Add interfaces and coordinating types for type checker.

checker/BUILD

@@ -0,0 +1,87 @@
+# 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.
+package(
+    # Under active development, not yet being released.
+    default_visibility = ["//visibility:public"],
+)
+
+cc_library(
+    name = "type_check_issue",
+    srcs = ["type_check_issue.cc"],
+    hdrs = ["type_check_issue.h"],
+    deps = [
+        "//common:source",
+        "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/strings:str_format",
+        "@com_google_absl//absl/strings:string_view",
+    ],
+)
+
+cc_test(
+    name = "type_check_issue_test",
+    srcs = ["type_check_issue_test.cc"],
+    deps = [
+        ":type_check_issue",
+        "//common:source",
+        "//internal:status_macros",
+        "//internal:testing",
+    ],
+)
+
+cc_library(
+    name = "validation_result",
+    hdrs = ["validation_result.h"],
+    deps = [
+        ":type_check_issue",
+        "//common:ast",
+        "@com_google_absl//absl/base:nullability",
+        "@com_google_absl//absl/status",
+        "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/types:span",
+    ],
+)
+
+cc_test(
+    name = "validation_result_test",
+    srcs = ["validation_result_test.cc"],
+    deps = [
+        ":type_check_issue",
+        ":validation_result",
+        "//base/ast_internal:ast_impl",
+        "//internal:testing",
+        "@com_google_absl//absl/status",
+        "@com_google_absl//absl/status:status_matchers",
+    ],
+)
+
+cc_library(
+    name = "type_checker",
+    hdrs = ["type_checker.h"],
+    deps = [
+        ":validation_result",
+        "//common:ast",
+        "@com_google_absl//absl/status:statusor",
+    ],
+)
+
+cc_library(
+    name = "type_checker_builder",
+    srcs = ["type_checker_builder.cc"],
+    hdrs = ["type_checker_builder.h"],
+    deps = [
+        ":type_checker",
+        "//checker/internal:type_checker_impl",
+        "@com_google_absl//absl/status:statusor",
+    ],
+)

checker/internal/BUILD

@@ -0,0 +1,32 @@
+# 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.
+
+package(
+    # Implementation details for the checker library.
+    default_visibility = ["//visibility:public"],
+)
+
+cc_library(
+    name = "type_checker_impl",
+    srcs = ["type_checker_impl.cc"],
+    hdrs = ["type_checker_impl.h"],
+    deps = [
+        "//checker:type_check_issue",
+        "//checker:type_checker",
+        "//checker:validation_result",
+        "//common:ast",
+        "//common:source",
+        "@com_google_absl//absl/status:statusor",
+    ],
+)

checker/internal/type_checker_impl.cc

@@ -0,0 +1,33 @@
+// 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 "checker/internal/type_checker_impl.h"
+
+#include <memory>
+
+#include "absl/status/statusor.h"
+#include "checker/type_check_issue.h"
+#include "checker/validation_result.h"
+#include "common/ast.h"
+#include "common/source.h"
+
+namespace cel::checker_internal {
+
+absl::StatusOr<ValidationResult> TypeCheckerImpl::Check(
+    std::unique_ptr<Ast> ast) const {
+  return ValidationResult(
+      {TypeCheckIssue::CreateError(SourceLocation{}, "Not yet implemented")});
+}
+
+}  // namespace cel::checker_internal

checker/internal/type_checker_impl.h

@@ -0,0 +1,45 @@
+// 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.
+
+#ifndef THIRD_PARTY_CEL_CPP_CHECKER_INTERNAL_TYPE_CHECKER_IMPL_H_
+#define THIRD_PARTY_CEL_CPP_CHECKER_INTERNAL_TYPE_CHECKER_IMPL_H_
+
+#include <memory>
+
+#include "absl/status/statusor.h"
+#include "checker/type_checker.h"
+#include "checker/validation_result.h"
+#include "common/ast.h"
+
+namespace cel::checker_internal {
+
+// Implementation of the TypeChecker interface.
+//
+// See cel::TypeCheckerBuilder for constructing instances.
+class TypeCheckerImpl : public TypeChecker {
+ public:
+  TypeCheckerImpl() = default;
+
+  TypeCheckerImpl(const TypeCheckerImpl&) = delete;
+  TypeCheckerImpl& operator=(const TypeCheckerImpl&) = delete;
+  TypeCheckerImpl(TypeCheckerImpl&&) = delete;
+  TypeCheckerImpl& operator=(TypeCheckerImpl&&) = delete;
+
+  absl::StatusOr<ValidationResult> Check(
+      std::unique_ptr<Ast> ast) const override;
+};
+
+}  // namespace cel::checker_internal
+
+#endif  // THIRD_PARTY_CEL_CPP_CHECKER_INTERNAL_TYPE_CHECKER_IMPL_H_

