Fix coverage gate

we copied the tree of the graalvm including the already generated pyc
files. unfortunately, that meant we were loading pyc files that had their
filename set to the original path, which conflicts with the target path we
copied to

Author: timfel

mx.graalpython/mx_graalpython.py

@@ -606,20 +606,22 @@ def run_python_unittests(python_binary, args=None, paths=None, aot_compatible=Tr
         # We need to make sure the arguments get passed to subprocesses, so we create a temporary launcher
         # with the arguments
         basedir = os.path.realpath(os.path.join(os.path.dirname(python_binary), '..'))
-        jacoco_basedir = "%s-jacoco" % basedir
-        shutil.rmtree(jacoco_basedir, ignore_errors=True)
-        shutil.copytree(basedir, jacoco_basedir, symlinks=True)
-        launcher_path = os.path.join(jacoco_basedir, 'bin', 'graalpython')
-        with open(launcher_path, 'r', encoding='ascii', errors='ignore') as launcher:
-            lines = launcher.readlines()
-        assert re.match(r'^#!.*bash', lines[0]), "jacoco needs a bash launcher"
-        lines.insert(-1, 'jvm_args+=(%s)\n' % agent_args)
-        with open(launcher_path, 'w') as launcher:
-            launcher.writelines(lines)
-        # jacoco only dumps the data on exit, and when we run all our unittests
-        # at once it generates so much data we run out of heap space
-        for testfile in testfiles:
-            mx.run([launcher_path] + args + [testfile], nonZeroIsFatal=True, env=env)
+        launcher_path = os.path.join(basedir, 'bin', 'graalpython')
+        launcher_path_bak = launcher_path + ".bak"
+        shutil.copy(launcher_path, launcher_path_bak)
+        try:
+            with open(launcher_path, 'r', encoding='ascii', errors='ignore') as launcher:
+                lines = launcher.readlines()
+            assert re.match(r'^#!.*bash', lines[0]), "jacoco needs a bash launcher"
+            lines.insert(-1, 'jvm_args+=(%s)\n' % agent_args)
+            with open(launcher_path, 'w') as launcher:
+                launcher.writelines(lines)
+            # jacoco only dumps the data on exit, and when we run all our unittests
+            # at once it generates so much data we run out of heap space
+            for testfile in testfiles:
+                mx.run([launcher_path] + args + [testfile], nonZeroIsFatal=True, env=env)
+        finally:
+            shutil.move(launcher_path_bak, launcher_path)
     else:
         args += testfiles
         mx.logv(" ".join([python_binary] + args))