PS: Add AST and CFG nodes for operator &.

powershell/ql/lib/semmle/code/powershell/Command.qll

@@ -1,4 +1,5 @@
 import powershell
+
 private predicate parseCommandName(Cmd cmd, string namespace, string name) {
   exists(string qualified | command(cmd, qualified, _, _, _) |
     namespace = qualified.regexpCapture("([^\\\\]+)\\\\([^\\\\]+)", 1) and
@@ -11,6 +12,7 @@ private predicate parseCommandName(Cmd cmd, string namespace, string name) {
   )
 }
 
+/** A call to a command. */
 class Cmd extends @command, CmdBase {
   override string toString() { result = "call to " + this.getQualifiedCommandName() }
 
@@ -88,3 +90,8 @@ class Cmd extends @command, CmdBase {
 
   Redirection getARedirection() { result = this.getRedirection(_) }
 }
+
+/** A call to operator `&`. */
+class CallOperator extends Cmd {
+  CallOperator() { this.getKind() = 28 }
+}

powershell/ql/lib/semmle/code/powershell/controlflow/CfgNodes.qll

@@ -597,6 +597,11 @@ module StmtNodes {
     final override string getName() { result = s.getCmdName().getValue().getValue() }
   }
 
+  /** A control-flow node that wraps a call to operator `&` */
+  class CallOperatorCfgNode extends CmdCfgNode {
+    CallOperatorCfgNode() { this.getStmt() instanceof CallOperator }
+  }
+
   private class AssignStmtChildMapping extends PipelineBaseChildMapping, AssignStmt {
     override predicate relevantChild(Ast n) {
       n = this.getLeftHandSide() or n = this.getRightHandSide()

powershell/ql/lib/semmle/code/powershell/dataflow/internal/DataFlowPublic.qll

@@ -448,9 +448,30 @@ class CallNode extends AstNode {
 
   Node getQualifier() { result.asExpr() = call.getQualifier() }
 
+  /** Gets the i'th argument to this call. */
+  Node getArgument(int i) { result.asExpr() = call.getArgument(i) }
+
+  /** Gets the i'th positional argument to this call. */
+  Node getPositionalArgument(int i) { result.asExpr() = call.getPositionalArgument(i) }
+
+  /** Gets the argument with the name `name`, if any. */
+  Node getNamedArgument(string name) { result.asExpr() = call.getNamedArgument(name) }
+
+  /**
+   * Gets any argument of this call.
+   *
+   * Note that this predicate doesn't get the pipeline argument, if any.
+   */
+  Node getAnArgument() { result.asExpr() = call.getAnArgument() }
+
   int getNumberOfArguments() { result = call.getNumberOfArguments() }
 }
 
+/** A call to operator `&`, viwed as a node in a data flow graph. */
+class CallOperatorNode extends CallNode {
+  CallOperatorNode() { this.getCallNode() instanceof CfgNodes::StmtNodes::CallOperatorCfgNode }
+}
+
 /** A use of a type name, viewed as a node in a data flow graph. */
 class TypeNameNode extends ExprNode {
   override CfgNodes::ExprNodes::TypeNameCfgNode n;