Configuration

The configuration mechanism is new in clangd 11, and more options will be exposed in this way in future.

Files

Configuration is stored in YAML files. These are either:

• project configuration: a file named .clangd in the source tree. (clangd searches in all parent directories of the active file).

  Generally this should be used for shared and checked-in settings.

• user configuration: a config.yaml file in an OS-specific directory:

  • Windows: %LocalAppData%\clangd\config.yaml, typically C:\Users\Bob\AppData\Local\clangd\config.yaml.

  • macOS: ~/Library/Preferences/clangd/config.yaml

  • Linux and others: $XDG_CONFIG_HOME/clangd/config.yaml, typically ~/.config/clangd/config.yaml.

  Private settings go here, and can be scoped to projects using If conditions.

Each file can contain multiple fragments separated by --- lines. (This is only useful if the fragments have different If conditions).

JSON is a subset of YAML, so you can use that syntax if you prefer.

Changes should take effect immediately as you continue to edit code. For now, config file errors are reported only in the clangd logs.

Loading and combining fragments

By default, user configuration applies to all files that are opened. Project configuration applies to files under its tree (proj/.clangd configures proj/**).

If conditions can further limit this, e.g. to configure only header files.

Configuration is combined when this is sensible. In case of conflicts, user config has the highest precedence, then inner project, then outer project.

Schema

At the top-level, a fragment is a key-value mapping that divides the document into “blocks” of related options, each of which is a key-value mapping.

In most places where an array of scalar values can be specified, a single value is also acceptable. e.g. Add: -Wall is equivalent to Add: [-Wall].

If

Conditions in the If block restrict when a fragment applies.

If:                               # Apply this config conditionally
  PathMatch: .*\.h                # to all headers...
  PathExclude: include/llvm-c/.*  # except those under include/llvm-c/

Each separate condition must match (combined with AND). When one condition has multiple values, any may match (combined with OR). e.g. PathMatch: [foo/.*, bar/.*] matches files in either directory.

Conditions based on a file’s path use the following form:

• if the fragment came from a project directory, the path is relative
• if the fragment is global (e.g. user config), the path is absolute
• paths always use forward-slashes (UNIX-style)

If no file is being processed, these conditions will not match.

PathMatch

The file being processed must fully match a regular expression.

PathExclude

The file being processed must not fully match a regular expression.

CompileFlags

Affects how a source file is parsed.

CompileFlags:                     # Tweak the parse settings
  Add: [-xc++, -Wall]             # treat all files as C++, enable more warnings
  Remove: -W*                     # strip all other warning-related flags

clangd emulates how clang would interpret a file. By default, it behaves roughly as clang $FILENAME, but real projects usually require setting the include path (with the -I flag), defining preprocessor symbols, configuring warnings etc.

Often, a compilation database specifies these compile commands. clangd searches for compile_commands.json in parents of the source file.

This section modifies how the compile command is constructed.

Add

List of flags to append to the compile command.

Remove

List of flags to remove from the compile command.

• If the value is a recognized clang flag (like -I) then it will be removed along with any arguments. Synonyms like --include-dir= will also be removed.
• Otherwise, if the value ends in * (like -DFOO=*) then any argument with the prefix will be removed.
• Otherwise any argument exactly matching the value is removed.

In all cases, -Xclang is also removed where needed.

Example:

• Command: clang++ --include-directory=/usr/include -DFOO=42 foo.cc
• Configuration: Remove: [-I, -DFOO=*]
• Result: clang++ foo.cc

Flags added by the same CompileFlags entry will not be removed.

Index

Controls how clangd understands code outside the current file.

Index:
  Background: Skip     # Disable slow background indexing of these files.

clangd’s indexes provide information about symbols that isn’t available to clang’s parser, such as incoming references.

Background

Whether files are built in the background to produce a project index. This is checked for translation units only, not headers they include. Legal values are Build (the default) or Skip.

External

Used to define an external index source:

• On-disk monolithic index produced by clangd-indexer or
• Address of a remote-index-server.

MountPoint can be used to specify source root for the index. This is necessary to handle relative path conversions. Overall schema looks like this:

Index:
  External:
    File: /abs/path/to/an/index.idx
    # OR
    Server: my.index.server.com:50051
    MountPoint: /files/under/this/project/

• Exactly one of File or Server needs to be specified.
• MountPoint defaults to location of the config fragment if not provided, must be absolute in global config and relative in local config.
• Declaring an External index disables background-indexing implicitly for files under the MountPoint. Users can turn it back on, by explicitly mentioning Background: Build in a later fragment.

Diagnostics

Suppress

Diagnostic codes that should be suppressed.

Valid values are:

• *, to disable all diagnostics
• diagnostic codes exposed by clangd (e.g unknown_type, -Wunused-result)
• clang internal diagnostic codes (e.g. err_unknown_type)
• warning categories (e.g. unused-result)
• clang-tidy check names (e.g. bugprone-narrowing-conversions)

This is a simple filter. Diagnostics can be controlled in other ways (e.g. by disabling a clang-tidy check, or the -Wunused compile flag). This often has other advantages, such as skipping some analysis.

ClangTidy

Configure how clang-tidy runs over your files.

The settings are merged with any settings found in .clang-tidy configuration files with the ones from clangd configs taking precedence.

Add

List of checks to enable, can be globs.

Remove

List of checks to disable, can be globs.

This takes precedence over Add, this supports enabling all checks from a module apart from some specific checks.

Example to use all modernize module checks apart from use trailing return type:

 ClangTidy:
   Add: modernize*
   Remove: modernize-use-trailing-return-type

CheckOptions

Key-value pairs of options for clang-tidy checks. Available options for all checks can be found here.

Note the format here is slightly different to .clang-tidy configuration files as we don’t specify key: <key>, value: <value>. Instead just use <key>: <value>

ClangTidy:
  CheckOptions:
    readability-identifier-naming.VariableCase: CamelCase