"-main-is" flag is broken for recent ghc-head (#15702) · Issues · Glasgow Haskell Compiler / GHC

"-main-is" flag is broken for recent ghc-head

Here is a minimal reproduction:

Main.hs:

main :: IO ()
main = putStrLn "Main"

Main2.hs:

module Main2 where

import Main

main2 :: IO ()
main2 = do
  putStrLn "Main2"
  main

Run ghc with something like /home/terrorjack/.stack/programs/x86_64-linux/ghc-8.7.20181003/bin/ghc -main-is Main2.main2 Main.hs Main2.hs, and it reports the following error:

[1 of 2] Compiling Main             ( Main.hs, Main.o )

Main.hs:1:1: error:
    Not in scope: ‘main2’
    Perhaps you meant ‘main’ (line 2)
  |
1 | main :: IO ()
  | ^

Meanwhile, the exact same flags work for ghc-8.6.1, and also a previous ghc-head build on d90946ce, so some accidental breakage might be in a recent commit.

Trac metadata

Trac field	Value
Version	8.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

Here is a minimal reproduction:

Main.hs:

```
main :: IO ()
main = putStrLn "Main"
```

Main2.hs:

```
module Main2 where

import Main

main2 :: IO ()
main2 = do
  putStrLn "Main2"
  main
```

Run ghc with something like `/home/terrorjack/.stack/programs/x86_64-linux/ghc-8.7.20181003/bin/ghc -main-is Main2.main2 Main.hs Main2.hs`, and it reports the following error:

```
[1 of 2] Compiling Main             ( Main.hs, Main.o )

Main.hs:1:1: error:
    Not in scope: ‘main2’
    Perhaps you meant ‘main’ (line 2)
  |
1 | main :: IO ()
  | ^
```

Meanwhile, the exact same flags work for ghc-8.6.1, and also a previous ghc-head build on d90946cea1357d3e99805c27dab1e811785a4088, so some accidental breakage might be in a recent commit.

<details><summary>Trac metadata</summary>

| Trac field             | Value        |
| ---------------------- | ------------ |
| Version                | 8.6.1        |
| Type                   | Bug          |
| TypeOfFailure          | OtherFailure |
| Priority               | normal       |
| Resolution             | Unresolved   |
| Component              | Compiler     |
| Test case              |              |
| Differential revisions |              |
| BlockedBy              |              |
| Related                |              |
| Blocking               |              |
| CC                     |              |
| Operating system       |              |
| Architecture           |              |

</details>