Merge pull request #345 from esben-semmle/js/intro-getUnderlying

Approved by xiemaisi

javascript/ql/src/semmle/javascript/Constants.qll

@@ -127,14 +127,32 @@ module SyntacticConstants {
   class WrappedConstant extends SyntacticConstant {
 
     WrappedConstant() {
-      stripParens() instanceof SyntacticConstant or
-      this.(SeqExpr).getLastOperand() instanceof SyntacticConstant or
-      this.(TypeAssertion).getExpression() instanceof SyntacticConstant or
-      this.(Assignment).getRhs() instanceof SyntacticConstant
+      getUnderlyingValue() instanceof SyntacticConstant
     }
 
   }
 
+  /**
+   * Holds if `c` evaluates to `undefined`.
+   */
+  predicate isUndefined(SyntacticConstant c) {
+    c.getUnderlyingValue() instanceof UndefinedConstant
+  }
+
+  /**
+   * Holds if `c` evaluates to `null`.
+   */
+  predicate isNull(SyntacticConstant c) {
+    c.getUnderlyingValue() instanceof NullConstant
+  }
+
+  /**
+   * Holds if `c` evaluates to `null` or `undefined`.
+   */
+  predicate isNullOrUndefined(SyntacticConstant c) {
+    isUndefined(c) or isNull(c)
+  }
+
 }
 
 /**

javascript/ql/src/semmle/javascript/Expr.qll

@@ -45,8 +45,45 @@ class ExprOrType extends @exprortype, Documentable {
     )
   }
 
-  /** Gets this expression or type, with any surrounding parentheses removed. */
+  /**
+   * Gets this expression or type, with any surrounding parentheses removed.
+   *
+   * Also see `getUnderlyingValue` and `getUnderlyingReference`.
+   */
   ExprOrType stripParens() { result = this }
+
+  /**
+   * Gets the innermost reference that this expression evaluates to, if any.
+   *
+   * Examples:
+   *
+   * - a variable or property access: the access itself.
+   * - a parenthesized expression `(e)`: the underlying reference of `e`.
+   * - a TypeScript type assertion `e as T`: the underlying reference of `e`.
+   *
+   * Also see `getUnderlyingValue` and `stripParens`.
+   */
+  Expr getUnderlyingReference() {
+    none()
+  }
+
+  /**
+   * Gets the innermost expression that this expression evaluates to.
+   *
+   * Examples:
+   *
+   * - a parenthesised expression `(e)`: the underlying value of `e`.
+   * - a sequence expression `e1, e2`: the underlying value of `e2`.
+   * - an assignment expression `v = e`: the underlying value of `e`.
+   * - a TypeScript type assertion `e as T`: the underlying value of `e`.
+   * - any other expression: the expression itself.
+   *
+   * Also see `getUnderlyingReference` and `stripParens`.
+   */
+  Expr getUnderlyingValue() {
+    result = this
+  }
+
 }
 
 /** An expression. */
@@ -210,6 +247,15 @@ class ParExpr extends @parexpr, Expr {
   override predicate isImpure() {
     getExpression().isImpure()
   }
+
+  override Expr getUnderlyingValue() {
+    result = getExpression().getUnderlyingValue()
+  }
+
+  override Expr getUnderlyingReference() {
+    result = getExpression().getUnderlyingReference()
+  }
+
 }
 
 /** A `null` literal. */
@@ -617,6 +663,11 @@ class SeqExpr extends @seqexpr, Expr {
   override string getStringValue() {
     result = getLastOperand().getStringValue()
   }
+
+  override Expr getUnderlyingValue() {
+    result = getLastOperand().getUnderlyingValue()
+  }
+
 }
 
 /** A conditional expression. */
@@ -862,6 +913,11 @@ class PropAccess extends @propaccess, Expr {
   override ControlFlowNode getFirstControlFlowNode() {
     result = getBase().getFirstControlFlowNode()
   }
+
+  override Expr getUnderlyingReference() {
+    result = this
+  }
+
 }
 
 /** A dot expression. */
@@ -1284,10 +1340,17 @@ class Assignment extends @assignment, Expr {
   override ControlFlowNode getFirstControlFlowNode() {
     result = getLhs().getFirstControlFlowNode()
   }
+
 }
 
 /** A simple assignment expression. */
-class AssignExpr extends @assignexpr, Assignment {}
+class AssignExpr extends @assignexpr, Assignment {
+
+  override Expr getUnderlyingValue() {
+    result = getRhs().getUnderlyingValue()
+  }
+
+}
 
 /** A compound assign expression. */
 abstract class CompoundAssignExpr extends Assignment {}

javascript/ql/src/semmle/javascript/TypeScript.qll

@@ -1315,6 +1315,15 @@ class TypeAssertion extends Expr, @typeassertion {
   override ControlFlowNode getFirstControlFlowNode() {
     result = getExpression().getFirstControlFlowNode()
   }
+
+  override Expr getUnderlyingValue() {
+    result = getExpression().getUnderlyingValue()
+  }
+
+  override Expr getUnderlyingReference() {
+    result = getExpression().getUnderlyingReference()
+  }
+
 }
 
 /**

javascript/ql/src/semmle/javascript/Variables.qll

@@ -298,6 +298,11 @@ class VarRef extends @varref, Identifier, BindingPattern, LexicalRef {
   override VarRef getABindingVarRef() { result = this }
 
   override predicate isImpure() { none() }
+
+  override Expr getUnderlyingReference() {
+    result = this
+  }
+
 }
 
 /** An identifier that refers to a variable in a non-declaring position. */