add ln()

Author: cherylEnkidu

Firestore/Swift/Source/ExpressionImplementation.swift

@@ -292,6 +292,10 @@ public extension Expression {
     return FunctionExpression("floor", [self])
   }
 
+  func ln() -> FunctionExpression {
+    return FunctionExpression("ln", [self])
+  }
+
   func exp() -> FunctionExpression {
     return FunctionExpression("exp", [self])
   }

Firestore/Swift/Source/SwiftAPI/Pipeline/Expressions/Expression.swift

@@ -36,7 +36,17 @@ public protocol Expression: Sendable {
 
   // --- Added Mathematical Operations ---
 
-  /// Creates an expression that returns the largest numeric value that isn't greater than X.
+  /// Creates an expression that returns the natural logarithm of self.
+  ///
+  /// ```swift
+  /// // Get the natural logarithm of the "amount" field.
+  /// Field("amount").ln()
+  /// ```
+  ///
+  /// - Returns: A new `FunctionExpression` representing the natural logarithm of the number.
+  func ln() -> FunctionExpression
+
+  /// Creates an expression that returns the largest numeric value that isn't greater than self.
   ///
   /// ```swift
   /// // Get the floor of the "amount" field.
@@ -46,7 +56,7 @@ public protocol Expression: Sendable {
   /// - Returns: A new `FunctionExpression` representing the floor of the number.
   func floor() -> FunctionExpression
 
-  /// Creates an expression that returns e to the power of X.
+  /// Creates an expression that returns e to the power of self.
   ///
   /// Returns zero on underflow and nil on overflow.
   ///

Firestore/Swift/Tests/Integration/PipelineTests.swift

@@ -2104,6 +2104,32 @@ class PipelineIntegrationTests: FSTIntegrationTestCase {
     TestHelper.compare(pipelineSnapshot: snapshot, expected: expectedResults, enforceOrder: true)
   }
 
+  func testLnWorks() async throws {
+    let collRef = collectionRef(withDocuments: [
+      "doc1": ["value": 1],
+      "doc2": ["value": exp(Double(2))],
+      "doc3": ["value": exp(Double(1))],
+    ])
+    let db = collRef.firestore
+
+    let pipeline = db.pipeline()
+      .collection(collRef.path)
+      .select([
+        Field("value").ln().as("lnValue"),
+      ])
+      .sort([Field("lnValue").ascending()])
+
+    let snapshot = try await pipeline.execute()
+
+    let expectedResults: [[String: Sendable]] = [
+      ["lnValue": 0],
+      ["lnValue": 1],
+      ["lnValue": 2],
+    ]
+
+    TestHelper.compare(pipelineSnapshot: snapshot, expected: expectedResults, enforceOrder: true)
+  }
+
   func testExpWorks() async throws {
     let collRef = collectionRef(withDocuments: [
       "doc1": ["value": 1],