unified: Add IdentifierExpr and use it in CFG

Author: asgerf

unified/ql/lib/codeql/unified/internal/AstExtra.qll

@@ -68,4 +68,16 @@ module Public {
   final class TopLevelStmt extends Stmt {
     TopLevelStmt() { this = any(TopLevel t).getBody().getAStmt() }
   }
+
+  /** An identifier appearing in the context of an expression, pattern, or type annotation. */
+  final class IdentifierExpr extends Identifier {
+    IdentifierExpr() {
+      not this = any(MemberAccessExpr e).getMemberNameNode() and
+      not this = any(Argument a).getNameNode() and
+      not this = any(Parameter p).getExternalNameNode() and
+      not this = any(LabeledStmt stmt).getLabelNameNode() and
+      not this = any(BreakExpr expr).getLabelNameNode() and
+      not this = any(ContinueExpr expr).getLabelNameNode()
+    }
+  }
 }

unified/ql/lib/codeql/unified/internal/ControlFlowGraph.qll

@@ -25,7 +25,11 @@ private module Ast implements AstSig<Location> {
 
   class AstNode = U::AstNode;
 
-  private predicate skipControlFlow(AstNode e) { e instanceof Modifier or e instanceof Identifier }
+  private predicate skipControlFlow(AstNode e) {
+    e instanceof Modifier
+    or
+    e instanceof Identifier and not e instanceof IdentifierExpr
+  }
 
   AstNode getChild(AstNode n, int index) {
     result.getParent() = n and

unified/ql/lib/codeql/unified/internal/LocalNameBinding.qll

@@ -387,16 +387,7 @@ module Public {
  * }
  * ```
  */
-class PotentialLocalNameAccess extends Identifier {
-  PotentialLocalNameAccess() {
-    not this = any(MemberAccessExpr e).getMemberNameNode() and
-    not this = any(Argument a).getNameNode() and
-    not this = any(Parameter p).getExternalNameNode() and
-    not this = any(LabeledStmt stmt).getLabelNameNode() and
-    not this = any(BreakExpr expr).getLabelNameNode() and
-    not this = any(ContinueExpr expr).getLabelNameNode()
-  }
-
+class PotentialLocalNameAccess extends IdentifierExpr {
   LocalName getLocalName() { result = this.(LocalNameBindingOutput::LocalAccess).getLocal() }
 
   string getName() { result = this.getValue() }