Don’t add loadable if it’s not used

[timneutkens]

Part of #7536 separated out so it can be merged.

This makes sure next/dynamic is not added when it's not used, decreasing default bundle sizes.

[github-actions]

Stats from current PR

Click to expand stats

	zeit/next.js canary	timneutkens/next.js fix/only-add-loadable-when-needed	Change
Build Duration	14.3s	13.1s	-1.2s
node_modules Size	45.5 MB	45.5 MB	-77 B
Total Bundle (main, webpack, commons) Size	210 kB	206 kB	-3.87 kB
Total Bundle (main, webpack, commons) gzip Size	68.8 kB	67.8 kB	-1.04 kB
Client _app Size	2.39 kB	2.39 kB	✓
Client _app gzip Size	1.08 kB	1.08 kB	✓
Client _error Size	8.45 kB	8.45 kB	✓
Client _error gzip Size	3.24 kB	3.24 kB	✓
Client pages/index Size	296 B	296 B	✓
Client pages/index gzip Size	222 B	222 B	✓
Client pages/link Size	4.14 kB	4.14 kB	✓
Client pages/link gzip Size	1.82 kB	1.82 kB	✓
Client pages/routerDirect Size	423 B	423 B	✓
Client pages/routerDirect gzip Size	306 B	306 B	✓
Client pages/withRouter Size	435 B	435 B	✓
Client pages/withRouter gzip Size	301 B	301 B	✓
Client main Size	23.7 kB	19.8 kB	-3.87 kB
Client main gzip Size	7.82 kB	6.78 kB	-1.04 kB
Client commons Size	184 kB	184 kB	✓
Client commons gzip Size	59.7 kB	59.7 kB	✓
Client webpack Size	1.49 kB	1.49 kB	✓
Client webpack gzip Size	770 B	770 B	✓
Base Rendered Size	1.36 kB	1.36 kB	✓
Build Dir Size	757 kB	737 kB	-19.7 kB

Click to expand serverless stats

	zeit/next.js canary	timneutkens/next.js fix/only-add-loadable-when-needed	Change
Build Duration	15.2s	15s	-159ms
node_modules Size	45.5 MB	45.5 MB	-77 B
Total Bundle (main, webpack, commons) Size	210 kB	206 kB	-3.87 kB
Total Bundle (main, webpack, commons) gzip Size	68.8 kB	67.8 kB	-1.04 kB
Client _app Size	2.39 kB	2.39 kB	✓
Client _app gzip Size	1.08 kB	1.08 kB	✓
Client _error Size	8.45 kB	8.45 kB	✓
Client _error gzip Size	3.24 kB	3.24 kB	✓
Client pages/index Size	296 B	296 B	✓
Client pages/index gzip Size	222 B	222 B	✓
Client pages/link Size	4.14 kB	4.14 kB	✓
Client pages/link gzip Size	1.82 kB	1.82 kB	✓
Client pages/routerDirect Size	423 B	423 B	✓
Client pages/routerDirect gzip Size	306 B	306 B	✓
Client pages/withRouter Size	435 B	435 B	✓
Client pages/withRouter gzip Size	301 B	301 B	✓
Client main Size	23.7 kB	19.8 kB	-3.87 kB
Client main gzip Size	7.82 kB	6.78 kB	-1.04 kB
Client commons Size	184 kB	184 kB	✓
Client commons gzip Size	59.7 kB	59.7 kB	✓
Client webpack Size	1.49 kB	1.49 kB	✓
Client webpack gzip Size	770 B	770 B	✓
Serverless pages/link Size	338 kB	338 kB	⚠️ +96 B
Serverless pages/link gzip Size	86.8 kB	86.9 kB	⚠️ +23 B
Serverless pages/index Size	Error getting size	Error getting size	✓
Serverless pages/index gzip Size	Error getting size	Error getting size	✓
Serverless pages/_error Size	328 kB	329 kB	⚠️ +96 B
Serverless pages/_error gzip Size	84.1 kB	84.2 kB	⚠️ +23 B
Serverless pages/routerDirect Size	330 kB	330 kB	⚠️ +96 B
Serverless pages/routerDirect gzip Size	84.4 kB	84.4 kB	⚠️ +17 B
Serverless pages/withRouter Size	330 kB	330 kB	⚠️ +96 B
Serverless pages/withRouter gzip Size	84.4 kB	84.4 kB	⚠️ +22 B
Build Dir Size	1.95 MB	1.94 MB	-7.23 kB