Refactor, add comments, update ChangeLog.md

Author: mpilgrem

ChangeLog.md

@@ -49,7 +49,9 @@ Bug fixes:
   set [#53](https://github.com/commercialhaskell/pantry/pull/53)
 * Pass any CPP options specified via `cpp-options:` in the `.cabal` file to GHCi
   using GHC's `-optP` flag. See
-  [#5608](https://github.com/commercialhaskell/stack/pull/5608) 
+  [#5608](https://github.com/commercialhaskell/stack/pull/5608)
+* On Unix-like operating systems, respect the `with-gcc` option when installing
+  GHC. See [#5609](https://github.com/commercialhaskell/stack/pull/5609)
 
 ## v2.7.5
 

src/Stack/Setup.hs

@@ -1460,10 +1460,21 @@ installGHCPosix downloadInfo _ archiveFile archiveType tempDir destDir = do
 
     dir <- expectSingleUnpackedDir archiveFile tempDir
 
-    gccEnvMaybe <- fmap (\gcc -> Map.fromList [("CC", T.pack (toFilePath gcc))]) <$> (view $ configL.to configOverrideGccPath)
+    mOverrideGccPath <- view $ configL.to configOverrideGccPath
+
+    -- The make application uses the CC environment variable to configure the
+    -- program for compiling C programs
+    let mGccEnv = let gccEnvFromPath p =
+                        Map.singleton "CC" $ T.pack (toFilePath p)
+                  in  gccEnvFromPath <$> mOverrideGccPath
+
+    -- Data.Map.union provides a left-biased union, so mGccEnv will prevail
+    let ghcConfigureEnv =
+          fromMaybe Map.empty mGccEnv `Map.union` gdiConfigureEnv downloadInfo
+    
     logSticky "Configuring GHC ..."
     runStep "configuring" dir
-        (fromMaybe Map.empty gccEnvMaybe `Map.union` gdiConfigureEnv downloadInfo)
+        ghcConfigureEnv
         (toFilePath $ dir </> relFileConfigure)
         (("--prefix=" ++ toFilePath destDir) : map T.unpack (gdiConfigureOpts downloadInfo))
 

stack.cabal

@@ -54,6 +54,7 @@ extra-source-files:
     doc/README.md
     doc/shell_autocompletion.md
     doc/SIGNING_KEY.md
+    doc/Stack_and_VS_Code.md
     doc/stack_yaml_vs_cabal_package_file.md
     doc/travis_ci.md
     doc/yaml_configuration.md