source-sqlserver: Exclude computed columns from discovery too

Since we neither backfill nor replicate the values of computed
columns it would be a little silly to continue mentioning them
in the discovered schemas.

source-sqlserver/.snapshots/TestComputedColumn-discovery

@@ -28,10 +28,6 @@ Binding 0:
                 "null"
               ]
             },
-            "computed": {
-              "type": "string",
-              "description": "(source type: non-nullable varchar(64))"
-            },
             "id": {
               "type": "integer",
               "description": "(source type: non-nullable int)"

source-sqlserver/discovery.go

@@ -60,10 +60,6 @@ func (db *sqlserverDatabase) discoverTables(ctx context.Context) (map[sqlcapture
 			table.OmitBinding = true
 		}
 		tableMap[streamID] = table
-
-		if details, ok := table.ExtraDetails.(*sqlserverTableDiscoveryDetails); ok {
-			details.ComputedColumns = computedColumns[streamID]
-		}
 	}
 	for _, column := range columns {
 		var streamID = sqlcapture.JoinStreamID(column.TableSchema, column.TableName)
@@ -99,6 +95,18 @@ func (db *sqlserverDatabase) discoverTables(ctx context.Context) (map[sqlcapture
 		tableMap[id] = info
 	}
 
+	// Add computed columns information
+	for streamID, table := range tableMap {
+		if details, ok := table.ExtraDetails.(*sqlserverTableDiscoveryDetails); ok {
+			details.ComputedColumns = computedColumns[streamID]
+		}
+		for _, columnName := range computedColumns[streamID] {
+			var info = table.Columns[columnName]
+			info.OmitColumn = true
+			table.Columns[columnName] = info
+		}
+	}
+
 	// For tables which have no primary key but have a valid secondary index,
 	// fill in that secondary index as the 'primary key' for our purposes.
 	for streamID, indexColumns := range secondaryIndexes {

sqlcapture/discovery.go

@@ -82,6 +82,10 @@ func DiscoverCatalog(ctx context.Context, db Database) ([]*pc.Response_Discovere
 		// Build `properties` schemas for each table column.
 		var properties = make(map[string]*jsonschema.Schema)
 		for _, column := range table.Columns {
+			if column.OmitColumn {
+				continue // Skip adding properties corresponding to omitted columns
+			}
+
 			var jsonType, err = db.TranslateDBToJSONType(column)
 			if err != nil {
 				// Unhandled types are translated to the catch-all schema {} but with

sqlcapture/interface.go

@@ -230,4 +230,5 @@ type ColumnInfo struct {
 	IsNullable  bool        // True if the column can contain nulls.
 	DataType    interface{} // The datatype of this column. May be a string name or a more complex struct.
 	Description *string     // Stored description of the column, if any.
+	OmitColumn  bool        // True if the column should be omitted from discovery JSON schema generation.
 }