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guide: A section on input file naming conventions

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Martin Atkins 2018-09-05 08:26:29 -07:00
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guide/language_design.rst
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@ -283,3 +283,36 @@ environment variable values available for use in expressions, and may do so
either as top-level variables (if no other variables are needed) or as an either as top-level variables (if no other variables are needed) or as an
object named ``env``, which can be used as in ``env.HOME``. object named ``env``, which can be used as in ``env.HOME``.
Text Editor and IDE Integrations
--------------------------------
Since HCL defines only low-level syntax, a text editor or IDE integration for
HCL itself can only really provide basic syntax highlighting.
For non-trivial HCL-based languages, a more specialized editor integration may
be warranted. For example, users writing configuration for HashiCorp Terraform
must recall the argument names for numerous different provider plugins, and so
auto-completion and documentation hovertips can be a great help, and
configurations are commonly spread over multiple files making "Go to Definition"
functionality useful. None of this functionality can be implemented generically
for all HCL-based languages since it relies on knowledge of the structure of
Terraform's own language.
Writing such text editor integrations is out of the scope of this guide. The
Go implementation of HCL does have some building blocks to help with this, but
it will always be an application-specific effort.
However, in order to *enable* such integrations, it is best to establish a
conventional file extension *other than* `.hcl` for each non-trivial HCL-based
language, thus allowing text editors to recognize it and enable the suitable
integration. For example, Terraform requires ``.tf`` and ``.tf.json`` filenames
for its main configuration, and the ``hcldec`` utility in the HCL repository
accepts spec files that should conventionally be named with an ``.hcldec``
extension.
For simple languages that are unlikely to benefit from specific editor
integrations, using the ``.hcl`` extension is fine and may cause an editor to
enable basic syntax highlighting, absent any other deeper features. An editor
extension for a specific HCL-based language should *not* match generically the
``.hcl`` extension, since this can cause confusing results for users
attempting to write configuration files targeting other applications.