testsuite: Clean up dynlib support predicates

Previously it was unclear whether req_shared_libs should require:

 * that the platform supports dynamic library loading,
 * that GHC supports dynamic linking of Haskell code, or
 * that the dyn way libraries were built

Clarify by splitting the predicate into two:

 * `req_dynamic_lib_support` demands that the platform support dynamic
   linking
 * `req_dynamic_hs` demands that the GHC support dynamic linking of
   Haskell code on the target platform

Naturally `req_dynamic_hs` cannot be true unless
`req_dynamic_lib_support` is also true.

3 files changed, 35 insertions, 7 deletions

diff --git a/testsuite/driver/runtests.py b/testsuite/driver/runtests.py
index 98d6c134b9..2c76661184 100644
--- a/testsuite/driver/runtests.py
+++ b/testsuite/driver/runtests.py
@@ -42,6 +42,7 @@ ghc_env['TERM'] = 'vt100'
 
 global config
 config = getConfig() # get it from testglobals
+config.validate()
 
 def signal_handler(signal, frame):
     stopNow()
diff --git a/testsuite/driver/testglobals.py b/testsuite/driver/testglobals.py
index f52aec281c..adb2109923 100644
--- a/testsuite/driver/testglobals.py
+++ b/testsuite/driver/testglobals.py
@@ -134,8 +134,16 @@ class TestConfig:
         # Do we have interpreter support?
         self.have_interp = False
 
-        # Do we have shared libraries?
-        self.have_shared_libs = False
+        # Does the platform support loading of dynamic shared libraries? e.g.
+        # some musl-based environments do not.
+        self.supports_dynamic_libs = True
+
+        # Does GHC support dynamic linking of Haskell objects (i.e. the dynamic
+        # way)?
+        self.supports_dynamic_hs = True
+
+        # Is the compiler dynamically linked?
+        self.ghc_dynamic = False
 
         # Do we have SMP support?
         self.have_smp = False
@@ -152,9 +160,6 @@ class TestConfig:
         # Are we testing an in-tree compiler?
         self.in_tree_compiler = True
 
-        # Is the compiler dynamically linked?
-        self.ghc_dynamic = False
-
         # Are we running in a ThreadSanitizer-instrumented build?
         self.have_thread_sanitizer = False
 
@@ -205,6 +210,15 @@ class TestConfig:
         # I have no idea what this does
         self.package_conf_cache_file = None # type: Optional[Path]
 
+    def validate(self) -> None:
+        """ Check the TestConfig for self-consistency """
+        def assert_implies(a: bool, b: bool):
+            if a:
+                assert(b)
+
+        assert_implies(self.supports_dynamic_hs, self.supports_dynamic_libs)
+        assert_implies(self.have_dynamic, self.supports_dynamic_hs)
+        assert_implies(self.ghc_dynamic, self.have_dynamic)
 
 global config
 config = TestConfig()
diff --git a/testsuite/driver/testlib.py b/testsuite/driver/testlib.py
index 1a12f5c086..3202bab65c 100644
--- a/testsuite/driver/testlib.py
+++ b/testsuite/driver/testlib.py
@@ -206,8 +206,20 @@ def req_profiling( name, opts ):
     if not config.have_profiling:
         opts.expect = 'fail'
 
-def req_shared_libs( name, opts ):
-    if not config.have_shared_libs:
+def req_dynamic_lib_support( name, opts ):
+    '''
+    Require that the platform have shared object support (N.B. this doesn't
+    necessary imply that GHC supports the dynamic way).
+    '''
+    if not config.supports_dynamic_libs:
+        opts.expect = 'fail'
+
+def req_dynamic_hs( name, opts ):
+    '''
+    Require that the GHC supports dynamic linking of Haskell objects on the
+    platform
+    '''
+    if not config.supports_dynamic_hs:
         opts.expect = 'fail'
 
 def req_interp( name, opts ):
@@ -571,6 +583,7 @@ def have_ncg( ) -> bool:
     return config.have_ncg
 
 def have_dynamic( ) -> bool:
+    ''' Were libraries built in the dynamic way? '''
     return config.have_dynamic
 
 def have_profiling( ) -> bool: