clangd with coc: where to put the "FastCheckFilter" option?

Question

I am using clangd and clang-tidy with coc in neovim. I just upgraded my clang and now I'm getting warnings for my config.yaml

Diagnostics:
  ClangTidy:
    Add: [
      # ...
    ]
    Remove: [
      # ...
      cert-msc24-c, # alias for bugprone-unsafe-functions
#     ~~~~~~~~~~~~
#     ^ Latency of clang-tidy check 'cert-msc24-c' is not known. It will only run if ClangTidy.FastCheckFilter is Loose or None (clangd-config)
      # ...
    ]
    CheckOptions:
      modernize-use-auto.MinTypeNameLength: 10
      # ...

However I can't figure out where to put this ClangTidy.FastCheckFilter option.

When I put it in CheckOptions, I get no feedback, the warnings don't go away:

Diagnostics:
  ClangTidy:
    Add: [
      # ...
    ]
    Remove: [
      # ...
    ]
    CheckOptions:
      ClangTidy.FastCheckFilter: None
      modernize-use-auto.MinTypeNameLength: 10
      # ...

When I put it in the root, I get a warning

Unknown Config key 'ClangTidy' (clangd-config)

ClangTidy:
  FastCheckFilter: None

Diagnostics:
  # ...

And when I place it into Diagnostics/ClangTidy, I get an error

Property FastCheckFilter is not allowed. (yaml-schema: clangtidy options)

Diagnostics:
  ClangTidy:
    FastCheckFilter: None
    # ...

In no case do the warnings for

Latency of clang-tidy check 'cert-msc24-c' is not known. It will only run if ClangTidy.FastCheckFilter is Loose or None (clangd-config)

and others go away.

I tried finding how to use FastCheckFilter by searching for the term, but google shows only a single hit for a doxygen comment for a struct in clang, which also doesn't tell me how to use it.

The configuration documentation also doesn't list that option.

Edit

I looked at the source code and found this snippet

    /// Controls how clang-tidy will run over the code base.
    ///
    /// The settings are merged with any settings found in .clang-tidy
    /// configuration files with these ones taking precedence.
    struct ClangTidyBlock {
      std::vector<Located<std::string>> Add;
      /// List of checks to disable.
      /// Takes precedence over Add. To enable all llvm checks except include
      /// order:
      ///   Add: llvm-*
      ///   Remove: llvm-include-order
      std::vector<Located<std::string>> Remove;
 
      /// A Key-Value pair list of options to pass to clang-tidy checks
      /// These take precedence over options specified in clang-tidy
      /// configuration files. Example:
      ///   CheckOptions:
      ///     readability-braces-around-statements.ShortStatementLines: 2
      std::vector<std::pair<Located<std::string>, Located<std::string>>>
          CheckOptions;
 
      /// Whether to run checks that may slow down clangd.
      ///   Strict: Run only checks measured to be fast. (Default)
      ///           This excludes recently-added checks we have not timed yet.
      ///   Loose: Run checks unless they are known to be slow.
      ///   None: Run checks regardless of their speed.
      std::optional<Located<std::string>> FastCheckFilter;
    };

It seems that the placement in

Diagnostics:
  ClangTidy:
    FastCheckFilter: None
    # ...

is the correct one. I guess my coc-yaml plugin doesn't know about the new fields. I also added the new InlayHints.BlockEnd field, which it doesn't like. But that one actually works.

But I still get the warnings from the clangd-config linter for the unknown speed.

Answer 1

The warning "Latency of clang-tidy check ... is not known." was added to the repo on 2023-10-20 as part of work on Issue 1337. As of 2023-11-07, the most recent released version is Clang+LLVM-17.0.4, which does not have this change in it. Thus, I think you must be using an unreleased version.

Based on how the change was made in clangd/ConfigFragment.h, the FastCheckFilter key is supposed to be a child of ClangTidy, itself a child of Diagnostics. However, the associated YAML schema has evidently not been updated (in another project; see HighCommander4's answer), so the key is rejected when in its proper place. At this moment, there is only one test of this feature (unittests/ReplayPreambleTests.cpp), and it bypasses YAML parsing. So, as far as I can tell, the warning cannot be suppressed in the bleeding-edge version.

I don't see any already-filed issues on this topic, so you could file one.

Answer 2

To add to Scott's answer:

• I can confirm that the correct placement of the option is

  Diagnostics:
    ClangTidy:
      FastCheckFilter: None
  

  The error that you got in this case ("Property FastCheckFilter is not allowed. (yaml-schema: clangtidy options)") is not from clangd, but from another plugin which is using a schema for clangd config files hosted on a third-party site (https://json.schemastore.org/clangd.json) which can sometimes lag behind the latest changes in clangd.
• The option, when placed correctly, should have the effect of allowing the "slow" checks to run (if they're otherwise enabled in .clang-tidy or .clangd).
  • Not suppressing the "Latency of clang-tidy check..." warning seems like a likely oversight, please do file an issue for this.

Lastly, please keep in mind that this option is newly added in clangd trunk, set to appear in the next release (clangd 18). As pre-release software, some rough edges, missing documentation, etc. are to be expected :)