Add auto text link generation for markdown files (#197)

Author: Mpdreamz

docs/source/syntax/applies.md

@@ -48,7 +48,7 @@ applies:
 Are equivalent, note `all` just means we won't be rendering the version portion in the html.
 
 
-## This section has its own applies annotations
+## This section has its own applies annotations [#sections]
 
 :::{applies}
 :stack: unavailable

docs/source/syntax/links.md

@@ -42,6 +42,32 @@ Cross links are links that point to a different docset.
 
 The syntax is `<scheme>://<path>`, where <scheme> is the repository name and <path> is the path to the file.
 
+## Auto Text Links
+
+If you link to a local markdown file but omit any link text `docs-builder` will use the target's [title](titles.md).
+
+```markdown
+[](applies.md)
+```
+will output: [](applies.md)
+
+You can go one step further to auto generate link text for headings within files:
+
+```markdown
+[](applies.md#sections)
+```
+
+will output: [](applies.md#sections)
+
+This also applies to local anchors
+
+
+```markdown
+[](#anchor-link)
+```
+
+will output: [](#anchor-link)
+
 ## Heading anchors
 
 Headings will automatically create anchor links in the resulting html. 

docs/source/testing/index.md

@@ -2,4 +2,7 @@
 title: Testing
 ---
 
-The files in this directory are used for testing purposes. Do not edit these files unless you are working on tests.
+The files in this directory are used for testing purposes. Do not edit these files unless you are working on tests.
+
+
+###### [#synthetics-config-file]

src/Elastic.Markdown/Myst/InlineParsers/DiagnosticLinkInlineParser.cs

@@ -108,9 +108,20 @@ public override bool Match(InlineProcessor processor, ref StringSlice slice)
 
 		if (link.FirstChild == null || !string.IsNullOrEmpty(anchor))
 		{
-			var file = string.IsNullOrWhiteSpace(url) ? context.Path
-				: context.Build.ReadFileSystem.FileInfo.New(Path.Combine(context.Build.SourcePath.FullName, url.TrimStart('/')));
+			var file = string.IsNullOrWhiteSpace(url)
+				? context.Path
+				: url.StartsWith('/')
+					? context.Build.ReadFileSystem.FileInfo.New(Path.Combine(context.Build.SourcePath.FullName, url.TrimStart('/')))
+					: context.Build.ReadFileSystem.FileInfo.New(Path.Combine(context.Path.Directory!.FullName, url));
 			var markdown = context.GetDocumentationFile?.Invoke(file) as MarkdownFile;
+			if (markdown == null)
+			{
+				processor.EmitWarning(line,
+					column,
+					length,
+					$"'{url}' could not be resolved to a markdown file while creating an auto text link, '{file.FullName}' does not exist.");
+			}
+
 			var title = markdown?.Title;
 
 			if (!string.IsNullOrEmpty(anchor))