Don't issue warnings on dead code

checker/src/main/java/org/checkerframework/checker/calledmethods/CalledMethodsAnnotatedTypeFactory.java

@@ -11,6 +11,7 @@
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.TypeElement;
+import javax.lang.model.type.DeclaredType;
 import javax.lang.model.type.TypeKind;
 import javax.lang.model.type.TypeMirror;
 import org.checkerframework.checker.calledmethods.builder.AutoValueSupport;
@@ -39,6 +40,7 @@
 import org.checkerframework.javacutil.AnnotationUtils;
 import org.checkerframework.javacutil.ElementUtils;
 import org.checkerframework.javacutil.TreeUtils;
+import org.checkerframework.javacutil.TypesUtils;
 import org.checkerframework.javacutil.UserError;
 
 /** The annotated type factory for the Called Methods Checker. */
@@ -428,4 +430,21 @@ private AnnotationMirror ensuresCMAnno(String[] expressions, List<String> called
     AnnotationMirror am = builder.build();
     return am;
   }
+
+  /**
+   * Returns true if the checker should ignore exceptional control flow due to the given exception
+   * type.
+   *
+   * @param exceptionType exception type
+   * @return {@code true} if {@code exceptionType} is a member of {@link
+   *     CalledMethodsAnalysis#ignoredExceptionTypes}, {@code false} otherwise
+   */
+  @Override
+  public boolean isIgnoredExceptionType(TypeMirror exceptionType) {
+    if (exceptionType.getKind() == TypeKind.DECLARED) {
+      return CalledMethodsAnalysis.ignoredExceptionTypes.contains(
+          TypesUtils.getQualifiedName((DeclaredType) exceptionType));
+    }
+    return false;
+  }
 }

checker/src/main/java/org/checkerframework/checker/nullness/NullnessVisitor.java

@@ -253,6 +253,9 @@ protected boolean commonAssignmentCheck(
   /** Case 1: Check for null dereferencing. */
   @Override
   public Void visitMemberSelect(MemberSelectTree tree, Void p) {
+    if (atypeFactory.isUnreachable(tree)) {
+      return super.visitMemberSelect(tree, p);
+    }
     Element e = TreeUtils.elementFromUse(tree);
     if (e.getKind() == ElementKind.CLASS) {
       if (atypeFactory.containsNullnessAnnotation(null, tree.getExpression())) {

checker/tests/nullness/Exceptions.java

@@ -12,9 +12,8 @@ void nonnullExceptionParam(@NonNull Exception m) {
 
   void exception(@Nullable Exception m) {
     try {
-
+      throwException();
     } catch (Exception e) {
-      // Note that this code is dead.
       e.getClass();
       // :: error: (dereference.of.nullable)
       m.getClass(); // should emit error
@@ -38,8 +37,8 @@ void throwException() {
 
   void reassignException() {
     try {
+      throwException();
     } catch (RuntimeException e) {
-      // Note that this code is dead.
       // :: error: (assignment)
       e = null;
       throw e;

checker/tests/nullness/TryCatch.java

@@ -23,7 +23,6 @@ void unreachableCatch(String[] xs) {
     try {
     } catch (Throwable e) {
       // Note that this code is dead.
-      // :: error: (dereference.of.nullable)
       t.toString();
     }
   }

dataflow/src/main/java/org/checkerframework/dataflow/cfg/ControlFlowGraph.java

@@ -20,6 +20,8 @@
 import java.util.Set;
 import java.util.StringJoiner;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Function;
+import javax.lang.model.type.TypeMirror;
 import org.checkerframework.checker.initialization.qual.UnknownInitialization;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.checkerframework.dataflow.analysis.AnalysisResult;
@@ -28,6 +30,7 @@
 import org.checkerframework.dataflow.cfg.block.ExceptionBlock;
 import org.checkerframework.dataflow.cfg.block.RegularBlock;
 import org.checkerframework.dataflow.cfg.block.SingleSuccessorBlock;
+import org.checkerframework.dataflow.cfg.block.SingleSuccessorBlockImpl;
 import org.checkerframework.dataflow.cfg.block.SpecialBlock;
 import org.checkerframework.dataflow.cfg.block.SpecialBlockImpl;
 import org.checkerframework.dataflow.cfg.node.Node;
@@ -276,6 +279,74 @@ public List<Node> getAllNodes(
     return result;
   }
 
