Read a currency symbol outside the parentheses in Parse [patch]

PreciseNumber.Test/PreciseNumberParseAffixTests.cs

@@ -117,6 +117,13 @@ public class PreciseNumberParseAffixTests
 	[DataRow("1 234,50 CHF", NumberStyles.Currency, "Swiss")]
 	[DataRow("CHF 1 234.50", NumberStyles.Currency, "Swiss")]
 	[DataRow("€1,5", NumberStyles.Any, "Mixed")]
+	[DataRow("$(45)", NumberStyles.Currency, "Dollars")]
+	[DataRow("$(1,234.50)", NumberStyles.Currency, "Dollars")]
+	[DataRow("(45)$", NumberStyles.Currency, "Dollars")]
+	[DataRow("$ (45)", NumberStyles.Currency, "Dollars")]
+	[DataRow("¤(45)", NumberStyles.Any, "Invariant")]
+	[DataRow("(¤45)", NumberStyles.Any, "Invariant")]
+	[DataRow("(45¤)", NumberStyles.Any, "Invariant")]
 	public void TestParseAcceptsWhatDecimalAccepts(string text, NumberStyles style, string format)
 	{
 		NumberFormatInfo numberFormat = Format(format);
@@ -173,6 +180,9 @@ public void TestParseAcceptsANoBreakSpaceBeforeACurrencySymbol()
 	[DataRow("-$ 5", NumberStyles.AllowCurrencySymbol | NumberStyles.AllowLeadingSign, "Dollars")]
 	[DataRow("5 $", NumberStyles.AllowCurrencySymbol | NumberStyles.AllowTrailingSign, "Dollars")]
 	[DataRow("CHF 1,5", NumberStyles.Currency, "Swiss")]
+	[DataRow("$($45)", NumberStyles.Currency, "Dollars")]
+	[DataRow("$(45)$", NumberStyles.Currency, "Dollars")]
+	[DataRow("$(45", NumberStyles.Currency, "Dollars")]
 	public void TestParseRejectsWhatDecimalRejects(string text, NumberStyles style, string format)
 	{
 		NumberFormatInfo numberFormat = Format(format);

PreciseNumber/PreciseNumber.cs

@@ -756,7 +756,7 @@
 	/// A fixed precision such as <c>E15</c> rounds values that need 17 digits, which turns
 	/// <see cref="double.MaxValue"/> into a number that converts back to infinity.
 	/// </remarks>
 	internal static string GetStringFormatForFloatType<TFloat>()
 		where TFloat : INumber<TFloat>
 		=> "R";
 
@@ -1217,7 +1217,7 @@
 	public static PreciseNumber MinMagnitudeNumber(PreciseNumber x, PreciseNumber y) => MinMagnitude(x, y);
 
 	/// <inheritdoc/>
 	public static PreciseNumber Parse(ReadOnlySpan<char> s, NumberStyles style, IFormatProvider? provider)
 	{
 		// Read the separator and signs from the same culture TryFormat writes them with, so that
 		// Parse(x.ToString(p), p) round-trips for every provider.
@@ -1277,7 +1277,7 @@
 					}
 
 					hasDecimal = true;
 					i += decimalLength - 1;
 					continue;
 				}
 
@@ -1285,7 +1285,7 @@
 				int groupLength = allowThousands && !hasDecimal && digitCount > 0 ? MatchSeparator(s[i..], groupSeparator, numberGroupSeparator) : 0;
 				if (groupLength > 0)
 				{
 					i += groupLength - 1;
 					continue;
 				}
 
