Add a reproducer for #6894

Author: phadej

Cabal/Distribution/Backpack/ComponentsGraph.hs

@@ -89,9 +89,10 @@ componentsGraphToList =
     map (\(N c _ cs) -> (c, cs)) . Graph.revTopSort
 
 -- | Error message when there is a cycle; takes the SCC of components.
-componentCycleMsg :: [ComponentName] -> Doc
-componentCycleMsg cnames =
-    text $ "Components in the package depend on each other in a cyclic way:\n  "
-       ++ intercalate " depends on "
+componentCycleMsg :: PackageIdentifier -> [ComponentName] -> Doc
+componentCycleMsg pn cnames =
+    text "Components in the package" <+> pretty pn <+> text "depend on each other in a cyclic way:"
+    $$
+    text (intercalate " depends on "
             [ "'" ++ showComponentName cname ++ "'"
-            | cname <- cnames ++ maybeToList (safeHead cnames) ]
+            | cname <- cnames ++ maybeToList (safeHead cnames) ])

Cabal/Distribution/Backpack/Configure.hs

@@ -78,7 +78,7 @@ configureComponentLocalBuildInfos
     -- NB: In single component mode, this returns a *single* component.
     -- In this graph, the graph is NOT closed.
     graph0 <- case mkComponentsGraph enabled pkg_descr of
-                Left ccycle -> dieProgress (componentCycleMsg ccycle)
+                Left ccycle -> dieProgress (componentCycleMsg (package pkg_descr) ccycle)
                 Right g -> return (componentsGraphToList g)
     infoProgress $ hang (text "Source component graph:") 4
                         (dispComponentsWithDeps graph0)

cabal-testsuite/PackageTests/MultipleLibraries/T6894/Bar.hs

@@ -0,0 +1 @@
+module Bar where

cabal-testsuite/PackageTests/MultipleLibraries/T6894/Foo.hs

@@ -0,0 +1 @@
+module Foo where

cabal-testsuite/PackageTests/MultipleLibraries/T6894/cabal.out

@@ -0,0 +1,5 @@
+# cabal v2-build
+Resolving dependencies...
+Error:
+    Dependency cycle between the following components: library
+    In the inplace package 'issue-6894'

cabal-testsuite/PackageTests/MultipleLibraries/T6894/cabal.project

@@ -0,0 +1 @@
+packages: .

cabal-testsuite/PackageTests/MultipleLibraries/T6894/cabal.test.hs

@@ -0,0 +1,3 @@
+import Test.Cabal.Prelude
+main = cabalTest $
+    fails $ cabal "v2-build" ["issue"]

cabal-testsuite/PackageTests/MultipleLibraries/T6894/issue.cabal

@@ -0,0 +1,13 @@
+cabal-version: 3.0
+name: issue
+version: 6894
+
+library
+  default-language: Haskell2010
+  build-depends: base, issue:sublib
+  exposed-modules: Foo
+
+library sublib
+  default-language: Haskell2010
+  build-depends: base
+  exposed-modules: Bar

cabal-testsuite/PackageTests/MultipleLibraries/T6894/setup.cabal.out

@@ -0,0 +1,7 @@
+# Setup configure
+Warning: issue.cabal:7:30: colon specifier is experimental feature (issue #5660)
+Configuring issue-6894...
+Error:
+    Components in the package issue-6894 depend on each other in a cyclic way:
+    'library' depends on 'library'
+# Setup build

cabal-testsuite/PackageTests/MultipleLibraries/T6894/setup.out

@@ -0,0 +1,7 @@
+# Setup configure
+Warning: issue.cabal:7:30: colon specifier is experimental feature (issue #5660)
+Configuring issue-6894...
+Error:
+    Components in the package issue-6894 depend on each other in a cyclic way:
+    'library' depends on 'library'
+# Setup build

cabal-testsuite/PackageTests/MultipleLibraries/T6894/setup.test.hs

@@ -0,0 +1,3 @@
+import Test.Cabal.Prelude
+main = setupAndCabalTest $ do
+    fails $ setup_build []