Fix type-checker to respect the ordering of type providers (protobuf then user provided)

checker/src/main/java/dev/cel/checker/CelCheckerLegacyImpl.java

@@ -446,7 +446,7 @@ public CelCheckerLegacyImpl build() {
       } else if (celTypeProvider != null) {
         messageTypeProvider =
             new CelTypeProvider.CombinedCelTypeProvider(
-                ImmutableList.of(celTypeProvider, messageTypeProvider));
+                ImmutableList.of(messageTypeProvider, celTypeProvider));
       }
 
       // Configure the declaration set, and possibly alter the type provider if ProtoDecl values

checker/src/test/java/dev/cel/checker/CelCheckerLegacyImplTest.java

@@ -19,6 +19,7 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 import com.google.protobuf.Duration;
 import com.google.protobuf.FieldMask;
 import com.google.protobuf.Timestamp;
@@ -40,6 +41,7 @@
 import dev.cel.common.types.ListType;
 import dev.cel.common.types.MapType;
 import dev.cel.common.types.SimpleType;
+import dev.cel.common.types.StructType;
 import dev.cel.common.types.StructTypeReference;
 import dev.cel.common.types.TypeType;
 import dev.cel.compiler.CelCompiler;
@@ -409,6 +411,47 @@ public Optional<CelType> findType(String typeName) {
     assertThat(ast.getResultType()).isEqualTo(preWrappedType);
   }
 
+  @Test
+  public void check_combinedTypeProviders_protoMessageTakesPrecedenceOverCustom() throws Exception {
+    StructType shadowingStructType =
+        StructType.create(
+            TestAllTypes.getDescriptor().getFullName(),
+            ImmutableSet.of("single_int64"),
+            fieldName -> Optional.of(SimpleType.STRING));
+    StructType customOnlyStructType =
+        StructType.create(
+            "custom.CustomStruct",
+            ImmutableSet.of("custom_field"),
+            fieldName -> Optional.of(SimpleType.STRING));
+    CelTypeProvider customTypeProvider =
+        new CelTypeProvider() {
+          @Override
+          public ImmutableList<CelType> types() {
+            return ImmutableList.of(shadowingStructType, customOnlyStructType);
+          }
+
+          @Override
+          public Optional<CelType> findType(String typeName) {
+            return types().stream().filter(t -> t.name().equals(typeName)).findFirst();
+          }
+        };
+    CelCompiler celCompiler =
+        CelCompilerFactory.standardCelCompilerBuilder()
+            .addMessageTypes(TestAllTypes.getDescriptor())
+            .setTypeProvider(customTypeProvider)
+            .build();
+
+    CelAbstractSyntaxTree protoAst =
+        celCompiler
+            .compile("cel.expr.conformance.proto3.TestAllTypes{single_int64: 1}.single_int64")
+            .getAst();
+    CelAbstractSyntaxTree customAst =
+        celCompiler.compile("custom.CustomStruct{custom_field: 'hello'}.custom_field").getAst();
+
+    assertThat(protoAst.getResultType()).isEqualTo(SimpleType.INT);
+    assertThat(customAst.getResultType()).isEqualTo(SimpleType.STRING);
+  }
+
   private enum FieldTypeTestCase {
     REPEATED_PRIMITIVE("msg.repeated_int64", ListType.create(SimpleType.INT)),
     MAP_PRIMITIVE("msg.map_string_string", MapType.create(SimpleType.STRING, SimpleType.STRING)),

runtime/src/test/java/dev/cel/runtime/DescriptorTypeResolverTest.java

@@ -45,9 +45,6 @@ public class DescriptorTypeResolverTest {
   private static final Cel CEL =
       CelFactory.plannerCelBuilder()
           .setTypeProvider(PROTO_MESSAGE_TYPE_PROVIDER)
-          // TODO: Replace setValueProvider with
-          // addMessageTypes(TestAllTypes.getDescriptor()) once CelRuntimeImpl prioritizes custom
-          // CelTypeProvider over its internal messageTypeProvider.
           .setValueProvider(
               (structType, fields) ->
                   structType.equals(TestAllTypes.getDescriptor().getFullName())