+# depend on project.mk, so we pick up the new version number if it changes.
+$(GHC_CABAL_DIR)/dist-dummy-ghc/build/dummy-ghc.hs : $(GHC_CABAL_DIR)/ghc.mk $(MKDIRHIER) mk/project.mk compiler/main/DynFlags.hs
+ "$(MKDIRHIER)" $(dir $@)
+ "$(RM)" $(RM_OPTS) $@
+ echo 'import System.Environment' >> $@
+ echo 'import System.Cmd' >> $@
+ echo 'import System.Exit' >> $@
+ echo 'main :: IO ()' >> $@
+ echo 'main = do args <- getArgs' >> $@
+ echo ' case args of' >> $@
+ echo ' ["--numeric-version"] ->' >> $@
+ echo ' putStrLn "$(ProjectVersion)"' >> $@
+ echo ' ["--supported-languages"] ->' >> $@
+ echo ' mapM_ putStrLn extensions' >> $@
+ echo ' _ ->' >> $@
+ echo ' do e <- rawSystem "$(GHC_STAGE0)" args' >> $@
+ echo ' exitWith e' >> $@
+# This unpleasant sed script grabs the lines between the
+# xFlags ::
+# line and the
+# ]
+# line of compiler/main/DynFlags.hs, and if they look like
+# ( "PostfixOperators", ...
+# then it translates them into
+# ["PostfixOperators"] ++
+# Tabs are a pain to handle portably with sed, so rather than worrying
+# about them we just use tr to remove them all before we start.
+ echo 'extensions :: [String]' >> $@
+ echo 'extensions =' >> $@
+ '$(TR)' -d '\t' < compiler/main/DynFlags.hs | '$(SED)' '/^xFlags/,/]/s/^ *( *\("[^"]*"\)[^"]*/ [\1] ++/p;d' >> $@
+ echo ' []' >> $@