checker/type_check_issue.cc

@@ -0,0 +1,53 @@
+// 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 "checker/type_check_issue.h"
+
+#include <string>
+
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_format.h"
+#include "absl/strings/string_view.h"
+#include "common/source.h"
+
+namespace cel {
+
+namespace {
+
+absl::string_view SeverityString(TypeCheckIssue::Severity severity) {
+  switch (severity) {
+    case TypeCheckIssue::Severity::kInformation:
+      return "INFORMATION";
+    case TypeCheckIssue::Severity::kWarning:
+      return "WARNING";
+    case TypeCheckIssue::Severity::kError:
+      return "ERROR";
+    case TypeCheckIssue::Severity::kDeprecated:
+      return "DEPRECATED";
+    default:
+      return "SEVERITY_UNSPECIFIED";
+  }
+}
+
+}  // namespace
+
+std::string TypeCheckIssue::ToDisplayString(const Source& source) const {
+  return absl::StrCat(
+      absl::StrFormat("%s: %s:%d:%d: %s", SeverityString(severity_),
+                      source.description(), location_.line, location_.column,
+                      message_),
+      source.DisplayErrorLocation(location_));
+}
+
+}  // namespace cel

checker/type_check_issue.h

@@ -0,0 +1,65 @@
+// 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.
+
+#ifndef THIRD_PARTY_CEL_CPP_CHECKER_TYPE_CHECK_ISSUE_H_
+#define THIRD_PARTY_CEL_CPP_CHECKER_TYPE_CHECK_ISSUE_H_
+
+#include <string>
+#include <utility>
+
+#include "absl/strings/string_view.h"
+#include "common/source.h"
+
+namespace cel {
+
+// Represents a single issue identified in type checking.
+class TypeCheckIssue {
+ public:
+  enum class Severity { kError, kWarning, kInformation, kDeprecated };
+
+  TypeCheckIssue(Severity severity, SourceLocation location,
+                 std::string message)
+      : severity_(severity),
+        location_(location),
+        message_(std::move(message)) {}
+
+  // Factory for error-severity issues.
+  static TypeCheckIssue CreateError(SourceLocation location,
+                                    std::string message) {
+    return TypeCheckIssue(Severity::kError, location, std::move(message));
+  }
+
+  // Factory for error-severity issues.
+  // line is 1-based, column is 0-based.
+  static TypeCheckIssue CreateError(int line, int column, std::string message) {
+    return TypeCheckIssue(Severity::kError, SourceLocation{line, column},
+                          std::move(message));
+  }
+
+  // Format the issue highlighting the source position.
+  std::string ToDisplayString(const Source& source) const;
+
+  absl::string_view message() const { return message_; }
+  Severity severity() const { return severity_; }
+  SourceLocation location() const { return location_; }
+
+ private:
+  Severity severity_;
+  SourceLocation location_;
+  std::string message_;
+};
+
+}  // namespace cel
+
+#endif  // THIRD_PARTY_CEL_CPP_CHECKER_TYPE_CHECK_ISSUE_H_

checker/type_check_issue_test.cc

@@ -0,0 +1,47 @@
+// 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 "checker/type_check_issue.h"
+
+#include "common/source.h"
+#include "internal/testing.h"
+
+namespace cel {
+namespace {
+
+TEST(TypeCheckIssueTest, DisplayString) {
+  ASSERT_OK_AND_ASSIGN(auto source, NewSource("test{\n\tfield1: 123\n}"));
+  TypeCheckIssue issue = TypeCheckIssue::CreateError(2, 2, "test error");
+  EXPECT_EQ(issue.ToDisplayString(*source),
+            "ERROR: <input>:2:2: test error\n"
+            " |  field1: 123\n"
+            " | ..^");
+}
+
+TEST(TypeCheckIssueTest, DisplayStringNoPosition) {
+  ASSERT_OK_AND_ASSIGN(auto source, NewSource("test{\n\tfield1: 123\n}"));
+  TypeCheckIssue issue = TypeCheckIssue::CreateError(-1, -1, "test error");
+  EXPECT_EQ(issue.ToDisplayString(*source), "ERROR: <input>:-1:-1: test error");
+}
+
+TEST(TypeCheckIssueTest, DisplayStringDeprecated) {
+  ASSERT_OK_AND_ASSIGN(auto source, NewSource("test{\n\tfield1: 123\n}"));
+  TypeCheckIssue issue = TypeCheckIssue(TypeCheckIssue::Severity::kDeprecated,
+                                        {-1, -1}, "test error 2");
+  EXPECT_EQ(issue.ToDisplayString(*source),
+            "DEPRECATED: <input>:-1:-1: test error 2");
+}
+
+}  // namespace
+}  // namespace cel