diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
index daf617389d..af96fce828 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.md
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -5,7 +5,7 @@ about: Report a bug in Stack
 
 Please follow the steps below for reporting a bug in Stack:
 
-Make sure that you are using the latest release (currently Stack 3.9.3). See the
+Make sure that you are using the latest release (currently Stack 3.11.1). See the
 [upgrade instructions](http://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade)
 to upgrade.
 
@@ -45,7 +45,7 @@ stack <your command here> <args> --verbose
 
 ~~~text
 stack --version
-Version 3.9.3, Git revision c7eb8487a82d5c3e0b88d56f8b8a98be23223eb5 x86_64 hpack-0.39.1
+Version 3.11.1, Git revision 979bf6339fd4d5837c4d2fa8166dc715eef30ee2 x86_64 hpack-0.39.6
 ~~~
 
 ### Method of installation
diff --git a/.github/ISSUE_TEMPLATE/feature_request.md b/.github/ISSUE_TEMPLATE/feature_request.md
index 699675f815..81c6f24a36 100644
--- a/.github/ISSUE_TEMPLATE/feature_request.md
+++ b/.github/ISSUE_TEMPLATE/feature_request.md
@@ -3,7 +3,7 @@ name: Feature Request
 about: Request a feature be added to Stack, or discuss such a feature
 ---
 
-Make sure that you are using the latest release (currently Stack 3.9.3). See the
+Make sure that you are using the latest release (currently Stack 3.11.1). See the
 [upgrade instructions](http://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade)
 to upgrade.
 
diff --git a/.github/ISSUE_TEMPLATE/question.md b/.github/ISSUE_TEMPLATE/question.md
index 90e340d705..68a14bf866 100644
--- a/.github/ISSUE_TEMPLATE/question.md
+++ b/.github/ISSUE_TEMPLATE/question.md
@@ -16,7 +16,7 @@ the [stack-templates](https://github.com/commercialhaskell/stack-templates)
 repository instead.
 
 If you still want to ask the question here instead, please make sure that you
-are using the latest release (currently Stack 3.9.3). See the
+are using the latest release (currently Stack 3.11.1). See the
 [upgrade instructions](http://docs.haskellstack.org/en/stable/install_and_upgrade/#upgrade)
 to upgrade.
 
@@ -24,7 +24,7 @@ to upgrade.
 
 ~~~text
 stack --version
-Version 3.9.3, Git revision c7eb8487a82d5c3e0b88d56f8b8a98be23223eb5 x86_64 hpack-0.39.1
+Version 3.11.1, Git revision 979bf6339fd4d5837c4d2fa8166dc715eef30ee2 x86_64 hpack-0.39.6
 ~~~
 
 ### Method of installation
diff --git a/.github/workflows/integration-tests.yml b/.github/workflows/integration-tests.yml
index 36880d2a9f..e289cfee80 100644
--- a/.github/workflows/integration-tests.yml
+++ b/.github/workflows/integration-tests.yml
@@ -76,22 +76,17 @@ jobs:
           ~\AppData\Roaming\stack
           ~\AppData\Local\Programs\stack
         key: ${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('stack.yaml') }}-${{ matrix.cache-bust }}
-    - name: Install NSIS 3.12 on Windows
+    # Also upgrades to a 'large strings' build of NSIS 3.12 tool. See
+    # https://nsis.sourceforge.io/Special_Builds.
+    - name: Install and upgrade NSIS 3.12 on Windows
       if: startsWith(runner.os, 'Windows')
-      uses: repolevedavaj/install-nsis@v1.2.0
+      uses: repolevedavaj/install-nsis@v1.2.1
       with:
         nsis-version: '3.12'
-    # Upgrades to a 'large strings' build of NSIS 3.10 tool. See
-    # https://nsis.sourceforge.io/Special_Builds.
-    - name: Upgrade NSIS 3.12 on Windows
+    - name: Check NSIS 3.12 on Windows
       if: startsWith(runner.os, 'Windows')
       shell: bash
       run: |
-        # wget is not available but the Stack-supplied MSYS2 will provide it
-        stack exec -- wget -O nsis-3.12-strlen_8192.zip https://downloads.sourceforge.net/nsis/NSIS%203/3.12/nsis-3.12-strlen_8192.zip
-        7z x -aoa -o"/c/Program Files (x86)/NSIS" nsis-3.12-strlen_8192.zip
-        # Clean up
-        rm nsis-3.12-strlen_8192.zip
         makensis -VERSION && echo
         # Should include defined symbol NSIS_MAX_STRLEN=8192
         makensis -HDRINFO
diff --git a/.stan.toml b/.stan.toml
index 066f2ef802..299b627745 100644
--- a/.stan.toml
+++ b/.stan.toml
@@ -140,14 +140,14 @@
 
 # Anti-pattern: Data.ByteString.Char8.pack
 [[ignore]]
-  id = "OBS-STAN-0203-erw24B-1079:3"
+  id = "OBS-STAN-0203-erw24B-1138:3"
 # ✦ Description:   Usage of 'pack' function that doesn't handle Unicode characters
 # ✦ Category:      #AntiPattern
 # ✦ File:          src\Stack\Build\ExecuteEnv.hs
 #
-#  1078 ┃
-#  1079 ┃   S8.pack . formatTime defaultTimeLocale "%Y-%m-%dT%H:%M:%S%6Q"
-#  1080 ┃   ^^^^^^^
+#  1137 ┃
+#  1138 ┃   S8.pack . formatTime defaultTimeLocale "%Y-%m-%dT%H:%M:%S%6Q"
+#  1139 ┃   ^^^^^^^
 
 # Anti-pattern: Data.ByteString.Char8.pack
 [[ignore]]
@@ -156,9 +156,9 @@
 # ✦ Category:      #AntiPattern
 # ✦ File:          src\Stack\Build\ExecutePackage.hs
 #
-#   249 ┃
-#   250 ┃   newConfigFileRoot <- S8.pack . toFilePath <$> view configFileRootL
-#   251 ┃                        ^^^^^^^
+#   251 ┃
+#   252 ┃   newConfigFileRoot <- S8.pack . toFilePath <$> view configFileRootL
+#   253 ┃                        ^^^^^^^
 
 # Anti-pattern: Data.ByteString.Char8.pack
 [[ignore]]
diff --git a/ChangeLog.md b/ChangeLog.md
index c900df9116..705214044a 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,6 +1,20 @@
 # Changelog
 
-## v3.11.1 - 2026-06-13
+## Unreleased changes
+
+Release notes:
+
+**Changes since v3.11.1:**
+
+Major changes:
+
+Behavior changes:
+
+Other enhancements:
+
+Bug fixes:
+
+##  v3.11.1 - 2026-06-13
 
 **Changes since v3.9.3:**
 
diff --git a/cabal.config b/cabal.config
index c76de115f5..d0ba24cd26 100644
--- a/cabal.config
+++ b/cabal.config
@@ -180,7 +180,7 @@ constraints:
   , silently ==1.2.5.4
   , split ==0.2.5
   , splitmix ==0.1.3.2
-  , stack ==3.11.2
+  , stack ==3.12.0
   , static-bytes ==0.1.1
   , stm ==2.5.3.1
   , stm-chans ==3.0.0.11
diff --git a/package.yaml b/package.yaml
index 9cbac5e3b7..47d3055feb 100644
--- a/package.yaml
+++ b/package.yaml
@@ -2,7 +2,7 @@
 spec-version: 0.35.0
 
 name: stack
-version: '3.11.2'
+version: '3.12.0'
 synopsis: A program for developing Haskell projects
 description: |
   Stack (the Haskell Tool Stack) is a program for developing Haskell projects.
diff --git a/src/Stack/Build/Cache.hs b/src/Stack/Build/Cache.hs
index 2f5aca0d3e..366ae18b39 100644
--- a/src/Stack/Build/Cache.hs
+++ b/src/Stack/Build/Cache.hs
@@ -79,9 +79,7 @@ import           Stack.Types.EnvConfig
                    )
 import           Stack.Types.GhcPkgId ( ghcPkgIdString )
 import           Stack.Types.Installed
-                   ( InstallLocation (..), Installed (..)
-                   , InstalledLibraryInfo (..), foldOnGhcPkgId'
-                   )
+                   ( InstallLocation (..), Installed (..), foldOnGhcPkgId' )
 import           Stack.Types.NamedComponent
                    ( NamedComponent (..), componentCachePath )
 import           Stack.Types.SourceMap ( smRelDir )
@@ -301,12 +299,9 @@ deleteCaches dir =
 flagCacheKey :: (HasEnvConfig env) => Installed -> RIO env ConfigCacheKey
 flagCacheKey installed = do
   installationRoot <- installationRootLocal
-  case installed of
-    Library _ installedInfo -> do
-      let gid = installedInfo.ghcPkgId
-      pure $ configCacheKey installationRoot (ConfigCacheTypeFlagLibrary gid)
-    Executable ident -> pure $
-      configCacheKey installationRoot (ConfigCacheTypeFlagExecutable ident)
+  pure $ configCacheKey installationRoot $ case installed of
+    Library ident _ -> ConfigCacheTypeFlagLibrary ident
+    Executable ident -> ConfigCacheTypeFlagExecutable ident
 
