Add a helper for formatting errors in a ValidationResult.

checker/BUILD

@@ -27,7 +27,6 @@ cc_library(
     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",
     ],
@@ -45,6 +44,7 @@ cc_test(
 
 cc_library(
     name = "validation_result",
+    srcs = ["validation_result.cc"],
     hdrs = ["validation_result.h"],
     deps = [
         ":type_check_issue",
@@ -53,6 +53,7 @@ cc_library(
         "@com_google_absl//absl/base:nullability",
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/status:statusor",
+        "@com_google_absl//absl/strings",
         "@com_google_absl//absl/types:span",
     ],
 )
@@ -64,6 +65,7 @@ cc_test(
         ":type_check_issue",
         ":validation_result",
         "//base/ast_internal:ast_impl",
+        "//common:source",
         "//internal:testing",
         "@com_google_absl//absl/status",
         "@com_google_absl//absl/status:status_matchers",

checker/type_check_issue.cc

@@ -16,7 +16,6 @@
 
 #include <string>
 
-#include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
 #include "common/source.h"
@@ -42,15 +41,19 @@ absl::string_view SeverityString(TypeCheckIssue::Severity severity) {
 
 }  // namespace
 
-std::string TypeCheckIssue::ToDisplayString(const Source& source) const {
+std::string TypeCheckIssue::ToDisplayString(const Source* source) const {
   int column = location_.column;
   // convert to 1-based if it's in range.
   int display_column = column >= 0 ? column + 1 : column;
-  return absl::StrCat(
-      absl::StrFormat("%s: %s:%d:%d: %s", SeverityString(severity_),
-                      source.description(), location_.line, display_column,
-                      message_),
-      source.DisplayErrorLocation(location_));
+  if (source) {
+    return absl::StrFormat("%s: %s:%d:%d: %s%s", SeverityString(severity_),
+                           source->description(), location_.line,
+                           display_column, message_,
+                           source->DisplayErrorLocation(location_));
+  }
+
+  return absl::StrFormat("%s: :%d:%d: %s", SeverityString(severity_),
+                         location_.line, display_column, message_);
 }
 
 }  // namespace cel

checker/type_check_issue.h

@@ -48,7 +48,11 @@ class TypeCheckIssue {
   }
 
   // Format the issue highlighting the source position.
-  std::string ToDisplayString(const Source& source) const;
+  std::string ToDisplayString(const Source* source) const;
+
+  std::string ToDisplayString(const Source& source) const {
+    return ToDisplayString(&source);
+  }
 
   absl::string_view message() const { return message_; }
   Severity severity() const { return severity_; }

checker/validation_result.cc

@@ -0,0 +1,32 @@
+// Copyright 2025 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/validation_result.h"
+
+#include <string>
+
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_join.h"
+#include "checker/type_check_issue.h"
+
+namespace cel {
+
+std::string ValidationResult::FormatError() const {
+  return absl::StrJoin(
+      issues_, "\n", [this](std::string* out, const TypeCheckIssue& issue) {
+        absl::StrAppend(out, issue.ToDisplayString(source_.get()));
+      });
+}
+
+}  // namespace cel

checker/validation_result.h

@@ -16,6 +16,7 @@
 #define THIRD_PARTY_CEL_CPP_CHECKER_VALIDATION_RESULT_H_
 
 #include <memory>
+#include <string>
 #include <utility>
 #include <vector>
 
@@ -68,6 +69,22 @@ class ValidationResult {
     return std::move(source_);
   }
 
+  // Returns a string representation of the issues in the result suitable for
+  // display.
+  //
+  // The result is empty if no issues are present.
+  //
+  // The result is formatted similarly to CEL-Java and CEL-Go, but we do not
+  // give strong guarantees on the format or stability.
+  //
+  // Example:
+  //
+  // ERROR: <source description>:1:3: Issue1
+  //  | source.cel
+  //  | ..^
+  // INFORMATION: <source description>:-1:-1: Issue2
+  std::string FormatError() const;
+
  private:
   absl::Nullable<std::unique_ptr<Ast>> ast_;
   std::vector<TypeCheckIssue> issues_;

checker/validation_result_test.cc

@@ -15,11 +15,13 @@
 #include "checker/validation_result.h"
 
 #include <memory>
+#include <utility>
 
 #include "absl/status/status.h"
 #include "absl/status/status_matchers.h"
 #include "base/ast_internal/ast_impl.h"
 #include "checker/type_check_issue.h"
+#include "common/source.h"
 #include "internal/testing.h"
 
 namespace cel {
@@ -65,5 +67,24 @@ TEST(ValidationResultTest, GetIssues) {
   EXPECT_THAT(result.GetIssues()[1].severity(), Severity::kInformation);
 }
 
+TEST(ValidationResultTest, FormatError) {
+  ValidationResult result(
+      {TypeCheckIssue::CreateError({1, 2}, "Issue1"),
+       TypeCheckIssue(Severity::kInformation, {-1, -1}, "Issue2")});
+  EXPECT_FALSE(result.IsValid());
+
+  ASSERT_OK_AND_ASSIGN(std::unique_ptr<Source> source,
+                       NewSource("source.cel", "<description>"));
+  result.SetSource(std::move(source));
+
+  ASSERT_THAT(result.GetIssues(), SizeIs(2));
+
+  EXPECT_THAT(result.FormatError(),
+              "ERROR: <description>:1:3: Issue1\n"
+              " | source.cel\n"
+              " | ..^\n"
+              "INFORMATION: <description>:-1:-1: Issue2");
+}
+
 }  // namespace
 }  // namespace cel