docs/yaml/functions/custom_target.yaml

name: custom_target
returns: custom_tgt
description: |
  Create a custom top level build target. The only positional argument
  is the name of this target and cannot contain path separators (`/` or `\`).
  The name of custom target might not be used by every backends, for instance with
  the Ninja backend, `subdir/meson.build` containing the example below,
  `ninja -C builddir foo` or `ninja -C builddir subdir/foo` won't work,
  it is instead `ninja -C builddir subdir/file.txt`. However, `meson compile subdir/foo`
  is accepted.
  ```meson
  custom_target('foo', output: 'file.txt', ...)
  ```

  The files passed to `output:` cannot contain path separators. See the 
  [manual on custom build targets](Custom-build-targets.md#details-on-command-invocation) for
  an explanation on where output files should be placed.

  You can install the outputted files with the `install_dir:` kwarg, see below.

  *Since 0.60.0* the name argument is optional and defaults to the basename of the first
  output (`file.txt` in the example above).

  The array of strings passed to the `command` keyword argument accept
  the following special string substitutions:

  - `@INPUT@`: the full path to the input passed to `input`. If more than
    one input is specified, all of them will be substituted as separate
    arguments only if the command uses `'@INPUT@'` as a
    standalone-argument. For instance, this would not work: `command :
    ['cp', './@INPUT@']`, but this would: `command : ['cp', '@INPUT@']`.
  - `@OUTPUT@`: the full path to the output passed to `output`. If more
    than one outputs are specified, the behavior is the same as
    `@INPUT@`.
  - `@INPUT0@` `@INPUT1@` `...`: the full path to the input with the specified array index in `input`
  - `@OUTPUT0@` `@OUTPUT1@` `...`: the full path to the output with the specified array index in `output`
  - `@OUTDIR@`: the full path to the directory where the output(s) must be written
  - `@DEPFILE@`: the full path to the dependency file passed to `depfile`
  - `@PLAINNAME@`: the input filename, without a path
  - `@PLAINNAME0@` `@PLAINNAME1@` `...` *(since 1.5.0)*: the input filename without a path, with the specified array index in `input`
  - `@BASENAME@`: the input filename, with extension removed
  - `@BASENAME0@` `@BASENAME1@` `...` *(since 1.5.0)*: the input filename with extension removed, with the specified array index in `input`
  - `@PRIVATE_DIR@` *(since 0.50.1)*: path to a directory where the custom target must store all its intermediate files.
  - `@SOURCE_ROOT@`: the path to the root of the source tree. Depending on the backend,
    this may be an absolute or a relative to current workdir path.
  - `@BUILD_ROOT@`: the path to the root of the build tree. Depending on the backend,
    this may be an absolute or a relative to current workdir path.
  - `@CURRENT_SOURCE_DIR@`: this is the directory where the currently
    processed meson.build is located in.  Depending on the backend,
    this may be an absolute or a relative to current workdir path.

  *(since 0.47.0)* The `depfile` keyword argument also accepts the
  `@BASENAME@` and `@PLAINNAME@` substitutions.

  The returned object also has methods that are documented in [[@custom_tgt]].

notes:
  - |
    Assuming that `command:` is executed by a POSIX `sh` shell
    is not portable, notably to Windows. Instead, consider using a
    `native: true` [[executable]], or a python script.

warnings:
  - the `install_mode` kwarg ignored integer values between 0.60.0 -- 1.1.0.

optargs:
  name:
    type: str
    description: |
      The *unique* id of the custom target

      This posarg is optional *since 0.60.0*. It defaults to the basename
      of the first output.

kwargs:
  build_by_default:
    type: bool
    since: 0.38.0
    description: |
      Causes, when set to true, to
      have this target be built by default. This means it will be built when
      `meson compile` is called without any arguments. The default value is `false`.

      *(since 0.50.0)* If `build_by_default` is explicitly set to false, `install`
      will no longer override it. If `build_by_default` is not set, `install` will
      still determine its default.

  build_always:
    type: bool
    deprecated: 0.47.0
    description: |
      If `true` this target is always considered out of
      date and is rebuilt every time.  Equivalent to setting both
      `build_always_stale` and `build_by_default` to true.

  build_always_stale:
    type: bool
    since: 0.47.0
    default: false
    description: |
      If `true` the target is always considered out of date.
      Useful for things such as build timestamps or revision control tags.
      The associated command is run even if the outputs are up to date.

  build_subdir:
    type: str
    since: 1.10.0
    description:
      Places the build results in a subdirectory of the given name
      rather than directly into the build directory. This does not
      affect the install directory, which uses install_dir.

      This allows inserting a directory name into the build path,
      either when needed to use the build result while building other
      targets or as a way to support multiple targets with the same
      basename by using unique build_subdir values for each one.