 -- | Loads the Cabal flag cache for the given installed extra-deps.
 tryGetFlagCache ::
diff --git a/src/Stack/Build/ConstructPlan.hs b/src/Stack/Build/ConstructPlan.hs
index 37959fe739..ddb92bed59 100644
--- a/src/Stack/Build/ConstructPlan.hs
+++ b/src/Stack/Build/ConstructPlan.hs
@@ -1081,7 +1081,7 @@ checkDirtiness ::
      PackageSource
   -> Installed
   -> Package
-  -> Map PackageIdentifier GhcPkgId
+  -> Map MungedPackageId GhcPkgId
   -> Bool
      -- ^ Is Haddock documentation being built?
   -> M Bool
diff --git a/src/Stack/Build/ExecuteEnv.hs b/src/Stack/Build/ExecuteEnv.hs
index d13be2be47..5ae611b9bb 100644
--- a/src/Stack/Build/ExecuteEnv.hs
+++ b/src/Stack/Build/ExecuteEnv.hs
@@ -79,7 +79,7 @@ import           Stack.Prelude
 import           Stack.Types.ApplyGhcOptions ( ApplyGhcOptions (..) )
 import           Stack.Types.Build
                    ( ConvertPathsToAbsolute (..), ExcludeTHLoading (..)
-                   , KeepOutputOpen (..)
+                   , KeepOutputOpen (..), RunCabalWithArgs
                    )
 import           Stack.Types.Build.Exception
                    ( BuildException (..), BuildPrettyException (..) )
@@ -97,7 +97,8 @@ import           Stack.Types.CompilerPaths
 import           Stack.Types.Config
                    ( Config (..), HasConfig (..), stackRootL )
 import           Stack.Types.ConfigureOpts ( BaseConfigOpts (..) )
-import           Stack.Types.Dependency ( DepValue(..) )
+import           Stack.Types.Dependency
+                   ( DepLibrary (..), DepType (..), DepValue (..) )
 import           Stack.Types.DumpLogs ( DumpLogs (..) )
 import           Stack.Types.DumpPackage ( DumpPackage (..) )
 import           Stack.Types.EnvConfig
@@ -108,7 +109,9 @@ import           Stack.Types.EnvSettings ( EnvSettings (..) )
 import           Stack.Types.GhcPkgId ( GhcPkgId, ghcPkgIdString )
 import           Stack.Types.Installed ( InstallLocation (..), Installed (..) )
 import           Stack.Types.Package
-                   ( LocalPackage (..), Package (..), packageIdentifier )
+                   ( LocalPackage (..), Package (..), packageIdentifier
+                   , toCabalMungedPackageName
+                   )
 import           Stack.Types.Plan
                    ( TaskType (..), taskTypeLocation, taskTypePackageIdentifier
                    )
@@ -596,21 +599,25 @@ withSingleContext ::
   => ActionContext
   -> ExecuteEnv
   -> TaskType
-  -> Map PackageIdentifier GhcPkgId
-     -- ^ All dependencies' package ids to provide to Setup.hs.
+  -> Map MungedPackageId GhcPkgId
+     -- ^ Ids of Installed packages that are assumed to be available to build a
+     -- package's custom @Setup.hs@, given its dependencies specified in its
+     -- @custom-setup@ stanza of its Cabal file.
   -> Maybe String
+     -- ^ An optional suffix for the build log's file name.
   -> (  Package        -- Package info
      -> Path Abs File  -- Cabal file path
      -> Path Abs Dir   -- Package root directory file path
         -- Note that the `Path Abs Dir` argument is redundant with the
         -- `Path Abs File` argument, but we provide both to avoid recalculating
         -- `parent` of the `File`.
-     -> (KeepOutputOpen -> ExcludeTHLoading -> [String] -> RIO env ())
-        -- Function to run Cabal with args
+     -> RunCabalWithArgs env
+        -- Function to run Cabal (the library) with arguments.
      -> (Utf8Builder -> RIO env ())
         -- An plain 'announce' function, for different build phases
      -> OutputType
-     -> RIO env a)
+     -> RIO env a
+     )
   -> RIO env a
 withSingleContext
     ac
@@ -708,7 +715,8 @@ withSingleContext
        Package
     -> Path Abs Dir
     -> OutputType
-    -> (  (KeepOutputOpen -> ExcludeTHLoading -> [String] -> RIO env ())
+    -> (  RunCabalWithArgs env
+          -- Function to run Cabal (the library) with arguments.
        -> RIO env a
        )
     -> RIO env a
@@ -795,25 +803,57 @@ withSingleContext
                       pure cabalPackageArg
                 matchedDeps <-
                   forM (Map.toList customSetupDeps) $ \(name, depValue) -> do
-                    let matches (PackageIdentifier name' version) =
-                             name == name'
+                    let mungedPkgNames = depToMungedPkgNames name depValue
+                        countMungedPkgNames = Set.size mungedPkgNames
+                        matches (MungedPackageId mungedPkgName version) _ =
+                             mungedPkgName `Set.member` mungedPkgNames
                           && version `withinRange` depValue.versionRange
-                    case filter (matches . fst) (Map.toList allDeps) of
-                      x:xs -> do
-                        unless (null xs) $
-                          prettyWarnL
-                            [ flow "Found multiple installed packages for \
-                                   \custom-setup dep:"
-                            , style Current (fromPackageName name) <> "."
-                            ]
-                        pure ("-package-id=" ++ ghcPkgIdString (snd x), Just (fst x))
-                      [] -> do
+                    case Map.filterWithKey matches allDeps of
+                      matchedDeps | Map.null matchedDeps -> do
                         prettyWarnL
                           [ flow "Could not find custom-setup dep:"
                           , style Current (fromPackageName name) <> "."
                           ]
-                        pure ("-package=" ++ packageNameString name, Nothing)
-                let depsArgs = map fst matchedDeps
+                        pure (["-package=" <> packageNameString name], Nothing)
+                      matchedDeps -> do
+                        let groupMatchedByVersion =
+                              Map.foldlWithKey'
+                                ( \acc k v ->
+                                    let p = mungedVersion k
+                                        innerMap = Map.singleton k v
+                                    in  Map.insertWith Map.union p innerMap acc
+                                )
+                                Map.empty
+                                matchedDeps
+                            countMatchedDeps = Map.size matchedDeps
+                        if Map.size groupMatchedByVersion == 1
+                          then do
+                            when (countMatchedDeps < countMungedPkgNames) $
+                              prettyWarnL
+                                [ flow "Found insufficent installed packages \
+                                       \for custom-setup dep:"
+                                , style Current (fromPackageName name) <> "."
+                                ]
+                          else do
+                            prettyWarnL
+                              [ flow "Found installed packages with multiple \
+                                     \versions for custom-setup dep:"
+                              , style Current (fromPackageName name) <> "."
+                              ]
+                        let packageIdOpt ghcPkgId =
+                              "-package-id=" <> ghcPkgIdString ghcPkgId
+                            -- The previous algorithm (arbitrarily?) selected
+                            -- the first relevant item yielded by Map.toList
+                            -- (which is Map.toAscList), so we select the
+                            -- minimum:
+                            selectedGroup = Map.findMin groupMatchedByVersion
+                            selectedVersion = fst selectedGroup
+                            packageIdOpts =
+                              map packageIdOpt $ Map.elems $ snd selectedGroup
+                            selectedPkgId =
+                              PackageIdentifier name selectedVersion
+                        pure (packageIdOpts, Just selectedPkgId)
+                let depsArgs = L.concatMap fst matchedDeps
                 -- Generate setup_macros.h and provide it to ghc
                 let macroDeps = mapMaybe snd matchedDeps
                     cppMacrosFile = setupDir </> relFileSetupMacrosH
@@ -875,6 +915,25 @@ withSingleContext
           setupArgs =
             ("--builddir=" ++ toFilePathNoTrailingSep distDir') : args
 
