Suppress ghc-pkg warnings emitted when an empty packages is being registered

When a package contains a library that has no modules, "./Setup register"
tries to register the library with fields "haddock-interfaces:" and
"haddock-html:" pointing at non-existent files or directories, and "ghc-pkg
register" warns about them.

To suppress the warnings prevent these fields from being generated when
there are no modules.

Author: depressed-pho

Cabal/src/Distribution/Simple/Register.hs

@@ -549,8 +549,8 @@ generalInstalledPackageInfo adjustRelIncDirs pkg abi_hash lib lbi clbi installDi
     , IPI.ldOptions = ldOptions bi
     , IPI.frameworks = map getSymbolicPath $ frameworks bi
     , IPI.frameworkDirs = map getSymbolicPath $ extraFrameworkDirs bi
-    , IPI.haddockInterfaces = [haddockdir installDirs </> haddockLibraryPath pkg lib]
-    , IPI.haddockHTMLs = [htmldir installDirs]
+    , IPI.haddockInterfaces = [haddockdir installDirs </> haddockLibraryPath pkg lib | hasModules]
+    , IPI.haddockHTMLs = [htmldir installDirs | hasModules]
     , IPI.pkgRoot = Nothing
     , IPI.libVisibility = libVisibility lib
     }

cabal-testsuite/PackageTests/HaddockEmptyLib/empty/empty.cabal

@@ -0,0 +1,6 @@
+name: emptyLib
+Cabal-version: >= 1.2
+version: 1.0
+build-type: Simple
+
+Library

cabal-testsuite/PackageTests/HaddockEmptyLib/setup.cabal.out

@@ -0,0 +1,13 @@
+# Setup configure
+Configuring emptyLib-1.0...
+# Setup build
+Preprocessing library for emptyLib-1.0...
+Building library for emptyLib-1.0...
+# Setup haddock
+Preprocessing library for emptyLib-1.0...
+Running Haddock on library for emptyLib-1.0...
+Warning: Haddocks are being requested, but there aren't any modules given to create documentation for.
+# Setup copy
+Installing library in <PATH>
+# Setup register
+Registering library for emptyLib-1.0...

cabal-testsuite/PackageTests/HaddockEmptyLib/setup.out

@@ -0,0 +1,13 @@
+# Setup configure
+Configuring emptyLib-1.0...
+# Setup build
+Preprocessing library for emptyLib-1.0...
+Building library for emptyLib-1.0...
+# Setup haddock
+Preprocessing library for emptyLib-1.0...
+Running Haddock on library for emptyLib-1.0...
+Warning: Haddocks are being requested, but there aren't any modules given to create documentation for.
+# Setup copy
+Installing library in <PATH>
+# Setup register
+Registering library for emptyLib-1.0...

cabal-testsuite/PackageTests/HaddockEmptyLib/setup.test.hs

@@ -0,0 +1,6 @@
+import Test.Cabal.Prelude
+-- Test install when the library is empty, for #9997
+main = setupAndCabalTest $
+       withPackageDb $
+       withDirectory "empty" $
+       setup_install_with_docs []

changelog.d/pr-9997

@@ -0,0 +1,15 @@
+synopsis: Suppress ghc-pkg warnings emitted when an empty packages is being registered
+packages: Cabal
+prs: #9997
+
+description: {
+
+When a package contains a library that has no modules, `./Setup register`
+tries to register the library with fields `haddock-interfaces:` and
+`haddock-html:` pointing at non-existent files or directories, and `ghc-pkg
+register` warns about them.
+
+To suppress the warnings prevent these fields from being generated when
+there are no modules.
+
+}