PS: AST support for 'this'.

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

@@ -33,16 +33,28 @@ abstract private class AbstractFunction extends Ast {
   /** Gets the number of function parameters. */
   final int getNumberOfFunctionParameters() { result = count(this.getAFunctionParameter()) }
 
-  /** Gets the number of parameters (both function and block). */
+  /**
+   * Gets the number of parameters (both function and block).
+   * Note: This excludes the `this` parameter.
+   */
   final int getNumberOfParameters() { result = count(this.getAParameter()) }
 
-  /** Gets the i'th parameter of this function, if any. */
+  /**
+   * Gets the i'th parameter of this function, if any.
+   *
+   * This does not include the `this` parameter.
+   */
   final Parameter getParameter(int i) {
     result = this.getFunctionParameter(i)
     or
     result = this.getBody().getParamBlock().getParameter(i)
   }
 
+  final Parameter getThisParameter() {
+    result.isThis() and
+    result.getFunction() = this
+  }
+
   /** Gets any parameter of this function. */
   final Parameter getAParameter() { result = this.getParameter(_) }
 

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

@@ -42,7 +42,8 @@ private newtype TParameterImpl =
   TInternalParameter(Internal::Parameter p) or
   TUnderscore(Scope scope) {
     exists(VarAccess va | va.getUserPath() = "_" and scope = va.getEnclosingScope())
-  }
+  } or
+  TThisParameter(Scope scope) { exists(scope.getEnclosingFunction().getDeclaringType()) }
 
 private class ParameterImpl extends TParameterImpl {
   abstract Location getLocation();
@@ -109,9 +110,22 @@ private class Underscore extends ParameterImpl, TUnderscore {
   final override Scope getEnclosingScope() { result = scope }
 }
 
+private class ThisParameter extends ParameterImpl, TThisParameter {
+  Scope scope;
+
+  ThisParameter() { this = TThisParameter(scope) }
+
+  override Location getLocation() { result = scope.getLocation() }
+
+  override string getName() { result = "this" }
+
+  final override Scope getEnclosingScope() { result = scope }
+}
+
 private newtype TVariable =
   TLocalVariable(string name, Scope scope) {
     not isParameterImpl(name, scope) and
+    not name = "this" and // This is modeled as a parameter
     exists(VarAccess va | va.getUserPath() = name and scope = va.getEnclosingScope())
   } or
   TParameter(ParameterImpl p)
@@ -186,8 +200,11 @@ class Parameter extends AbstractLocalScopeVariable, TParameter {
 
   predicate hasDefaultValue() { exists(this.getDefaultValue()) }
 
+  /** Holds if this is the `this` parameter. */
+  predicate isThis() { p instanceof ThisParameter }
+
   /**
-   * Gets the index of this parameter.
+   * Gets the index of this parameter, if any.
    *
    * The parameter may be in a parameter block or a function parameter.
    */

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

@@ -217,7 +217,11 @@ module ExprNodes {
     /** Gets the name of this argument, if any. */
     string getName() { result = e.getName() }
 
-    StmtNodes::CmdCfgNode getCmd() { result.getAnArgument() = this }
+    /** Holds if `this` is a qualifier to a call. */
+    predicate isQualifier() { e.isQualifier() }
+
+    /** Gets the call for which this is an argument. */
+    CallCfgNode getCall() { result.getAnArgument() = this or result.getQualifier() = this }
   }
 
   private class InvokeMemberChildMapping extends ExprChildMapping, InvokeMemberExpr {

powershell/ql/lib/semmle/code/powershell/controlflow/internal/Scope.qll

@@ -36,4 +36,11 @@ class Scope extends Ast, @script_block {
    * This may be both function paramters and parameter block parameters.
    */
   Parameter getAParameter() { result = this.getParameter(_) }
+
+  Parameter getThisParameter() {
+    exists(Function func |
+      func.getBody() = this and
+      result = func.getThisParameter()
+    )
+  }
 }