Fixes issue spotbugs#1313

fix for issue 1313, do not report volatile problems in synthetic code

With the fix for Eclipse bug 544521,
https://bugs.eclipse.org/bugs/show_bug.cgi?id=544521, the Eclipse 4.17+
Java compiler will generate synthetic code for switch expressions.
spotbugs reports VO_VOLATILE_REFERENCE_TO_ARRAY issues in this synthetic
code.

This changes makes spotbugs ignore synthetic fields during
VO_VOLATILE_REFERENCE_TO_ARRAY analysis.

CHANGELOG.md

@@ -5,6 +5,8 @@ This is the changelog for SpotBugs. This follows [Keep a Changelog v1.0.0](http:
 Currently the versioning policy of this project follows [Semantic Versioning v2.0.0](http://semver.org/spec/v2.0.0.html).
 
 ## Unreleased - 2020-??-??
+### Fixed
+* spotbugs reports `VO_VOLATILE_REFERENCE_TO_ARRAY` in synthetic code generated by Eclipse 4.17+ Java compiler ([#1313](https://github.com/spotbugs/spotbugs/issues/1313))
 
 ## 4.1.4 - 2020-10-15
 ### Fixed

spotbugs/src/main/java/edu/umd/cs/findbugs/detect/VolatileUsage.java

@@ -144,7 +144,7 @@ public void report() {
         Subtypes2 subtypes2 = AnalysisContext.currentAnalysisContext().getSubtypes2();
 
         for (XField f : AnalysisContext.currentXFactory().allFields()) {
-            if (isVolatileArray(f) && subtypes2.isApplicationClass(f.getClassDescriptor())) {
+            if (!f.isSynthetic() && isVolatileArray(f) && subtypes2.isApplicationClass(f.getClassDescriptor())) {
                 int priority = LOW_PRIORITY;
                 if (initializationWrites.contains(f) && !otherWrites.contains(f)) {
                     priority = NORMAL_PRIORITY;

spotbugsTestCases/src/java/ghIssues/issue1313/Issue1313.java

@@ -0,0 +1,24 @@
+package ghIssues.issue1313;
+
+/**
+ * Manual test snippet for issue 1313.
+ */
+public class Issue1313 {
+
+    enum TestEnum {
+        TEST_ENUM_VALUE1, TEST_ENUM_VALUE2,
+    }
+
+    static void println(TestEnum testEnum) {
+        switch (testEnum) {
+        case TEST_ENUM_VALUE1:
+            System.out.println("TEST_ENUM_VALUE1");
+            break;
+        case TEST_ENUM_VALUE2:
+            System.out.println("TEST_ENUM_VALUE2");
+            break;
+        default:
+            System.out.println("unknown enum value");
+        }
+    }
+}