiple packages in React Native here:

react-native-community/cli#1168

Each individual package maintainer has the ability to work around the issue, however, by simply exporting package.json. I'll submit a PR to do this and leave it up to you @fb55 if you'd like to merge.

[fb55]

Hi @brianlenz, do you know why the package.json is loaded in the first place?

[brianlenz]

Hi @fb55, honestly, I don't fully understand the background, but from the issue I linked, here's the explanation:

The reason is that, starting in Node.js 14.x, as soon as an npm module defines the exports field in package.json, only the files listed there are exported. If package.json is not included in that list, it's no longer possible to do things like require.resolve('uuid/package.json');.

The problematic piece of code is:

https://github.com/react-native-community/cli/blob/5819a17d148726a1185420b6df345dad6c81c81b/packages/cli/src/tools/config/resolveNodeModuleDir.ts#L11-L13

And then there is further background provided in a comment here:

react-native-community/cli#1168 (comment)

Given that the issue has been open in React Native for years, it seems there isn't a resolution coming on their end anytime soon. Most other projects in this situation have addressed the problem as I addressed it in the PR here (which you can see by all of the links to other projects in the issue).

Since React Native is such a popular framework, I figured it would be best for domutils to apply the same workaround to prevent the warning.

[fb55]

I will follow Sindre's lead here (react-native-community/cli#1168 (comment)), and won't be adding the package.json file to itself. As a workaround, you can use an earlier version of this module that doesn't provide an export map yet (the 2.x releases are fine). Hope that's okay!

[brianlenz]

@fb55, bummer, that's too bad. I guess we are stuck patching your package for the foreseeable future 😩 For anyone else who comes here with the same issue, you can use this patch file to fix it (either with Yarn 2 patch or patch-package):

diff --git a/package.json b/package.json
index 7955573aded67b578c6014d5e1bc94056f67f5a1..edc4e30427ff7e01b7869f3ea8b81b74488b1dcb 100644
--- a/package.json
+++ b/package.json
@@ -12,8 +12,11 @@
     "types": "lib/index.d.ts",
     "module": "lib/esm/index.js",
     "exports": {
-        "require": "./lib/index.js",
-        "import": "./lib/esm/index.js"
+        "./package.json": "./package.json",
+        ".": {
+            "require": "./lib/index.js",
+            "import": "./lib/esm/index.js"
+        }
     },
     "files": [
         "lib/**/*"

[fb55]

Is there a particular feature you need from the 3.x releases? Staying on an older version seems like much simpler solution here — but don't let me stop you from doing what's best for you.

[brianlenz]

Is there a particular feature you need from the 3.x releases? Staying on an older version seems like much simpler solution here — but don't let me stop you from doing what's best for you.

@fb55, I appreciate the consideration and help! 🙏 In our case, it's a transitive dependency that we don't have direct control over. I suppose forcing a downgrade through resolution may work, but it doesn't seem like a particularly good idea.

It may not ultimately matter, as it looks like react-native-cli may actually be addressing the root cause, though! Just now:

react-native-community/cli#1655

Glad to see after 2+ years 😁