feat: Adding Has macro

src/helper.ts

@@ -327,3 +327,17 @@ export const size = (arr: unknown) => {
 
   throw new CelEvaluationError(`invalid_argument: ${arr}`)
 }
+
+/**
+ * Macro definition for the CEL has() function that checks if a path exists in an object.
+ * 
+ * @param path - The path to check for existence
+ * @returns boolean - True if the path exists (is not undefined), false otherwise
+ * 
+ * @example
+ * has(obj.field) // returns true if field exists on obj
+ */
+export const has = (path: unknown): boolean => {
+  // If the path itself is undefined, it means the field/index doesn't exist
+  return !(path === undefined)
+}

src/spec/macros.spec.ts

@@ -4,6 +4,95 @@ import { CelEvaluationError, CelTypeError, evaluate } from '..'
 import { Operations } from '../helper'
 
 describe('lists expressions', () => {
+
+  describe('has', () => {
+    it('should return true when nested property exists', () => {
+      const expr = 'has(object.property)'
+
+      const result = evaluate(expr, { object: { property: true } })
+
+      expect(result).toBe(true)
+    })
+
+    it('should return false when property does not exists', () => {
+      const expr = 'has(object.nonExisting)'
+
+      const result = evaluate(expr, { object: { property: true } })
+
+      expect(result).toBe(false)
+    })
+
+    it('should return false when property does not exists, combined with property usage', () => {
+      const expr = 'has(object.nonExisting) && object.nonExisting'
+
+      const result = evaluate(expr, { object: { property: true } })
+
+      expect(result).toBe(false)
+    })
+
+    it('should throw when no arguments are passed', () => {
+      const expr = 'has()'
+      const context = { object: { property: true } }
+
+      expect(() => evaluate(expr, context))
+        .toThrow('has() requires exactly one argument')
+    })
+
+    it('should throw when argument is not an object', () => {
+      const context = { object: { property: true } }
+      const errorMessages = 'has() requires a field selection';
+
+      expect(() => evaluate('has(object)', context))
+        .toThrow(errorMessages)
+
+      expect(() => evaluate('has(object[0])', context))
+        .toThrow(errorMessages)
+
+      expect(() => evaluate('has(object[property])', context))
+        .toThrow(errorMessages)  
+    })
+
+    describe('should throw when argument is an atomic expresion of type', () => {
+      const errorMessages = 'has() does not support atomic expressions'
+      const context = { object: { property: true } }
+
+      it('string', () => {
+        expect(() => evaluate('has("")', context))
+          .toThrow(errorMessages)
+
+        expect(() => evaluate('has("string")', context))
+          .toThrow(errorMessages)
+      })
+
+      it('array', () => {
+        expect(() => evaluate('has([])', context))
+          .toThrow(errorMessages)
+
+        expect(() => evaluate('has([1, 2, 3])', context))
+          .toThrow(errorMessages)
+      })
+
+      it('boolean', () => {
+        expect(() => evaluate('has(true)', context))
+          .toThrow(errorMessages)
+
+        expect(() => evaluate('has(false)', context))
+          .toThrow(errorMessages)
+      })
+
+      it('number', () => {
+        expect(() => evaluate('has(42)', context))
+          .toThrow(errorMessages)
+
+        expect(() => evaluate('has(0)', context))
+          .toThrow(errorMessages)
+
+        expect(() => evaluate('has(0.3)', context))
+          .toThrow(errorMessages)
+      })
+    })    
+  })
+
   describe('size', () => {
     describe('list', () => {
       it('should return 0 for empty list', () => {

src/visitor.ts

@@ -26,7 +26,8 @@ import {
   getPosition,
   getResult,
   getUnaryResult,
-  size,
+  has,
+  size
 } from './helper.js'
 import { CelEvaluationError } from './index.js'
 
@@ -35,7 +36,8 @@ const parserInstance = new CelParser()
 const BaseCelVisitor = parserInstance.getBaseCstVisitorConstructor()
 
 const defaultFunctions = {
-  size: size,
+  has,
+  size
 };
 
 export class CelVisitor
@@ -62,6 +64,47 @@ export class CelVisitor
     return this.visit(ctx.conditionalOr) as unknown
   }
 
