Backtrack when no pkgconfigdb is present

cabal-install-solver/src/Distribution/Solver/Types/PkgConfigDb.hs

@@ -12,7 +12,7 @@
 -- Read the list of packages available to pkg-config.
 -----------------------------------------------------------------------------
 module Distribution.Solver.Types.PkgConfigDb
-    ( PkgConfigDb
+    ( PkgConfigDb (..)
     , readPkgConfigDb
     , pkgConfigDbFromList
     , pkgConfigPkgIsPresent
@@ -95,11 +95,12 @@ pkgConfigPkgIsPresent (PkgConfigDb db) pn vr =
       Nothing       -> False    -- Package not present in the DB.
       Just Nothing  -> True     -- Package present, but version unknown.
       Just (Just v) -> withinPkgconfigVersionRange v vr
--- If we could not read the pkg-config database successfully we allow
--- the check to succeed. The plan found by the solver may fail to be
--- executed later on, but we have no grounds for rejecting the plan at
--- this stage.
-pkgConfigPkgIsPresent NoPkgConfigDb _ _ = True
+-- If we could not read the pkg-config database successfully we fail.
+-- The plan found by the solver can't be executed later, because pkg-config itself
+-- is going to be called in the build phase to get the library location for linking
+-- so even if there is a library, it would need to be passed manual flags anyway.
+pkgConfigPkgIsPresent NoPkgConfigDb _ _ = False
+
 
 
 -- | Query the version of a package in the @pkg-config@ database.

cabal-install/tests/UnitTests/Distribution/Solver/Modular/DSL/TestCaseUtils.hs

@@ -43,7 +43,7 @@ import Distribution.Verbosity
 
 -- cabal-install
 import qualified Distribution.Solver.Types.PackagePath as P
-import Distribution.Solver.Types.PkgConfigDb (PkgConfigDb, pkgConfigDbFromList)
+import Distribution.Solver.Types.PkgConfigDb (PkgConfigDb (..), pkgConfigDbFromList)
 import Distribution.Solver.Types.Settings
 import Distribution.Solver.Types.Variable
 import Distribution.Client.Dependency (foldProgress)
@@ -166,41 +166,41 @@ mkTest :: ExampleDb
        -> [String]
        -> SolverResult
        -> SolverTest
-mkTest = mkTestExtLangPC Nothing Nothing []
+mkTest = mkTestExtLangPC Nothing Nothing (Just [])
 
 mkTestExts :: [Extension]
            -> ExampleDb
            -> String
            -> [String]
            -> SolverResult
            -> SolverTest
-mkTestExts exts = mkTestExtLangPC (Just exts) Nothing []
+mkTestExts exts = mkTestExtLangPC (Just exts) Nothing (Just [])
 
 mkTestLangs :: [Language]
             -> ExampleDb
             -> String
             -> [String]
             -> SolverResult
             -> SolverTest
-mkTestLangs langs = mkTestExtLangPC Nothing (Just langs) []
+mkTestLangs langs = mkTestExtLangPC Nothing (Just langs) (Just [])
 
-mkTestPCDepends :: [(String, String)]
+mkTestPCDepends :: Maybe [(String, String)]
                 -> ExampleDb
                 -> String
                 -> [String]
                 -> SolverResult
                 -> SolverTest
-mkTestPCDepends pkgConfigDb = mkTestExtLangPC Nothing Nothing pkgConfigDb
+mkTestPCDepends mPkgConfigDb = mkTestExtLangPC Nothing Nothing mPkgConfigDb
 
 mkTestExtLangPC :: Maybe [Extension]
                 -> Maybe [Language]
-                -> [(String, String)]
+                -> Maybe [(String, String)]
                 -> ExampleDb
                 -> String
                 -> [String]
                 -> SolverResult
                 -> SolverTest
-mkTestExtLangPC exts langs pkgConfigDb db label targets result = SolverTest {
+mkTestExtLangPC exts langs mPkgConfigDb db label targets result = SolverTest {
     testLabel                = label
   , testTargets              = targets
   , testResult               = result
@@ -219,7 +219,7 @@ mkTestExtLangPC exts langs pkgConfigDb db label targets result = SolverTest {
   , testDb                   = db
   , testSupportedExts        = exts
   , testSupportedLangs       = langs
-  , testPkgConfigDb          = pkgConfigDbFromList pkgConfigDb
+  , testPkgConfigDb          = maybe NoPkgConfigDb pkgConfigDbFromList mPkgConfigDb
   , testEnableAllTests       = EnableAllTests False
   }
 

