GHC 8.6.4 Haddocks don't have source links
Usually, binary distributions include Haddock documentation pages for all the bundled libraries with source links (the sources have historically been generated with HsColour, although with Hadrian binary dists we've moved to using Haddock's own Hyperlinker backend). It looks like 8.6.4 bindists are missing the source links and files altogether:
$ l ~/.ghcup/ghc/8.6.4/share/doc/ghc-8.6.4/html/libraries/base-4.12.0.0/src
ls: /Users/atheriault/.ghcup/ghc/8.6.4/share/doc/ghc-8.6.4/html/libraries/base-4.12.0.0/src: No such file or directory
$ l ~/.ghcup/ghc/8.6.3/share/doc/ghc-8.6.3/html/libraries/base-4.12.0.0/src
total 21400
drwxr-xr-x 240 atheriault staff 8.0K Dec 14 08:30 .
drwxr-xr-x 231 atheriault staff 7.7K Dec 14 08:30 ..
-rw-r--r-- 1 atheriault staff 26K Dec 14 08:30 Control-Applicative.html
-rw-r--r-- 1 atheriault staff 68K Dec 14 08:30 Control-Arrow.html
-rw-r--r-- 1 atheriault staff 11K Dec 14 08:30 Control-Category.html
-rw-r--r-- 1 atheriault staff 19K Dec 14 08:30 Control-Concurrent-Chan.html
...
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