Number Python and JavaScript enum members on from the previous value

Coder.Test/Ast/TypeDeclarationTests.cs

@@ -111,13 +111,58 @@ public void Enum_IsSpelledByEachLanguage()
 			StringComparison.Ordinal);
 		Assert.Contains("Dynamic = 7,", new CppGenerator().Generate(kind), StringComparison.Ordinal);
 
-		// Python and JavaScript have no enumeration, so a member with no value of its own is numbered
-		// from its position rather than left to a keyword that does not exist.
+		// Python and JavaScript have no enumeration, so a member with no value of its own is given one
+		// rather than left to a keyword that does not exist.
 		Assert.Contains("Static = 0", new PythonGenerator().Generate(kind), StringComparison.Ordinal);
 		Assert.Contains("Static: 0,", new JavaScriptGenerator().Generate(kind), StringComparison.Ordinal);
 		Assert.Contains("Object.freeze({", new JavaScriptGenerator().Generate(kind), StringComparison.Ordinal);
 	}
 
+	/// <summary>
+	/// A member with no value of its own follows the one before it, as every language with real
+	/// enumerations numbers it, rather than taking its position — which would disagree with those
+	/// languages and could repeat an earlier member's value.
+	/// </summary>
+	[TestMethod]
+	public void Enum_NumbersAMemberAfterAnExplicitValueFromThatValue()
+	{
+		EnumDeclaration colour = new("Colour");
+		colour.Members.Add(new EnumMember("Red"));
+		colour.Members.Add(new EnumMember("Green") { Value = "5" });
+		colour.Members.Add(new EnumMember("Blue"));
+
+		string python = new PythonGenerator().Generate(colour);
+		Assert.Contains("Red = 0", python, StringComparison.Ordinal);
+		Assert.Contains("Green = 5", python, StringComparison.Ordinal);
+		Assert.Contains("Blue = 6", python, StringComparison.Ordinal);
+
+		string javaScript = new JavaScriptGenerator().Generate(colour);
+		Assert.Contains("Red: 0,", javaScript, StringComparison.Ordinal);
+		Assert.Contains("Green: 5,", javaScript, StringComparison.Ordinal);
+		Assert.Contains("Blue: 6,", javaScript, StringComparison.Ordinal);
+	}
+
+	/// <summary>
+	/// A member following a value that is not a plain number counts on from that value's expression,
+	/// since the generator cannot work out what it comes to.
+	/// </summary>
+	[TestMethod]
+	public void Enum_CountsOnFromAnExplicitValueThatIsNotANumber()
+	{
+		EnumDeclaration flags = new("Flags");
+		flags.Members.Add(new EnumMember("High") { Value = "1 << 4" });
+		flags.Members.Add(new EnumMember("Next"));
+		flags.Members.Add(new EnumMember("After"));
+
+		string python = new PythonGenerator().Generate(flags);
+		Assert.Contains("Next = (1 << 4) + 1", python, StringComparison.Ordinal);
+		Assert.Contains("After = (1 << 4) + 2", python, StringComparison.Ordinal);
+
+		string javaScript = new JavaScriptGenerator().Generate(flags);
+		Assert.Contains("Next: (1 << 4) + 1,", javaScript, StringComparison.Ordinal);
+		Assert.Contains("After: (1 << 4) + 2,", javaScript, StringComparison.Ordinal);
+	}
+
 	/// <summary>
 	/// A class body is not a block, so the namespace-scope spelling of an enumeration cannot simply
 	/// be nested inside one.

