unikernel/duniverse/dune_/doc/reference/aliases/fmt.rst

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+@fmt
+====
+
+This alias is used by formatting rules: when it is built, code formatters will
+be executed (using :doc:`promotion </concepts/promotion>`).
+
+``dune fmt`` is a shortcut for ``dune build @fmt --auto-promote``.
+
+It is possible to build on top of this convention. If some actions are manually
+attached to the ``fmt`` alias, they will be executed by ``dune fmt``.
+
+Example:
+
+.. code:: dune
+
+   (rule
+    (with-stdout-to
+     data.json.formatted
+     (run jq . %{dep:data.json})))
+
+   (rule
+    (alias fmt)
+    (action
+     (diff data.json data.json.formatted)))