+          depToMungedPkgNames ::
+               PackageName
+               -- ^ The name of the Cabal package.
+            -> DepValue
+               -- ^ The dependency value for that package.
+            -> Set.Set MungedPackageName
+          depToMungedPkgNames pkgName depValue
+            | AsLibrary depLibrary <- depValue.depType =
+                let addMain = if depLibrary.main
+                      then Set.insert mungedMainPkgName
+                      else id
+                    mungedMainPkgName = toCabalMungedPackageName pkgName Nothing
+                    subLibSet =
+                      Set.map
+                        (toCabalMungedPackageName pkgName . Just)
+                        depLibrary.subLib
+                in  addMain subLibSet
+            | otherwise = Set.empty
+
           runExe :: Path Abs File -> [String] -> RIO env ()
           runExe exeName fullArgs = do
             runAndOutput `catch` \ece -> do
diff --git a/src/Stack/Build/ExecutePackage.hs b/src/Stack/Build/ExecutePackage.hs
index 903a647b77..233a9a56b9 100644
--- a/src/Stack/Build/ExecutePackage.hs
+++ b/src/Stack/Build/ExecutePackage.hs
@@ -88,6 +88,7 @@ import           Stack.Package
                    )
 import           Stack.PackageDump ( conduitDumpPackage, ghcPkgDescribe )
 import           Stack.Prelude
+import           Stack.Types.Build ( RunCabalWithArgs )
 import           Stack.Types.Build.Exception
                    ( BuildException (..), BuildPrettyException (..) )
 import           Stack.Types.BuildConfig
@@ -129,7 +130,7 @@ import           Stack.Types.GhcPkgId ( GhcPkgId, ghcPkgIdToText )
 import           Stack.Types.GlobalOpts ( GlobalOpts (..) )
 import           Stack.Types.Installed
                    ( InstallLocation (..), Installed (..), InstalledMap
-                   , InstalledLibraryInfo (..)
+                   , InstalledLibraryInfo (..), simpleInstalledLib
                    )
 import           Stack.Types.IsMutable ( IsMutable (..) )
 import           Stack.Types.NamedComponent
@@ -138,8 +139,7 @@ import           Stack.Types.NamedComponent
                    )
 import           Stack.Types.Package
                    ( LocalPackage (..), Package (..), installedPackageToGhcPkgId
-                   , runMemoizedWith, simpleInstalledLib
-                   , toCabalMungedPackageName
+                   , runMemoizedWith, toCabalMungedPackageName
                    )
 import           Stack.Types.PackageFile ( PackageWarning (..) )
 import           Stack.Types.Plan
@@ -163,7 +163,7 @@ getConfigCache ::
   -> InstalledMap
   -> Bool
   -> Bool
-  -> RIO env (Map PackageIdentifier GhcPkgId, ConfigCache)
+  -> RIO env (Map MungedPackageId GhcPkgId, ConfigCache)
 getConfigCache ee task installedMap enableTest enableBench = do
   let extra =
         -- We enable tests if the test suite dependencies are already
@@ -198,11 +198,11 @@ getConfigCache ee task installedMap enableTest enableBench = do
       -- collision for the return here. But unifying things with configureOpts
       -- where it was the opposite resulted in this. It doesn't seem to make any
       -- difference anyway.
-      allDepsMap = Map.union missing' task.present
+      allDeps = Map.union missing' task.present
       configureOpts' = configureOptsFromBase
         cOpts.envConfig
         cOpts.baseConfigOpts
-        allDepsMap
+        allDeps
         cOpts.isLocalNonExtraDep
         cOpts.isMutable
         pcOpts
@@ -221,7 +221,7 @@ getConfigCache ee task installedMap enableTest enableBench = do
         , pkgSrc = task.cachePkgSrc
         , pathEnvVar = ee.pathEnvVar
         }
-  pure (allDepsMap, cache)
+  pure (allDeps, cache)
 
 -- | Ensure that the configuration for the package matches what is given
 ensureConfig ::
@@ -384,7 +384,7 @@ singleBuild
     installedMap
     isFinalBuild
   = do
-    (allDepsMap, cache) <-
+    (allDeps, cache) <-
       getConfigCache ee task installedMap enableTests enableBenchmarks
     let bcoSnapInstallRoot = ee.baseConfigOpts.snapInstallRoot
     mprecompiled <- getPrecompiled cache task.taskType bcoSnapInstallRoot
@@ -402,7 +402,7 @@ singleBuild
             (isFinalBuild, buildingFinals)
             cache
             curator
-            allDepsMap
+            allDeps
     whenJust minstalled $ \installed -> do
       writeFlagCache installed cache
       liftIO $ atomically $ modifyTVar ee.ghcPkgIds $ Map.insert pkgId installed
@@ -424,7 +424,10 @@ realConfigAndBuild ::
      -- ^ (isFinalBuild, buildingFinals)
   -> ConfigCache
   -> Maybe Curator
-  -> Map PackageIdentifier GhcPkgId
+  -> Map MungedPackageId GhcPkgId
+     -- ^ Ids of installed packages that are assumed to be available to build a
+     -- package's custom @Setup.hs@, given its dependencies specified in its
+     -- @custom-setup@ stanza of its Cabal file.
   -> RIO env (Maybe Installed)
 realConfigAndBuild
     ac
@@ -435,8 +438,8 @@ realConfigAndBuild
     (isFinalBuild, buildingFinals)
     cache
     mcurator0
-    allDepsMap
-  = withSingleContext ac ee task.taskType allDepsMap Nothing $
+    allDeps
+  = withSingleContext ac ee task.taskType allDeps Nothing $
       \package cabalFP pkgDir cabal0 announce _outputType -> do
         let cabal = cabal0 CloseOnException
         _neededConfig <-
@@ -508,9 +511,10 @@ realConfigAndBuild
   realBuild ::
        Package
     -> Path Abs Dir
-    -> (KeepOutputOpen -> ExcludeTHLoading -> [String] -> RIO env ())
+    -> RunCabalWithArgs env
+       -- ^ Function to run Cabal (the library) with arguments.
     -> (Utf8Builder -> RIO env ())
-       -- ^ A plain 'announce' function
+       -- ^ A plain 'announce' function.
     -> RIO env Installed
   realBuild package pkgDir cabal0 announce = do
     let cabal = cabal0 CloseOnException
@@ -721,27 +725,28 @@ fetchAndMarkInstalledPackage ::
   -> PackageIdentifier
   -> RIO env Installed
 fetchAndMarkInstalledPackage ee taskInstallLocation package pkgId = do
-  let ghcPkgIdLoader = fetchGhcPkgIdForLib ee taskInstallLocation package.name
-  -- Only pure the sub-libraries to cache them if we also cache the main
-  -- library (that is, if it exists)
-  if hasBuildableMainLibrary package
+  let hasMainLibrary = hasBuildableMainLibrary package
+      subLibs = package.subLibraries
+  if not hasMainLibrary && null subLibs
     then do
-      let foldSubLibToMap subLib mapInMonad = do
-            maybeGhcpkgId <- ghcPkgIdLoader (Just subLib.name)
-            mapInMonad <&> case maybeGhcpkgId of
-              Just v -> Map.insert subLib.name v
-              _ -> id
-      subLibsPkgIds <- foldComponentToAnotherCollection
-        package.subLibraries
-        foldSubLibToMap
-        mempty
-      ghcPkgIdLoader Nothing >>= \case
-        Nothing -> throwM $ Couldn'tFindPkgId package.name
-        Just ghcPkgId -> pure $ simpleInstalledLib pkgId ghcPkgId subLibsPkgIds
-    else do
-      markExeInstalled taskInstallLocation pkgId -- TODO unify somehow
-                                                  -- with writeFlagCache?
+      markExeInstalled taskInstallLocation pkgId
+      -- TODO: Unify the above somehow with writeFlagCache?
       pure $ Executable pkgId
+    else do
+      ghcPkgId <- if hasMainLibrary
+        then ghcPkgIdLoader Nothing
+        else pure Nothing
+      subLibsPkgIds <-
+        foldComponentToAnotherCollection subLibs foldSubLibToMap mempty
+      pure $ simpleInstalledLib pkgId ghcPkgId subLibsPkgIds
+ where
+  ghcPkgIdLoader = fetchGhcPkgIdForLib ee taskInstallLocation package.name
+
+  foldSubLibToMap subLib mapInMonad = do
+    maybeGhcpkgId <- ghcPkgIdLoader (Just subLib.name)
+    mapInMonad <&> case maybeGhcpkgId of
+      Just v -> Map.insert subLib.name v
+      _ -> id
 
 fetchGhcPkgIdForLib ::
      (HasTerm env, HasEnvConfig env)
@@ -750,7 +755,7 @@ fetchGhcPkgIdForLib ::
   -> PackageName
   -> Maybe Component.StackUnqualCompName
   -> RIO env (Maybe GhcPkgId)
-fetchGhcPkgIdForLib ee installLocation pkgName libName = do
+fetchGhcPkgIdForLib ee installLocation pkgName mLibName = do
   let baseConfigOpts = ee.baseConfigOpts
       (installedPkgDb, installedDumpPkgsTVar) =
         case installLocation of
@@ -761,11 +766,9 @@ fetchGhcPkgIdForLib ee installLocation pkgName libName = do
             ( baseConfigOpts.localDB
             , ee.localDumpPkgs )
   let commonLoader = loadInstalledPkg [installedPkgDb] installedDumpPkgsTVar
-  case libName of
-    Nothing -> commonLoader pkgName
-    Just v -> do
-      let mungedName = encodeCompatPackageName $ toCabalMungedPackageName pkgName v
-      commonLoader mungedName
+      mungedPkgName = toCabalMungedPackageName pkgName mLibName
+      encodedPkgName = encodeCompatPackageName mungedPkgName
+  commonLoader encodedPkgName
 
 -- | Copy ddump-* files, if we are building finals and a non-empty ddump-dir
 -- has been specified.
@@ -921,7 +924,7 @@ copyPreCompiled ee task pkgId (PrecompiledCache mlib subLibs exes) = do
       pure $ Just $
         case mpkgid of
           Nothing -> assert False $ Executable pkgId
-          Just pkgid -> simpleInstalledLib pkgId pkgid mempty
+          _ -> simpleInstalledLib pkgId mpkgid mempty
  where
   bindir = ee.baseConfigOpts.snapInstallRoot </> bindirSuffix
 
