Tweak to flag parsing (#5921)

-o2/Main.exe should be an invalid flag, not a linker input

1 files changed, 5 insertions, 0 deletions

diff --git a/ghc/Main.hs b/ghc/Main.hs
index 204c54fa70..a8202f2853 100644
--- a/ghc/Main.hs
+++ b/ghc/Main.hs
@@ -255,6 +255,10 @@ partition_args (arg:args) srcs objs
 
        - module names (not forgetting hierarchical module names),
 
+       - things beginning with '-' are flags that were not recognised by
+         the flag parser, and we want them to generate errors later in
+         checkOptions, so we class them as source files (#5921)
+
        - and finally we consider everything not containing a '.' to be
          a comp manager input, as shorthand for a .hs or .lhs filename.
 
@@ -264,6 +268,7 @@ partition_args (arg:args) srcs objs
 looks_like_an_input :: String -> Bool
 looks_like_an_input m =  isSourceFilename m
                       || looksLikeModuleName m
+                      || "-" `isPrefixOf` m
                       || '.' `notElem` m
 
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