Ensure uncaught yaml parsing errors are recoverable

src/Elastic.Markdown/Diagnostics/DiagnosticsChannel.cs

@@ -141,13 +141,16 @@ public virtual async Task StopAsync(CancellationToken cancellationToken)
 	}
 
 
-	public void EmitError(string file, string message)
+	public void EmitError(string file, string message, Exception? e = null)
 	{
 		var d = new Diagnostic
 		{
 			Severity = Severity.Error,
 			File = file,
-			Message = message,
+			Message = message
+					  + (e != null ? Environment.NewLine + e : string.Empty)
+					  + (e?.InnerException != null ? Environment.NewLine + e.InnerException : string.Empty),
+
 		};
 		Channel.Write(d);
 	}

src/Elastic.Markdown/IO/ConfigurationFile.cs

@@ -23,11 +23,7 @@ public record ConfigurationFile : DocumentationFile
 	public HashSet<string> Files { get; } = new(StringComparer.OrdinalIgnoreCase);
 	public HashSet<string> ImplicitFolders { get; } = new(StringComparer.OrdinalIgnoreCase);
 	public Glob[] Globs { get; } = [];
-	public HashSet<string> ExternalLinkHosts { get; } = new(StringComparer.OrdinalIgnoreCase)
-	{
-		"elastic.co",
-		"github.com",
-	};
+	public HashSet<string> ExternalLinkHosts { get; } = new(StringComparer.OrdinalIgnoreCase) { "elastic.co", "github.com", };
 
 	private readonly Dictionary<string, string> _substitutions = new(StringComparer.OrdinalIgnoreCase);
 	public IReadOnlyDictionary<string, string> Substitutions => _substitutions;
@@ -57,41 +53,49 @@ public ConfigurationFile(IFileInfo sourceFile, IDirectoryInfo rootPath, BuildCon
 			return;
 		}
 
-		// Examine the stream
-		var mapping = (YamlMappingNode)yaml.Documents[0].RootNode;
-
-		foreach (var entry in mapping.Children)
+		try
 		{
-			var key = ((YamlScalarNode)entry.Key).Value;
-			switch (key)
-			{
-				case "project":
-					Project = ReadString(entry);
-					break;
-				case "exclude":
-					Exclude = ReadStringArray(entry)
-						.Select(Glob.Parse)
-						.ToArray();
-					break;
-				case "subs":
-					_substitutions = ReadDictionary(entry);
-					break;
-				case "external_hosts":
-					var hosts = ReadStringArray(entry)
-						.ToArray();
-					foreach (var host in hosts)
-						ExternalLinkHosts.Add(host);
-					break;
-				case "toc":
-					var entries = ReadChildren(entry, string.Empty);
+			// Examine the stream
+			var mapping = (YamlMappingNode)yaml.Documents[0].RootNode;
 
-					TableOfContents = entries;
-					break;
-				default:
-					EmitWarning($"{key} is not a known configuration", entry.Key);
-					break;
+			foreach (var entry in mapping.Children)
+			{
+				var key = ((YamlScalarNode)entry.Key).Value;
+				switch (key)
+				{
+					case "project":
+						Project = ReadString(entry);
+						break;
+					case "exclude":
+						Exclude = ReadStringArray(entry)
+							.Select(Glob.Parse)
+							.ToArray();
+						break;
+					case "subs":
+						_substitutions = ReadDictionary(entry);
+						break;
+					case "external_hosts":
+						var hosts = ReadStringArray(entry)
+							.ToArray();
+						foreach (var host in hosts)
+							ExternalLinkHosts.Add(host);
+						break;
+					case "toc":
+						var entries = ReadChildren(entry, string.Empty);
+
+						TableOfContents = entries;
+						break;
+					default:
+						EmitWarning($"{key} is not a known configuration", entry.Key);
+						break;
+				}
 			}
 		}
+		catch (Exception e)
+		{
+			EmitError("Could not load docset.yml", e);
+		}
+
 		Globs = ImplicitFolders.Select(f => Glob.Parse($"{f}/*.md")).ToArray();
 	}
 
@@ -100,8 +104,14 @@ private List<ITocItem> ReadChildren(KeyValuePair<YamlNode, YamlNode> entry, stri
 		var entries = new List<ITocItem>();
 		if (entry.Value is not YamlSequenceNode sequence)
 		{
-			var key = ((YamlScalarNode)entry.Key).Value;
-			EmitWarning($"'{key}' is not an array");
+			if (entry.Key is YamlScalarNode scalarKey)
+			{
+				var key = scalarKey.Value;
+				EmitWarning($"'{key}' is not an array");
+			}
+			else
+				EmitWarning($"'{entry.Key}' is not an array");
+
 			return entries;
 		}
 