+  /**
+   * Returns the set of all basic blocks in this control flow graph, <b>except</b> those that are
+   * only reachable via an exception whose type is ignored by parameter {@code
+   * shouldIgnoreException}.
+   *
+   * @param shouldIgnoreException returns true if it is passed a {@code TypeMirror} that should be
+   *     ignored
+   * @return the set of all basic blocks in this control flow graph, <b>except</b> those that are
+   *     only reachable via an exception whose type is ignored by {@code shouldIgnoreException}
+   */
+  public Set<Block> getAllBlocks(
+      @UnknownInitialization(ControlFlowGraph.class) ControlFlowGraph this,
+      Function<TypeMirror, Boolean> shouldIgnoreException) {
+    // This is the return value of the method.
+    Set<Block> visited = new LinkedHashSet<>();
+    // `worklist` is always a subset of `visited`; any block in `worklist` is also in `visited`.
+    Queue<Block> worklist = new ArrayDeque<>();
+    Block cur = entryBlock;
+    visited.add(entryBlock);
+
+    // Traverse the whole control flow graph.
+    while (cur != null) {
+      if (cur instanceof ExceptionBlock) {
+        for (Map.Entry<TypeMirror, Set<Block>> entry :
+            ((ExceptionBlock) cur).getExceptionalSuccessors().entrySet()) {
+          if (!shouldIgnoreException.apply(entry.getKey())) {
+            for (Block b : entry.getValue()) {
+              if (visited.add(b)) {
+                worklist.add(b);
+              }
+            }
+          }
+        }
+        Block b = ((SingleSuccessorBlockImpl) cur).getSuccessor();
+        if (b != null && visited.add(b)) {
+          worklist.add(b);
+        }
+
+      } else {
+        for (Block b : cur.getSuccessors()) {
+          if (visited.add(b)) {
+            worklist.add(b);
+          }
+        }
+      }
+      cur = worklist.poll();
+    }
+
+    return visited;
+  }
+
+  /**
+   * Returns the list of all nodes in this control flow graph, <b>except</b> those that are only
+   * reachable via an exception whose type is ignored by parameter {@code shouldIgnoreException}.
+   *
+   * @param shouldIgnoreException returns true if it is passed a {@code TypeMirror} that should be
+   *     ignored
+   * @return the list of all nodes in this control flow graph, <b>except</b> those that are only
+   *     reachable via an exception whose type is ignored by {@code shouldIgnoreException}
+   */
+  public List<Node> getAllNodes(
+      @UnknownInitialization(ControlFlowGraph.class) ControlFlowGraph this,
+      Function<TypeMirror, Boolean> shouldIgnoreException) {
+    List<Node> result = new ArrayList<>();
+    getAllBlocks(shouldIgnoreException).forEach(b -> result.addAll(b.getNodes()));
+    return result;
+  }
+
   /**
    * Returns all basic blocks in this control flow graph, in reversed depth-first postorder. Blocks
    * may appear more than once in the sequence.

framework/src/main/java/org/checkerframework/common/basetype/BaseTypeVisitor.java

@@ -4815,7 +4815,9 @@ protected TypeValidator createTypeValidator() {
    */
   protected final boolean shouldSkipUses(ExpressionTree exprTree) {
     // System.out.printf("shouldSkipUses: %s: %s%n", exprTree.getClass(), exprTree);
-
+    if (atypeFactory.isUnreachable(exprTree)) {
+      return true;
+    }
     Element elm = TreeUtils.elementFromTree(exprTree);
     return checker.shouldSkipUses(elm);
   }

framework/src/main/java/org/checkerframework/framework/type/GenericAnnotatedTypeFactory.java

