Java: Count second level scopes for fieldFlowBranchLimit.

Author: aschackmull

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowImplSpecific.qll

@@ -20,6 +20,8 @@ module JavaDataFlow implements InputSig<Location> {
 
   Node exprNode(DataFlowExpr e) { result = Public::exprNode(e) }
 
+  predicate getSecondLevelScope = Private::getSecondLevelScope/1;
+
   predicate mayBenefitFromCallContext = Private::mayBenefitFromCallContext/1;
 
   predicate viableImplInCallContext = Private::viableImplInCallContext/2;

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowPrivate.qll

@@ -576,7 +576,80 @@ predicate lambdaCall(DataFlowCall call, LambdaCallKind kind, Node receiver) {
 /** Extra data-flow steps needed for lambda flow analysis. */
 predicate additionalLambdaFlowStep(Node nodeFrom, Node nodeTo, boolean preservesValue) { none() }
 
-class DataFlowSecondLevelScope = Unit;
+private predicate isTopLevel(Stmt s) {
+  any(Callable c).getBody() = s
+  or
+  exists(BlockStmt b | s = b.getAStmt() and isTopLevel(b))
+}
+
+private Stmt getAChainedBranch(IfStmt s) {
+  result = s.getThen()
+  or
+  exists(Stmt elseBranch | s.getElse() = elseBranch |
+    result = getAChainedBranch(elseBranch)
+    or
+    result = elseBranch and not elseBranch instanceof IfStmt
+  )
+}
+
+private newtype TDataFlowSecondLevelScope =
+  TTopLevelIfBranch(Stmt s) {
+    exists(IfStmt ifstmt | s = getAChainedBranch(ifstmt) and isTopLevel(ifstmt))
+  } or
+  TTopLevelSwitchCase(SwitchCase s) {
+    exists(SwitchStmt switchstmt | s = switchstmt.getACase() and isTopLevel(switchstmt))
+  }
+
+private SwitchCase getPrecedingCase(Stmt s) {
+  result = s
+  or
+  exists(SwitchStmt switch, int i |
+    s = switch.getStmt(i) and
+    not s instanceof SwitchCase and
+    result = getPrecedingCase(switch.getStmt(i - 1))
+  )
+}
+
+/**
+ * A second-level control-flow scope in a `switch` or a chained `if` statement.
+ *
+ * This is a `switch` case or a branch of a chained `if` statement, given that
+ * the `switch` or `if` statement is top level, that is, it is not nested inside
+ * other CFG constructs.
+ */
+class DataFlowSecondLevelScope extends TDataFlowSecondLevelScope {
+  /** Gets a textual representation of this element. */
+  string toString() {
+    exists(Stmt s | this = TTopLevelIfBranch(s) | result = s.toString())
+    or
+    exists(SwitchCase s | this = TTopLevelSwitchCase(s) | result = s.toString())
+  }
+
+  /**
+   * Gets a statement directly contained in this scope. For an `if` branch, this
+   * is the branch itself, and for a `switch case`, this is one the statements
+   * of that case branch.
+   */
+  private Stmt getAStmt() {
+    exists(Stmt s | this = TTopLevelIfBranch(s) | result = s)
+    or
+    exists(SwitchCase s | this = TTopLevelSwitchCase(s) |
+      result = s.getRuleStatement() or
+      s = getPrecedingCase(result)
+    )
+  }
+
+  /** Gets a data-flow node nested within this scope. */
+  Node getANode() { getRelatedExpr(result).getAnEnclosingStmt() = this.getAStmt() }
+}
+
+private Expr getRelatedExpr(Node n) {
+  n.asExpr() = result or
+  n.(PostUpdateNode).getPreUpdateNode().asExpr() = result
+}
+
+/** Gets the second-level scope containing the node `n`, if any. */
+DataFlowSecondLevelScope getSecondLevelScope(Node n) { result.getANode() = n }
 
 /**
  * Holds if flow is allowed to pass from parameter `p` and back to itself as a