Disable -dynamic-too if -dynamic is also passedwip/T20436

Before if you passed both options then you would generate two identical
hi/dyn_hi and o/dyn_o files, both in the dynamic way. It's better to
warn this is happening rather than duplicating the work and causing
potential confusion.

-dynamic-too should only be used with -static.

Fixes #20436

6 files changed, 36 insertions, 0 deletions

diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index f69f2da243..12f0e8be33 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -4609,6 +4609,12 @@ makeDynFlagsConsistent dflags
     = let dflags' = gopt_unset dflags Opt_BuildDynamicToo
           warn    = "-dynamic-too is not supported on Windows"
       in loop dflags' warn
+ -- Disable -dynamic-too if we are are compiling with -dynamic already, otherwise
+ -- you get two dynamic object files (.o and .dyn_o). (#20436)
+ | ways dflags `hasWay` WayDyn && gopt Opt_BuildDynamicToo dflags
+    = let dflags' = gopt_unset dflags Opt_BuildDynamicToo
+          warn = "-dynamic-too is ignored when using -dynamic"
+      in loop dflags' warn
 
    -- Via-C backend only supports unregisterised ABI. Switch to a backend
    -- supporting it if possible.
diff --git a/docs/users_guide/phases.rst b/docs/users_guide/phases.rst
index 6833ce36d7..0c334f037f 100644
--- a/docs/users_guide/phases.rst
+++ b/docs/users_guide/phases.rst
@@ -707,6 +707,8 @@ Options affecting code generation
     and ``-dynhisuf`` are the counterparts of ``-o``, ``-osuf``, and
     ``-hisuf`` respectively, but applying to the dynamic compilation.
 
+    ``-dynamic-too`` is ignored if :ghc-flag:`-dynamic` is also specified.
+
 .. ghc-flag:: -split-objs
     :shortdesc: Split generated object files into smaller files
     :type: dynamic
diff --git a/testsuite/tests/driver/T20436/A.hs b/testsuite/tests/driver/T20436/A.hs
new file mode 100644
index 0000000000..d843c00b78
--- /dev/null
+++ b/testsuite/tests/driver/T20436/A.hs
@@ -0,0 +1 @@
+module A where
diff --git a/testsuite/tests/driver/T20436/Makefile b/testsuite/tests/driver/T20436/Makefile
new file mode 100644
index 0000000000..de28eab08d
--- /dev/null
+++ b/testsuite/tests/driver/T20436/Makefile
@@ -0,0 +1,23 @@
+TOP=../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk
+
+# Test for passing -dynamic and -dynamic-too together
+
+checkExists = [ -f $1 ] || echo $1 missing
+checkNotExists = [ ! -f $1  ] || echo $1 not missing
+
+clean:
+	rm -f *.o
+	rm -f *.hi
+	rm -f *.dyn_o
+	rm -f *.dyn_hi
+
+T20436: clean
+	'$(TEST_HC)' $(TEST_HC_OPTS) -dynamic -dynamic-too -v0 A.hs
+	$(call checkExists,A.hi)
+	$(call checkExists,A.o)
+	$(call checkNotExists,A.dyn_hi)
+	$(call checkNotExists,A.dyn_o)
+
+
diff --git a/testsuite/tests/driver/T20436/T20436.stderr b/testsuite/tests/driver/T20436/T20436.stderr
new file mode 100644
index 0000000000..1fda220263
--- /dev/null
+++ b/testsuite/tests/driver/T20436/T20436.stderr
@@ -0,0 +1,3 @@
+
+when making flags consistent: warning:
+    -dynamic-too is ignored when using -dynamic
diff --git a/testsuite/tests/driver/T20436/all.T b/testsuite/tests/driver/T20436/all.T
new file mode 100644
index 0000000000..3a2aa6a46a
--- /dev/null
+++ b/testsuite/tests/driver/T20436/all.T
@@ -0,0 +1 @@
+test('T20436', [extra_files(['A.hs']), when(opsys('mingw32'), skip)], makefile_test, [])