      To prevent collisions within the build directory, build_subdir
      is not allowed to match a file or directory in the source
      directory, nor contain '..' to refer to the parent of the build
      directory.

  capture:
    type: bool
    default: false
    description: |
      There are some compilers that can't be told to write
      their output to a file but instead write it to standard output. When
      this argument is set to true, Meson captures `stdout` and writes it
      to the target file. Note that your command argument array may not
      contain `@OUTPUT@` when capture mode is active.

  console:
    type: bool
    since: 0.48.0
    description: |
      Keyword argument conflicts with `capture`, and is meant
      for commands that are resource-intensive and take a long time to
      finish. With the Ninja backend, setting this will add this target
      to [Ninja's `console` pool](https://ninja-build.org/manual.html#_the_literal_console_literal_pool),
      which has special properties such as not buffering stdout and
      serializing all targets in this pool.

  command:
    type: array[str | file | exe | program]
    description: |
      Command to run to create outputs from inputs. The command
      may be strings or the return value of functions that return file-like
      objects such as [[find_program]],
      [[executable]], [[configure_file]],
      [[files]], [[custom_target]], etc.
      Meson will automatically insert the appropriate dependencies on
      targets and files listed in this keyword argument.
      Note: always specify commands in array form `['commandname',
      '-arg1', '-arg2']` rather than as a string `'commandname -arg1
      -arg2'` as the latter will *not* work.

      *Note:* due to an [issue with path handling](https://github.com/mesonbuild/meson/issues/1564)
      any backslash (`\`) characters are rewritten as slash (`/`).

  depend_files:
    type: array[str | file]
    description: |
      files ([[@str]],
      [[@file]], or the return value of [[configure_file]] that
      this target depends on but are not listed in the `command` keyword
      argument. Useful for adding regen dependencies.

  depends:
    type: array[build_tgt | custom_tgt | custom_idx | program]
    description: |
      Specifies that this target depends on the specified
      target(s), even though it does not take any of them as a command
      line argument. This is meant for cases where you have a tool that
      e.g. does globbing internally. Usually you should just put the
      generated sources as inputs and Meson will set up all dependencies
      automatically (custom_idx was unavailable as a type between 0.60
      and 1.4.0).  `program` is supported *since 1.11.2*.

  depfile:
    type: str
    description: |
      A dependency file that the command can write listing
      all the additional files this target depends on, for example a C
      compiler would list all the header files it included, and a change
      in any one of these files triggers a recompilation.

      *(since 0.47.0)* the `@BASENAME@` and `@PLAINNAME@` substitutions
      are also accepted.

  input:
    type: array[str | file | program]
    description: |
      Array of source files. *(since 0.41.0)* the array is flattened.
      `program` is supported *since 1.11.2*.

  install:
    type: bool
    description: When true, one or more files of this target are installed during
      the install step (see `install_dir` for details).

  install_dir:
    type: str | array[str | bool]
    description: |
      If only one install_dir is provided, all outputs are installed there.
      *Since 0.40.0* Allows you to specify the installation directory for each
      corresponding output. For example:
      ```meson
      custom_target('different-install-dirs',
        output : ['first.file', 'second.file'],
        install : true,
        install_dir : ['somedir', 'otherdir'])
      ```
      This would install `first.file` to `somedir` and `second.file` to `otherdir`.

      To only install some outputs, pass `false` for the outputs that you
      don't want installed. For example:
      ```meson
          custom_target('only-install-second',
            output : ['first.file', 'second.file'],
            install : true,
            install_dir : [false, 'otherdir'])
      ```
      This would install `second.file` to `otherdir` and not install `first.file`.

  install_mode:
    type: array[str | int]
    since: 0.47.0
    description: |
      The file mode and optionally the owner/uid and group/gid.
      See the `install_mode` kwarg of [[install_data]] for more information.

  install_tag:
    type: array[str]
    since: 0.60.0
    description: |
      An array of strings, one per output, used by the `meson install --tags` command
      to install only a subset of the files.

      By default all outputs have no install tag which means they are not being
      installed when `--tags` argument is specified. If only one tag is specified,
      it is assumed that all outputs have the same tag. `false` can be used for
      outputs that have no tag or are not installed.

  output:
    type: array[str]
    description: |
      Array of output files. These cannot contain path separators.

  env:
    since: 0.57.0
    type: env | array[str] | dict[str]
    description: |
      environment variables to set, such as
      `{'NAME1': 'value1', 'NAME2': 'value2'}` or `['NAME1=value1', 'NAME2=value2']`,
      or an [[@env]] object which allows more
      sophisticated environment juggling.

  feed:
    type: bool
    since: 0.59.0
    default: false
    description: |
      There are some compilers that can't be told to read
      their input from a file and instead read it from standard input. When this
      argument is set to `true`, Meson feeds the input file to `stdin`. Note that
      your argument array may not contain `@INPUT@` when feed mode is active.