Cross-reference silently ignored

[djee-ms]

Operation System: Windows

DocFX Version Used: 2.51.0 (NuGet)

Template used: default

Steps to Reproduce:

1. Unzip the attached minimal repro : docfx-bug.zip
2. Run docfx with docfx.exe --intermediateFolder .\obj -o .\build --serve --debug
3. Observe the warning Invalid cref value "!:A.B.BaseClass.Field" found in triple-slash-comments for OtherClass, ignored
4. Open http://localhost:8080/api/A.B.C.html and observe the "See: ." missing the reference to A.B.BaseClass.Field.

So far so good, even though I am not sure why cref doesn't work here. Anyway, on to the actual bug:

5. Change other.cs and replace cref with xref
6. Run docfx again (same args)
7. Observe no warning
8. Open http://localhost:8080/api/A.B.C.html and observe again the "See: ." missing the reference to A.B.BaseClass.Field.

Expected Behavior:

• Either a warning about an invalid reference (although I don't see why... but I am not an xref expert)
• Or actually the cross-reference generating a text with a link (hyperlink)

Actual Behavior:

Cross-reference XML tag is copied as-is to the output, and not rendered by the browser which cannot understand e.g. <see> tags.

[djee-ms]

Ping -- this is breaking a large amount of the documentation of our project since we have some Unity library in a sub-namespace of a lower-level C# library, with the former doing frequent references to types in the latter. We are planning a release of this project soon, and this is a blocker with documentation broken that way. Can someone please triage this issue and validate whether we are doing something stupid or there is an actual bug?

[superyyrrzz]

This seems to be mixture use of 2 syntaxes:

1. XML comments <see>: <see cref="xxx"/>. We can replace cref with href to reference an URL here, but xref is not supported.

2. DFM (DocFX flavored Markdown) xref: <xref:xxx> is one of the supported form.

So DocFX recognizes <see xref="xxx"/> neither a valid <see> nor a valid xref, then silently passes it to output. Useing cref instead should fix this.

But I agree DocFX can improve validation: if an unknown attribute other than cref/href is found within <see>, warn it.

[djee-ms]

Hi @superyyrrzz, thanks for the quick reply! I was under the impression <see> was supporting xref too, I guess I was wrong. I will try to replace the references with the DFM <xref:> syntax, that should work.

One question though, why is <see cref="A.B.BaseClass.MyType"/> not working inside the A.B.C namespace? Is it because A.B.BaseClass is parsed in the context of a .csproj but A.B.C is parsed in the context of a standalone file not part of this .csproj? Shouldn't those be merged under a same "cref umbrella" when parsing them all as a single docfx invocation? I would think xref is only for types from external third-party assemblies, like the System types etc. And even for that, looking at the docs you linked for XML comments <see> their example uses <see cref="System.Console.WriteLine(System.String)"/> which is clearly not meant to be part of the same assembly than the TestClass of the example.

[superyyrrzz]

I think standalone file can be a cause. Roslyn may not be able to find the referenced type in cref when parsing it. Resolving from csproj seems to work.

However, xref is resolved in a later phase. All UIDs within one docfx.json are taken under the same scope, so it can resolve properly.

[djee-ms]

Yes I looked around in SO & co. and it seems people have the same issue and are working around with either of:

• Create a fake .csproj just for docfx; we are using Unity so we don't have an actual project shipped, it's generated locally by Unity on each user's machine. This has the added benefit of solving the annoying cs.temp.dll.dll assembly name in the documentation to whatever name we want.

• Have Unity generate the .csproj, which unfortunately is only supported via GUI (so nor working on CI), although there seems to be one unofficial unsupported way to access internal APIs via reflection to force project generation by code. I am not too keen on using internal APIs like that though.

I prefer the former but we have only 2-3 assemblies; other projects like microsoft/MixedRealityToolkit-Unity have 20+, and manually maintaining fake .csproj doesn't seem like a good option for them.

[KalleOlaviNiemitalo]

<xref:id_of_another_file> in Markdown is a URI autolink with xref as the URI scheme. Does <see href="xref:id_of_another_file">content override</see> likewise work in XML documentation comments?

manually maintaining fake .csproj doesn't seem like a good option

If you use MSBuild wildcards in the fake .csproj, you won't have to edit it when you add or remove source files.

<ItemGroup>
  <Compile Include="**\*.cs" />
</ItemGroup>

Perhaps this will need to exclude AssemblyInfo.cs, to avoid compiler errors when AssemblyInfo.cs files intended for different assemblies add the same attributes.

[djee-ms]

Good catch, might give it a try, thanks @KalleOlaviNiemitalo!

[djee-ms]

I actually made a few discoveries:

• The <xref:System.String> (from @superyyrrzz's point 2. above and docs) and <xref:System.String/> syntax both fail with Badly formed XML comment ignored error. I literally copied the example from the docs linked in the Shorthand form section.
• The [some desc](xref:xxx) syntax does work, although it's not ideal (DocFX-specific, need to type the name twice)
• The --cleanupCacheHistory argument doesn't seem to work, at least how I expect it, as running docfx docfx.json --intermediateFolder build -o output --serve --cleanupCacheHistory --debugOutput --debug a second time reuses the metadata caches, and therefore makes warnings disappear in the console, which is quite error-prone when trying to debug (only the first run will show the warnings above)
• Adding some <see cref="System.String"/> inside the base.cs file, that is the one which is included via a C# project (base.csproj) and not as a standalone file, does produce some warning Invalid cref value "!:System.String". Note that the class has 2 fields, one with string and one with System.String, and does a using System;. Just run the attached docs/repro.bat from within the docs folder : docfx-bug-invalid-cref.zip. Conversely, adding <see cref="System.String"/> inside the standalone file other.cs does work, and docfx resolves the reference and links to the dotnet docs as expected.

[djee-ms]

Also note : I checked, and currently microsoft/MixedRealityToolkit-Unity is using the syntax [some link](xref:System.String) in their XML comments inside .cs files (I am not interested about markdown files, everything works as expected with them). They seem to have just a few links like that.

[KalleOlaviNiemitalo]

Re docfx-bug-invalid-cref.zip, if I replace <TargetFramework>netstandard2.0</TargetFramework> with <TargetFramework>net4.8</TargetFramework>, then DocFX 2.45.1.0 with Visual Studio 15.9.21 and .NET Core SDK 2.1.513 can extract the metadata just fine.

Does DocFX support getting a MSBuild diagnostic log from the metadata extraction, to see which targets it calls and which items it defines?

Perhaps you can work around the bug by running the MSBuild and C# compiler first, and then only giving the DLL and XML files to DocFX.