cabal-install/tests/UnitTests/Distribution/Solver/Modular/Solver.hs

@@ -253,10 +253,11 @@ tests = [
         , runTest $ mkTest dbBuildable2 "choose version that sets buildable to false" ["A"] (solverSuccess [("A", 1), ("B", 2)])
          ]
     , testGroup "Pkg-config dependencies" [
-          runTest $ mkTestPCDepends [] dbPC1 "noPkgs" ["A"] anySolverFailure
-        , runTest $ mkTestPCDepends [("pkgA", "0")] dbPC1 "tooOld" ["A"] anySolverFailure
-        , runTest $ mkTestPCDepends [("pkgA", "1.0.0"), ("pkgB", "1.0.0")] dbPC1 "pruneNotFound" ["C"] (solverSuccess [("A", 1), ("B", 1), ("C", 1)])
-        , runTest $ mkTestPCDepends [("pkgA", "1.0.0"), ("pkgB", "2.0.0")] dbPC1 "chooseNewest" ["C"] (solverSuccess [("A", 1), ("B", 2), ("C", 1)])
+          runTest $ mkTestPCDepends Nothing dbPC1 "noPkgs" ["A"] anySolverFailure
+        , runTest $ mkTestPCDepends (Just [("pkgA", "0")]) dbPC1 "tooOld" ["A"] anySolverFailure
+        , runTest $ mkTestPCDepends (Just [("pkgA", "1.0.0"), ("pkgB", "1.0.0")]) dbPC1 "pruneNotFound" ["C"] (solverSuccess [("A", 1), ("B", 1), ("C", 1)])
+        , runTest $ mkTestPCDepends (Just [("pkgA", "1.0.0"), ("pkgB", "2.0.0")]) dbPC1 "chooseNewest" ["C"] (solverSuccess [("A", 1), ("B", 2), ("C", 1)])
+        , runTest $ mkTestPCDepends Nothing dbPC1 "noPkgConfig" ["D"] (solverSuccess [("D",1)])
         ]
     , testGroup "Independent goals" [
           runTest $ indep $ mkTest db16 "indepGoals1" ["A", "B"] (solverSuccess [("A", 1), ("B", 1), ("C", 1), ("D", 1), ("D", 2), ("E", 1)])
@@ -1665,7 +1666,7 @@ dbLangs1 = [
 testBuildable :: String -> ExampleDependency -> TestTree
 testBuildable testName unavailableDep =
     runTest $
-    mkTestExtLangPC (Just []) (Just [Haskell98]) [] db testName ["pkg"] expected
+    mkTestExtLangPC (Just []) (Just [Haskell98]) (Just []) db testName ["pkg"] expected
   where
     expected = solverSuccess [("false-dep", 1), ("pkg", 1)]
     db = [
@@ -1718,12 +1719,14 @@ dbBuildable2 = [
   ]
 
 -- | Package databases for testing @pkg-config@ dependencies.
+-- when no pkgconfig db is present, cabal must pick flag1 false and flag2 true to avoid the pkg dependency.
 dbPC1 :: ExampleDb
 dbPC1 = [
     Right $ exAv "A" 1 [ExPkg ("pkgA", 1)]
   , Right $ exAv "B" 1 [ExPkg ("pkgB", 1), ExAny "A"]
   , Right $ exAv "B" 2 [ExPkg ("pkgB", 2), ExAny "A"]
   , Right $ exAv "C" 1 [ExAny "B"]
+  , Right $ exAv "D" 1 [exFlagged "flag1" [ExAny "A"] [], exFlagged "flag2" [] [ExAny "A"]]
   ]
 
 -- | Test for the solver's summarized log. The final conflict set is {A, F},

changelog.d/pr-7621

@@ -0,0 +1,10 @@
+synopsis: Backtrack when no pkg-config is present
+packages: Cabal
+prs: #7621
+issues: #7448
+
+description: {
+
+When solving for pkgconfig-depends, when pkg-config is not present, the cabal solver will now backtrack and try a different automatic flag and dependency configuration, just as it does if pkg-config is present, but does not contain the specified package.
+
+}