Moved ToNewUnderlyingValue in from EWL

EWL ReSharper Settings.DotSettings

@@ -478,6 +478,7 @@
 	<s:String x:Key="/Default/Environment/InlayHints/VBParameterNameHintsOptions/ShowParameterNameHints/@EntryValue">Never</s:String>
 	<s:Boolean x:Key="/Default/Environment/ParameterNameHintsOptions/ShowParameterNameHints/@EntryValue">False</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SearchAndNavigation/MergeOccurences/@EntryValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EPsiFeatures_002EVisualStudio_002EBackend_002EDaemon_002EHighlightingSettingsMigrator/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EFeature_002EServices_002ECSharp_002EParameterNameHints_002ECSharpParameterNameHintsOptionsMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EFeature_002EServices_002EVB_002EParameterNameHints_002EVBParameterNameHintsOptionsMigration/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpAttributeForSingleLineMethodUpgrade/@EntryIndexedValue">True</s:Boolean>
@@ -1311,6 +1312,7 @@
 	<s:Boolean x:Key="/Default/Housekeeping/VsActionManager/KeyboardShortcutToVsCommand/=Up/Commands/=_003Cdata_0020id_003D_0022_0028_007B1496a755_002D94de_002D11d0_002D8c3f_002D00c04fc2aae2_007D_003A11_0029_0022_0020shortcut_003D_0022Up_0022_0020_002F_003E/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Housekeeping/VsActionManager/KeyboardShortcutToVsCommand/=Up/Commands/=_003Cdata_0020id_003D_0022_0028_007B1496a755_002D94de_002D11d0_002D8c3f_002D00c04fc2aae2_007D_003A1227_0029_0022_0020shortcut_003D_0022Up_0022_0020_002F_003E/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/Housekeeping/VsActionManager/KeyboardShortcutToVsCommand/=Up/Commands/=_003Cdata_0020id_003D_0022_0028_007B1496a755_002D94de_002D11d0_002D8c3f_002D00c04fc2aae2_007D_003A1502_0029_0022_0020shortcut_003D_0022Up_0022_0020_002F_003E/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Housekeeping/VsHighlighting/SuppressVsSquiggles/@EntryValue">True</s:Boolean>
 	<s:String x:Key="/Default/Housekeeping/VsSavedAutocompletionValue/OverrideParameterInfo/=CSharp/@EntryIndexedValue">NotOverridden</s:String>
 	<s:String x:Key="/Default/Housekeeping/VsSavedAutocompletionValue/OverrideParameterInfo/=Css/@EntryIndexedValue">NotOverridden</s:String>
 	<s:String x:Key="/Default/Housekeeping/VsSavedAutocompletionValue/OverrideParameterInfo/=Html/@EntryIndexedValue">NotOverridden</s:String>

Tewl/ICalendar/ICalendarTools.cs

@@ -0,0 +1,21 @@
+using Ical.Net.DataTypes;
+using NodaTime;
+
+namespace Tewl.ICalendar;
+
+/// <summary>
+/// Static methods pertaining to the iCalendar format.
+/// </summary>
+[ PublicAPI ]
+public static class ICalendarTools {
+	/// <summary>
+	/// Creates an iCalendar date/time from this ZonedDateTime.
+	/// </summary>
+	public static CalDateTime ToICalendarTime( this ZonedDateTime time ) =>
+		new( time.Year, time.Month, time.Day, time.Hour, time.Minute, time.Second, time.Zone.Id );
+
+	/// <summary>
+	/// Creates an iCalendar date from this LocalDate.
+	/// </summary>
+	public static CalDateTime ToICalendarDate( this LocalDate date ) => new( date.Year, date.Month, date.Day );
+}

Tewl/IO/ExcelWorksheet.cs

@@ -83,31 +83,26 @@ private void addRowToWorksheet( bool bold, params string[] cellValues ) {
 	}
 
 	private void putRowValueInCell( IXLCell cell, string value ) {
-		var v = new Validator();
-		var detectedDate = v.GetNullableDateTime(
-			new ValidationErrorHandler( "" ),
-			value,
-			DateTimeTools.DayMonthYearFormats.Concat( DateTimeTools.MonthDayYearFormats ).ToArray(),
-			false,
-			DateTime.MinValue,
-			DateTime.MaxValue );
-		if( !v.ErrorsOccurred ) {
+		if( new Validator().GetNullableDateTime(
+				    new ValidationErrorHandler( "" ),
+				    value,
+				    DateTimeTools.DayMonthYearFormats.Concat( DateTimeTools.MonthDayYearFormats ).ToArray(),
+				    false,
+				    DateTime.MinValue,
+				    DateTime.MaxValue )
+			    .Error( out var detectedDate ) is null ) {
 			setOrAddCellStyle( cell, date: true );
 			cell.Value = detectedDate;
 			return;
 		}
 
