7d046551a7
Substitute missing trait items suggestion correctly Properly substitute missing item suggestions, so that when they reference generics from their parent trait they actually have the right time for the impl. Also, some other minor tweaks like using `/* Type */` to signify a GAT's type is actually missing, and fixing generic arg suggestions for GATs in general.
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.