Rollup merge of #27617 - AlisdairO:diagnostics193, r=Manishearth
Rollup merge of #27617 - AlisdairO:diagnostics193, r=Manishearth

As title :-)
Part of #24407.

r? @Manishearth

pshc/rust,GBGamer/rust,pshc/rust,GBGamer/rust,dwillmer/rust,aidancully/rust,pshc/rust,graydon/rust,dwillmer/rust,graydon/rust,aidancully/rust,pshc/rust,dwillmer/rust,dwillmer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,pshc/rust,graydon/rust,GBGamer/rust,dwillmer/rust,GBGamer/rust,aidancully/rust,dwillmer/rust,graydon/rust,pshc/rust,pshc/rust,dwillmer/rust,graydon/rust,aidancully/rust,graydon/rust,dwillmer/rust,aidancully/rust,GBGamer/rust,pshc/rust,aidancully/rust