-		v = new Validator();
-		v.GetEmailAddress( new ValidationErrorHandler( "" ), value, false );
-		if( !v.ErrorsOccurred ) {
+		if( new Validator().GetEmailAddress( new ValidationErrorHandler( "" ), value, false ).Error( out _ ) is null ) {
 			cell.Value = value;
 			cell.SetHyperlink( new XLHyperlink( "mailto:" + value ) );
 			return;
 		}
 
-		v = new Validator();
-		var validatedUrl = v.GetUrl( new ValidationErrorHandler( "" ), value, false );
-		if( !v.ErrorsOccurred ) {
+		if( new Validator().GetUrl( new ValidationErrorHandler( "" ), value, false ).Error( out var validatedUrl ) is null ) {
 			cell.Value = value;
 			cell.SetHyperlink( new XLHyperlink( validatedUrl ) );
 			return;

Tewl/IO/IoMethods.cs

@@ -1,4 +1,5 @@
 using System.Net;
+using System.Text;
 using System.Threading;
 
 namespace Tewl.IO;
@@ -146,13 +147,16 @@ public static long GetFolderSize( string path ) =>
 		File.Exists( path ) ? new FileInfo( path ).Length : Directory.GetFileSystemEntries( path ).Sum( filePath => GetFolderSize( filePath ) );
 
 	/// <summary>
-	/// Returns a text writer for writing a new file or overwriting an existing file.
-	/// Automatically creates any folders needed in the given path, if necessary.
-	/// We recommend passing an absolute path. If a relative path is passed, the working folder
-	/// is used as the root path.
-	/// Caller is responsible for properly disposing the stream.
+	/// Returns a text writer for writing a new file or overwriting an existing file, using UTF-8 encoding. Automatically creates any folders needed in the given
+	/// path, if necessary. We recommend passing an absolute path. If a relative path is passed, the working folder is used as the root path. Caller is
+	/// responsible for properly disposing the stream.
 	/// </summary>
-	public static TextWriter GetTextWriterForWrite( string filePath ) => new StreamWriter( GetFileStreamForWrite( filePath ) );
+	/// <param name="filePath"></param>
+	/// <param name="includeBom">Pass true to include a byte-order mark (BOM) indicating that the file is encoded with UTF-8. This helps avoid misinterpreted
+	/// characters when reading the file, especially if it is plain text. Pass false for XML files or any other format that has its own encoding declaration.
+	/// </param>
+	public static TextWriter GetTextWriterForWrite( string filePath, bool includeBom ) =>
+		new StreamWriter( GetFileStreamForWrite( filePath ), new UTF8Encoding( includeBom, true ) );
 
 	/// <summary>
 	/// Returns a file stream for writing a new file or overwriting an existing file.

Tewl/IO/TabularDataParsing/CsvLineParser.cs

@@ -1,116 +1,88 @@
-using System.Collections.Generic;
-using System.IO;
 using System.Text;
-using JetBrains.Annotations;
-using Tewl.Tools;
 
-namespace Tewl.IO.TabularDataParsing {
+namespace Tewl.IO.TabularDataParsing;
+
+/// <summary>
+/// Parses a line of a Microsoft Excel CSV file using the definition of CSV at
+/// http://en.wikipedia.org/wiki/Comma-separated_values.
+/// </summary>
+[ PublicAPI ]
+internal class CsvLineParser: TextBasedTabularDataParser {
 	/// <summary>
-	/// Parses a line of a Microsoft Excel CSV file using the definition of CSV at
-	/// http://en.wikipedia.org/wiki/Comma-separated_values.
+	/// Creates a parser designed to parse a CSV file.  Passing true for hasHeaderRow will result in the first row being used to map
+	/// header names to column indices.  This will allow you to access fields using the header name in addition to the column index.
 	/// </summary>
-	[PublicAPI]
-	internal class CsvLineParser: TextBasedTabularDataParser {
-		private readonly Dictionary<string, int> columnHeadersToIndexes = new Dictionary<string, int>();
-
-		/// <summary>
-		/// Creates a line parser with no header row.  Fields will be access via indexes rather than by column name.
-		/// </summary>
-		public CsvLineParser() { }
-
-		/// <summary>
-		/// Creates a parser designed to parse a CSV file.  Passing true for hasHeaderRow will result in the first row being used to map
-		/// header names to column indices.  This will allow you to access fields using the header name in addition to the column index.
-		/// </summary>
-		public static TabularDataParser CreateWithFilePath( string filePath, bool hasHeaderRow ) {
-			return new CsvLineParser { fileReader = new FileReader( filePath ), hasHeaderRow = hasHeaderRow };
-		}
-
-		/// <summary>
-		/// Creates a parser designed to parse a CSV file.  Passing true for hasHeaderRow will result in the first row being used to map
-		/// header names to column indices.  This will allow you to access fields using the header name in addition to the column index.
-		/// </summary>
-		public static TabularDataParser CreateWithStream( Stream stream, bool hasHeaderRow ) {
-			return new CsvLineParser { fileReader = new FileReader( stream ), hasHeaderRow = hasHeaderRow };
-		}
-
-		/// <summary>
-		/// Creates a line parser with a header row.  The column names are extracted from the header row, and
-		/// parsed CsvLines will allow field access through column name or column index.
-		/// </summary>
-		public CsvLineParser( string headerLine ) {
-			var index = 0;
-			foreach( var columnHeader in ( Parse( headerLine ) as TextBasedParsedLine ).Fields ) {
-				columnHeadersToIndexes[ columnHeader.ToLower() ] = index;
-				index++;
-			}
-		}
+	public CsvLineParser( string filePath ) {
+		fileReader = new FileReader( filePath );
+	}
 
