chore: drop Docfx.MarkdigEngine.Validators

[yufeih]

The IMarkdownObjectValidator was originally designed as an extension mechanism for adding custom markdown validation rules for MSLearn. MSLearn never really used that interface for custom markdown validation and this interface didn't gain much traction in the community.

To add custom markdown validation rules, or custom markdown extensions, use the standard markdig extensions interface, where it exposed the markdown AST at various stages.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.09 ⚠️

Comparison is base (7ab1ad6) 76.93% compared to head (f74d3eb) 76.85%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8971      +/-   ##
==========================================
- Coverage   76.93%   76.85%   -0.09%     
==========================================
  Files         605      601       -4     
  Lines       25054    24968      -86     
==========================================
- Hits        19275    19188      -87     
- Misses       5779     5780       +1     

Impacted Files	Coverage Δ
src/Docfx.Build.Engine/DocumentBuilder.cs	79.19% <ø> (-0.24%)	⬇️
src/Docfx.Plugins/MarkdownTagValidationRule.cs	100.00% <ø> (+14.28%)	⬆️
src/Docfx.MarkdigEngine/MarkdigMarkdownService.cs	87.23% <100.00%> (-0.14%)	⬇️
src/Docfx.MarkdigEngine/MarkdigServiceProvider.cs	100.00% <100.00%> (ø)
...rkdigEngine/Validation/MarkdownValidatorBuilder.cs	89.58% <100.00%> (-0.42%)	⬇️
src/Docfx.MarkdigEngine/Validation/TagValidator.cs	96.29% <100.00%> (+0.64%)	⬆️

... and 4 files with indirect coverage changes

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[filzrev]

To add custom markdown validation rules, or custom markdown extensions, use the standard markdig extensions interface, where it exposed the markdown AST at various stages.

For custom Markdown validation rules.
Docfx seems supporting custom validation by placing md.style file to docs root or template directory's md.styles folder.

docfx/src/Docfx.MarkdigEngine/Validation/MarkdownValidatorBuilder.cs

Lines 165 to 190 in 7ab1ad6

	private static void LoadValidatorConfig(string baseDir, string templateDir, MarkdownValidatorBuilder builder)
	{
	if (string.IsNullOrEmpty(baseDir))
	{
	return;
	}
	if (templateDir != null)
	{
	var configFolder = Path.Combine(templateDir, MarkdownStyleDefinition.MarkdownStyleDefinitionFolderName);
	if (Directory.Exists(configFolder))
	{
	LoadValidatorDefinition(configFolder, builder);
	}
	}
	var configFile = Path.Combine(baseDir, MarkdownStyleConfig.MarkdownStyleFileName);
	if (EnvironmentContext.FileAbstractLayer.Exists(configFile))
	{
	var config = JsonUtility.Deserialize<MarkdownStyleConfig>(configFile);
	builder.AddValidators(config.Rules);
	builder.AddTagValidators(config.TagRules);
	builder.AddSettings(config.Settings);
	}
	builder.EnsureDefaultValidator();
	}

sample of md.style usage in tests

docfx/test/Docfx.Build.Engine.Tests/DocumentBuilderTest.cs

Lines 400 to 442 in 7ab1ad6

	File.WriteAllText(MarkdownStyleConfig.MarkdownStyleFileName, @"{
	settings : [
	{ category: ""div"", disable: true},
	{ category: ""p"", id: ""p-3"", disable: true}
	],
	}");
	CreateFile(
	MarkdownStyleDefinition.MarkdownStyleDefinitionFolderName + "/p" + MarkdownStyleDefinition.MarkdownStyleDefinitionFilePostfix,
	@"{
	tagRules : {
	""p-1"": {
	tagNames: [""p""],
	behavior: ""Warning"",
	messageFormatter: ""Tag {0} is not valid."",
	openingTagOnly: true
	},
	""p-2"": {
	tagNames: [""p""],
	behavior: ""Warning"",
	messageFormatter: ""Tag {0} is not valid."",
	openingTagOnly: false,
	disable: true
	},
	""p-3"": {
	tagNames: [""p""],
	behavior: ""Warning"",
	messageFormatter: ""Tag {0} is not valid."",
	openingTagOnly: false,
	}
	}
	}
	", _templateFolder);
	CreateFile(
	MarkdownStyleDefinition.MarkdownStyleDefinitionFolderName + "/div" + MarkdownStyleDefinition.MarkdownStyleDefinitionFilePostfix,
	@"{
	tagRules : {
	""div-1"": {
	tagNames: [""div""],
	behavior: ""Warning"",
	messageFormatter: ""Tag {0} is not valid."",
	openingTagOnly: true
	}
	}

This features is not documented. and It seems not be used by any public repository and custom templates.
Is this feature support is continued?
(or is it better to use some standard tools like markdownlint?)

[yufeih]

You are right, the md.style file was introduced a long time ago and wasn't documented. It does seem to have low usage and I agree that standard tools like markdown lint is a better alternative. We could drop it as a separate PR.