cel-expr · copybara-service · Apr 13, 2026 · Apr 13, 2026
diff --git a/validator/BUILD b/validator/BUILD
@@ -96,6 +96,41 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "homogeneous_literal_validator",
+    srcs = ["homogeneous_literal_validator.cc"],
+    hdrs = ["homogeneous_literal_validator.h"],
+    deps = [
+        ":validator",
+        "//common:ast",
+        "//common:expr",
+        "//common:navigable_ast",
+        "@com_google_absl//absl/strings",
+    ],
+)
+
+cc_test(
+    name = "homogeneous_literal_validator_test",
+    srcs = ["homogeneous_literal_validator_test.cc"],
+    deps = [
+        ":homogeneous_literal_validator",
+        ":validator",
+        "//checker:validation_result",
+        "//common:decl",
+        "//common:type",
+        "//compiler",
+        "//compiler:compiler_factory",
+        "//compiler:optional",
+        "//compiler:standard_library",
+        "//extensions:strings",
+        "//internal:status_macros",
+        "//internal:testing",
+        "//internal:testing_descriptor_pool",
+        "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/strings:string_view",
+    ],
+)
+
 cc_test(
     name = "ast_depth_validator_test",
     srcs = ["ast_depth_validator_test.cc"],

diff --git a/validator/homogeneous_literal_validator.cc b/validator/homogeneous_literal_validator.cc
@@ -0,0 +1,190 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "validator/homogeneous_literal_validator.h"
+
+#include <cstdint>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+#include "common/ast.h"
+#include "common/expr.h"
+#include "common/navigable_ast.h"
+#include "validator/validator.h"
+
+namespace cel {
+
+namespace {
+
+bool InExemptFunction(const NavigableAstNode& node,
+                      const std::vector<std::string>& exempt_functions) {
+  const NavigableAstNode* parent = node.parent();
+  while (parent != nullptr) {
+    if (parent->node_kind() == NodeKind::kCall) {
+      absl::string_view fn_name = parent->expr()->call_expr().function();
+      for (const auto& exempt : exempt_functions) {
+        if (exempt == fn_name) {
+          return true;
+        }
+      }
+    }
+    parent = parent->parent();
+  }
+  return false;
+}
+
+bool IsOptional(const TypeSpec& t) {
+  return t.has_abstract_type() && t.abstract_type().name() == "optional_type";
+}
+
+const TypeSpec& GetOptionalParameter(const TypeSpec& t) {
+  return t.abstract_type().parameter_types()[0];
+}
+
+void TypeMismatch(ValidationContext& context, int64_t id,
+                  const TypeSpec& expected, const TypeSpec& actual) {
+  context.ReportErrorAt(
+      id, absl::StrCat("expected type '", FormatTypeSpec(expected),
+                       "' but found '", FormatTypeSpec(actual), "'"));
+}
+
+bool TypeEquiv(const TypeSpec& a, const TypeSpec& b) {
+  if (a == b) {
+    return true;
+  }
+
+  if (a.has_error() || b.has_error()) {
+    // Don't report mismatch if there's an error (type checking failed for the
+    // expression).