@@ -994,11 +997,11 @@ singleTest ::
 singleTest topts testsToRun ac ee task installedMap = do
   -- FIXME: Since this doesn't use cabal, we should be able to avoid using a
   -- full blown 'withSingleContext'.
-  (allDepsMap, _cache) <- getConfigCache ee task installedMap True False
+  (allDeps, _cache) <- getConfigCache ee task installedMap True False
   mcurator <- view $ buildConfigL . to (.curator)
   let pname = pkgName $ taskProvides task
       expectFailure = expectTestFailure pname mcurator
-  withSingleContext ac ee task.taskType allDepsMap (Just "test") $
+  withSingleContext ac ee task.taskType allDeps (Just "test") $
     \package _cabalfp pkgDir _cabal announce outputType -> do
       config <- view configL
       let needHpc = topts.coverage
@@ -1062,8 +1065,8 @@ singleTest topts testsToRun ac ee task installedMap = do
               idMap <- liftIO $ readTVarIO ee.ghcPkgIds
               pure $ Map.lookup (taskProvides task) idMap
           let pkgGhcIdList = case installed of
-                               Just (Library _ libInfo) -> [libInfo.ghcPkgId]
-                               _ -> []
+                Just (Library _ libInfo) -> maybeToList libInfo.mMainGhcPkgId
+                _ -> []
           -- doctest relies on template-haskell in QuickCheck-based tests
           thGhcId <-
             case L.find ((== "template-haskell") . pkgName . (.packageIdent) . snd)
@@ -1103,7 +1106,7 @@ singleTest topts testsToRun ac ee task installedMap = do
                          <> display (ghcPkgIdToText ghcId)
                          <> "\n"
                      )
-                     (pkgGhcIdList ++ thGhcId:Map.elems allDepsMap)
+                     (pkgGhcIdList ++ thGhcId : Map.elems allDeps)
           writeFileUtf8Builder fp ghcEnv
           menv <- liftIO $
             setEnv fp =<< config.processContextSettings EnvSettings
@@ -1302,8 +1305,8 @@ singleBench ::
   -> InstalledMap
   -> RIO env ()
 singleBench beopts benchesToRun ac ee task installedMap = do
-  (allDepsMap, _cache) <- getConfigCache ee task installedMap False True
-  withSingleContext ac ee task.taskType allDepsMap (Just "bench") $
+  (allDeps, _cache) <- getConfigCache ee task installedMap False True
+  withSingleContext ac ee task.taskType allDeps (Just "bench") $
     \_package _cabalfp _pkgDir cabal announce _outputType -> do
       let args = map unqualCompToString benchesToRun <> maybe []
                        ((:[]) . ("--benchmark-options=" <>))
diff --git a/src/Stack/Build/Installed.hs b/src/Stack/Build/Installed.hs
index 1e2d4d5b45..609175df4d 100644
--- a/src/Stack/Build/Installed.hs
+++ b/src/Stack/Build/Installed.hs
@@ -287,7 +287,7 @@ toLoadHelper compiler pkgDb dp = LoadHelper
     if name `Set.member` wiredInPackages compiler
       then []
       else dp.depends
-  installedLibInfo = InstalledLibraryInfo ghcPkgId (Right <$> dp.license) mempty
+  installedLibInfo = InstalledLibraryInfo (Just ghcPkgId) mempty
 
   toInstallLocation :: PackageDbVariety -> InstallLocation
   toInstallLocation GlobalDb = Snap
@@ -313,23 +313,26 @@ gatherAndTransformSubLoadHelper lh =
       (_, Library _ existingLibInfo)
     = ( pLoc
       , Library pn existingLibInfo
-          { subLib = Map.union
-              incomingLibInfo.subLib
-              existingLibInfo.subLib
-          , ghcPkgId = if isJust lh.subLibDump
-                      then existingLibInfo.ghcPkgId
-                      else incomingLibInfo.ghcPkgId
+          { subLib = Map.union incomingLibInfo.subLib existingLibInfo.subLib
+          , mMainGhcPkgId =
+              if isJust lh.subLibDump
+                then existingLibInfo.mMainGhcPkgId
+                else incomingLibInfo.mMainGhcPkgId
           }
       )
   onPreviousLoadHelper newVal _oldVal = newVal
   (key, value) = case lh.subLibDump of
     Nothing -> (rawPackageName, rawValue)
     Just sd -> (sd.packageName, updateAsSublib sd <$> rawValue)
+  -- rawValue should always have a main library: see toLoadHelper.
   (rawPackageName, rawValue) = lh.pair
   updateAsSublib
       sd
       (Library (PackageIdentifier _sublibMungedPackageName version) libInfo)
-    = Library
-        (PackageIdentifier key version)
-        libInfo { subLib = Map.singleton sd.libraryName libInfo.ghcPkgId }
+    = case libInfo.mMainGhcPkgId of
+        Nothing ->
+          error "gatherAndTransformSubLoadHelper: the impossible happened!"
+        Just ghcPkgId' -> Library
+          (PackageIdentifier key version)
+          libInfo { subLib = Map.singleton sd.libraryName ghcPkgId' }
   updateAsSublib _ v = v
diff --git a/src/Stack/ConfigureOpts.hs b/src/Stack/ConfigureOpts.hs
index 539d12ddcc..6a31ed3740 100644
--- a/src/Stack/ConfigureOpts.hs
+++ b/src/Stack/ConfigureOpts.hs
@@ -18,8 +18,6 @@ module Stack.ConfigureOpts
 import qualified Data.Map as Map
 import qualified Data.Text as T
 import           Database.Persist ( Entity, entityVal )
-import           Distribution.Types.MungedPackageName
-                   ( decodeCompatPackageName )
 import           Distribution.Types.PackageName ( unPackageName )
 import           Distribution.Types.UnqualComponentName
                    ( unUnqualComponentName )
@@ -70,7 +68,7 @@ configureOptsFromDb x y = ConfigureOpts
 configureOptsFromBase ::
      EnvConfig
   -> BaseConfigOpts
-  -> Map PackageIdentifier GhcPkgId -- ^ dependencies
+  -> Map MungedPackageId GhcPkgId -- ^ dependencies
   -> Bool -- ^ local non-extra-dep?
   -> IsMutable
   -> PackageConfigureOpts
@@ -119,7 +117,7 @@ configureOptsPathRelated bco isMutable pkgOpts = concat
 configureOptsNonPathRelated ::
      EnvConfig
   -> BaseConfigOpts
-  -> Map PackageIdentifier GhcPkgId -- ^ Dependencies.
+  -> Map MungedPackageId GhcPkgId -- ^ Dependencies.
   -> Bool -- ^ Is this a local, non-extra-dep?
   -> PackageConfigureOpts
   -> [String]
@@ -197,18 +195,18 @@ configureOptsNonPathRelated econfig bco deps isLocal package = concat
 
   depOptions = mapAndAppend toDepOption [] deps
 
-  toDepOption (PackageIdentifier name _) gid = concat
+  toDepOption (MungedPackageId name _) gid = concat
     [ "--dependency="
     , depOptionKey
     , "="
     , ghcPkgIdString gid
     ]
    where
-    MungedPackageName subPkgName lib = decodeCompatPackageName name
-    depOptionKey = case lib of
-      LMainLibName -> unPackageName name
-      LSubLibName cn ->
-        unPackageName subPkgName <> ":" <> unUnqualComponentName cn
+    MungedPackageName pkgName libName = name
+    pkgName' = unPackageName pkgName
+    depOptionKey = case libName of
+      LMainLibName -> pkgName'
+      LSubLibName cn -> pkgName' <> ":" <> unUnqualComponentName cn
 
 -- | Render configure options as a single list of options.
 renderConfigureOpts :: ConfigureOpts -> [String]
diff --git a/src/Stack/Ghci.hs b/src/Stack/Ghci.hs
index 8db0e71196..d6cca1d93a 100644
--- a/src/Stack/Ghci.hs
+++ b/src/Stack/Ghci.hs
@@ -182,6 +182,7 @@ data GhciPkgDesc = GhciPkgDesc
   { package :: !Package
   , cabalFP :: !(Path Abs File)
   , target :: !Target
+    -- ^ How the package is intended to be built.
   }
 
