Schema Compare: Fabric Warehouse platform detection + constraint script preservation

src/Microsoft.SqlTools.ServiceLayer/SchemaCompare/Contracts/SchemaCompareRequest.cs

@@ -49,6 +49,25 @@ public class SchemaCompareResult : ResultStatus
         public bool AreEqual { get; set; }
 
         public List<DiffEntry> Differences { get; set; }
+
+        /// <summary>
+        /// Short name of the DacFx <c>SqlPlatforms</c> value detected for the source endpoint
+        /// after the comparison runs (e.g. "Sql160", "SqlDwUnified", "SqlAzure"). Populated
+        /// from <c>DatabaseSchemaProvider.Platform</c> via
+        /// <c>SchemaCompareUtils.GetComparisonPlatform</c>, which differs from
+        /// <c>TSqlModel.Version</c> (the latter reports "Sql150" for Fabric Warehouse models).
+        /// Null if the comparison did not produce a source model.
+        /// </summary>
+        public string SourcePlatform { get; set; }
+
+        /// <summary>
+        /// Short name of the DacFx <c>SqlPlatforms</c> value detected for the target endpoint.
+        /// Populated from <c>DatabaseSchemaProvider.Platform</c> via
+        /// <c>SchemaCompareUtils.GetComparisonPlatform</c>, which differs from
+        /// <c>TSqlModel.Version</c> (the latter reports "Sql150" for Fabric Warehouse models).
+        /// Null if the comparison did not produce a target model.
+        /// </summary>
+        public string TargetPlatform { get; set; }
     }
 
     /// <summary>

src/Microsoft.SqlTools.ServiceLayer/SchemaCompare/SchemaCompareService.cs

@@ -87,7 +87,9 @@ await requestContext.SendResult(new SchemaCompareResult()
                         Success = operation.ComparisonResult.IsValid,
                         ErrorMessage = operation.ErrorMessage,
                         AreEqual = operation.ComparisonResult.IsEqual,
-                        Differences = operation.Differences
+                        Differences = operation.Differences,
+                        SourcePlatform = operation.SourcePlatform,
+                        TargetPlatform = operation.TargetPlatform
                     });
 
                     // clean up cancellation action now that the operation is complete (using try remove to avoid exception)

src/Microsoft.SqlTools.SqlCore/SchemaCompare/Contracts/SchemaCompareResults.cs

@@ -27,6 +27,25 @@ public class SchemaCompareResult : SchemaCompareResultBase
         /// List of differences found between source and target.
         /// </summary>
         public List<DiffEntry> Differences { get; set; }
+
+        /// <summary>
+        /// Short name of the DacFx <c>SqlPlatforms</c> value detected for the source endpoint
+        /// after the comparison runs (e.g. "Sql160", "SqlDwUnified", "SqlAzure"). Populated
+        /// from <c>DatabaseSchemaProvider.Platform</c> via
+        /// <see cref="SchemaCompareUtils.GetComparisonPlatform"/>, which differs from
+        /// <c>TSqlModel.Version</c> (the latter reports "Sql150" for Fabric Warehouse models).
+        /// Null if the comparison did not produce a source model.
+        /// </summary>
+        public string SourcePlatform { get; set; }
+
+        /// <summary>
+        /// Short name of the DacFx <c>SqlPlatforms</c> value detected for the target endpoint.
+        /// Populated from <c>DatabaseSchemaProvider.Platform</c> via
+        /// <see cref="SchemaCompareUtils.GetComparisonPlatform"/>, which differs from
+        /// <c>TSqlModel.Version</c> (the latter reports "Sql150" for Fabric Warehouse models).
+        /// Null if the comparison did not produce a target model.
+        /// </summary>
+        public string TargetPlatform { get; set; }
     }
 
     /// <summary>

src/Microsoft.SqlTools.SqlCore/SchemaCompare/SchemaCompareOperation.cs

@@ -36,6 +36,22 @@ public class SchemaCompareOperation : IDisposable
 
         public List<DiffEntry> Differences;
 