@@ -159,10 +169,17 @@ private Dictionary<string, string> ReadDictionary(KeyValuePair<YamlNode, YamlNod
 		var dictionary = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
 		if (entry.Value is not YamlMappingNode mapping)
 		{
-			var key = ((YamlScalarNode)entry.Key).Value;
-			EmitWarning($"'{key}' is not a dictionary");
+			if (entry.Key is YamlScalarNode scalarKey)
+			{
+				var key = scalarKey.Value;
+				EmitWarning($"'{key}' is not a dictionary");
+			}
+			else
+				EmitWarning($"'{entry.Key}' is not a dictionary");
+
 			return dictionary;
 		}
+
 		foreach (var entryValue in mapping.Children)
 		{
 			if (entryValue.Key is not YamlScalarNode scalar || scalar.Value is null)
@@ -172,6 +189,7 @@ private Dictionary<string, string> ReadDictionary(KeyValuePair<YamlNode, YamlNod
 			if (value is not null)
 				dictionary.Add(key, value);
 		}
+
 		return dictionary;
 	}
 
@@ -187,6 +205,7 @@ private Dictionary<string, string> ReadDictionary(KeyValuePair<YamlNode, YamlNod
 			else
 				found = true;
 		}
+
 		return folder;
 	}
 
@@ -212,9 +231,14 @@ private Dictionary<string, string> ReadDictionary(KeyValuePair<YamlNode, YamlNod
 		if (entry.Value is YamlScalarNode scalar)
 			return scalar.Value;
 
-		var key = ((YamlScalarNode)entry.Key).Value;
+		if (entry.Key is YamlScalarNode scalarKey)
+		{
+			var key = scalarKey.Value;
+			EmitError($"'{key}' is not a string", entry.Key);
+			return null;
+		}
 
-		EmitError($"'{key}' is not a string", entry.Key);
+		EmitError($"'{entry.Key}' is not a string", entry.Key);
 		return null;
 	}
 
@@ -239,6 +263,9 @@ private void EmitError(string message, YamlNode? node) =>
 	private void EmitWarning(string message, YamlNode? node) =>
 		EmitWarning(message, node?.Start, node?.End, (node as YamlScalarNode)?.Value?.Length);
 
+	private void EmitError(string message, Exception e) =>
+		_context.Collector.EmitError(_sourceFile.FullName, message, e);
+
 	private void EmitError(string message, Mark? start = null, Mark? end = null, int? length = null)
 	{
 		length ??= start.HasValue && end.HasValue ? (int)start.Value.Column - (int)end.Value.Column : null;
@@ -269,4 +296,3 @@ private void EmitWarning(string message, Mark? start = null, Mark? end = null, i
 		_context.Collector.Channel.Write(d);
 	}
 }
-

src/Elastic.Markdown/IO/MarkdownFile.cs

@@ -23,6 +23,7 @@ public MarkdownFile(IFileInfo sourceFile, IDirectoryInfo rootPath, MarkdownParse
 		: base(sourceFile, rootPath)
 	{
 		FileName = sourceFile.Name;
+		FilePath = sourceFile.FullName;
 		UrlPathPrefix = context.UrlPathPrefix;
 		MarkdownParser = parser;
 		Collector = context.Collector;
@@ -47,6 +48,7 @@ public string? NavigationTitle
 	private readonly HashSet<string> _additionalLabels = new();
 	public IReadOnlySet<string> AdditionalLabels => _additionalLabels;
 
+	public string FilePath { get; }
 	public string FileName { get; }
 	public string Url => $"{UrlPathPrefix}/{RelativePath.Replace(".md", ".html")}";
 
@@ -75,7 +77,7 @@ private void ReadDocumentInstructions(MarkdownDocument document)
 		if (document.FirstOrDefault() is YamlFrontMatterBlock yaml)
 		{
 			var raw = string.Join(Environment.NewLine, yaml.Lines.Lines);
-			YamlFrontMatter = YamlSerialization.Deserialize<YamlFrontMatter>(raw);
+			YamlFrontMatter = ReadYamlFrontMatter(document, raw);
 			Title = YamlFrontMatter.Title;
 			NavigationTitle = YamlFrontMatter.NavigationTitle;
 		}
@@ -110,6 +112,19 @@ private void ReadDocumentInstructions(MarkdownDocument document)
 		_instructionsParsed = true;
 	}
 
+	private YamlFrontMatter ReadYamlFrontMatter(MarkdownDocument document, string raw)
+	{
+		try
+		{
+			return YamlSerialization.Deserialize<YamlFrontMatter>(raw);
+		}
+		catch (Exception e)
+		{
+			Collector.EmitError(FilePath, "Failed to parse yaml front matter block.", e);
+			return new YamlFrontMatter();
+		}
+	}
+
 
 	public string CreateHtml(MarkdownDocument document) =>
 		// var writer = new StringWriter();