pedrosakuma · pedrosakuma · Aug 29, 2026 · Aug 29, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - **Per-schema incremental invalidation for XML AdditionalFiles (#170)**: `SBESourceGenerator` no longer `.Collect()`s the entire schema set before generation. Each schema now flows through its own `RegisterSourceOutput` path, so editing one XML file only re-runs the generators for that schema. Runtime helpers (`SpanReader` / `SpanWriter`) are emitted in a separate namespace-deduplicated step to preserve shared helper generation without reintroducing whole-project schema invalidation.
 
+### Fixed
+
+- **Accurate XML locations for schema diagnostics (#171)**: schema diagnostics now point at the offending XML element or attribute when line/column information is available from the additional-file source text, instead of reporting `Location.None`. Diagnostics still fall back to `Location.None` for cases where a reliable XML location cannot be determined.
+
 ## [1.7.0] - 2026-04-30
 
 ### Added

diff --git a/src/SbeCodeGenerator/Diagnostics/README.md b/src/SbeCodeGenerator/Diagnostics/README.md
@@ -133,7 +133,8 @@ Diagnostics are automatically reported during source generation. When you build
 
 ## Implementation Notes
 
-- Diagnostics use `Location.None` as source generators don't have access to the original XML file locations
+- Diagnostics now use `Location.Create(path, textSpan, lineSpan)` for XML additional files whenever the generator can determine the offending schema node or attribute position from the parsed `XmlReader` line info and the `AdditionalText` source text
+- Diagnostics still fall back to `Location.None` when no reliable source position exists (for example, some malformed-schema failures or diagnostics originating from non-XML inputs such as invalid MSBuild properties)
 - The generator gracefully handles errors by using fallback values and continuing generation
 - Each generator phase (Types, Messages, Utilities, Validation) runs in isolation — a failure in one phase does not block the others
 - Test code uses `default(SourceProductionContext)` which has special handling to skip diagnostic reporting
diff --git a/src/SbeCodeGenerator/Diagnostics/XmlDiagnosticLocation.cs b/src/SbeCodeGenerator/Diagnostics/XmlDiagnosticLocation.cs
@@ -0,0 +1,55 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Text;
+using System;
+using System.Xml;
+
+namespace SbeSourceGenerator.Diagnostics
+{
+    /// <summary>
+    /// Creates Roslyn <see cref="Location"/> instances for XML additional files.
+    /// </summary>
+    internal static class XmlDiagnosticLocation
+    {
+        public static Location Create(SourceText? sourceText, string? filePath, int lineNumber, int linePosition, int width = 1)
+        {
+            if (sourceText == null || string.IsNullOrWhiteSpace(filePath))
+                return Location.None;
+
+            string safeFilePath = filePath!;
+
+            if (lineNumber <= 0 || linePosition <= 0)
+                return Location.None;
+
+            int lineIndex = lineNumber - 1;
+            if (lineIndex >= sourceText.Lines.Count)
+                return Location.None;
+
+            var line = sourceText.Lines[lineIndex];
+            int columnIndex = Math.Max(0, Math.Min(linePosition - 1, line.Span.Length));
+            int start = line.Start + columnIndex;
+            int remaining = line.End - start;
+            int safeWidth = remaining == 0 ? 0 : Math.Max(1, Math.Min(width, remaining));
+
+            var span = new TextSpan(start, safeWidth);
+            var startPosition = new LinePosition(lineIndex, columnIndex);
+            var endPosition = new LinePosition(lineIndex, columnIndex + safeWidth);
+            return Location.Create(safeFilePath, span, new LinePositionSpan(startPosition, endPosition));
+        }
+
+        public static Location CreateFromLineInfo(SourceText? sourceText, string? filePath, IXmlLineInfo lineInfo, int width = 1)
+        {
+            if (lineInfo == null || !lineInfo.HasLineInfo())
+                return Location.None;
+
+            return Create(sourceText, filePath, lineInfo.LineNumber, lineInfo.LinePosition, width);
+        }
+
+        public static Location CreateFromException(SourceText? sourceText, string? filePath, XmlException exception)
+        {
+            if (exception == null)
+                throw new ArgumentNullException(nameof(exception));
+
+            return Create(sourceText, filePath, exception.LineNumber, exception.LinePosition);
+        }
+    }
+}
diff --git a/src/SbeCodeGenerator/Generators/MessagesCodeGenerator.cs b/src/SbeCodeGenerator/Generators/MessagesCodeGenerator.cs
@@ -1,6 +1,7 @@
 using Microsoft.CodeAnalysis;
 using SbeSourceGenerator.Diagnostics;
 using SbeSourceGenerator.Generators.Fields;
+using SbeSourceGenerator.Helpers;
 using SbeSourceGenerator.Schema;
 using SbeSourceGenerator.SemanticTypes;
 using System.Collections.Generic;
@@ -21,7 +22,11 @@ internal class MessagesCodeGenerator : ICodeGenerator
 