 -- | Type synonym representing maps from a module name to a map with all of the
@@ -292,8 +293,12 @@ ghci opts = do
     localTargets
     mainFile
     pkgs
+    -- Files targets with unknown GHC options:
     (maybe [] snd mfileTargets)
+    -- The names of packages to be exposed:
     (nonLocalTargets ++ addPkgs)
+    -- A map of package names and sequences of their sublibrary components
+    -- depended upon (if any):
     relevantDependencies
 
 preprocessTargets ::
@@ -301,6 +306,7 @@ preprocessTargets ::
   => BuildOptsCLI
   -> SMActual GlobalPackage
   -> [Text]
+     -- ^ Raw (unprocessed) targets from the command line.
   -> RIO env (Either [Path Abs File] (Map PackageName Target))
 preprocessTargets buildOptsCLI sma rawTargets = do
   let (fileTargetsRaw, normalTargetsRaw) =
@@ -349,7 +355,12 @@ findFileTargets ::
      HasEnvConfig env
   => [LocalPackage]
   -> [Path Abs File]
-  -> RIO env (Map PackageName Target, Map PackageName [Path Abs File], [Path Abs File])
+  -> RIO
+       env
+       ( Map PackageName Target
+       , Map PackageName [Path Abs File]
+       , [Path Abs File]
+       )
 findFileTargets locals fileTargets = do
   filePackages <- forM locals $ \lp -> do
     PackageComponentFile _ compFiles _ _ <- getPackageFile lp.package lp.cabalFP
@@ -486,10 +497,17 @@ runGhci ::
   => GhciOpts
   -> [(PackageName, (Path Abs File, Target))]
   -> Maybe (Path Abs File)
+     -- ^ Path to source file for selected main module. 'Nothing' if no main
+     -- module is to be loaded and imported.
   -> [GhciPkgInfo]
   -> [Path Abs File]
+     -- ^ Files targets with unknown GHC options.
   -> [PackageName]
+     -- ^ The names of packages to be exposed.
   -> Map PackageName (Seq NamedComponent)
+     -- ^ A map of package names and their sublibraries depended on (if
+     -- any), the package names to be exposed if any sublibraries are
+     -- depended on.
   -> RIO env ()
 runGhci
     ghciOpts
@@ -650,21 +668,31 @@ writeHashedFile outputDirectory relFile contents = do
 renderScript ::
      [GhciPkgInfo]
   -> Maybe (Path Abs File)
+     -- ^ Path to source file for selected main module. 'Nothing' if no main
+     -- module is to be loaded and imported.
   -> Bool
+     -- ^ Only load and import the main module?
   -> [Path Abs File]
+     -- ^ Files targets with unknown GHC options.
   -> GhciScript
 renderScript pkgs mainFile onlyMain extraFiles = do
-  let addPhase = cmdAdd $ S.fromList (map Left allModules ++ addMain)
-      addMain = maybe [] (L.singleton . Right) mainFile
-      modulePhase = cmdModule $ S.fromList allModules
-      allModules = nubOrd $ concatMap (M.keys . (.modules)) pkgs
+  let allModules = S.unions $ map (M.keysSet . (.modules)) pkgs
+      addMain = maybe S.empty (S.singleton . Right) mainFile
+      -- If a main module is to be :add-ed, the context will be set to
+      -- it:
+      addPhase = cmdAdd $ S.map Left allModules <> addMain
+      modulePhase = cmdModule allModules
   case getFileTargets pkgs <> extraFiles of
     [] ->
       if onlyMain
         then
           if isJust mainFile
-            then cmdAdd (S.fromList addMain)
-            else mempty
+            then
+              -- If a main module is to be :add-ed, the context will be set to
+              -- it:
+              cmdAdd addMain
+            else
+              mempty
         else addPhase <> modulePhase
     fileTargets -> cmdAdd (S.fromList (map Right fileTargets))
 
diff --git a/src/Stack/Ghci/Script.hs b/src/Stack/Ghci/Script.hs
index 0379087e61..36b639b25d 100644
--- a/src/Stack/Ghci/Script.hs
+++ b/src/Stack/Ghci/Script.hs
@@ -35,7 +35,15 @@ instance Monoid GhciScript where
 
 data GhciCommand
   = AddCmd (Set (Either ModuleName (Path Abs File)))
+    -- ^ Add the specified modules (specified by module name or source file) to
+    -- the current target set and perform a reload (that is, load the target set
+    -- of modules and the all the modules they depend on in dependency order).
+    -- The modules specified by name are added first (in ascending order), then
+    -- the modules specified by source file (in ascending order). The context is
+    -- set to the most recently successfully loaded module.
   | ModuleCmd (Set ModuleName)
+    -- ^ Add the specified modules to the context. The modules are added in
+    -- ascending order.
   deriving Show
 
 cmdAdd :: Set (Either ModuleName (Path Abs File)) -> GhciScript
diff --git a/src/Stack/Package.hs b/src/Stack/Package.hs
index aac9443d09..590262d106 100644
--- a/src/Stack/Package.hs
+++ b/src/Stack/Package.hs
@@ -571,6 +571,7 @@ buildLogPath ::
      (MonadReader env m, HasBuildConfig env, MonadThrow m)
   => Package
   -> Maybe String
+     -- ^ An optional suffix for the log's file name.
   -> m (Path Abs File)
 buildLogPath package' msuffix = do
   env <- ask
@@ -817,6 +818,7 @@ setOfPackageDeps pkg = runIdentity $
 topSortPackageComponent ::
      Package
   -> Target
+     -- ^ How the package is intended to be built.
   -> Bool
      -- ^ Include directTarget or not. False here means we won't include the
      -- actual targets in the result, only their deps. Using it with False here
@@ -844,6 +846,7 @@ topProcessPackageComponent ::
      forall b.
      Package
   -> Target
+     -- ^ How the package is intended to be built.
   -> (    forall component. (HasComponentInfo component)
        => PackageType
        -> component
diff --git a/src/Stack/SDist.hs b/src/Stack/SDist.hs
index a27f117ad6..e018b39def 100644
--- a/src/Stack/SDist.hs
+++ b/src/Stack/SDist.hs
@@ -81,12 +81,11 @@ import           Stack.Types.EnvConfig
                    ( EnvConfig (..), HasEnvConfig (..), actualCompilerVersionL )
 import           Stack.Types.GhcPkgId ( GhcPkgId )
 import           Stack.Types.Installed
-                   ( InstallMap, Installed (..), InstalledMap
-                   , InstalledLibraryInfo (..), installedVersion
+                   ( InstallMap, InstalledMap, installedVersion
                    )
 import           Stack.Types.Package
                    ( LocalPackage (..), Package (..), PackageConfig (..)
-                   , packageIdentifier
+                   , installedPackageToGhcPkgId', packageIdentifier
                    )
 import           Stack.Types.Plan ( TaskType (..) )
 import           Stack.Types.Platform ( HasPlatform (..) )
@@ -204,8 +203,7 @@ getSDistTarball ::
      -- ^ Filename, tarball contents, and option Cabal file revision to upload
 getSDistTarball mpvpBounds pkgDir = do
   config <- view configL
-  let PvpBounds pvpBounds asRevision =
-        fromMaybe config.pvpBounds mpvpBounds
+  let PvpBounds pvpBounds asRevision = fromMaybe config.pvpBounds mpvpBounds
       tweakCabal = pvpBounds /= PvpBoundsNone
       pkgFp = toFilePath pkgDir
   lp <- readLocalPackage pkgDir
@@ -226,14 +224,13 @@ getSDistTarball mpvpBounds pkgDir = do
   installMap <- toInstallMap sourceMap
   (installedMap, _globalDumpPkgs, _snapshotDumpPkgs, _localDumpPkgs) <-
     getInstalled installMap
-  let deps = Map.fromList
-        [ (pid, libInfo.ghcPkgId)
-        | (_, Library pid libInfo) <- Map.elems installedMap]
+  let allDeps =
+        Map.unions $ Map.map (installedPackageToGhcPkgId' . snd) installedMap
   prettyInfoL
     [ flow "Getting the file list for"
     , style File (fromString  pkgFp) <> "."
     ]
-  (fileList, cabalFP) <- getSDistFileList lp deps
+  (fileList, cabalFP) <- getSDistFileList lp allDeps
   prettyInfoL
     [ flow "Building a compressed archive file in the sdist format for"
     , style File (fromString pkgFp) <> "."
@@ -477,19 +474,22 @@ readLocalPackage pkgDir = do
 getSDistFileList ::
      HasEnvConfig env
   => LocalPackage
-  -> Map PackageIdentifier GhcPkgId
+  -> Map MungedPackageId GhcPkgId
+     -- ^ Ids of installed packages that are assumed to be available to build a
+     -- package's custom @Setup.hs@, given its dependencies specified in its
+     -- @custom-setup@ stanza of its Cabal file.
   -> RIO env (String, Path Abs File)
-getSDistFileList lp deps =
+getSDistFileList lp allDeps =
   withSystemTempDir (stackProgName <> "-sdist") $ \tmpdir -> do
     let bopts = defaultBuildOpts
     let boptsCli = defaultBuildOptsCLI
     baseConfigOpts <- mkBaseConfigOpts boptsCli
     locals <- projectLocalPackages
-    withExecuteEnv bopts boptsCli baseConfigOpts locals
-      [] [] [] Nothing -- provide empty list of globals. This is a hack around
-                       -- custom Setup.hs files
+    -- We provide three empty lists of dumped installed packages. This is a hack
+    -- around custom Setup.hs files:
+    withExecuteEnv bopts boptsCli baseConfigOpts locals [] [] [] Nothing
       $ \ee ->
-      withSingleContext ac ee taskType deps (Just "sdist") $
+      withSingleContext ac ee taskType allDeps (Just "sdist") $
         \_package cabalFP _pkgDir cabal _announce _outputType -> do
           let outFile = toFilePath tmpdir FP.</> "source-files-list"
           cabal
diff --git a/src/Stack/Types/Build.hs b/src/Stack/Types/Build.hs
index ea64c0fe0b..9bae8b5265 100644
--- a/src/Stack/Types/Build.hs
+++ b/src/Stack/Types/Build.hs
@@ -9,13 +9,19 @@ Build-specific types.
 -}
 