+        /// <summary>
+        /// The platform the comparison ran under (DacFx <c>SqlPlatforms</c> enum name, e.g.
+        /// "Sql160", "SqlAzureV12", "SqlDwUnified"). Sourced from the comparison's
+        /// <c>DatabaseSchemaProvider.Platform</c> (the unified DSP the comparison normalized
+        /// to). Source and Target carry the same value because DacFx runs a single comparison
+        /// under a single DSP — see <see cref="SchemaCompareUtils.GetComparisonPlatform"/>.
+        /// Null if the
+        /// platform could not be detected (e.g. the comparison was never run).
+        /// </summary>
+        public string SourcePlatform { get; set; }
+
+        /// <summary>
+        /// The platform the comparison ran under. See <see cref="SourcePlatform"/>.
+        /// </summary>
+        public string TargetPlatform { get; set; }
+
         public SchemaCompareOperation(SchemaCompareParams parameters, ISchemaCompareConnectionProvider connectionProvider)
         {
             Validate.IsNotNull("parameters", parameters);
@@ -117,6 +133,26 @@ public void Execute()
                     }
                 }
 
+                // Expose the platform the comparison actually ran under so clients can show
+                // the user which T-SQL dialect Schema Compare is using (e.g. "SqlDwUnified"
+                // when comparing Fabric Warehouse endpoints).
+                //
+                // We CANNOT use ComparisonResult.SourceModel.Version because DacFx maps the
+                // SqlDwUnified platform to SqlServerVersion.Sql150 in
+                // InternalModelUtils.CalculateVersionsForPlatform (it predates the
+                // SqlServerVersion.SqlDwUnified enum value). The TSqlModel.Version surface
+                // therefore reports "Sql150" for every Fabric Warehouse model, which would
+                // mislabel the platform pill in the UI.
+                //
+                // Instead, read the comparison's normalized DSP from
+                // SchemaComparisonResult.DataModel.DatabaseSchemaProvider.Platform via
+                // reflection. DatabaseSchemaProvider is internal-abstract in DacFx, but
+                // .Platform is a public abstract SqlPlatforms property (a public enum), and
+                // the cascade fix in PR 2143938 confirms this value is reliably populated.
+                string comparisonPlatform = SchemaCompareUtils.GetComparisonPlatform(this.ComparisonResult);
+                this.SourcePlatform = comparisonPlatform;
+                this.TargetPlatform = comparisonPlatform;
+
                 // Appending the set of errors that are stopping the schema compare to the ErrorMessage
                 // GetErrors return all type of warnings, and error messages. Only filtering the error type messages here
                 var errorsList = ComparisonResult.GetErrors().Where(x => x.MessageType.Equals(DacMessageType.Error)).Select(e => e.Message).Distinct().ToList();

src/Microsoft.SqlTools.SqlCore/SchemaCompare/SchemaCompareUtils.cs

@@ -6,11 +6,14 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Reflection;
+using System.Runtime.CompilerServices;
 using System.Text.RegularExpressions;
 using Microsoft.SqlServer.Dac;
 using Microsoft.SqlServer.Dac.Compare;
 using Microsoft.SqlServer.Dac.Model;
 using Microsoft.SqlTools.SqlCore.SchemaCompare.Contracts;
+using Microsoft.SqlTools.Utility;
 
 namespace Microsoft.SqlTools.SqlCore.SchemaCompare
 {
@@ -22,6 +25,23 @@ internal static class SchemaCompareUtils
     {
         private static readonly Regex ExcessWhitespaceRegex = new Regex(" {2,}", RegexOptions.Compiled);
 
+        // The DacFx full type-name suffixes for the constraint kinds that, on SqlDwUnified
+        // (Fabric Warehouse), are always emitted as standalone "ALTER TABLE ... ADD CONSTRAINT"
+        // statements rather than inlined into CREATE TABLE. We need to preserve their child
+        // scripts so the diff editor and aggregated generated script include the constraint
+        // definitions. Match SchemaComparisonExcludedObjectId.TypeName which is the
+        // full .NET type name like "Microsoft.Data.Tools.Schema.Sql.SchemaModel.SqlPrimaryKeyConstraint".
+        private static readonly string[] ConstraintTypeNameSuffixes = new[]
+        {
+            "PrimaryKeyConstraint",
+            "ForeignKeyConstraint",
+            "UniqueConstraint",
+            "CheckConstraint",
+            "DefaultConstraint",
+        };
+
+        private const string SqlDwUnifiedPlatformName = "SqlDwUnified";
+
         internal static DiffEntry CreateDiffEntry(SchemaDifference difference, DiffEntry parent, SchemaComparisonResult schemaComparisonResult)
         {
             if (difference == null)
@@ -51,14 +71,23 @@ internal static DiffEntry CreateDiffEntry(SchemaDifference difference, DiffEntry
 
