Run pod_setup.sh when Source files are added or removed

Summary:
Issue fixed: #1022

- [ ] All tests pass. Demo project builds and runs.
- [ ] I added tests, an experiment, or detailed why my change isn't tested.
- [ ] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Closes https://github.com/Instagram/IGListKit/pull/1031

Reviewed By: jeremycohen

Differential Revision: D6657283

Pulled By: rnystrom

fbshipit-source-id: 3033e08dbe1a0fd5b52f254dbefc924693b84b51

Dangerfile

@@ -27,6 +27,16 @@ if has_doc_changes && !has_doc_gen_title
   message("Docs are generated by using [Jazzy](https://github.com/realm/jazzy). If you want to contribute, please update [markdown guides](https://github.com/Instagram/IGListKit/tree/master/Guides)")
 end
 
+# Warn if Source files were added or removed but examples are not updated
+added_source_files = !git.added_files.grep(/Source/).empty?
+deleted_source_files = !git.deleted_files.grep(/Source/).empty?
+ios_pods_not_updated = !git.modified_files.include?("Examples/Examples-iOS/Podfile.lock")
+macos_pods_not_updated = !git.modified_files.include?("Examples/Examples-macOS/Podfile.lock")
+tvos_pods_not_updated = !git.modified_files.include?("Examples/Examples-tvOS/Podfile.lock")
+if (added_source_files || deleted_source_files) && (ios_pods_not_updated || macos_pods_not_updated || tvos_pods_not_updated)
+  warn("Adding or removing library source files requires updating the examples. Please run `./scripts/pod_setup.sh` from the root directory and commit the changes.")
+end
+
 swiftlint.verbose = true
 swiftlint.config_file = '.swiftlint_CI.yml'
 swiftlint.lint_files(inline_mode: true)