Give Tab warning only once per file
Currently, when compiling a tabbed file, GHC spits out a huge number of warnings:
Main.hs:1:1: Warning: Tab character [..] Main.hs:89:1: Warning: Tab character Main.hs:90:1: Warning: Tab character Main.hs:91:1: Warning: Tab character Main.hs:92:1: Warning: Tab character Main.hs:99:4: Warning: Tab character Main.hs:100:4: Warning: Tab character Main.hs:101:4: Warning: Tab character
This is annoying and not very nice to our users.
I suggest to replace it by
This file contains tabs (e.g. line n column m); please use spaces instead
or (to be nice to tools that parse this output)
Main.hs:1:1: Tab found here, and in n further locations. Please use spaces instead.
(This is clearly a low priority request, but also possibly some low-hanging fruit for new contributors.)