@@ -1500,7 +1500,17 @@
 	/// <exception cref="FormatException">Thrown when the parentheses enclose a sign.</exception>
 	private static ReadOnlySpan<char> StripAffixes(ReadOnlySpan<char> s, NumberStyles style, NumberFormatInfo numberFormat, out bool isNegative, out bool hasLeadingCurrencySymbol)
 	{
-		bool hasParentheses = style.HasFlag(NumberStyles.AllowParentheses) && s.Length >= 2 && s[0] == '(' && s[^1] == ')';
+		ReadOnlySpan<char> currencySymbol = style.HasFlag(NumberStyles.AllowCurrencySymbol) ? numberFormat.CurrencySymbol : [];
+		bool hasCurrencySymbol = false;
+		bool hasOuterLeadingCurrencySymbol = false;
+
+		bool allowParentheses = style.HasFlag(NumberStyles.AllowParentheses);
+		if (allowParentheses)
+		{
+			StripCurrencySymbolOutsideParentheses(ref s, style, currencySymbol, ref hasCurrencySymbol, ref hasOuterLeadingCurrencySymbol);
+		}
+
+		bool hasParentheses = allowParentheses && IsEnclosedInParentheses(s);
 		if (hasParentheses)
 		{
 			s = s[1..^1];
@@ -1517,13 +1527,12 @@
 			}
 		}
 
-		ReadOnlySpan<char> currencySymbol = style.HasFlag(NumberStyles.AllowCurrencySymbol) ? numberFormat.CurrencySymbol : [];
 		bool hasSign = false;
 		isNegative = false;
-		bool hasCurrencySymbol = false;
+		bool hadCurrencySymbol = hasCurrencySymbol;
 
 		StripLeadingAffixes(ref s, style, numberFormat, currencySymbol, ref hasSign, ref isNegative, ref hasCurrencySymbol);
-		hasLeadingCurrencySymbol = hasCurrencySymbol;
+		hasLeadingCurrencySymbol = hasOuterLeadingCurrencySymbol || (hasCurrencySymbol && !hadCurrencySymbol);
 		StripTrailingAffixes(ref s, style, numberFormat, currencySymbol, ref hasSign, ref isNegative, ref hasCurrencySymbol);
 
 		if (hasParentheses)
@@ -1539,6 +1548,47 @@
 		return s;
 	}
 
+	/// <summary>
+	/// Removes a currency symbol written outside the parentheses, as in <c>$(45)</c>, <c>$ (45)</c> and
+	/// <c>(45)$</c>, for <see cref="StripAffixes"/>, along with the spaces it may have beside it.
+	/// </summary>
+	/// <remarks>
+	/// The BCL takes the symbol either inside or outside the parentheses. It is removed only when what
+	/// is left is wholly enclosed in them, and it counts as the one symbol a number may have, so
+	/// <c>$($45)</c> and <c>$(45)$</c> still fail.
+	/// </remarks>
+	private static void StripCurrencySymbolOutsideParentheses(ref ReadOnlySpan<char> s, NumberStyles style, ReadOnlySpan<char> currencySymbol, ref bool hasCurrencySymbol, ref bool isLeading)
+	{
+		if (currencySymbol.IsEmpty)
+		{
+			return;
+		}
+
+		if (s.StartsWith(currencySymbol, StringComparison.Ordinal))
+		{
+			ReadOnlySpan<char> rest = s[currencySymbol.Length..].TrimStart(SpacesBesideCurrencySymbol(style.HasFlag(NumberStyles.AllowLeadingWhite)));
+			if (IsEnclosedInParentheses(rest))
+			{
+				hasCurrencySymbol = true;
+				isLeading = true;
+				s = rest;
+				return;
+			}
+		}
+
+		if (s.EndsWith(currencySymbol, StringComparison.Ordinal))
+		{
+			ReadOnlySpan<char> rest = s[..^currencySymbol.Length].TrimEnd(SpacesBesideCurrencySymbol(style.HasFlag(NumberStyles.AllowTrailingWhite)));
+			if (IsEnclosedInParentheses(rest))
+			{
+				hasCurrencySymbol = true;
+				s = rest;
+			}
+		}
+	}
+
+	private static bool IsEnclosedInParentheses(ReadOnlySpan<char> s) => s.Length >= 2 && s[0] == '(' && s[^1] == ')';
+
 	/// <summary>
 	/// Removes a leading sign and a leading currency symbol, in either order, for <see cref="StripAffixes"/>.
 	/// </summary>