 module Stack.Types.Build
-  ( ExcludeTHLoading (..)
+  ( RunCabalWithArgs
+  , ExcludeTHLoading (..)
   , ConvertPathsToAbsolute (..)
   , KeepOutputOpen (..)
   ) where
 
 import           Stack.Prelude
 
+-- | Type synonym that represents functions that run Cabal (the library) with
+-- arguments.
+type RunCabalWithArgs env =
+  KeepOutputOpen -> ExcludeTHLoading -> [String] -> RIO env ()
+
 -- | Type representing treatments of GHC's informational messages during
 -- compilation when it evaluates Template Haskell code.
 data ExcludeTHLoading
diff --git a/src/Stack/Types/Build/ConstructPlan.hs b/src/Stack/Types/Build/ConstructPlan.hs
index 35a6c8b9a9..3f06cda318 100644
--- a/src/Stack/Types/Build/ConstructPlan.hs
+++ b/src/Stack/Types/Build/ConstructPlan.hs
@@ -154,7 +154,7 @@ adrHasLibrary (ADRFound _ Executable{}) = False
 
 data MissingPresentDeps = MissingPresentDeps
   { missingPackages :: !(Set PackageIdentifier)
-  , presentPackages :: !(Map PackageIdentifier GhcPkgId)
+  , presentPackages :: !(Map MungedPackageId GhcPkgId)
   , isMutable :: !IsMutable
   }
   deriving Show
diff --git a/src/Stack/Types/Cache.hs b/src/Stack/Types/Cache.hs
index 154b6499b5..f114d51652 100644
--- a/src/Stack/Types/Cache.hs
+++ b/src/Stack/Types/Cache.hs
@@ -29,14 +29,13 @@ import           Database.Persist.Sql
                    )
 import           Stack.Prelude
 import           Stack.Types.ConfigureOpts ( ConfigureOpts )
-import           Stack.Types.GhcPkgId
-                   ( GhcPkgId, ghcPkgIdToText, parseGhcPkgId )
+import           Stack.Types.GhcPkgId ( GhcPkgId )
 
 -- | Type representing types of cache in the Stack project SQLite database.
 data ConfigCacheType
   = ConfigCacheTypeConfig
     -- ^ Cabal configuration cache.
-  | ConfigCacheTypeFlagLibrary GhcPkgId
+  | ConfigCacheTypeFlagLibrary PackageIdentifier
     -- ^ Library Cabal flag cache.
   | ConfigCacheTypeFlagExecutable PackageIdentifier
     -- ^ Executable Cabal flag cache.
@@ -45,25 +44,35 @@ data ConfigCacheType
 instance PersistField ConfigCacheType where
   toPersistValue ConfigCacheTypeConfig = PersistText "config"
   toPersistValue (ConfigCacheTypeFlagLibrary v) =
-    PersistText $ "lib:" <> ghcPkgIdToText v
+    PersistText $ "lib:" <> T.pack (packageIdentifierString v)
   toPersistValue (ConfigCacheTypeFlagExecutable v) =
     PersistText $ "exe:" <> T.pack (packageIdentifierString v)
+
   fromPersistValue (PersistText t) =
     fromMaybe (Left $ "Unexpected ConfigCacheType value: " <> t) $
-    config <|> fmap lib (T.stripPrefix "lib:" t) <|>
-    fmap exe (T.stripPrefix "exe:" t)
+          config
+      <|> flagCache ConfigCacheTypeFlagLibrary "lib:"
+      <|> flagCache ConfigCacheTypeFlagExecutable "exe:"
    where
     config
       | t == "config" = Just (Right ConfigCacheTypeConfig)
       | otherwise = Nothing
-    lib v = do
-      ghcPkgId <- mapLeft tshow (parseGhcPkgId v)
-      Right $ ConfigCacheTypeFlagLibrary ghcPkgId
-    exe v = do
-      pkgId <-
-        maybe (Left $ "Unexpected ConfigCacheType value: " <> t) Right $
-        parsePackageIdentifier (T.unpack v)
-      Right $ ConfigCacheTypeFlagExecutable pkgId
+
+    flagCache ::
+         (PackageIdentifier -> ConfigCacheType)
+         -- ^ Constructor
+      -> Text
+         -- ^ Prefex
+      -> Maybe (Either Text ConfigCacheType)
+    flagCache constructor prefix =
+      fmap toConfigCacheType (T.stripPrefix prefix t)
+     where
+      toConfigCacheType :: Text -> Either Text ConfigCacheType
+      toConfigCacheType v = do
+        pkgId <-
+          maybe (Left $ "Unexpected ConfigCacheType value: " <> t) Right $
+          parsePackageIdentifier (T.unpack v)
+        Right $ constructor pkgId
   fromPersistValue _ = Left "Unexpected ConfigCacheType type"
 
 instance PersistFieldSql ConfigCacheType where
diff --git a/src/Stack/Types/GhciOpts.hs b/src/Stack/Types/GhciOpts.hs
index 15b9f322f7..17c6ecff07 100644
--- a/src/Stack/Types/GhciOpts.hs
+++ b/src/Stack/Types/GhciOpts.hs
@@ -20,6 +20,7 @@ import           Stack.Types.BuildOptsCLI ( ApplyCLIFlag (..) )
 -- commands.
 data GhciOpts = GhciOpts
   { targets            :: ![Text]
+    -- ^ Raw (unprocessed) targets from the command line.
   , args               :: ![String]
   , ghcOptions         :: ![String]
   , flags              :: !(Map ApplyCLIFlag (Map FlagName Bool))
@@ -31,5 +32,6 @@ data GhciOpts = GhciOpts
   , hidePackages       :: !(Maybe Bool)
   , noBuild            :: !Bool
   , onlyMain           :: !Bool
+    -- ^ Only load and import the main module?
   }
   deriving Show
diff --git a/src/Stack/Types/Installed.hs b/src/Stack/Types/Installed.hs
index ba84f66b1e..6b7a159207 100644
--- a/src/Stack/Types/Installed.hs
+++ b/src/Stack/Types/Installed.hs
@@ -28,8 +28,6 @@ module Stack.Types.Installed
   ) where
 
 import qualified Data.Map as M
-import qualified Distribution.SPDX.License as SPDX
-import           Distribution.License ( License )
 import           Stack.Prelude
 import           Stack.Types.ComponentUtils ( StackUnqualCompName )
 import           Stack.Types.GhcPkgId ( GhcPkgId, ghcPkgIdString )
@@ -101,37 +99,43 @@ type InstallMap = Map PackageName (InstallLocation, Version)
 -- information about what is installed.
 type InstalledMap = Map PackageName (InstallLocation, Installed)
 
+-- TODO: This may not be the best type, as it allows invalid values to be
+-- represented.
 data InstalledLibraryInfo = InstalledLibraryInfo
-  { ghcPkgId :: GhcPkgId
-  , license :: Maybe (Either SPDX.License License)
+  { mMainGhcPkgId :: Maybe GhcPkgId
+    -- ^ The main library, if present. If absent, there must be one or more
+    -- installed sublibraries.
   , subLib :: Map StackUnqualCompName GhcPkgId
+    -- ^ If there are no sublibraries, there must be a main library.
   }
   deriving (Eq, Show)
 
 -- | Type representing information about what is installed.
 data Installed
   = Library PackageIdentifier InstalledLibraryInfo
-    -- ^ A library, including its installed package id and, optionally, its
-    -- license.
+    -- ^ A library, including the ids of its installed packages.
   | Executable PackageIdentifier
     -- ^ An executable.
   deriving (Eq, Show)
 
 installedLibraryInfoFromGhcPkgId :: GhcPkgId -> InstalledLibraryInfo
 installedLibraryInfoFromGhcPkgId ghcPkgId =
-  InstalledLibraryInfo ghcPkgId Nothing mempty
+  InstalledLibraryInfo (Just ghcPkgId) mempty
 
 simpleInstalledLib ::
      PackageIdentifier
-  -> GhcPkgId
+  -> Maybe GhcPkgId
+     -- ^ The id of the installed main library, if any.
   -> Map StackUnqualCompName GhcPkgId
+     -- ^ The id of any sublibraries.
   -> Installed
-simpleInstalledLib pkgIdentifier ghcPkgId =
-  Library pkgIdentifier . InstalledLibraryInfo ghcPkgId Nothing
+simpleInstalledLib pkgIdentifier mMainGhcPkgId =
+  Library pkgIdentifier . InstalledLibraryInfo mMainGhcPkgId
 
 installedToPackageIdOpt :: InstalledLibraryInfo -> [String]
 installedToPackageIdOpt libInfo =
-  M.foldr' (iterator (++)) (pure $ toStr libInfo.ghcPkgId) libInfo.subLib
+  let acc0 = toStr <$> maybeToList libInfo.mMainGhcPkgId
+  in  M.foldr' (iterator (++)) acc0 libInfo.subLib
  where
   toStr ghcPkgId = "-package-id=" <> ghcPkgIdString ghcPkgId
   iterator op ghcPkgId acc = pure (toStr ghcPkgId) `op` acc
@@ -141,17 +145,17 @@ installedPackageIdentifier (Library pid _) = pid
 installedPackageIdentifier (Executable pid) = pid
 