-		/// <summary>
-		/// Parses a line of a Microsoft Excel CSV file and returns a collection of string fields.
-		/// Internal use only.
-		/// Use ParseAndProcessAllLines instead.
-		/// </summary>
-		internal override TextBasedParsedLine Parse( string line ) {
-			var fields = new List<string>();
-			if( !line.IsNullOrWhiteSpace() ) {
-				using( TextReader tr = new StringReader( line ) )
-					parseCommaSeparatedFields( tr, fields );
-			}
-			var parsedLine = new TextBasedParsedLine( fields );
-			parsedLine.ColumnHeadersToIndexes = columnHeadersToIndexes;
-			return parsedLine;
-		}
+	/// <summary>
+	/// Creates a parser designed to parse a CSV file.  Passing true for hasHeaderRow will result in the first row being used to map
+	/// header names to column indices.  This will allow you to access fields using the header name in addition to the column index.
+	/// </summary>
+	public CsvLineParser( Stream stream ) {
+		fileReader = new FileReader( stream );
+	}
 
-		private static void parseCommaSeparatedFields( TextReader tr, List<string> fields ) {
-			parseCommaSeparatedField( tr, fields );
-			while( tr.Peek() == ',' ) {
-				tr.Read();
+	/// <summary>
+	/// Parses a line of a Microsoft Excel CSV file and returns a collection of string fields.
+	/// </summary>
+	protected override IReadOnlyList<string> parseLine( string? line ) {
+		var fields = new List<string>();
+		if( !line.IsNullOrWhiteSpace() )
+			using( TextReader tr = new StringReader( line ) )
 				parseCommaSeparatedFields( tr, fields );
-			}
-		}
+		return fields;
+	}
 
-		private static void parseCommaSeparatedField( TextReader tr, List<string> fields ) {
-			if( tr.Peek() != -1 ) {
-				string field;
-				if( tr.Peek() != '"' )
-					field = parseSimpleField( tr );
-				else
-					field = parseQuotedField( tr );
-				fields.Add( field.Trim() );
-			}
+	private void parseCommaSeparatedFields( TextReader tr, List<string> fields ) {
+		parseCommaSeparatedField( tr, fields );
+		while( tr.Peek() == ',' ) {
+			tr.Read();
+			parseCommaSeparatedFields( tr, fields );
 		}
+	}
 
-		private static string parseSimpleField( TextReader tr ) {
-			var sb = new StringBuilder();
+	private void parseCommaSeparatedField( TextReader tr, List<string> fields ) {
+		if( tr.Peek() != -1 ) {
+			string field;
+			if( tr.Peek() != '"' )
+				field = parseSimpleField( tr );
+			else
+				field = parseQuotedField( tr );
+			fields.Add( field.Trim() );
+		}
+	}
 
-			var ch = tr.Peek();
-			while( ch != -1 && ch != ',' ) {
-				sb.Append( (char)tr.Read() );
-				ch = tr.Peek();
-			}
+	private string parseSimpleField( TextReader tr ) {
+		var sb = new StringBuilder();
 
-			return sb.ToString();
+		var ch = tr.Peek();
+		while( ch != -1 && ch != ',' ) {
+			sb.Append( (char)tr.Read() );
+			ch = tr.Peek();
 		}
 
-		private static string parseQuotedField( TextReader tr ) {
-			var sb = new StringBuilder();
+		return sb.ToString();
+	}
 
-			// Skip the opening quote
-			tr.Read();
+	private string parseQuotedField( TextReader tr ) {
+		var sb = new StringBuilder();
 
