GHC uses source files from `.` even when `.` is not passed to `-i` (or is excluded).

Summary

(Relevant cabal bug)

The problem regards -i. Specifically you cannot exclude . (pwd) from the search path. Manual section.

Steps to reproduce

f@mkiii:/tmp/ghc-test$ tree .
.
├── Foo.hs
└── src
    └── Foo.hs

2 directories, 2 files
f@mkiii:/tmp/ghc-test$ cat Foo.hs
module Foo where

foo :: Int
foo = "bar"

f@mkiii:/tmp/ghc-test$ cat src/Foo.hs
module Foo where

foo :: Int
foo = 23

Notice how ./Foo.hs has an error in it, but ./src/Foo.hs is correct.

f@mkiii:/tmp/ghc-test$ ghc -i -isrc Foo

Note we are invoking ghc with an empty -i, which, according to the manual, “resets the search path back to nothing.”

[1 of 1] Compiling Foo              ( Foo.hs, Foo.o )

Foo.hs:4:7: error: [GHC-83865]
    • Couldn't match type ‘[Char]’ with ‘Int’
      Expected: Int
        Actual: String
    • In the expression: "bar"
      In an equation for ‘foo’: foo = "bar"
  |
4 | foo = "bar"
  |       ^^^^^

but Foo.hs is not ignored.

Expected behavior

./Foo.hs is ignored, compilations end without errors.

Environment

• GHC version used: 9.6.2

Optional:

• Operating System: Debian 12.1
• System Architecture: Linux x86_64