Fix support for non-ASCII module names

ChangeLog.md

@@ -55,6 +55,9 @@ Bug fixes:
 
 * Expose package library when running tests.
 
+* Fix support for non-ASCII module names. See
+  [4938](https://github.com/commercialhaskell/stack/issues/4938)
+
 ## v2.1.1.1
 
 Hackage-only release that removes `stack.yaml` from the sdist.  This is because

src/Stack/Package.hs

@@ -27,7 +27,6 @@ module Stack.Package
   ,applyForceCustomBuild
   ) where
 
-import qualified Data.ByteString.Char8 as B8
 import           Data.List (find, isPrefixOf, unzip)
 import           Data.Maybe (maybe)
 import qualified Data.Map.Strict as M
@@ -1117,7 +1116,8 @@ parseHI hiPath = do
         ]
       pure (S.empty, [])
     Right iface -> do
-      let moduleNames = fmap (fromString . B8.unpack . fst) . Iface.unList . Iface.dmods . Iface.deps
+      let moduleNames = fmap (fromString . T.unpack . decodeUtf8Lenient . fst) .
+                        Iface.unList . Iface.dmods . Iface.deps
           resolveFileDependency file = do
             resolved <- liftIO (forgivingAbsence (resolveFile dir file)) >>= rejectMissingFile
             when (isNothing resolved) $

test/integration/tests/4938-non-ascii-module-names/Main.hs

@@ -0,0 +1,5 @@
+import StackTest
+
+main :: IO ()
+main = do
+  stack ["build"]

test/integration/tests/4938-non-ascii-module-names/files/.gitignore

@@ -0,0 +1 @@
+*.cabal

test/integration/tests/4938-non-ascii-module-names/files/Lib.hs

@@ -0,0 +1,9 @@
+module Lib
+    ( foo
+    , bar
+    ) where
+
+import Täst
+
+bar :: Int
+bar = 42

test/integration/tests/4938-non-ascii-module-names/files/Täst.hs

@@ -0,0 +1,4 @@
+module Täst where
+
+foo :: Int
+foo = 42

test/integration/tests/4938-non-ascii-module-names/files/app/Main.hs

@@ -0,0 +1,6 @@
+module Main where
+
+import Täst
+
+main :: IO ()
+main = putStrLn "42"

test/integration/tests/4938-non-ascii-module-names/files/package.yaml

@@ -0,0 +1,10 @@
+name: umlaut
+dependencies: [base]
+library:
+  source-dirs: .
+executables:
+  exe:
+    main: Main.hs
+    source-dirs: app
+    dependencies:
+    - umlaut

test/integration/tests/4938-non-ascii-module-names/files/stack.yaml

@@ -0,0 +1 @@
+resolver: lts-11.22