-			var ch = tr.Read();
-			// Continue until the end of the file or until we reach an unescaped quote.
-			while( ch != -1 && !( ch == '"' && tr.Peek() != '"' ) ) {
-				// If we encounter an escaped double quote, skip one of the double quotes.
-				if( ch == '"' && tr.Peek() == '"' )
-					tr.Read();
+		// Skip the opening quote
+		tr.Read();
 
-				sb.Append( (char)ch );
-				ch = tr.Read();
-			}
+		var ch = tr.Read();
+		// Continue until the end of the file or until we reach an unescaped quote.
+		while( ch != -1 && !( ch == '"' && tr.Peek() != '"' ) ) {
+			// If we encounter an escaped double quote, skip one of the double quotes.
+			if( ch == '"' && tr.Peek() == '"' )
+				tr.Read();
 
-			return sb.ToString();
+			sb.Append( (char)ch );
+			ch = tr.Read();
 		}
+
+		return sb.ToString();
 	}
 }

Tewl/IO/TabularDataParsing/DataValidationError.cs

@@ -0,0 +1,32 @@
+namespace Tewl.IO.TabularDataParsing;
+
+/// <summary>
+/// Holds information about a validation error generated as a result of processing a parsed line.
+/// </summary>
+[ PublicAPI ]
+public class DataValidationError {
+	/// <summary>
+	/// An explanation of the place in the original data that caused the error.  For example, "Line 32".
+	/// </summary>
+	public string ErrorSource { get; set; }
+
+	/// <summary>
+	/// True if this is a fatal error.
+	/// </summary>
+	public bool IsFatal { get; }
+
+	/// <summary>
+	/// The error message.
+	/// </summary>
+	public string ErrorMessage { get; }
+
+	/// <summary>
+	/// Creates a validation error that occurred when processing the given line number.
+	/// Error source is an explanation of the place in the original data that caused the error.  For example, "Line 32".
+	/// </summary>
+	public DataValidationError( string errorSource, bool isFatal, string errorMessage ) {
+		ErrorSource = errorSource;
+		ErrorMessage = errorMessage;
+		IsFatal = isFatal;
+	}
+}

Tewl/IO/TabularDataParsing/ExcelParsedLine.cs

@@ -1,26 +1,30 @@
-using System.Collections.Generic;
-using ClosedXML.Excel;
+using ClosedXML.Excel;
 
-namespace Tewl.IO.TabularDataParsing {
-	internal class ExcelParsedLine: ParsedLine {
-		private readonly List<string> headerFields;
-		private readonly IXLRangeRow row;
+namespace Tewl.IO.TabularDataParsing;
 
-		public ExcelParsedLine( List<string> headerFields, IXLRangeRow row ) {
-			this.headerFields = headerFields;
-			this.row = row;
-		}
+internal class ExcelParsedLine: ParsedLine {
+	private readonly IReadOnlyDictionary<string, int> columnIndicesByName;
+	private readonly IXLRangeRow row;
 
-		public bool ContainsData => !row.IsEmpty();
+	public ExcelParsedLine( IReadOnlyDictionary<string, int> columnIndicesByName, IXLRangeRow row ) {
+		this.columnIndicesByName = columnIndicesByName;
+		this.row = row;
+	}
 
-		public int LineNumber => row.RowNumber();
+	bool ParsedLine.ContainsData => !row.IsEmpty();
 
-		// Index is zero-based. The Cell() function on the IXLRangeRow is 1-based. 
-		public string this[ int index ] => row.Cell( index + 1 ).Value.ToString();
+	int ParsedLine.LineNumber => row.RowNumber();
 
-		// Index is zero-based. The Cell() function on the IXLRangeRow is 1-based. 
-		public string this[ string columnName ] => row.Cell( headerFields.IndexOf( columnName.ToLower() ) + 1 ).Value.ToString();
+	public string this[ int index ] =>
+		// Index is zero-based. The Cell() function on the IXLRangeRow is 1-based.
+		row.Cell( index + 1 ).Value.ToString();
 
-		public bool ContainsField( string fieldName ) => headerFields.Contains( fieldName );
-	}
+
+	string ParsedLine.this[ string columnName ] =>
+		columnIndicesByName.TryGetValue( columnName, out var index )
+			? this[ index ]
+			: throw new ArgumentException(
+				  $"Column “{columnName}” does not exist. The columns are {StringTools.GetEnglishListPhrase( columnIndicesByName.Keys.Select( i => $"“{i}”" ), true )}." );
+
+	bool ParsedLine.ContainsField( string fieldName ) => columnIndicesByName.ContainsKey( fieldName );
 }