Fix #2755 by always respecting enable flags on configure.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

cabal-install/Distribution/Client/Configure.hs

@@ -386,8 +386,13 @@ configurePackage verbosity platform comp scriptOptions configFlags
       -- Use '--exact-configuration' if supported.
       configExactConfiguration = toFlag True,
       configVerbosity          = toFlag verbosity,
-      configBenchmarks         = toFlag (BenchStanzas `elem` stanzas),
+      -- NB: if the user explicitly specified
+      -- --enable-tests/--enable-benchmarks, always respect it.
+      -- (But if they didn't, let solver decide.)
+      configBenchmarks         = toFlag (BenchStanzas `elem` stanzas)
+                                    `mappend` configBenchmarks configFlags,
       configTests              = toFlag (TestStanzas `elem` stanzas)
+                                    `mappend` configTests configFlags
     }
 
     pkg = case finalizePD flags (enableStanzas stanzas)

cabal-install/cabal-install.cabal

@@ -97,6 +97,10 @@ Extra-Source-Files:
   tests/IntegrationTests/new-build/monitor_cabal_files/q/Setup.hs
   tests/IntegrationTests/new-build/monitor_cabal_files/q/q-broken.cabal.in
   tests/IntegrationTests/new-build/monitor_cabal_files/q/q-fixed.cabal.in
+  tests/IntegrationTests/regression/t2755.sh
+  tests/IntegrationTests/regression/t2755/A.hs
+  tests/IntegrationTests/regression/t2755/Setup.hs
+  tests/IntegrationTests/regression/t2755/test-t2755.cabal
   tests/IntegrationTests/regression/t3199.sh
   tests/IntegrationTests/regression/t3199/Main.hs
   tests/IntegrationTests/regression/t3199/Setup.hs

cabal-install/tests/IntegrationTests/regression/t2755.sh

+. ./common.sh
+
+cd t2755
+cabal configure --enable-tests
+(cabal test || true) | tee result.log
+! grep "Re-configuring" result.log > /dev/null

cabal-install/tests/IntegrationTests/regression/t2755/A.hs

+module A where

cabal-install/tests/IntegrationTests/regression/t2755/Setup.hs

+import Distribution.Simple
+main = defaultMain

cabal-install/tests/IntegrationTests/regression/t2755/test-t2755.cabal

+name:                test-t2755
+version:             0.1.0.0
+license:             BSD3
+author:              Edward Z. Yang
+maintainer:          ezyang@cs.stanford.edu
+category:            Test
+build-type:          Simple
+cabal-version:       >=1.10
+
+library
+    exposed-modules: A
+    build-depends: base
+    default-language: Haskell2010