Rollup merge of #28195 - AlisdairO:diagnostics214, r=Manishearth
Rollup merge of #28195 - AlisdairO:diagnostics214, r=Manishearth

As title :-)
Part of #24407.

r? @Manishearth

GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,graydon/rust