Re #6905 Add another test with a genuine cycle

tests/integration/tests/6905-invalid-cycle/Main.hs

@@ -0,0 +1,35 @@
+-- | The test's project has project packages A, B, C and D.
+--
+-- In terms of main libraries, the dependencies are (->- is 'depends on'):
+--
+--     A ->- B and C ->- D, D ->- C (a cycle)
+--
+-- In terms of executables (a test suite):
+--
+--     B ->- A, B ->- C
+--
+-- As, overall, A ->- B and B ->- A, packages A and B cannot be built
+-- 'all-in-one'. However, if the test suite of B is not being built, A and B can
+-- be built.
+
+-- The test suite of B cannot be built, because C ->- D and D ->- C.
+--
+-- See: https://github.com/commercialhaskell/stack/issues/6905
+
+import           Control.Monad ( unless )
+import           Data.List ( isInfixOf )
+import           StackTest
+
+main :: IO ()
+main = do
+  stack ["build", "myPackageA", "myPackageB"]
+  stackErrStderr ["test", "myPackageB"] (expectMessage dependencyCycleDetected)
+
+dependencyCycleDetected :: String
+dependencyCycleDetected =
+  "myPackageC dependency cycle detected: myPackageC, myPackageD, myPackageC"
+
+expectMessage :: String -> String -> IO ()
+expectMessage msg stderr =
+  unless (words msg `isInfixOf` words stderr)
+    (error $ "Expected a warning: \n" ++ show msg)

tests/integration/tests/6905-invalid-cycle/files/.gitignore

@@ -0,0 +1,4 @@
+myPackageA.cabal
+myPackageB.cabal
+myPackageC.cabal
+myPackageD.cabal

tests/integration/tests/6905-invalid-cycle/files/myPackageA/package.yaml

@@ -0,0 +1,11 @@
+spec-version: 0.36.0
+
+name: myPackageA
+
+dependencies:
+- base
+
+library:
+  source-dirs: src
+  dependencies:
+  - myPackageB

tests/integration/tests/6905-invalid-cycle/files/myPackageA/src/LibA.hs

@@ -0,0 +1,5 @@
+module LibA
+  ( funcB
+  ) where
+
+import LibB ( funcB )

tests/integration/tests/6905-invalid-cycle/files/myPackageB/package.yaml

@@ -0,0 +1,17 @@
+spec-version: 0.36.0
+
+name: myPackageB
+
+dependencies:
+- base
+
+library:
+  source-dirs: src
+
+tests:
+  test:
+    source-dirs: test
+    main: Main.hs
+    dependencies:
+    - myPackageA
+    - myPackageC

tests/integration/tests/6905-invalid-cycle/files/myPackageB/src/LibB.hs

@@ -0,0 +1,6 @@
+module LibB
+ ( funcB
+ ) where
+
+funcB :: IO ()
+funcB = pure ()

tests/integration/tests/6905-invalid-cycle/files/myPackageB/test/Main.hs

@@ -0,0 +1,7 @@
+import LibA ( funcB )
+import LibC ( funcC )
+
+main :: IO ()
+main = do
+  funcB
+  funcC

tests/integration/tests/6905-invalid-cycle/files/myPackageC/package.yaml

@@ -0,0 +1,11 @@
+spec-version: 0.36.0
+
+name: myPackageC
+
+dependencies:
+- base
+
+library:
+  source-dirs: src
+  dependencies:
+  - myPackageD

tests/integration/tests/6905-invalid-cycle/files/myPackageC/src/LibC.hs

@@ -0,0 +1,8 @@
+module LibC
+ ( funcC
+ ) where
+
+import LibD ( funcD )
+
+funcC :: IO ()
+funcC = funcD

tests/integration/tests/6905-invalid-cycle/files/myPackageD/package.yaml

@@ -0,0 +1,11 @@
+spec-version: 0.36.0
+
+name: myPackageD
+
+dependencies:
+- base
+
+library:
+  source-dirs: src
+  dependencies:
+  - myPackageC

tests/integration/tests/6905-invalid-cycle/files/myPackageD/src/LibD.hs

@@ -0,0 +1,8 @@
+module LibD
+  ( funcD
+  ) where
+
+import LibC ( funcC )
+
+funcD :: IO ()
+funcD = funcC

tests/integration/tests/6905-invalid-cycle/files/stack.yaml

@@ -0,0 +1,7 @@
+snapshot: ghc-9.10.3
+
+packages:
+- myPackageA
+- myPackageB
+- myPackageC
+- myPackageD