Coder/Languages/JavaScriptGenerator.cs

@@ -3,7 +3,6 @@
 namespace ktsu.Coder.Languages;
 
 using System.Collections.ObjectModel;
-using System.Globalization;
 using System.Linq;
 using ktsu.Coder.Ast;
 using ktsu.CodeBlocker;
@@ -137,10 +136,8 @@ private void GenerateNestedEnum(EnumDeclaration enumDecl, CodeBlocker code)
 	/// <param name="code">The writer to emit into.</param>
 	private static void WriteEnumMembers(EnumDeclaration enumDecl, CodeBlocker code)
 	{
-		for (int index = 0; index < enumDecl.Members.Count; index++)
+		foreach ((EnumMember member, string value) in enumDecl.Members.Zip(EnumMemberValues(enumDecl)))
 		{
-			EnumMember member = enumDecl.Members[index];
-			string value = member.Value ?? index.ToString(CultureInfo.InvariantCulture);
 			code.WriteLine($"{member.Name ?? "UNNAMED"}: {value},");
 		}
 	}

Coder/Languages/LanguageGeneratorBase.cs

@@ -792,4 +792,44 @@
 	/// <exception cref="NotSupportedException">The operator has no mapping.</exception>
 	/// <remarks>Every language the generators target spells these identically.</remarks>
 	protected static string GetAssignmentOperator(AssignmentOperator op) => OperatorSymbols.GetSymbol(op);
+
+	/// <summary>
+	/// Gives the value each member of an enumeration stands for, for a language that has to write
+	/// every one out.
+	/// </summary>
+	/// <param name="enumDecl">The declaration whose members to number.</param>
+	/// <returns>One value per member, in order.</returns>
+	/// <remarks>
+	/// A member with no value of its own is one more than the member before it, which is what every
+	/// language with real enumerations gives it; numbering it from its position instead would disagree
+	/// with those languages once any member has a value, and could repeat one. When the value being
+	/// counted on from is not a plain integer, it is counted on from as an expression, since the
+	/// generator cannot work out what it comes to.
+	/// </remarks>
+	protected static IEnumerable<string> EnumMemberValues(EnumDeclaration enumDecl)
+	{
+		Ensure.NotNull(enumDecl);
+
+		string? origin = null;
+		long offset = 0;
+
+		foreach (EnumMember member in enumDecl.Members)
+		{
+			if (member.Value is not null)
+			{
+				bool isNumber = long.TryParse(member.Value, NumberStyles.AllowLeadingSign, CultureInfo.InvariantCulture, out long number);
+				origin = isNumber ? null : member.Value;
+				offset = isNumber ? number : 0;
+				yield return member.Value;
+			}
+			else
+			{
+				yield return origin is null
+					? offset.ToString(CultureInfo.InvariantCulture)
+					: $"({origin}) + {offset.ToString(CultureInfo.InvariantCulture)}";
+			}
+
+			offset++;
+		}
+	}
 }

Coder/Languages/PythonGenerator.cs

@@ -3,7 +3,6 @@
 namespace ktsu.Coder.Languages;
 
 using System.Collections.ObjectModel;
-using System.Globalization;
 using System.Linq;
 using ktsu.Coder.Ast;
 using ktsu.CodeBlocker;
@@ -277,8 +276,8 @@ private void WriteArguments(ConstructionExpression construction, CodeBlocker cod
 	/// <inheritdoc/>
 	/// <remarks>
 	/// Python has no enumeration syntax; <c>enum.Enum</c> is a class. A member with no value of its
-	/// own is numbered from its position, matching what a language with real enumerations would give
-	/// it. The <c>from enum import Enum</c> this needs belongs to the file rather than to the
+	/// own is one more than the member before it, matching what a language with real enumerations
+	/// would give it; see <see cref="LanguageGeneratorBase.EnumMemberValues"/>. The <c>from enum import Enum</c> this needs belongs to the file rather than to the
 	/// declaration.
 	/// </remarks>
 	protected override void GenerateEnumDeclaration(EnumDeclaration enumDecl, CodeBlocker code)
@@ -296,10 +295,8 @@ protected override void GenerateEnumDeclaration(EnumDeclaration enumDecl, CodeBl
 			return;
 		}
 
-		for (int index = 0; index < enumDecl.Members.Count; index++)
+		foreach ((EnumMember member, string value) in enumDecl.Members.Zip(EnumMemberValues(enumDecl)))
 		{
-			EnumMember member = enumDecl.Members[index];
-			string value = member.Value ?? index.ToString(CultureInfo.InvariantCulture);
 			code.WriteLine($"{member.Name ?? "UNNAMED"} = {value}");
 		}
 	}