Include CPP preprocessor dependencies in -M output

Issue #16521

1 files changed, 14 insertions, 1 deletions

diff --git a/compiler/main/DriverMkDepend.hs b/compiler/main/DriverMkDepend.hs
index 741104596a..6368d8c785 100644
--- a/compiler/main/DriverMkDepend.hs
+++ b/compiler/main/DriverMkDepend.hs
@@ -41,6 +41,7 @@ import System.IO
 import System.IO.Error  ( isEOFError )
 import Control.Monad    ( when )
 import Data.Maybe       ( isJust )
+import Data.IORef
 
 -----------------------------------------------------------------
 --
@@ -85,7 +86,7 @@ doMkDependHS srcs = do
     -- Print out the dependencies if wanted
     liftIO $ debugTraceMsg dflags 2 (text "Module dependencies" $$ ppr sorted)
 
-    -- Prcess them one by one, dumping results into makefile
+    -- Process them one by one, dumping results into makefile
     -- and complaining about cycles
     hsc_env <- getSession
     root <- liftIO getCurrentDirectory
@@ -224,6 +225,18 @@ processDeps dflags hsc_env excl_mods root hdl (AcyclicSCC node)
                 -- Something like       A.o : A.hs
         ; writeDependency root hdl obj_files src_file
 
+                -- Emit a dependency for each CPP import
+        ; when (depIncludeCppDeps dflags) $ do
+            -- CPP deps are descovered in the module parsing phase by parsing
+            -- comment lines left by the preprocessor.
+            -- Note that GHC.parseModule may throw an exception if the module
+            -- fails to parse, which may not be desirable (see #16616).
+          { session <- Session <$> newIORef hsc_env
+          ; parsedMod <- reflectGhc (GHC.parseModule node) session
+          ; mapM_ (writeDependency root hdl obj_files)
+                  (GHC.pm_extra_src_files parsedMod)
+          }
+
                 -- Emit a dependency for each import
 
         ; let do_imps is_boot idecls = sequence_