Do an early check for unbuildable deps, and give good error.

When a library/executable is unbuildable, the solver may still
return a reference to it.  Handle this gracefully in ProjectPlanning
with a nice error message, rather than an assert failure.

Fixes haskell#3978.

Signed-off-by: Edward Z. Yang <[email protected]>

Author: ezyang

cabal-install/Distribution/Client/ProjectPlanning.hs

@@ -130,7 +130,7 @@ import           Distribution.Text
 import qualified Distribution.Compat.Graph as Graph
 import           Distribution.Compat.Graph(IsNode(..))
 
-import           Text.PrettyPrint (text, (<+>))
+import           Text.PrettyPrint hiding ((<>))
 import qualified Data.Map as Map
 import           Data.Set (Set)
 import qualified Data.Set as Set
@@ -1142,6 +1142,21 @@ elaborateInstallPlan verbosity platform compiler compilerprogdb pkgConfigDB
                   Map ComponentId FilePath),
                 ElaboratedConfiguredPackage)
         buildComponent (cc_map, lc_map, exe_map) comp = do
+            -- Before we get too far, check if we depended on something
+            -- unbuildable.  If we did, give a good error.  (If we don't
+            -- check, the 'toConfiguredComponent' will assert fail, see #3978).
+            case unbuildable_external_lib_deps of
+                [] -> return ()
+                deps -> failProgress $
+                            text "The package" <+> disp pkgid <+>
+                            text "depends on unbuildable libraries:" <+>
+                            hsep (punctuate comma (map (disp.solverSrcId) deps))
+            case unbuildable_external_exe_deps of
+                [] -> return ()
+                deps -> failProgress $
+                            text "The package" <+> disp pkgid <+>
+                            text "depends on unbuildable executables:" <+>
+                            hsep (punctuate comma (map (disp.solverSrcId) deps))
             infoProgress $ dispConfiguredComponent cc
             let -- Use of invariant: DefUnitId indicates that if
                 -- there is no hash, it must have an empty
@@ -1270,6 +1285,11 @@ elaborateInstallPlan verbosity platform compiler compilerprogdb pkgConfigDB
             external_cc_map = Map.fromList (map mkPkgNameMapping external_lib_dep_pkgs)
             external_lc_map = Map.fromList (map mkShapeMapping external_lib_dep_pkgs)
 
+            unbuildable_external_lib_deps =
+                filter (null . elaborateLibSolverId mapDep) external_lib_dep_sids
+            unbuildable_external_exe_deps =
+                filter (null . elaborateExeSolverId mapDep) external_exe_dep_sids
+
             mkPkgNameMapping :: ElaboratedPlanPackage
                              -> (PackageName, (ComponentId, PackageId))
             mkPkgNameMapping dpkg =

cabal-install/cabal-install.cabal

@@ -134,6 +134,11 @@ Extra-Source-Files:
   tests/IntegrationTests/new-build/T3460/sub-package-B/B.hs
   tests/IntegrationTests/new-build/T3460/sub-package-B/Setup.hs
   tests/IntegrationTests/new-build/T3460/sub-package-B/sub-package-B.cabal
+  tests/IntegrationTests/new-build/T3978.err
+  tests/IntegrationTests/new-build/T3978.sh
+  tests/IntegrationTests/new-build/T3978/cabal.project
+  tests/IntegrationTests/new-build/T3978/p/p.cabal
+  tests/IntegrationTests/new-build/T3978/q/q.cabal
   tests/IntegrationTests/new-build/executable/Main.hs
   tests/IntegrationTests/new-build/executable/Setup.hs
   tests/IntegrationTests/new-build/executable/Test.hs

cabal-install/tests/IntegrationTests/new-build/T3978.err

@@ -0,0 +1 @@
+RE:^cabal(\.exe)?: The package q-1.0 depends on unbuildable libraries: p-1.0

cabal-install/tests/IntegrationTests/new-build/T3978.sh

@@ -0,0 +1,3 @@
+. ./common.sh
+cd T3978
+! cabal new-build q

cabal-install/tests/IntegrationTests/new-build/T3978/cabal.project

@@ -0,0 +1,2 @@
+packages: p q
+allow-older: p:base

cabal-install/tests/IntegrationTests/new-build/T3978/p/p.cabal

@@ -0,0 +1,7 @@
+name: p
+version: 1.0
+build-type: Simple
+cabal-version: >= 1.10
+
+library
+    buildable: False

cabal-install/tests/IntegrationTests/new-build/T3978/q/q.cabal

@@ -0,0 +1,7 @@
+name: q
+version: 1.0
+build-type: Simple
+cabal-version: >= 1.10
+
+library
+    build-depends: p