 -- | A strict fold over the 'GhcPkgId' of the given installed package. This will
--- iterate on both sub and main libraries, if any.
+-- iterate on the main library (if any) and sublibraries (if any).
 foldOnGhcPkgId' ::
-     (Maybe StackUnqualCompName -> GhcPkgId -> resT -> resT)
+     (Maybe StackUnqualCompName -> GhcPkgId -> a -> a)
   -> Installed
-  -> resT
-  -> resT
+  -> a
+  -> a
 foldOnGhcPkgId' _ Executable{} res = res
 foldOnGhcPkgId' fn (Library _ libInfo) res =
-  M.foldrWithKey' (fn . Just) (base res) libInfo.subLib
+  M.foldrWithKey' (fn . Just) base libInfo.subLib
  where
-  base = fn Nothing libInfo.ghcPkgId
+  base = maybe res (\ghcPkgId -> fn Nothing ghcPkgId res) libInfo.mMainGhcPkgId
 
 -- | Get the installed Version.
 installedVersion :: Installed -> Version
diff --git a/src/Stack/Types/Package.hs b/src/Stack/Types/Package.hs
index 488415ddea..a316fb397d 100644
--- a/src/Stack/Types/Package.hs
+++ b/src/Stack/Types/Package.hs
@@ -33,6 +33,7 @@ module Stack.Types.Package
   , dotCabalModulePath
   , installedMapGhcPkgId
   , installedPackageToGhcPkgId
+  , installedPackageToGhcPkgId'
   , lpFiles
   , lpFilesForComponents
   , memoizeRefWith
@@ -40,7 +41,7 @@ module Stack.Types.Package
   , packageIdentifier
   , psVersion
   , runMemoizedWith
-  , simpleInstalledLib
+  , toCabalMungedPackageId
   , toCabalMungedPackageName
   , toPackageDbVariety
   ) where
@@ -54,8 +55,6 @@ import           Distribution.License ( License )
 import           Distribution.ModuleName ( ModuleName )
 import           Distribution.PackageDescription ( BuildType )
 import           Distribution.System ( Platform (..) )
-import           Distribution.Types.MungedPackageName
-                   ( encodeCompatPackageName )
 import qualified RIO.Text as T
 import           Stack.Prelude
 import           Stack.Types.Cache ( FileCache )
@@ -74,7 +73,7 @@ import           Stack.Types.Installed
                    ( InstallLocation (..), InstallMap, Installed (..)
                    , InstalledLibraryInfo (..), InstalledMap
                    , InstalledPackageLocation (..), PackageDatabase (..)
-                   , PackageDbVariety(..), simpleInstalledLib
+                   , PackageDbVariety(..), installedPackageIdentifier
                    , toPackageDbVariety
                    )
 import           Stack.Types.NamedComponent ( NamedComponent )
@@ -386,43 +385,57 @@ dotCabalGetPath dcp =
     DotCabalFilePath fp -> fp
     DotCabalCFilePath fp -> fp
 
--- | Gathers all the GhcPkgId provided by a library into a map
+-- | Gathers all the GhcPkgId provided by a library into a map, where the
+-- package identifier of a sublibrary is its munged package identifier.
 installedMapGhcPkgId ::
      PackageIdentifier
+     -- ^ The name and version of a Cabal package.
   -> InstalledLibraryInfo
-  -> Map PackageIdentifier GhcPkgId
-installedMapGhcPkgId pkgId@(PackageIdentifier pkgName version) installedLib =
-  finalMap
+  -> Map MungedPackageId GhcPkgId
+installedMapGhcPkgId pkgId libInfo =
+  mAddMainGhcPkgId libInfo.mMainGhcPkgId subLibMap
  where
-  finalMap = M.insert pkgId installedLib.ghcPkgId baseMap
-  baseMap =
-    M.mapKeysMonotonic
-      (toCabalMungedPackageIdentifier pkgName version)
-      installedLib.subLib
+  mAddMainGhcPkgId = maybe id (M.insert mungedMainPkgId)
+  mungedMainPkgId = toCabalMungedPackageId pkgId Nothing
+  subLibMap =
+    M.mapKeysMonotonic (toCabalMungedPackageId pkgId . Just) libInfo.subLib
 
 installedPackageToGhcPkgId ::
      PackageIdentifier
+     -- ^ The name and version of a Cabal package.
   -> Installed
-  -> Map PackageIdentifier GhcPkgId
-installedPackageToGhcPkgId ident (Library ident' libInfo) =
-  assert (ident == ident') (installedMapGhcPkgId ident libInfo)
-installedPackageToGhcPkgId _ (Executable _) = mempty
-
--- | Creates a t'MungedPackageName' identifier.
-toCabalMungedPackageIdentifier ::
-     PackageName
-  -> Version
-  -> StackUnqualCompName
-  -> PackageIdentifier
-toCabalMungedPackageIdentifier pkgName version = flip PackageIdentifier version
-  . encodeCompatPackageName . toCabalMungedPackageName pkgName
+     -- ^ Assumed to be for the same Cabal package name and version.
+  -> Map MungedPackageId GhcPkgId
+installedPackageToGhcPkgId pkgId installed =
+  assert (pkgId == installedPackageIdentifier installed)
+    (installedPackageToGhcPkgId' installed)
+
+installedPackageToGhcPkgId' :: Installed -> Map MungedPackageId GhcPkgId
+installedPackageToGhcPkgId' (Library pkgId libInfo) =
+  installedMapGhcPkgId pkgId libInfo
+installedPackageToGhcPkgId' (Executable _) = mempty
+
+-- | Creates a munged package identifier.
+toCabalMungedPackageId ::
+     PackageIdentifier
+     -- ^ The name and version of a Cabal package.
+  -> Maybe StackUnqualCompName
+     -- ^ 'Nothing', if a main library.
+  -> MungedPackageId
+toCabalMungedPackageId pkgId mLibName =
+  MungedPackageId (toCabalMungedPackageName pkgName mLibName) version
+ where
+  PackageIdentifier pkgName version = pkgId
 
+-- | Creates a munged package name.
 toCabalMungedPackageName ::
      PackageName
-  -> StackUnqualCompName
+     -- ^ The name of a Cabal package.
+  -> Maybe StackUnqualCompName
+     -- ^ 'Nothing', if a main library.
   -> MungedPackageName
-toCabalMungedPackageName pkgName =
-  MungedPackageName pkgName . LSubLibName . toCabalName
+toCabalMungedPackageName pkgName mLibName = MungedPackageName pkgName $
+  maybe LMainLibName (LSubLibName . toCabalName) mLibName
 
 -- | Type representing inputs to 'Stack.Package.generateBuildInfoOpts'.
 data BioInput = BioInput
diff --git a/src/Stack/Types/Plan.hs b/src/Stack/Types/Plan.hs
index 8789f3f0d9..3a10ea02a3 100644
--- a/src/Stack/Types/Plan.hs
+++ b/src/Stack/Types/Plan.hs
@@ -63,8 +63,8 @@ data Task = Task
     -- are missing and a function which yields configure options, given a
     -- dictionary of those identifiers and their 'GhcPkgId'.
   , buildHaddocks   :: !Bool
-  , present         :: !(Map PackageIdentifier GhcPkgId)
-    -- ^ A dictionary of the package identifiers of already-installed
+  , present         :: !(Map MungedPackageId GhcPkgId)
+    -- ^ A dictionary of the munged package identifiers of already-installed
     -- dependencies, and their 'GhcPkgId'.
   , allInOne        :: !Bool
     -- ^ indicates that the package can be built in one step
diff --git a/stack.cabal b/stack.cabal
index 6f173ade3e..9ea64af05e 100644
--- a/stack.cabal
+++ b/stack.cabal
@@ -5,7 +5,7 @@ cabal-version: 2.2
 -- see: https://github.com/sol/hpack
 
