factor AbstractDetectorForParameterArray2 out of ManualMessageDetector

so that in the next commit the upcoming ManualGetStackTraceDetector for
a SLF4J_GET_STACK_TRACE (issue KengoTODA#70) does not have to copy/paste 3/4 of
the ManualMessageDetector

bug-pattern/src/main/java/jp/skypencil/findbugs/slf4j/ManualMessageDetector.java

@@ -1,31 +1,29 @@
 package jp.skypencil.findbugs.slf4j;
 
-import static org.apache.bcel.Const.INVOKEVIRTUAL;
-
 import com.google.common.base.Objects;
+import jp.skypencil.findbugs.slf4j.parameter.AbstractDetectorForParameterArray2;
+import jp.skypencil.findbugs.slf4j.parameter.ArrayData;
 import edu.umd.cs.findbugs.BugInstance;
 import edu.umd.cs.findbugs.BugReporter;
 import edu.umd.cs.findbugs.OpcodeStack.CustomUserValue;
 import edu.umd.cs.findbugs.OpcodeStack.Item;
 import javax.annotation.Nullable;
 import jp.skypencil.findbugs.slf4j.parameter.AbstractDetectorForParameterArray;
-import jp.skypencil.findbugs.slf4j.parameter.ArrayData;
 import jp.skypencil.findbugs.slf4j.parameter.ArrayDataHandler.Strategy;
 
 @CustomUserValue
 public final class ManualMessageDetector extends AbstractDetectorForParameterArray {
+
   @Item.SpecialKind
   private final int isMessage = Item.defineSpecialKind("message generated by throwable object");
 
   public ManualMessageDetector(BugReporter bugReporter) {
-    super(bugReporter);
+    super(bugReporter, "SLF4J_MANUALLY_PROVIDED_MESSAGE");
   }
 
   @Override
   protected Strategy createArrayCheckStrategy() {
-    return new Strategy() {
-      @Override
-      public void store(Item storedItem, ArrayData arrayData, int index) {
+    return (storedItem, arrayData, index) -> {
         if (arrayData == null) {
           return;
         }
@@ -39,8 +37,7 @@ public void store(Item storedItem, ArrayData arrayData, int index) {
         if (index == arrayData.getSize() - 1 && !getThrowableHandler().checkThrowable(storedItem)) {
           arrayData.mark(false);
         }
-      }
-    };
+      };
   }
 
   @Override
@@ -53,6 +50,20 @@ public void afterOpcode(int seen) {
     }
   }
 
+
+  @Override
+  protected int getIsOfInterestKind() {
+      return isMessage;
+  }
+
+  @Override
+  protected boolean isReallyOfInterest(Item storedItem, ArrayData arrayData, int index) {
+      // Let developer logs exception message, only when argument does not have throwable instance
+      // https://github.com/KengoTODA/findbugs-slf4j/issues/31
+      return !(index == arrayData.getSize() - 1
+              && !getThrowableHandler().checkThrowable(storedItem));
+  }
+
   private boolean isInvokingGetMessage(int seen) {
     return seen == INVOKEVIRTUAL
         && !stack.isTop()
@@ -73,4 +84,13 @@ protected void onLog(@Nullable String format, @Nullable ArrayData arrayData) {
             .addCalledMethod(this);
     getBugReporter().reportBug(bugInstance);
   }
+
+    @Override
+    protected boolean isWhatWeWantToDetect(int seen) {
+        return seen == INVOKEVIRTUAL && !stack.isTop()
+                && getThrowableHandler().checkThrowable(getStack().getStackItem(0))
+                && (Objects.equal("getMessage", getNameConstantOperand())
+                        || Objects.equal("getLocalizedMessage", getNameConstantOperand()));
+    }
+
 }

bug-pattern/src/main/java/jp/skypencil/findbugs/slf4j/parameter/AbstractDetectorForParameterArray2.java

@@ -0,0 +1,65 @@
+package jp.skypencil.findbugs.slf4j.parameter;
+
+import edu.umd.cs.findbugs.BugInstance;
+import edu.umd.cs.findbugs.BugReporter;
+import edu.umd.cs.findbugs.OpcodeStack.Item;
+import javax.annotation.Nullable;
+import jp.skypencil.findbugs.slf4j.parameter.ArrayDataHandler.Strategy;
+
+public abstract class AbstractDetectorForParameterArray2 extends AbstractDetectorForParameterArray {
+
+    private final String bugPatternName;
+
+    public AbstractDetectorForParameterArray2(BugReporter bugReporter, String bugPatternName) {
+        super(bugReporter);
+        this.bugPatternName = bugPatternName;
+    }
+
+    @Override
+    protected final Strategy createArrayCheckStrategy() {
+        return (storedItem, arrayData, index) -> {
+            if (arrayData == null) {
+                return;
+            }
+
+            if (storedItem.getSpecialKind() == getIsOfInterestKind()) {
+                arrayData.mark(true);
+            }
+
+            if (!isReallyOfInterest(storedItem, arrayData, index)) {
+                arrayData.mark(false);
+            }
+        };
+    }
+
+    protected boolean isReallyOfInterest(Item storedItem, ArrayData arrayData, int index) {
+        return true;
+    }
+
+    @Override
+    public final void afterOpcode(int seen) {
+        boolean isInvokingGetMessage = isWhatWeWantToDetect(seen);
+        super.afterOpcode(seen);
+
+        if (isInvokingGetMessage && !stack.isTop()) {
+            stack.getStackItem(0).setSpecialKind(getIsOfInterestKind());
+        }
+    }
+
+    @Override
+    protected final void onLog(@Nullable String format, @Nullable ArrayData arrayData) {
+        if (arrayData == null || !arrayData.isMarked()) {
+            return;
+        }
+        BugInstance bugInstance = new BugInstance(this,
+                bugPatternName, NORMAL_PRIORITY)
+                .addSourceLine(this).addClassAndMethod(this)
+                .addCalledMethod(this);
+        getBugReporter().reportBug(bugInstance);
+    }
+
+    abstract protected boolean isWhatWeWantToDetect(int seen);
+
+    abstract protected int getIsOfInterestKind();
+
+}