Rust: Make improvements to data flow based on PR feedback

Author: paldepind

rust/ql/lib/codeql/rust/dataflow/internal/DataFlowImpl.qll

@@ -95,6 +95,26 @@ module Node {
 
   final class ArgumentNode = NaNode;
 
+  /** An SSA node. */
+  abstract class SsaNode extends Node, TSsaNode {
+    SsaImpl::DataFlowIntegration::SsaNode node;
+    SsaImpl::DefinitionExt def;
+
+    SsaNode() {
+      this = TSsaNode(node) and
+      def = node.getDefinitionExt()
+    }
+
+    SsaImpl::DefinitionExt getDefinitionExt() { result = def }
+
+    /** Holds if this node should be hidden from path explanations. */
+    abstract predicate isHidden();
+
+    override Location getLocation() { result = node.getLocation() }
+
+    override string toString() { result = node.toString() }
+  }
+
   final class ReturnNode extends NaNode {
     RustDataFlow::ReturnKind getKind() { none() }
   }
@@ -154,7 +174,7 @@ module SsaFlow {
  * For instance, the predicate holds for if expressions as `if b { e1 } else {
  * e2 }` evalates to the value of one of the subexpressions `e1` or `e2`.
  */
-predicate propagatesValue(Expr e) {
+private predicate propagatesValue(Expr e) {
   e instanceof IfExpr or
   e instanceof LoopExpr or
   e instanceof ReturnExpr or

rust/ql/lib/codeql/rust/dataflow/internal/SsaImpl.qll

@@ -461,14 +461,18 @@ class PhiReadNode extends DefinitionExt, Impl::PhiReadNode {
 }
 
 private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInputSig {
-  class Expr extends CfgNodes::ExprCfgNode {
+  class Expr extends CfgNodes::AstCfgNode {
     predicate hasCfgNode(SsaInput::BasicBlock bb, int i) { this = bb.getNode(i) }
   }
 
   Expr getARead(Definition def) { result = Cached::getARead(def) }
 
   /** Holds if SSA definition `def` assigns `value` to the underlying variable. */
-  predicate ssaDefAssigns(WriteDefinition def, Expr value) { none() }
+  predicate ssaDefAssigns(WriteDefinition def, Expr value) {
+    exists(CfgNode node, BasicBlock bb, int i |
+      def.definesAt(_, bb, i) and value.getAstNode() = node.getAstNode().(AssignmentExpr).getLhs()
+    )
+  }
 
   class Parameter = Param;