 name:           stack
-version:        3.11.2
+version:        3.12.0
 synopsis:       A program for developing Haskell projects
 description:    Stack (the Haskell Tool Stack) is a program for developing Haskell projects.
                 It is aimed at new and experienced users of Haskell and seeks to support them
diff --git a/tests/integration/tests/6896-custom-setup/Main.hs b/tests/integration/tests/6896-custom-setup/Main.hs
new file mode 100644
index 0000000000..18cdffa792
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/Main.hs
@@ -0,0 +1,36 @@
+-- | Stack can build:
+--
+-- * a project package with a custom @Setup.hs@ (see @myPackageA@);
+--
+-- * a project package with a custom @Setup.hs@ that depends on the main library
+--   of another project package (see @myPackageB@ and @myPackageD@); and
+--
+-- * a project package with a custom @Setup.hs@ that depends on the public
+--   sublibrary of another project package that does not have a main library
+--   (see @myPackageC@ amd @myPackageE@).
+--
+-- See: https://github.com/commercialhaskell/stack/issues/6896
+
+import           Control.Monad ( unless)
+import           Data.List ( isInfixOf )
+import           StackTest
+
+main :: IO ()
+main = do
+  stackCheckStderr ["build", "myPackageA"] (expectMessage usingCustomA)
+  stackCheckStderr ["build", "myPackageB"] (expectMessage usingCustomB)
+  stackCheckStderr ["build", "myPackageC"] (expectMessage usingCustomC)
+
+usingCustomA :: String
+usingCustomA = "Using my custom Setup.hs for myPackageA"
+
+usingCustomB :: String
+usingCustomB = "messageD: Using my custom Setup.hs for myPackageB"
+
+usingCustomC :: String
+usingCustomC = "messageE: Using my custom Setup.hs for myPackageC"
+
+expectMessage :: String -> String -> IO ()
+expectMessage msg stderr = do
+  unless (words msg `isInfixOf` words stderr) $
+    error $ "Expected output: \n" ++ show msg
diff --git a/tests/integration/tests/6896-custom-setup/files/.gitignore b/tests/integration/tests/6896-custom-setup/files/.gitignore
new file mode 100644
index 0000000000..ec90d3285d
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/.gitignore
@@ -0,0 +1,5 @@
+myPackageA.cabal
+myPackageB.cabal
+myPackageC.cabal
+myPackageD.cabal
+myPackageE.cabal
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageA/Setup.hs b/tests/integration/tests/6896-custom-setup/files/myPackageA/Setup.hs
new file mode 100644
index 0000000000..dcc59c17b5
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageA/Setup.hs
@@ -0,0 +1,4 @@
+import Distribution.Simple
+main = do
+  putStrLn "Using my custom Setup.hs for myPackageA"
+  defaultMain
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageA/package.yaml b/tests/integration/tests/6896-custom-setup/files/myPackageA/package.yaml
new file mode 100644
index 0000000000..4cdfea8748
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageA/package.yaml
@@ -0,0 +1,13 @@
+spec-version: 0.36.0
+
+name: myPackageA
+
+dependencies:
+- base
+
+custom-setup:
+  dependencies:
+  - base
+
+library:
+  source-dirs: src
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageA/src/LibA.hs b/tests/integration/tests/6896-custom-setup/files/myPackageA/src/LibA.hs
new file mode 100644
index 0000000000..a02dbb2486
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageA/src/LibA.hs
@@ -0,0 +1 @@
+module LibA where
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageB/Setup.hs b/tests/integration/tests/6896-custom-setup/files/myPackageB/Setup.hs
new file mode 100644
index 0000000000..d1b4ae8498
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageB/Setup.hs
@@ -0,0 +1,6 @@
+import           Distribution.Simple
+import           LibD ( messageD )
+
+main = do
+  putStrLn messageD
+  defaultMain
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageB/package.yaml b/tests/integration/tests/6896-custom-setup/files/myPackageB/package.yaml
new file mode 100644
index 0000000000..06acaf9aac
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageB/package.yaml
@@ -0,0 +1,14 @@
+spec-version: 0.36.0
+
+name: myPackageB
+
+dependencies:
+- base
+
+custom-setup:
+  dependencies:
+  - base
+  - myPackageD
+
+library:
+  source-dirs: src
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageB/src/LibB.hs b/tests/integration/tests/6896-custom-setup/files/myPackageB/src/LibB.hs
new file mode 100644
index 0000000000..913d829c0a
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageB/src/LibB.hs
@@ -0,0 +1 @@
+module LibB where
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageC/Setup.hs b/tests/integration/tests/6896-custom-setup/files/myPackageC/Setup.hs
new file mode 100644
index 0000000000..282159a3b8
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageC/Setup.hs
@@ -0,0 +1,6 @@
+import           Distribution.Simple
+import           SublibE ( messageE )
+
+main = do
+  putStrLn messageE
+  defaultMain
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageC/package.yaml b/tests/integration/tests/6896-custom-setup/files/myPackageC/package.yaml
new file mode 100644
index 0000000000..0f504d627a
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageC/package.yaml
@@ -0,0 +1,17 @@
+spec-version: 0.36.0
+
+verbatim:
+  cabal-version: 3.4
+
+name: myPackageC
+
+dependencies:
+- base
+
+custom-setup:
+  dependencies:
+  - base
+  - myPackageE:myPackageE-sub
+
+library:
+  source-dirs: src
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageC/src/LibC.hs b/tests/integration/tests/6896-custom-setup/files/myPackageC/src/LibC.hs
new file mode 100644
index 0000000000..48da7c9108
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageC/src/LibC.hs
@@ -0,0 +1 @@
+module LibC where
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageD/package.yaml b/tests/integration/tests/6896-custom-setup/files/myPackageD/package.yaml
new file mode 100644
index 0000000000..3d51f11ae8
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageD/package.yaml
@@ -0,0 +1,9 @@
+spec-version: 0.36.0
+
+name: myPackageD
+
+dependencies:
+- base
+
+library:
+  source-dirs: src
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageD/src/LibD.hs b/tests/integration/tests/6896-custom-setup/files/myPackageD/src/LibD.hs
new file mode 100644
index 0000000000..19c7c8dead
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageD/src/LibD.hs
@@ -0,0 +1,6 @@
+module LibD
+  ( messageD
+  ) where
+
+messageD :: String
+messageD = "messageD: Using my custom Setup.hs for myPackageB"
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageE/package.yaml b/tests/integration/tests/6896-custom-setup/files/myPackageE/package.yaml
new file mode 100644
index 0000000000..1edcb2d54d
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageE/package.yaml
@@ -0,0 +1,11 @@
+spec-version: 0.36.0
+
+name: myPackageE
+
+dependencies:
+- base
+
+internal-libraries:
+  myPackageE-sub:
+    visibility: public
+    source-dirs: sub
diff --git a/tests/integration/tests/6896-custom-setup/files/myPackageE/sub/SublibE.hs b/tests/integration/tests/6896-custom-setup/files/myPackageE/sub/SublibE.hs
new file mode 100644
index 0000000000..34f4adc5ec
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/myPackageE/sub/SublibE.hs
@@ -0,0 +1,6 @@
+module SublibE
+  ( messageE
+  ) where
+
+messageE :: String
+messageE = "messageE: Using my custom Setup.hs for myPackageC"
diff --git a/tests/integration/tests/6896-custom-setup/files/stack.yaml b/tests/integration/tests/6896-custom-setup/files/stack.yaml
new file mode 100644
index 0000000000..f5e344c0bf
--- /dev/null
+++ b/tests/integration/tests/6896-custom-setup/files/stack.yaml
@@ -0,0 +1,8 @@
+snapshot: ghc-9.10.3
+
+packages:
+- myPackageA
+- myPackageB
+- myPackageC
+- myPackageD
+- myPackageE
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/Main.hs b/tests/integration/tests/6896-dep-with-no-main-lib/Main.hs
new file mode 100644
index 0000000000..36b1ff3ab4
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/Main.hs
@@ -0,0 +1,7 @@
+-- | Stack can support a dependency package that has one or more public
+-- sublibraries but no unnamed main library.
+
+import           StackTest
+
+main :: IO ()
+main = stack ["build"]
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/files/.gitignore b/tests/integration/tests/6896-dep-with-no-main-lib/files/.gitignore
new file mode 100644
index 0000000000..f9a6e152d2
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/files/.gitignore
@@ -0,0 +1,2 @@
+myPackageA.cabal
+myPackageB.cabal
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageA/package.yaml b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageA/package.yaml
new file mode 100644
index 0000000000..89c90db88c
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageA/package.yaml
@@ -0,0 +1,11 @@
+spec-version: 0.36.0
+
+name: myPackageA
+
+dependencies:
+- base
+
+library:
+  source-dirs: src
+  dependencies:
+  - myPackageB:myPackageB-sub
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageA/src/Lib.hs b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageA/src/Lib.hs
new file mode 100644
index 0000000000..6d85a26fe1
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageA/src/Lib.hs
@@ -0,0 +1 @@
+module Lib where
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageB/package.yaml b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageB/package.yaml
new file mode 100644
index 0000000000..05fd49c434
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageB/package.yaml
@@ -0,0 +1,13 @@
+# This package has no unnamed main library.
+
+spec-version: 0.36.0
+
+name: myPackageB
+
+dependencies:
+- base
+
+internal-libraries:
+  myPackageB-sub:
+    visibility: public
+    source-dirs: sub
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageB/sub/Sublib.hs b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageB/sub/Sublib.hs
new file mode 100644
index 0000000000..c41d4cbf16
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/files/myPackageB/sub/Sublib.hs
@@ -0,0 +1 @@
+module Sublib where
diff --git a/tests/integration/tests/6896-dep-with-no-main-lib/files/stack.yaml b/tests/integration/tests/6896-dep-with-no-main-lib/files/stack.yaml
new file mode 100644
index 0000000000..68891a8d7c
--- /dev/null
+++ b/tests/integration/tests/6896-dep-with-no-main-lib/files/stack.yaml
@@ -0,0 +1,5 @@
+snapshot: ghc-9.10.3
+
+packages:
+- myPackageA
+- myPackageB