From 5fd73de1a9bf07e47dc57bf77a21889a582dd145 Mon Sep 17 00:00:00 2001
From: Oleg Grenrus <oleg.grenrus@iki.fi>
Date: Tue, 14 Jul 2020 22:16:08 +0300
Subject: [PATCH] Fix #6961. Depending on a private component from the same
 package is fine.

---
 cabal-install/Distribution/Solver/Modular/Index.hs     |  5 +++--
 cabal-install/Distribution/Solver/Modular/Validate.hs  |  6 ++++--
 .../PackageTests/Regression/T6961/Test/cabal.out       | 10 ++++------
 .../PackageTests/Regression/T6961/Test/cabal.test.hs   |  4 +---
 .../PackageTests/Regression/T6961/Test/issue6961.cabal |  2 +-
 5 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/cabal-install/Distribution/Solver/Modular/Index.hs b/cabal-install/Distribution/Solver/Modular/Index.hs
index c1a8c0be412..2f28d12de85 100644
--- a/cabal-install/Distribution/Solver/Modular/Index.hs
+++ b/cabal-install/Distribution/Solver/Modular/Index.hs
@@ -42,14 +42,15 @@ data ComponentInfo = ComponentInfo {
     compIsVisible   :: IsVisible
   , compIsBuildable :: IsBuildable
   }
+  deriving Show
 
 -- | Whether a component is visible in the current environment.
 newtype IsVisible = IsVisible Bool
-  deriving Eq
+  deriving (Eq, Show)
 
 -- | Whether a component is made unbuildable by a "buildable: False" field.
 newtype IsBuildable = IsBuildable Bool
-  deriving Eq
+  deriving (Eq, Show)
 
 mkIndex :: [(PN, I, PInfo)] -> Index
 mkIndex xs = M.map M.fromList (groupMap (L.map (\ (pn, i, pi) -> (pn, (i, pi))) xs))
diff --git a/cabal-install/Distribution/Solver/Modular/Validate.hs b/cabal-install/Distribution/Solver/Modular/Validate.hs
index 9c20c9bc321..690e5dcc549 100644
--- a/cabal-install/Distribution/Solver/Modular/Validate.hs
+++ b/cabal-install/Distribution/Solver/Modular/Validate.hs
@@ -543,7 +543,7 @@ extendRequiredComponents available = foldM extendSingle
     extendSingle :: Map QPN ComponentDependencyReasons
                  -> LDep QPN
                  -> Either Conflict (Map QPN ComponentDependencyReasons)
-    extendSingle required (LDep dr (Dep (PkgComponent qpn comp) _)) =
+    extendSingle required (LDep dr@(DependencyReason drQpn _ _) (Dep (PkgComponent qpn comp) _)) =
       let compDeps = M.findWithDefault M.empty qpn required
           success = Right $ M.insertWith M.union qpn (M.insert comp dr compDeps) required
       in -- Only check for the existence of the component if its package has
@@ -554,7 +554,9 @@ extendRequiredComponents available = foldM extendSingle
                  Nothing ->
                      Left $ mkConflict qpn comp dr PackageRequiresMissingComponent
                  Just compInfo
-                   | compIsVisible compInfo == IsVisible False ->
+                   | compIsVisible compInfo == IsVisible False
+                   , drQpn /= qpn -- package components can depend on other components
+                   ->
                      Left $ mkConflict qpn comp dr PackageRequiresPrivateComponent
                    | compIsBuildable compInfo == IsBuildable False ->
                      Left $ mkConflict qpn comp dr PackageRequiresUnbuildableComponent
diff --git a/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.out b/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.out
index 96820cffdc9..8f28d66058a 100644
--- a/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.out
+++ b/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.out
@@ -1,8 +1,6 @@
 # cabal v2-build
 Resolving dependencies...
-cabal: Could not resolve dependencies:
-[__0] trying: issue6961-0 (user goal)
-[__1] rejecting: issue6961:!test (constraint from config file, command line flag, or user target requires opposite flag selection)
-[__1] rejecting: issue6961:*test (requires library 'internal-lib' from issue6961, but the component is private)
-[__1] fail (backjumping, conflict set: issue6961, issue6961:test)
-After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: issue6961 (3), issue6961:test (3)
+Build profile: -w ghc-<GHCVER> -O1
+In order, the following would be built:
+ - issue6961-0 (lib:internal-lib) (first run)
+ - issue6961-0 (test:example) (first run)
diff --git a/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.test.hs b/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.test.hs
index a0c89658e3a..915337859f5 100644
--- a/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/Regression/T6961/Test/cabal.test.hs
@@ -1,5 +1,3 @@
 import Test.Cabal.Prelude
 main = cabalTest $
-  -- fails, but it shouldn't.
-  -- https://github.com/haskell/cabal/issues/6961
-  fails $ cabal "v2-build" ["all", "--dry-run", "--enable-tests"]
+  cabal "v2-build" ["all", "--dry-run", "--enable-tests"]
diff --git a/cabal-testsuite/PackageTests/Regression/T6961/Test/issue6961.cabal b/cabal-testsuite/PackageTests/Regression/T6961/Test/issue6961.cabal
index f2fff29c5e5..490ec5f55f9 100644
--- a/cabal-testsuite/PackageTests/Regression/T6961/Test/issue6961.cabal
+++ b/cabal-testsuite/PackageTests/Regression/T6961/Test/issue6961.cabal
@@ -15,6 +15,6 @@ library internal-lib
 test-suite example
   type: exitcode-stdio-1.0
   default-language: Haskell2010
-  hs-source-dirs: exe
+  hs-source-dirs: tests
   main-is: Main.hs
   build-depends: base, internal-lib