+  /**
+   * Handles the special 'has' macro which checks for the existence of a field.
+   * 
+   * @param ctx - The macro expression context containing the argument to check
+   * @returns boolean indicating if the field exists
+   * @throws CelEvaluationError if argument is missing or invalid
+   */
+  private handleHasMacro(ctx: MacrosExpressionCstChildren): boolean {
+    if (!ctx.arg) {
+      throw new CelEvaluationError('has() requires exactly one argument')
+    }
+
+    this.context.inHas = true
+    try {
+      const result = this.visit(ctx.arg)
+      return this.functions.has(result)
+    } catch (error) {
+      // Only convert to false if it's not a validation error
+      if (error instanceof CelEvaluationError) {
+        throw error
+      }
+      return false
+    } finally {
+      this.context.inHas = false
+    }
+  }
+
+  /**
+   * Handles execution of generic macro functions by evaluating and passing their arguments.
+   * 
+   * @param fn - The macro function to execute
+   * @param ctx - The macro expression context containing the arguments
+   * @returns The result of executing the macro function with the evaluated arguments
+   */
+  private handleGenericMacro(fn: CallableFunction, ctx: MacrosExpressionCstChildren): unknown {
+    return fn(...[
+      ...(ctx.arg ? [this.visit(ctx.arg)] : []),
+      ...(ctx.args ? ctx.args.map((arg) => this.visit(arg)) : [])
+    ])
+  }
+
   conditionalOr(ctx: ConditionalOrCstChildren): boolean {
     let left = this.visit(ctx.lhs)
 
@@ -77,9 +120,27 @@ export class CelVisitor
     return left
   }
 
+  /**
+   * Evaluates a logical AND expression by visiting left and right hand operands.
+   * 
+   * @param ctx - The conditional AND context containing left and right operands
+   * @returns The boolean result of evaluating the AND expression
+   * 
+   * This method implements short-circuit evaluation - if the left operand is false,
+   * it returns false immediately without evaluating the right operand. This is required
+   * for proper handling of the has() macro.
+   * 
+   * For multiple right-hand operands, it evaluates them sequentially, combining results
+   * with logical AND operations.
+   */
   conditionalAnd(ctx: ConditionalAndCstChildren): boolean {
     let left = this.visit(ctx.lhs)
 
+    // Short circuit if left is false. Required to quick fail for has() macro.
+    if (left === false) {
+      return false
+    }
+
     if (ctx.rhs) {
       ctx.rhs.forEach((rhsOperand) => {
         const right = this.visit(rhsOperand)
@@ -237,21 +298,63 @@ export class CelVisitor
     return [key, value]
   }
 
+  /**
+   * Evaluates a macros expression by executing the corresponding macro function.
+   * 
+   * @param ctx - The macro expression context containing the macro identifier and arguments
+   * @returns The result of executing the macro function
+   * @throws Error if the macro function is not recognized
+   * 
+   * This method handles two types of macros:
+   * 1. The special 'has' macro which checks for field existence
+   * 2. Generic macros that take evaluated arguments
+   */
   macrosExpression(ctx: MacrosExpressionCstChildren): unknown {
-    const macrosIdentifier = ctx.Identifier[0]
-    const fn = this.functions[macrosIdentifier.image];
-    if (fn) {
-      return fn(...[...(ctx.arg ? [this.visit(ctx.arg)] : []), ...(ctx.args ? ctx.args.map((arg) => this.visit(arg)) : [])])
+    const [ macrosIdentifier ] = ctx.Identifier
+    const fn = this.functions[macrosIdentifier.image]
+
+    if (!fn) {
+      throw new Error(`Macros ${macrosIdentifier.image} not recognized`)
+    }
+
+    // Handle special case for `has` macro
+    if (macrosIdentifier.image === 'has') {
+      return this.handleHasMacro(ctx)
     }
-    throw new Error(`Macros ${macrosIdentifier.image} not recognized`)
+
+    return this.handleGenericMacro(fn, ctx)
   }
 
-  // these two visitor methods will return a string.
+  /**
+   * Evaluates an atomic expression node in the AST.
+   * 
+   * @param ctx - The atomic expression context containing the expression type and value
+   * @returns The evaluated value of the atomic expression
+   * @throws CelEvaluationError if invalid atomic expression is used in has() macro
+   * @throws Error if reserved identifier is used or expression type not recognized
+   *
+   * Handles the following atomic expression types:
+   * - Null literals
+   * - Parenthesized expressions 
+   * - String literals
+   * - Boolean literals
+   * - Float literals
+   * - Integer literals
+   * - Identifier expressions
+   * - List expressions
+   * - Map expressions
+   * - Macro expressions
+   */
   atomicExpression(ctx: AtomicExpressionCstChildren) {
     if (ctx.Null) {
       return null
     }
 
+    // Check if we are in a has() macro, and if so, throw an error if we are not in a field selection
+    if (this.context.inHas && !ctx.identifierExpression) {
+      throw new CelEvaluationError('has() does not support atomic expressions')
+    }
+
     if (ctx.parenthesisExpression) {
       return this.visit(ctx.parenthesisExpression)
     }
@@ -296,6 +399,11 @@ export class CelVisitor
   }
 
   identifierExpression(ctx: IdentifierExpressionCstChildren): unknown {
+    // Validate that we have a dot expression when in a has() macro
+    if (this.context.inHas && !ctx.identifierDotExpression?.length) {  
+      throw new CelEvaluationError('has() requires a field selection')
+    }
+
     const data = this.context
     const result = this.getIdentifier(data, ctx.Identifier[0].image)