             foreach (var messageDto in schema.Messages)
             {
-                var generatedMessageName = TypeResolverHelper.RegisterGeneratedTypeName(context, messageDto.Name, sourceContext);
+                var generatedMessageName = TypeResolverHelper.RegisterGeneratedTypeName(
+                    context,
+                    messageDto.Name,
+                    sourceContext,
+                    messageDto.Source.GetAttributeOrElement("name"));
 
                 var versions = GetMessageVersions(messageDto, schemaVersion, sourceContext);
                 var baseNamespace = StripSchemaVersion(ns);
@@ -162,11 +167,11 @@ private static List<int> GetMessageVersions(SchemaMessageDto messageDto, int sch
                 {
                     if (int.TryParse(field.SinceVersion, out int sinceVersion))
                     {
-                        if (schemaVersion >= 0 && sinceVersion > schemaVersion && sourceContext.CancellationToken != default)
+                        if (schemaVersion >= 0 && sinceVersion > schemaVersion && sourceContext.CanReportDiagnostics())
                         {
                             sourceContext.ReportDiagnostic(Diagnostic.Create(
                                 SbeDiagnostics.SinceVersionExceedsSchemaVersion,
-                                Location.None,
+                                field.Source.GetAttributeOrElement("sinceVersion"),
                                 field.Name,
                                 sinceVersion.ToString(),
                                 schemaVersion.ToString()));
@@ -177,11 +182,11 @@ private static List<int> GetMessageVersions(SchemaMessageDto messageDto, int sch
                             versions.Add(v);
                         }
                     }
-                    else if (sourceContext.CancellationToken != default)
+                    else if (sourceContext.CanReportDiagnostics())
                     {
                         sourceContext.ReportDiagnostic(Diagnostic.Create(
                             SbeDiagnostics.InvalidIntegerAttribute,
-                            Location.None,
+                            field.Source.GetAttributeOrElement("sinceVersion"),
                             "sinceVersion",
                             field.SinceVersion,
                             field.Name));
@@ -195,11 +200,11 @@ private static List<int> GetMessageVersions(SchemaMessageDto messageDto, int sch
                 {
                     if (int.TryParse(data.SinceVersion, out int sinceVersion))
                     {
-                        if (schemaVersion >= 0 && sinceVersion > schemaVersion && sourceContext.CancellationToken != default)
+                        if (schemaVersion >= 0 && sinceVersion > schemaVersion && sourceContext.CanReportDiagnostics())
                         {
                             sourceContext.ReportDiagnostic(Diagnostic.Create(
                                 SbeDiagnostics.SinceVersionExceedsSchemaVersion,
-                                Location.None,
+                                data.Source.GetAttributeOrElement("sinceVersion"),
                                 data.Name,
                                 sinceVersion.ToString(),
                                 schemaVersion.ToString()));
@@ -208,11 +213,11 @@ private static List<int> GetMessageVersions(SchemaMessageDto messageDto, int sch
                         for (int v = 0; v <= sinceVersion; v++)
                             versions.Add(v);
                     }
-                    else if (sourceContext.CancellationToken != default)
+                    else if (sourceContext.CanReportDiagnostics())
                     {
                         sourceContext.ReportDiagnostic(Diagnostic.Create(
                             SbeDiagnostics.InvalidIntegerAttribute,
-                            Location.None,
+                            data.Source.GetAttributeOrElement("sinceVersion"),
                             "sinceVersion",
                             data.SinceVersion,
                             data.Name));
@@ -318,7 +323,7 @@ private static List<IFileContentGenerator> GetFieldsForVersion(
                             field.Id,
                             resolvedType,
                             field.Description,
-                            ParseOffset(field.Offset, field.Name, sourceContext),
+                            ParseOffset(field.Offset, field.Name, sourceContext, field.Source.GetAttributeOrElement("offset")),
