Use -Wdefault when running Python testdriver (#22727)

hadrian/src/Settings/Builders/RunTest.hs

@@ -181,7 +181,7 @@ assertSameCompilerArgs stg = do
     ]
 
 
--- Command line arguments for invoking the @runtest.py@ script. A lot of this
+-- Command line arguments for invoking the @runtests.py@ script. A lot of this
 -- mirrors @testsuite/mk/test.mk@.
 runTestBuilderArgs :: Args
 runTestBuilderArgs = builder Testsuite ? do
@@ -227,7 +227,8 @@ runTestBuilderArgs = builder Testsuite ? do
         asBool s b = s ++ show b
 
     -- TODO: set CABAL_MINIMAL_BUILD/CABAL_PLUGIN_BUILD
-    mconcat [ arg $ "testsuite/driver/runtests.py"
+    mconcat [ arg "-Wdefault"  -- see #22727
+            , arg $ "testsuite/driver/runtests.py"
             , pure [ "--rootdir=" ++ testdir | testdir <- rootdirs ]
             , arg "--top", arg (top -/- "testsuite")
             , arg "-e", arg $ "windows=" ++ show windowsHost

testsuite/driver/cpu_features.py

@@ -17,7 +17,8 @@ cpu_feature_cache = None
 
 def get_cpu_features():
     if config.os in ['mingw32', 'linux'] and os.path.exists('/proc/cpuinfo'):
-        f = open('/proc/cpuinfo').read()
+        with open('/proc/cpuinfo') as x:
+            f = x.read()
         flags = re.search(r'flags\s*:\s*.*$', f, re.M)
         if flags is None:
             print('get_cpu_features: failed to find cpu features')

testsuite/driver/runtests.py

@@ -99,7 +99,8 @@ if args.e:
 
 if args.config_file:
     for arg in args.config_file:
-        exec(open(arg).read())
+        with io.open(arg) as f:
+            exec(f.read())
 
 if args.config:
     for arg in args.config:
@@ -349,8 +350,6 @@ except Exception as e:
     print('Failed to detect CPU features: ', e)
 
 sys.stdout.flush()
-# we output text, which cannot be unbuffered
-sys.stdout = os.fdopen(sys.__stdout__.fileno(), "w")
 
 if config.local:
     tempdir = ''
@@ -607,6 +606,7 @@ else:
       print("WARNING - skipping all tests and only reporting required hadrian dependencies:", config.hadrian_deps)
       for d in config.hadrian_deps:
         print(d,file=config.only_report_hadrian_deps)
+      config.only_report_hadrian_deps.close()
 
 if len(t.unexpected_failures) > 0 or \
    len(t.unexpected_stat_failures) > 0 or \

testsuite/tests/codeGen/should_compile/all.T

@@ -96,7 +96,7 @@ test('T14373c',
      switch_skeleton_only])
 
 switch_skeleton_and_entries_only = (r'grep -e "switch \[" -e "case " -e "default: " -e "Default_entry(" -e "R1 = .*_closure+2;"'
-                                     '| sed -e "s|\] .*|\]|g" -e "s|goto .*|goto |g" -e "s|R1 = .*_closure+2;.*|R1 = XYZ_closure+2;|g" -e "s|//.*|//|g"')
+                                    r'| sed -e "s|\] .*|\]|g" -e "s|goto .*|goto |g" -e "s|R1 = .*_closure+2;.*|R1 = XYZ_closure+2;|g" -e "s|//.*|//|g"')
 
 test('T14373d',
       [ js_skip # JS backend doesn't produce Cmm