fix: ignore RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE right after try-…

…block

close #259

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

@@ -35,6 +35,7 @@
 import javax.annotation.Nonnull;
 import javax.annotation.meta.When;
 
+import edu.umd.cs.findbugs.annotations.NonNull;
 import org.apache.bcel.Const;
 import org.apache.bcel.classfile.Code;
 import org.apache.bcel.classfile.CodeException;
@@ -49,6 +50,7 @@
 import org.apache.bcel.generic.INVOKEDYNAMIC;
 import org.apache.bcel.generic.Instruction;
 import org.apache.bcel.generic.InstructionHandle;
+import org.apache.bcel.generic.InstructionList;
 import org.apache.bcel.generic.InstructionTargeter;
 import org.apache.bcel.generic.InvokeInstruction;
 import org.apache.bcel.generic.MethodGen;
@@ -126,6 +128,8 @@
 import edu.umd.cs.findbugs.props.WarningPropertyUtil;
 import edu.umd.cs.findbugs.util.Values;
 import edu.umd.cs.findbugs.visitclass.Util;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * A Detector to find instructions where a NullPointerException might be raised.
@@ -137,6 +141,7 @@
  * @see edu.umd.cs.findbugs.ba.npe.IsNullValueAnalysis
  */
 public class FindNullDeref implements Detector, UseAnnotationDatabase, NullDerefAndRedundantComparisonCollector {
+    private final Logger log = LoggerFactory.getLogger(getClass());
 
     public static final boolean DEBUG = SystemProperties.getBoolean("fnd.debug");
 
@@ -922,7 +927,6 @@ public boolean skipIfInsideCatchNull() {
      *             instead
      */
     @Override
-    @Deprecated
     public void foundNullDeref(Location location, ValueNumber valueNumber, IsNullValue refValue, ValueNumberFrame vnaFrame) {
         foundNullDeref(location, valueNumber, refValue, vnaFrame, true);
     }
@@ -1153,6 +1157,9 @@ public void foundRedundantNullCheck(Location location, RedundantBranch redundant
             if (redundantBranch.firstValue.isDefinitelyNull()) {
                 warning = "RCN_REDUNDANT_NULLCHECK_OF_NULL_VALUE";
                 priority = NORMAL_PRIORITY;
+            } else if (isGeneratedCodeInCatchBlock(method.getConstantPool(), pc)) {
+                log.debug("skip RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE found in the generated code at {}", location);
+                return;
             } else {
                 warning = "RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE";
                 valueIsNull = false;
@@ -1783,4 +1790,42 @@ boolean inIndirectCatchNullBlock(Location loc) {
                 "java/lang/Throwable", pc);
         return catchSize < 5;
     }
+
+    /**
+     * Java 11+ compiler generates redundant null checks for try-with-resources.
+     * This methods detects the {@code ifnull} bytecode generated by javac,
+     * to help detector to avoid to report needless {@code RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE} bug.
+     *
+     * @param cp the constant pool
+     * @param pc the program counter
+     * @return true if the pc specifies redundant null check generated by javac
+     * @see <a href="https://github.com/spotbugs/spotbugs/issues/259">false positive RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE on try-with-resources</a>
+     */
+    private boolean isGeneratedCodeInCatchBlock(@NonNull ConstantPool cp, int pc) {
+        Code code = method.getCode();
+        if (code == null) {
+            return false;
+        }
+        CodeException[] table = code.getExceptionTable();
+
+        // TODO: This instantiation could be high cost computation
+        InstructionList list = new InstructionList(code.getCode());
+
+        return Arrays.stream(table)
+                .filter(codeException -> {
+                    // assume that programmers rarely catch java.lang.Throwable instance explicitly
+                    int catchType = codeException.getCatchType();
+                    if (catchType == 0) {
+                        // '0' means it catches any exceptions
+                        return true;
+                    }
+                    String exceptionName = cp.getConstantString(catchType, Const.CONSTANT_Class);
+                    return "java/lang/Throwable".equals(exceptionName);
+                })
+                .anyMatch(codeException -> {
+                    InstructionHandle handle = list.findHandle(codeException.getEndPC());
+                    int insnLength = handle.getInstruction().getLength();
+                    return codeException.getEndPC() + insnLength == pc;
+                });
+    }
 }

spotbugsTestCases/build.gradle

@@ -54,11 +54,6 @@ javadoc {
   }
 }
 
-tasks.compileJava {
-  // workaround for https://github.com/spotbugs/spotbugs/issues/996
-  exclude 'sfBugsNew/Bug1169.java'
-}
-
 task classesJava8(type:JavaCompile) {
   destinationDir = file("$buildDir/classes/java/java8")
   classpath = sourceSets.main.compileClasspath