                             TypeResolverHelper.GetTypeLength(field.Type, context),
                             field.SinceVersion,
                             field.Deprecated,
@@ -354,7 +359,7 @@ private static List<IFileContentGenerator> GetFieldsForVersion(
                             fieldType,
                             effectivePrimitiveType,
                             field.Description,
-                            ParseOffset(field.Offset, field.Name, sourceContext),
+                            ParseOffset(field.Offset, field.Name, sourceContext, field.Source.GetAttributeOrElement("offset")),
                             TypeResolverHelper.GetTypeLength(field.Type, context),
                             field.SinceVersion,
                             field.Deprecated,
@@ -372,7 +377,7 @@ private static List<IFileContentGenerator> GetFieldsForVersion(
                         field.Id,
                         resolvedType,
                         field.Description,
-                        ParseOffset(field.Offset, field.Name, sourceContext),
+                        ParseOffset(field.Offset, field.Name, sourceContext, field.Source.GetAttributeOrElement("offset")),
                         TypeResolverHelper.GetTypeLength(field.Type, context),
                         field.SinceVersion,
                         field.Deprecated,
@@ -429,7 +434,7 @@ private static void TryAppendSemanticAccessor(
             {
                 sourceContext.ReportDiagnostic(Diagnostic.Create(
                     SbeDiagnostics.SemanticConverterWireMismatch,
-                    registration.Location ?? Location.None,
+                    field.Source.GetAttributeOrElement("semanticType"),
                     registration.ConverterFullyQualifiedName,
                     registration.SemanticType,
                     PrimitiveSpecialTypeMap.ToCSharpKeyword(registration.WireSpecialType),
@@ -454,7 +459,7 @@ private static void TryAppendSemanticAccessor(
                 {
                     sourceContext.ReportDiagnostic(Diagnostic.Create(
                         SbeDiagnostics.SemanticAccessorNameCollision,
-                        registration.Location ?? Location.None,
+                        field.Source.GetAttributeOrElement("semanticType"),
                         generatedFieldName,
                         "<message>",
                         registration.SemanticType));
@@ -508,7 +513,11 @@ private static List<IFileContentGenerator> BuildGroups(
             var result = new List<IFileContentGenerator>(groups.Count);
             foreach (var group in groups)
             {
-                var groupName = TypeResolverHelper.RegisterGeneratedTypeName(context, group.Name, sourceContext);
+                var groupName = TypeResolverHelper.RegisterGeneratedTypeName(
+                    context,
+                    group.Name,
+                    sourceContext,
+                    group.Source.GetAttributeOrElement("name"));
 
                 var groupFields = new List<IFileContentGenerator>(group.Fields.Count);
                 foreach (var field in group.Fields)
@@ -522,7 +531,7 @@ private static List<IFileContentGenerator> BuildGroups(
                         field.Id,
                         resolvedFieldType,
                         field.Description,
-                        ParseOffset(field.Offset, field.Name, sourceContext),
+                        ParseOffset(field.Offset, field.Name, sourceContext, field.Source.GetAttributeOrElement("offset")),
                         TypeResolverHelper.GetTypeLength(field.Type, context),
                         field.SinceVersion,
                         field.Deprecated,
@@ -533,7 +542,9 @@ private static List<IFileContentGenerator> BuildGroups(
                 }
 
                 var groupConstants = BuildConstants(group.Constants, context);
-                var numInGroupType = TypeResolverHelper.ResolveTypeName(GetNumInGroupType(group.DimensionType, context, sourceContext), context);
+                var numInGroupType = TypeResolverHelper.ResolveTypeName(
+                    GetNumInGroupType(group.DimensionType, group.Source, context, sourceContext),
+                    context);
 
                 result.Add(new GroupDefinition(
                     versionNamespace,
@@ -600,7 +611,7 @@ private static List<IFileContentGenerator> GetDataForVersion(List<SchemaDataDto>
             return null;
         }
 
