Fix #723 (Instance declarations in hs-boot files result in GHC errors)

ghcide/src/Development/IDE/Core/Compile.hs

@@ -229,14 +229,23 @@ mkHiFileResultCompile
 mkHiFileResultCompile session' tcm simplified_guts ltype = catchErrs $ do
   let session = session' { hsc_dflags = ms_hspp_opts ms }
       ms = pm_mod_summary $ tmrParsed tcm
-  -- give variables unique OccNames
-  (guts, details) <- tidyProgram session simplified_guts
+      tcGblEnv = tmrTypechecked tcm
 
   let genLinkable = case ltype of
         ObjectLinkable -> generateObjectCode
         BCOLinkable -> generateByteCode
 
-  (diags, linkable) <- genLinkable session ms guts
+  (linkable, details, diags) <-
+    if mg_hsc_src simplified_guts == HsBootFile
+    then do
+        -- give variables unique OccNames
+        details <- mkBootModDetailsTc session tcGblEnv
+        pure (Nothing, details, [])
+    else do
+        -- give variables unique OccNames
+        (guts, details) <- tidyProgram session simplified_guts
+        (diags, linkable) <- genLinkable session ms guts
+        pure (linkable, details, diags)
 #if MIN_GHC_API_VERSION(8,10,0)
   let !partial_iface = force (mkPartialIface session details simplified_guts)
   final_iface <- mkFullIface session partial_iface

ghcide/test/data/boot/A.hs

@@ -1,8 +1,10 @@
+{-# LANGUAGE TemplateHaskell #-}
 module A where
 
 import B( TB(..) )
 
 newtype TA = MkTA Int
+    deriving Eq
 
 f :: TB -> TA
 f (MkTB x) = MkTA x

ghcide/test/data/boot/A.hs-boot

@@ -1,2 +1,3 @@
 module A where
 newtype TA = MkTA Int
+instance Eq TA

ghcide/test/exe/Main.hs

@@ -3673,7 +3673,7 @@ bootTests = testCase "boot-def-test" $ runWithExtraFiles "boot" $ \dir -> do
 
   cdoc <- createDoc cPath "haskell" cSource
   locs <- getDefinitions cdoc (Position 7 4)
-  let floc = mkR 7 0 7 1
+  let floc = mkR 9 0 9 1
   checkDefs locs (pure [floc])
 
 -- | test that TH reevaluates across interfaces