Move the definition of __GHCIDE__ (#377)

* Move the definition of __GHCIDE__ so we don't modify upstream copied code

* Add a test that __GHCIDE__ works

Author: ndmitchell

Diff for: src/Development/IDE/Core/Preprocessor.hs

@@ -167,10 +167,18 @@ runLhs dflags filename contents = withTempDir $ \dir -> do
     escape []        = []
 
 
+modifyOptP :: ([String] -> [String]) -> DynFlags -> DynFlags
+modifyOptP op = onSettings (onOptP op)
+  where
+    onSettings f x = x{settings = f $ settings x}
+    onOptP f x = x{sOpt_P = f $ sOpt_P x}
+
 -- | Run CPP on a file
 runCpp :: DynFlags -> FilePath -> Maybe SB.StringBuffer -> IO SB.StringBuffer
 runCpp dflags filename contents = withTempDir $ \dir -> do
     let out = dir </> takeFileName filename <.> "out"
+    dflags <- pure $ modifyOptP ("-D__GHCIDE__":) dflags
+
     case contents of
         Nothing -> do
             -- Happy case, file is not modified, so run CPP on it in-place

Diff for: src/Development/IDE/GHC/CPP.hs

@@ -116,8 +116,6 @@ doCpp dflags raw input_fn output_fn = do
                     ++ map SysTools.Option sse_defs
                     ++ map SysTools.Option avx_defs
                     ++ mb_macro_include
-        -- Define a special macro "__GHCIDE__"
-                    ++ [ SysTools.Option "-D__GHCIDE__"]
         -- Set the language mode to assembler-with-cpp when preprocessing. This
         -- alleviates some of the C99 macro rules relating to whitespace and the hash
         -- operator, which we tend to abuse. Clang in particular is not very happy

Diff for: test/exe/Main.hs

@@ -1281,22 +1281,35 @@ pluginTests = testSessionWait "plugins" $ do
 
 cppTests :: TestTree
 cppTests =
-  testCase "cpp" $ do
-    let content =
-          T.unlines
-            [ "{-# LANGUAGE CPP #-}",
-              "module Testing where",
-              "#ifdef FOO",
-              "foo = 42"
-            ]
-    -- The error locations differ depending on which C-preprocessor is used.
-    -- Some give the column number and others don't (hence -1). Assert either
-    -- of them.
-    (run $ expectError content (2, -1))
-      `catch` ( \e -> do
-                  let _ = e :: HUnitFailure
-                  run $ expectError content (2, 1)
-              )
+  testGroup "cpp"
+    [ testCase "cpp-error" $ do
+        let content =
+              T.unlines
+                [ "{-# LANGUAGE CPP #-}",
+                  "module Testing where",
+                  "#ifdef FOO",
+                  "foo = 42"
+                ]
+        -- The error locations differ depending on which C-preprocessor is used.
+        -- Some give the column number and others don't (hence -1). Assert either
+        -- of them.
+        (run $ expectError content (2, -1))
+          `catch` ( \e -> do
+                      let _ = e :: HUnitFailure
+                      run $ expectError content (2, 1)
+                  )
+    , testSessionWait "cpp-ghcide" $ do
+        _ <- openDoc' "A.hs" "haskell" $ T.unlines
+          ["{-# LANGUAGE CPP #-}"
+          ,"main ="
+          ,"#ifdef __GHCIDE__"
+          ,"  worked"
+          ,"#else"
+          ,"  failed"
+          ,"#endif"
+          ]
+        expectDiagnostics [("A.hs", [(DsError, (3, 2), "Variable not in scope: worked")])]
+    ]
   where
     expectError :: T.Text -> Cursor -> Session ()
     expectError content cursor = do