@@ -445,6 +445,7 @@ public void setRoot(@Nullable CompilationUnitTree root) {
 
     super.setRoot(root);
     this.scannedClasses.clear();
+    this.reachableNodes.clear();
     this.flowResult = null;
     this.regularExitStores.clear();
     this.exceptionalExitStores.clear();
@@ -1056,6 +1057,32 @@ public IPair<JavaExpression, String> getExpressionAndOffsetFromJavaExpressionStr
     return value != null ? value.getAnnotations().iterator().next() : null;
   }
 
+  /**
+   * Returns true if the {@code exprTree} is unreachable. This is a conservative estimate and may
+   * return {@code false} even though the {@code exprTree} is unreachable.
+   *
+   * @param exprTree an expression tree
+   * @return true if the {@code exprTree} is unreachable
+   */
+  public boolean isUnreachable(ExpressionTree exprTree) {
+    if (!everUseFlow) {
+      return false;
+    }
+    Set<Node> nodes = getNodesForTree(exprTree);
+    if (nodes == null) {
+      // Dataflow has no any information about the tree, so conservatively consider the tree
+      // reachable.
+      return false;
+    }
+    for (Node n : nodes) {
+      if (n.getTree() != null && reachableNodes.contains(n.getTree())) {
+        return false;
+      }
+    }
+    // None of the corresponding nodes is reachable, so this tree is dead.
+    return true;
+  }
+
   /**
    * Track the state of org.checkerframework.dataflow analysis scanning for each class tree in the
    * compilation unit.
@@ -1070,6 +1097,16 @@ protected enum ScanState {
   /** Map from ClassTree to their dataflow analysis state. */
   protected final Map<ClassTree, ScanState> scannedClasses = new HashMap<>();
 
+  /**
+   * A set of trees whose corresponding nodes are reachable. This is not an exhaustive set of
+   * reachable trees. Use {@link #isUnreachable(ExpressionTree)} instead of this set directly.
+   *
+   * <p>This cannot be a set of Nodes, because two LocalVariableNodes are equal if they have the
+   * same name but represent different uses of the variable. So instead of storing Nodes, it stores
+   * the result of {@code Node#getTree}.
+   */
+  private final Set<Tree> reachableNodes = new HashSet<>();
+
   /**
    * The result of the flow analysis. Invariant:
    *
@@ -1264,10 +1301,11 @@ public Store getStoreAfter(Node node) {
   /**
    * See {@link org.checkerframework.dataflow.analysis.AnalysisResult#getNodesForTree(Tree)}.
    *
+   * @param tree a tree
    * @return the {@link Node}s for a given {@link Tree}
    * @see org.checkerframework.dataflow.analysis.AnalysisResult#getNodesForTree(Tree)
    */
-  public Set<Node> getNodesForTree(Tree tree) {
+  public @Nullable Set<Node> getNodesForTree(Tree tree) {
     return flowResult.getNodesForTree(tree);
   }
 
@@ -1531,7 +1569,13 @@ protected void analyze(
       boolean isStatic,
       @Nullable Store capturedStore) {
     ControlFlowGraph cfg = CFCFGBuilder.build(root, ast, checker, this, processingEnv);
-
+    cfg.getAllNodes(this::isIgnoredExceptionType)
+        .forEach(
+            node -> {
+              if (node.getTree() != null) {
+                reachableNodes.add(node.getTree());
+              }
+            });
     if (isInitializationCode) {
       Store initStore = !isStatic ? initializationStore : initializationStaticStore;
       if (initStore != null) {
@@ -1610,6 +1654,16 @@ protected void analyze(
     postAnalyze(cfg);
   }
 
+  /**
+   * Returns true if {@code typeMirror} is an exception type that should be ignored.
+   *
+   * @param typeMirror an exception type
+   * @return true if {@code typeMirror} is an exception type that should be ignored
+   */
+  public boolean isIgnoredExceptionType(TypeMirror typeMirror) {
+    return false;
+  }
+
   /**
    * Perform any additional operations on a CFG. Called once per CFG, after the CFG has been
    * analyzed by {@link #analyze(Queue, Queue, UnderlyingAST, List, ClassTree, boolean, boolean,