+    return true;
+  }
+
+  if (a.has_wrapper() && b.has_primitive()) {
+    return a.wrapper() == b.primitive();
+  } else if (a.has_primitive() && b.has_wrapper()) {
+    return a.primitive() == b.wrapper();
+  }
+
+  if (a.has_list_type() && b.has_list_type()) {
+    return TypeEquiv(a.list_type().elem_type(), b.list_type().elem_type());
+  }
+
+  if (a.has_map_type() && b.has_map_type()) {
+    return TypeEquiv(a.map_type().key_type(), b.map_type().key_type()) &&
+           TypeEquiv(a.map_type().value_type(), b.map_type().value_type());
+  }
+
+  if (a.has_abstract_type() && b.has_abstract_type() &&
+      a.abstract_type().name() == b.abstract_type().name() &&
+      a.abstract_type().parameter_types().size() ==
+          b.abstract_type().parameter_types().size()) {
+    for (int i = 0; i < a.abstract_type().parameter_types().size(); ++i) {
+      if (!TypeEquiv(a.abstract_type().parameter_types()[i],
+                     b.abstract_type().parameter_types()[i])) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  return false;
+}
+
+}  // namespace
+
+Validation HomogeneousLiteralValidator(
+    std::vector<std::string> exempt_functions) {
+  return Validation([exempt_functions = std::move(exempt_functions)](
+                        ValidationContext& context) -> bool {
+    bool valid = true;
+    for (const auto& node :
+         context.navigable_ast().Root().DescendantsPostorder()) {
+      if (node.node_kind() == NodeKind::kList) {
+        if (InExemptFunction(node, exempt_functions)) {
+          continue;
+        }
+        const auto& list_expr = node.expr()->list_expr();
+        const auto& elements = list_expr.elements();
+        const TypeSpec* expected_type = nullptr;
+
+        for (const auto& element : elements) {
+          int64_t id = element.expr().id();
+          const TypeSpec& actual_type = context.ast().GetTypeOrDyn(id);
+          const TypeSpec* type_to_check = &actual_type;
+
+          if (element.optional() && IsOptional(actual_type)) {
+            type_to_check = &GetOptionalParameter(actual_type);
+          }
+
+          if (expected_type == nullptr) {
+            expected_type = type_to_check;
+            continue;
+          }
+
+          if (!(TypeEquiv(*expected_type, *type_to_check))) {
+            TypeMismatch(context, id, *expected_type, *type_to_check);
+            valid = false;
+            break;
+          }
+        }
+      } else if (node.node_kind() == NodeKind::kMap) {
+        if (InExemptFunction(node, exempt_functions)) {
+          continue;
+        }
+        const auto& map_expr = node.expr()->map_expr();
+        const auto& entries = map_expr.entries();
+        const TypeSpec* expected_key_type = nullptr;
+        const TypeSpec* expected_value_type = nullptr;
+
+        for (const auto& entry : entries) {
+          int64_t key_id = entry.key().id();
+          int64_t val_id = entry.value().id();
+          const TypeSpec& actual_key_type = context.ast().GetTypeOrDyn(key_id);
+          const TypeSpec& actual_val_type = context.ast().GetTypeOrDyn(val_id);
+          const TypeSpec* key_type_to_check = &actual_key_type;
+          const TypeSpec* val_type_to_check = &actual_val_type;
+
+          if (entry.optional() && IsOptional(actual_val_type)) {
+            val_type_to_check = &GetOptionalParameter(actual_val_type);
+          }
+
+          if (expected_key_type == nullptr) {
+            expected_key_type = key_type_to_check;
+            expected_value_type = val_type_to_check;
+            continue;
+          }
+
+          if (!(TypeEquiv(*expected_key_type, *key_type_to_check))) {
+            TypeMismatch(context, key_id, *expected_key_type,
+                         *key_type_to_check);
+            valid = false;
+            break;
+          }
+          if (!(TypeEquiv(*expected_value_type, *val_type_to_check))) {
+            TypeMismatch(context, val_id, *expected_value_type,
+                         *val_type_to_check);
+            valid = false;
+            break;
+          }
+        }
+      }
+    }
+    return valid;
+  });
+}
+
+}  // namespace cel
diff --git a/validator/homogeneous_literal_validator.h b/validator/homogeneous_literal_validator.h
@@ -0,0 +1,38 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef THIRD_PARTY_CEL_CPP_VALIDATOR_HOMOGENEOUS_LITERAL_VALIDATOR_H_
+#define THIRD_PARTY_CEL_CPP_VALIDATOR_HOMOGENEOUS_LITERAL_VALIDATOR_H_
+
+#include <string>
+#include <vector>
+
+#include "validator/validator.h"
+
+namespace cel {
+
+// Returns a `Validation` that checks that all literals in map or list literals
+// are the same type. If the list or map is part of an argument to an exempted
+// function, it is not checked.
+Validation HomogeneousLiteralValidator(
+    std::vector<std::string> exempt_functions);
+
+inline Validation HomogeneousLiteralValidator() {
+  // Default to exempting the strings extension "format" function.
+  return HomogeneousLiteralValidator({"format"});
+}
+
+}  // namespace cel
+
+#endif  // THIRD_PARTY_CEL_CPP_VALIDATOR_HOMOGENEOUS_LITERAL_VALIDATOR_H_