-        private static string GetNumInGroupType(string dimensionType, SchemaContext context, SourceProductionContext sourceContext = default)
+        private static string GetNumInGroupType(string dimensionType, SchemaSourceInfo source, SchemaContext context, SourceProductionContext sourceContext = default)
         {
             var key = $"{dimensionType}.numInGroup";
             if (context.CompositeFieldTypes.TryGetValue(key, out string? numInGroupType))
@@ -611,15 +622,15 @@ private static string GetNumInGroupType(string dimensionType, SchemaContext cont
             {
                 sourceContext.ReportDiagnostic(Diagnostic.Create(
                     SbeDiagnostics.UnsupportedConstruct,
-                    Location.None,
+                    source.GetAttributeOrElement("dimensionType"),
                     "dimensionType",
                     dimensionType,
                     $"Composite type '{dimensionType}' not found. Falling back to ushort for numInGroup."));
             }
             return "ushort";
         }
 
-        private static int? ParseOffset(string offset, string fieldName, SourceProductionContext sourceContext)
+        private static int? ParseOffset(string offset, string fieldName, SourceProductionContext sourceContext, Location location)
         {
             if (string.IsNullOrEmpty(offset))
                 return null;
@@ -628,12 +639,12 @@ private static string GetNumInGroupType(string dimensionType, SchemaContext cont
                 return result;
 
             // Only report diagnostic if context has a valid CancellationToken (not default)
-            if (sourceContext.CancellationToken != default)
+            if (sourceContext.CanReportDiagnostics())
             {
                 // Report diagnostic for invalid offset
                 sourceContext.ReportDiagnostic(Diagnostic.Create(
                     SbeDiagnostics.InvalidIntegerAttribute,
-                    Location.None,
+                    location,
                     "offset",
                     offset,
                     fieldName));

diff --git a/src/SbeCodeGenerator/Generators/TypeResolverHelper.cs b/src/SbeCodeGenerator/Generators/TypeResolverHelper.cs
@@ -96,7 +96,12 @@ public static string NormalizeValueRef(string valueRef, SchemaContext context)
             return string.Concat(normalizedType, separator, remainder);
         }
 
-        public static int GetTypeLength(string type, SchemaContext context, SourceProductionContext sourceContext = default, string elementName = "")
+        public static int GetTypeLength(
+            string type,
+            SchemaContext context,
+            SourceProductionContext sourceContext = default,
+            string elementName = "",
+            Location? location = null)
         {
             if (TypesCatalog.PrimitiveTypeLengths.TryGetValue(type, out int length))
                 return length;
@@ -112,14 +117,18 @@ public static int GetTypeLength(string type, SchemaContext context, SourceProduc
             {
                 sourceContext.ReportDiagnostic(Diagnostic.Create(
                     SbeDiagnostics.UnresolvedTypeReference,
-                    Location.None,
+                    location ?? Location.None,
                     type,
                     elementName));
             }
             return 0;
         }
 
-        public static string RegisterGeneratedTypeName(SchemaContext context, string originalName, SourceProductionContext sourceContext = default)
+        public static string RegisterGeneratedTypeName(
+            SchemaContext context,
+            string originalName,
+            SourceProductionContext sourceContext = default,
+            Location? location = null)
         {
             if (string.IsNullOrEmpty(originalName))
                 return originalName;
@@ -132,7 +141,7 @@ public static string RegisterGeneratedTypeName(SchemaContext context, string ori
                 {
                     sourceContext.ReportDiagnostic(Diagnostic.Create(
                         SbeDiagnostics.DuplicateTypeName,
-                        Location.None,
+                        location ?? Location.None,
                         originalName));
                 }
             }