Add authToken for the npm registry to user-level .npmrc if it is not there (#110)

Author: Andarist

dist/index.js

@@ -42,14 +42,32 @@ const getOptionalInput = (name: string) => core.getInput(name) || undefined;
         "No changesets found, attempting to publish any unpublished packages to npm"
       );
 
-      let npmrcPath = `${process.env.HOME}/.npmrc`;
-      if (fs.existsSync(npmrcPath)) {
-        console.log("Found existing .npmrc file");
+      let userNpmrcPath = `${process.env.HOME}/.npmrc`;
+      if (fs.existsSync(userNpmrcPath)) {
+        console.log("Found existing user .npmrc file");
+        const userNpmrcContent = await fs.readFile(userNpmrcPath, "utf8");
+        const authLine = userNpmrcContent.split("\n").find((line) => {
+          // check based on https://github.com/npm/cli/blob/8f8f71e4dd5ee66b3b17888faad5a7bf6c657eed/test/lib/adduser.js#L103-L105
+          return /^\/\/registry\.npmjs\.org\/:[_-]authToken=/i.test(line);
+        });
+        if (authLine) {
+          console.log(
+            "Found existing auth token for the npm registry in the user .npmrc file"
+          );
+        } else {
+          console.log(
+            "Didn't find existing auth token for the npm registry in the user .npmrc file, creating one"
+          );
+          fs.appendFileSync(
+            userNpmrcPath,
+            `\n//registry.npmjs.org/:_authToken=${process.env.NPM_TOKEN}\n`
+          );
+        }
       } else {
-        console.log("No .npmrc file found, creating one");
+        console.log("No user .npmrc file found, creating one");
         fs.writeFileSync(
-          npmrcPath,
-          `//registry.npmjs.org/:_authToken=${process.env.NPM_TOKEN}`
+          userNpmrcPath,
+          `//registry.npmjs.org/:_authToken=${process.env.NPM_TOKEN}\n`
         );
       }