Reuse the same compiler instance for all tests in a JUnit class

Note that JUnit creates a new instance of the test class for running
each test method. So the compiler instance is added to the companion.
However, the JVM would quickly run out of memory when running multiple
tests, as the compilers cannot be GCd. So we make it a `var`, and set
it to null when a class is done. For that we use JUnit's `@AfterClass`
which is required to be on a static method. Therefore we add a Java
class with such a static method that we can extend from Scala.

1 files changed, 20 insertions, 0 deletions

diff --git a/test/junit/scala/tools/testing/ClearAfterClass.java b/test/junit/scala/tools/testing/ClearAfterClass.java
new file mode 100644
index 0000000000..232d459c4e
--- /dev/null
+++ b/test/junit/scala/tools/testing/ClearAfterClass.java
@@ -0,0 +1,20 @@
+package scala.tools.testing;
+
+import org.junit.AfterClass;
+
+/**
+ * Extend this class to use JUnit's @AfterClass. This annotation only works on static methods,
+ * which cannot be written in Scala.
+ *
+ * Example: {@link scala.tools.nsc.backend.jvm.opt.InlinerTest}
+ */
+public class ClearAfterClass {
+    public static interface Clearable {
+        void clear();
+    }
+
+    public static Clearable stateToClear;
+
+    @AfterClass
+    public static void clearState() { stateToClear.clear(); }
+}