GHC fails when GHC_PACKAGE_PATH contains trailing slash

When the directory given in GHC_PACKAGE_PATH contains a trailing slash, GHC stops working completely.

For example, this works:

env GHC_PACKAGE_PATH=/raid/src/ghc/ghc-atomic-writes/_build/stage1/lib/package.conf.d /raid/src/ghc/ghc-atomic-writes/_build/stage1/bin/ghc "--make" "-outputdir" "example-programs-build/" "example-programs/Hello.hs" "-o" "example-programs-build/haskell-hello"

but adding a trailing / like GHC_PACKAGE_PATH=/path/to/package.conf.d/ fails:

env GHC_PACKAGE_PATH=/raid/src/ghc/ghc-atomic-writes/_build/stage1/lib/package.conf.d/ /raid/src/ghc/ghc-atomic-writes/_build/stage1/bin/ghc "--make" "-outputdir" "example-programs-build/" "example-programs/Hello.hs" "-o" "example-programs-build/haskell-hello"    

[1 of 1] Compiling Main             ( example-programs/Hello.hs, example-programs-build/Main.o ) [Prelude changed]

example-programs/Hello.hs:1:1: error:
    Could not find module ‘Prelude’
    There are files missing in the ‘base-4.12.0.0’ package,
    try running 'ghc-pkg check'.
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
  |
1 | main :: IO ()
  | ^

This is surprising; most programs accept trailing slashes where directories are expected, and shells ofthen TAB-complete directories this way. It wastes developer time when they don't notice.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	nh2
Operating system
Architecture