Refuse a line break in a doc comment cref or name before writing [patch]

CodeBlocker.Test/DocCommentTests.cs

@@ -287,6 +287,39 @@ public void ATemplateWritesItsDocumentationAboveItsAttributes()
 			Render(method.WriteTo));
 	}
 
+	[TestMethod]
+	[DataRow("\n", DisplayName = "LF")]
+	[DataRow("\r\n", DisplayName = "CRLF")]
+	[DataRow("\r", DisplayName = "CR")]
+	[DataRow("\u0085", DisplayName = "NEL")]
+	[DataRow("\u2028", DisplayName = "LINE SEPARATOR")]
+	[DataRow("\u2029", DisplayName = "PARAGRAPH SEPARATOR")]
+	public void ALineBreakInAnAttributeValueIsRejectedBeforeWriting(string terminator)
+	{
+		string value = $"A{terminator}B";
+		DocComment[] comments =
+		[
+			new() { Summary = "s", SeeAlso = { value } },
+			new() { Summary = "s", InheritDoc = true, InheritDocCref = value },
+			new() { Summary = "s", Params = { new DocTag { Name = value, Text = "t" } } },
+			new() { Summary = "s", TypeParams = { new DocTag { Name = value, Text = "t" } } },
+			new() { Summary = "s", Exceptions = { new DocTag { Name = value, Text = "t" } } },
+		];
+
+		foreach (DocComment documentation in comments)
+		{
+			using CodeBlocker codeBlocker = CodeBlocker.Create(CodeBlocker.DefaultIndentString, NewLines.Lf);
+			Assert.ThrowsExactly<ArgumentException>(() => documentation.WriteTo(codeBlocker));
+			Assert.AreEqual(string.Empty, codeBlocker.ToString(), "Nothing should be written before the check.");
+		}
+	}
+
+	[TestMethod]
+	public void AnUnusedInheritDocCrefIsNotChecked() =>
+		Assert.AreEqual(
+			"/// <summary>s</summary>\n",
+			Render(new DocComment { Summary = "s", InheritDocCref = "A\nB" }));
+
 	[TestMethod]
 	public void NullCodeBlockerIsRejected() =>
 		Assert.ThrowsExactly<ArgumentNullException>(() => new DocComment().WriteTo(null!));

CodeBlocker/Templates/DocComment.cs

@@ -97,10 +97,19 @@ public class DocComment
 	/// </summary>
 	/// <param name="codeBlocker">The <see cref="CodeBlocker"/> to write to.</param>
 	/// <exception cref="ArgumentNullException"><paramref name="codeBlocker"/> is <see langword="null"/>.</exception>
+	/// <exception cref="ArgumentException">
+	/// <see cref="InheritDocCref"/>, a <see cref="SeeAlso"/> entry, or the <see cref="DocTag.Name"/> of
+	/// a <see cref="TypeParams"/>, <see cref="Params"/> or <see cref="Exceptions"/> entry contains a
+	/// line break. Nothing is written.
+	/// </exception>
 	public void WriteTo(CodeBlocker codeBlocker)
 	{
 		Ensure.NotNull(codeBlocker);
 
+		// Checked before the first line is written: a cref or name cannot be split across /// lines
+		// the way element text is, and left as it is the rest of it would be compiled as code.
+		EnsureAttributesFitOnOneLine();
+
 		if (InheritDoc)
 		{
 			codeBlocker.WriteLine(string.IsNullOrEmpty(InheritDocCref)
@@ -181,6 +190,39 @@ void Check(Collection<DocTag> tags, HashSet<string> declared, string tagName, st
 		}
 	}
 
+	private void EnsureAttributesFitOnOneLine()
+	{
+		if (InheritDoc)
+		{
+			EnsureSingleLine(InheritDocCref, "inheritdoc cref", nameof(InheritDocCref));
+		}
+
+		EnsureNamesSingleLine(TypeParams, "typeparam name", nameof(TypeParams));
+		EnsureNamesSingleLine(Params, "param name", nameof(Params));
+		EnsureNamesSingleLine(Exceptions, "exception cref", nameof(Exceptions));
+
+		foreach (string cref in SeeAlso)
+		{
+			EnsureSingleLine(cref, "seealso cref", nameof(SeeAlso));
+		}
+
+		static void EnsureNamesSingleLine(Collection<DocTag> tags, string what, string paramName)
+		{
+			foreach (DocTag tag in tags)
+			{
+				EnsureSingleLine(tag.Name, what, paramName);
+			}
+		}
+
+		static void EnsureSingleLine(string? value, string what, string paramName)
+		{
+			if (value is not null && LineTerminators.Contains(value))
+			{
+				throw new ArgumentException($"A doc comment {what} must fit on one /// line.", paramName);
+			}
+		}
+	}
+
 	private void WriteElement(CodeBlocker codeBlocker, string tagName, string? attributes, string? text)
 	{
 		if (string.IsNullOrEmpty(text))