Add realtime tests for mapGet. Fixup implementation.

Author: tom-andersen

firebase-firestore/src/main/java/com/google/firebase/firestore/pipeline/evaluation.kt

@@ -359,6 +359,12 @@ private fun notEqAny(value: Value, list: List<Value>): EvaluateResult {
   return if (foundNull) EvaluateResult.NULL else EvaluateResult.TRUE
 }
 
+// === Map Functions ===
+
+internal val evaluateMapGet = binaryFunction { map: Map<String, Value>, key: String ->
+  EvaluateResultValue(map[key] ?: return@binaryFunction EvaluateResultUnset)
+}
+
 // === String Functions ===
 
 internal val evaluateStrConcat = variadicFunction { strings: List<String> ->
@@ -741,6 +747,18 @@ private inline fun binaryFunction(
   }
 }
 
+@JvmName("binaryMapStringFunction")
+private inline fun binaryFunction(
+  crossinline function: (Map<String, Value>, String) -> EvaluateResult
+): EvaluateFunction =
+  binaryFunctionType(
+    ValueTypeCase.MAP_VALUE,
+    { v: Value -> v.mapValue.fieldsMap },
+    ValueTypeCase.STRING_VALUE,
+    Value::getStringValue,
+    function
+  )
+
 @JvmName("binaryValueArrayFunction")
 private inline fun binaryFunction(
   crossinline function: (Value, List<Value>) -> EvaluateResult

firebase-firestore/src/main/java/com/google/firebase/firestore/pipeline/expressions.kt

@@ -1821,7 +1821,7 @@ abstract class Expr internal constructor() {
      */
     @JvmStatic
     fun mapGet(mapExpression: Expr, key: String): Expr =
-      FunctionExpr("map_get", notImplemented, mapExpression, key)
+      FunctionExpr("map_get", evaluateMapGet, mapExpression, key)
 
     /**
      * Accesses a value from a map (object) field using the provided [key].
@@ -1832,7 +1832,29 @@ abstract class Expr internal constructor() {
      */
     @JvmStatic
     fun mapGet(fieldName: String, key: String): Expr =
-      FunctionExpr("map_get", notImplemented, fieldName, key)
+      FunctionExpr("map_get", evaluateMapGet, fieldName, key)
+
+    /**
+     * Accesses a value from a map (object) field using the provided [keyExpression].
+     *
+     * @param mapExpression The expression representing the map.
+     * @param keyExpression The key to access in the map.
+     * @return A new [Expr] representing the value associated with the given key in the map.
+     */
+    @JvmStatic
+    fun mapGet(mapExpression: Expr, keyExpression: Expr): Expr =
+      FunctionExpr("map_get", evaluateMapGet, mapExpression, keyExpression)
+
+    /**
+     * Accesses a value from a map (object) field using the provided [keyExpression].
+     *
+     * @param fieldName The field name of the map field.
+     * @param keyExpression The key to access in the map.
+     * @return A new [Expr] representing the value associated with the given key in the map.
+     */
+    @JvmStatic
+    fun mapGet(fieldName: String, keyExpression: Expr): Expr =
+      FunctionExpr("map_get", evaluateMapGet, fieldName, keyExpression)
 
     /**
      * Creates an expression that merges multiple maps into a single map. If multiple maps have the

firebase-firestore/src/test/java/com/google/firebase/firestore/pipeline/MapTests.kt

@@ -0,0 +1,50 @@
+package com.google.firebase.firestore.pipeline
+
+import com.google.firebase.firestore.model.Values.encodeValue
+import com.google.firebase.firestore.pipeline.Expr.Companion.constant
+import com.google.firebase.firestore.pipeline.Expr.Companion.map
+import com.google.firebase.firestore.pipeline.Expr.Companion.mapGet
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+
+@RunWith(RobolectricTestRunner::class)
+class MapTests {
+
+  @Test
+  fun `mapGet - get existing key returns value`() {
+    val mapExpr = map(mapOf("a" to 1L, "b" to 2L, "c" to 3L))
+    val expr = mapGet(mapExpr, constant("b"))
+    assertEvaluatesTo(evaluate(expr), encodeValue(2L), "mapGet existing key should return value")
+  }
+
+  @Test
+  fun `mapGet - get missing key returns unset`() {
+    val mapExpr = map(mapOf("a" to 1L, "b" to 2L, "c" to 3L))
+    val expr = mapGet(mapExpr, "d")
+    assertEvaluatesToUnset(evaluate(expr), "mapGet missing key should return unset")
+  }
+
+  @Test
+  fun `mapGet - get from empty map returns unset`() {
+    val mapExpr = map(emptyMap())
+    val expr = mapGet(mapExpr, "d")
+    assertEvaluatesToUnset(evaluate(expr), "mapGet from empty map should return unset")
+  }
+
+  @Test
+  fun `mapGet - wrong map type returns error`() {
+    val mapExpr = constant("not a map") // Pass a string instead of a map
+    val expr = mapGet(mapExpr, "d")
+    // This should evaluate to an error because the first argument is not a map.
+    assertEvaluatesToError(evaluate(expr), "mapGet with wrong map type should return error")
+  }
+
+  @Test
+  fun `mapGet - wrong key type returns error`() {
+    val mapExpr = map(emptyMap())
+    val expr = mapGet(mapExpr, constant(false))
+    // This should evaluate to an error because the key argument is not a string.
+    assertEvaluatesToError(evaluate(expr), "mapGet with wrong key type should return error")
+  }
+}