repo-tools: fix peer-deps check to skip unreferenced dependencies

The peer-deps verification was requiring all tracked peer dependencies
(including react-router-dom) for every package that references any of
them. Now it only requires a peer dependency if the package actually
references it or if it belongs to a group containing a referenced dep.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/fix-peer-deps-check-optional-deps.md

@@ -0,0 +1,5 @@
+---
+'@backstage/repo-tools': patch
+---
+
+Fixed the `peer-deps` command to only require peer dependencies that are actually referenced by each package, rather than requiring all tracked peer dependencies for every package with any React dependency.

packages/repo-tools/src/commands/peer-deps/peer-deps.ts

@@ -143,7 +143,22 @@ export default async ({ fix }: { fix: boolean }) => {
   for (const pkg of packagesWithRelevantDependencies) {
     const packageJson = pkg.packageJson as ExtendedPackageJSON;
     const expectedPeerDeps = getExpectedPeerDependencies(packageJson);
+    const allDeps = {
+      ...packageJson.dependencies,
+      ...packageJson.devDependencies,
+      ...packageJson.peerDependencies,
+    };
     for (const dep of Object.keys(peerDependencies)) {
+      const isReferencedInPackage = !!allDeps[dep];
+      const isInGroupWithReferencedDep = groupsOfPeerDependencies.some(
+        group =>
+          group.includes(dep) && group.some(groupDep => !!allDeps[groupDep]),
+      );
+
+      if (!isReferencedInPackage && !isInGroupWithReferencedDep) {
+        continue;
+      }
+
       // Validate that the peer dependencies are present.
       if (isPeerDependency(dep, packageJson)) {
         if (isOptional(dep) && !isMarkedAsOptional(dep, packageJson)) {