             if (difference.DifferenceType == SchemaDifferenceType.Object)
             {
+                // Fabric Warehouse (SqlDwUnified) never inlines PK/FK/UNIQUE/CHECK/DEFAULT
+                // constraints into CREATE TABLE — every constraint is emitted as a standalone
+                // "ALTER TABLE ... ADD CONSTRAINT ..." script. The legacy filter below skips
+                // child scripts that start with "alter" on the assumption that they're
+                // duplicates of inline constraints already present in the parent's CREATE.
+                // For SqlDwUnified that assumption is wrong: the ALTER script is the ONLY
+                // place the constraint is defined, so we must keep it.
+                bool keepAlterScript = IsConstraintChildOnSqlDwUnified(diffEntry, schemaComparisonResult);
+
                 // set source and target scripts
                 if (difference.SourceObject != null)
                 {
                     string sourceScript = schemaComparisonResult.GetDiffEntrySourceScript(difference);
 
                     // Child scripts that do not use alter need to be added if they are being changed, ex: "EXECUTE sp_addextendedproperty...".
                     // Don't add scripts that start with alter because those are handled by a top level element's create
-                    if (!sourceScript.ToLowerInvariant().StartsWith("alter"))
+                    if (keepAlterScript || !sourceScript.ToLowerInvariant().StartsWith("alter"))
                     {
                         diffEntry.SourceScript = FormatScript(sourceScript);
                     }
@@ -69,7 +98,7 @@ internal static DiffEntry CreateDiffEntry(SchemaDifference difference, DiffEntry
 
                     // Child scripts that do not use alter need to be added if they are being changed, ex: "EXECUTE sp_addextendedproperty...".
                     // Don't add scripts that start with alter because those are handled by a top level element's create
-                    if (!targetScript.ToLowerInvariant().StartsWith("alter"))
+                    if (keepAlterScript || !targetScript.ToLowerInvariant().StartsWith("alter"))
                     {
                         diffEntry.TargetScript = FormatScript(targetScript);
                     }
@@ -86,6 +115,54 @@ internal static DiffEntry CreateDiffEntry(SchemaDifference difference, DiffEntry
             return diffEntry;
         }
 
