Add failing test case for #2781

Author: snoyberg

test/integration/tests/2781-shadow-bug/Main.hs

@@ -0,0 +1,10 @@
+import StackTest
+import System.Directory
+
+main :: IO ()
+main = do
+  createDirectoryIfMissing True "foo/src"
+  readFile "foo/v1/Foo.hs" >>= writeFile "foo/src/Foo.hs"
+  stack ["bench"]
+  readFile "foo/v2/Foo.hs" >>= writeFile "foo/src/Foo.hs"
+  stack ["bench"]

test/integration/tests/2781-shadow-bug/files/bar/bar.cabal

@@ -0,0 +1,18 @@
+name:                bar
+version:             0.1.0.0
+build-type:          Simple
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  exposed-modules:     Bar
+  build-depends:       base, foo
+  default-language:    Haskell2010
+
+benchmark bench
+  type:                exitcode-stdio-1.0
+  hs-source-dirs:      bench
+  main-is:             bench.hs
+  build-depends:       base
+                     , bar
+  default-language:    Haskell2010

test/integration/tests/2781-shadow-bug/files/bar/bench/bench.hs

@@ -0,0 +1,2 @@
+main :: IO ()
+main = return ()

test/integration/tests/2781-shadow-bug/files/bar/src/Bar.hs

@@ -0,0 +1,8 @@
+module Bar
+    ( bar
+    ) where
+
+import Foo
+
+bar :: IO ()
+bar = foo

test/integration/tests/2781-shadow-bug/files/foo/foo.cabal

@@ -0,0 +1,10 @@
+name:                foo
+version:             0.1.0.0
+build-type:          Simple
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  exposed-modules:     Foo
+  build-depends:       base
+  default-language:    Haskell2010

test/integration/tests/2781-shadow-bug/files/foo/v1/Foo.hs

@@ -0,0 +1,6 @@
+module Foo
+    ( foo
+    ) where
+
+foo :: IO ()
+foo = putStrLn "foo1"

test/integration/tests/2781-shadow-bug/files/foo/v2/Foo.hs

@@ -0,0 +1,6 @@
+module Foo
+    ( foo
+    ) where
+
+foo :: IO ()
+foo = putStrLn "foo2"

test/integration/tests/2781-shadow-bug/files/stack.yaml

@@ -0,0 +1,4 @@
+resolver: ghc-8.2.1
+packages:
+- foo
+- bar