From 666632f3880ec321df205db0e1c340601271a706 Mon Sep 17 00:00:00 2001
From: Michael Sloan <mgsloan@gmail.com>
Date: Wed, 1 Feb 2017 15:31:02 -0800
Subject: [PATCH] Only run "cabal copy" if there are exes or lib #2862

---
 src/Stack/Build/Execute.hs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Stack/Build/Execute.hs b/src/Stack/Build/Execute.hs
index f0033caccf..46fa12d702 100644
--- a/src/Stack/Build/Execute.hs
+++ b/src/Stack/Build/Execute.hs
@@ -1306,7 +1306,8 @@ singleBuild runInBase ac@ActionContext {..} ee@ExecuteEnv {..} task@Task {..} in
             cabal False (concat [["haddock", "--html", "--hoogle", "--html-location=../$pkg-$version/"]
                                 ,sourceFlag, ["--internal" | boptsHaddockInternal eeBuildOpts]])
 
-        unless isFinalBuild $ withMVar eeInstallLock $ \() -> do
+        let shouldCopy = not isFinalBuild && (packageHasLibrary package || not (Set.null (packageExes package)))
+        when shouldCopy $ withMVar eeInstallLock $ \() -> do
             announce "copy/register"
             eres <- try $ cabal False ["copy"]
             case eres of