+        private static bool IsConstraintChildOnSqlDwUnified(DiffEntry diffEntry, SchemaComparisonResult schemaComparisonResult)
+        {
+            string typeName = diffEntry.SourceObjectType ?? diffEntry.TargetObjectType;
+            string platform = GetComparisonPlatform(schemaComparisonResult);
+            return ShouldPreserveAlterScriptForConstraint(typeName, platform);
+        }
+
+        /// <summary>
+        /// Pure helper: decides whether a diff-entry's "starts-with-alter" script must be
+        /// preserved instead of stripped. Returns true when the given DacFx object type name
+        /// is one of the constraint kinds we fold under a parent table
+        /// (<see cref="ConstraintTypeNameSuffixes"/>) and the comparison is running under the
+        /// Fabric Warehouse DSP (<see cref="SqlDwUnifiedPlatformName"/>). All other inputs
+        /// — non-constraint types, non-Fabric platforms, null/empty type or platform —
+        /// return false, preserving the legacy strip-on-alter behaviour for SQL Server,
+        /// Azure SQL, and Synapse comparisons.
+        /// </summary>
+        /// <remarks>
+        /// Extracted from <see cref="IsConstraintChildOnSqlDwUnified"/> so it can be unit
+        /// tested without manufacturing a real <see cref="SchemaComparisonResult"/> graph
+        /// (DacFx's comparison types are sealed with no public constructor that yields a
+        /// usable platform projection).
+        /// </remarks>
+        internal static bool ShouldPreserveAlterScriptForConstraint(string objectTypeName, string platform)
+        {
+            if (string.IsNullOrEmpty(objectTypeName))
+            {
+                return false;
+            }
+
+            bool isConstraint = false;
+            foreach (string suffix in ConstraintTypeNameSuffixes)
+            {
+                if (objectTypeName.EndsWith(suffix, StringComparison.Ordinal))
+                {
+                    isConstraint = true;
+                    break;
+                }
+            }
+            if (!isConstraint)
+            {
+                return false;
+            }
+
+            return string.Equals(platform, SqlDwUnifiedPlatformName, StringComparison.Ordinal);
+        }
+
+
         internal static SchemaComparisonExcludedObjectId CreateExcludedObject(SchemaCompareObjectId sourceObj)
         {
             try
@@ -155,5 +232,134 @@ internal static string FormatScript(string script)
             }
             return script;
         }
+
+        // Cached reflection accessors for SchemaComparisonResult.DataModel.DatabaseSchemaProvider.Platform.
+        // Resolved lazily and atomically on first use so we pay the lookup cost once per process.
+        private static PropertyInfo s_dataModelProp;
+        private static PropertyInfo s_dspProp;
+        private static PropertyInfo s_platformProp;
+        private static bool s_reflectionInitFailed;
+        private static readonly object s_reflectionInitLock = new object();
+
+        // Per-result cache so CreateDiffEntry's recursive walk does not re-reflect for every child.
+        // ConditionalWeakTable doesn't allow null values, so we sentinel "unknown" as empty string.
+        private static readonly ConditionalWeakTable<SchemaComparisonResult, string> s_platformByResult =
+            new ConditionalWeakTable<SchemaComparisonResult, string>();
+
+        /// <summary>
+        /// Returns the comparison's DSP platform as a string (e.g. "Sql160", "SqlDwUnified")
+        /// by reflecting into the internal <c>SchemaCompareDataModel.DatabaseSchemaProvider</c>
+        /// reachable from <see cref="SchemaComparisonResult"/>. Returns <c>null</c> if any step
+        /// of the lookup fails or returns null. Result is cached per <c>SchemaComparisonResult</c>
+        /// instance so repeated calls are O(1) after the first.
+        /// </summary>
+        /// <remarks>
+        /// This is a reflection workaround for the lack of a public DacFx accessor exposing
+        /// the comparison's platform. <c>TSqlModel.Version</c> would be the natural API but
+        /// returns <c>Sql150</c> for Fabric Warehouse models (see
+        /// <c>InternalModelUtils.CalculateVersionsForPlatform</c>). If DacFx adds a public
+        /// <c>SchemaComparisonResult.Platform</c> property in the future, replace this with
+        /// the direct call.
+        /// </remarks>
+        internal static string GetComparisonPlatform(SchemaComparisonResult result)
+        {
+            if (result == null)
+            {
+                return null;
+            }
+
+            // ConditionalWeakTable is thread-safe, but TryGetValue+Add can still race on the same key.
+            // Cache empty string as the sentinel for "unknown" since ConditionalWeakTable does not allow null values.
+            string cached = s_platformByResult.GetValue(result, r => TryGetComparisonPlatformCore(r) ?? string.Empty);
+            return string.IsNullOrEmpty(cached) ? null : cached;
+        }
+
+        private static string TryGetComparisonPlatformCore(SchemaComparisonResult result)
+        {
+            try
+            {
+                if (!EnsureReflectionMembers(result.GetType()))
+                {
+                    return null;
+                }
+
+                object dataModel = s_dataModelProp.GetValue(result);
+                if (dataModel == null)
+                {
+                    return null;
+                }
+
+                PropertyInfo dspProp = s_dspProp ?? dataModel.GetType().GetProperty(
+                    "DatabaseSchemaProvider",
+                    BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
+                if (dspProp == null)
+                {
+                    return null;
+                }
+                s_dspProp = dspProp;
+
+                object dsp = dspProp.GetValue(dataModel);
+                if (dsp == null)
+                {
+                    return null;
+                }
+
+                PropertyInfo platformProp = s_platformProp ?? dsp.GetType().GetProperty(
+                    "Platform",
+                    BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
+                if (platformProp == null)
+                {
+                    return null;
+                }
+                s_platformProp = platformProp;
+
+                object platformValue = platformProp.GetValue(dsp);
+                return platformValue?.ToString();
+            }
+            catch (Exception ex)
+            {
+                // Reflection failures are non-fatal: the platform pill simply won't render
+                // and the user keeps their compare results. Log so the failure is diagnosable
+                // from the STS log file without surfacing to the UI.
+                Logger.Warning(string.Format("Schema compare: failed to detect comparison platform via reflection: {0}", ex));
+                return null;
+            }
+        }
+
+        private static bool EnsureReflectionMembers(Type resultType)
+        {
+            if (s_dataModelProp != null)
+            {
+                return true;
+            }
+            if (s_reflectionInitFailed)
+            {
+                return false;
+            }
+
+            lock (s_reflectionInitLock)
+            {
+                if (s_dataModelProp != null)
+                {
+                    return true;
+                }
+                if (s_reflectionInitFailed)
+                {
+                    return false;
+                }
+
+                PropertyInfo prop = resultType.GetProperty(
+                    "DataModel",
+                    BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
+                if (prop == null)
+                {
+                    s_reflectionInitFailed = true;
+                    Logger.Warning("Schema compare: SchemaComparisonResult.DataModel property not found via reflection; platform pill will be unavailable.");
+                    return false;
+                }
+                s_dataModelProp = prop;
+                return true;
+            }
+        }
     }
 }