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# Configuration files proposal
No one will ever agree on the ideal configuration file format.
Therefore, we should allow people to use their preferred configuration file format in all programs.
## Rough idea
Write libraries for as many languages as possible that read files like:
```
#? yaml
my configuration:
option: value
```
```
#? json
{"my configuration": {"option": "value"}}
```
and produces a JSON string with the "parsed" input from the second line onwards.
(Or optionally, a data structure appropriate for the language that you are using.)
If your program uses this library to read configuration, then your users can write their configuration in their preferred language.
## Challenges
* How to prevent arbitrary code execution and other attacks?
* How to support as many configuration languages as possible?
## Possible solutions
Use capability-based runtimes and embed capabilities in the first line of the configuration file:
```
# Allow the specific format parser to...
+file(./**) # ... read files in the same directory as the configuration file and descendants.
+hostname # ... access the hostname.
+load(https://example.com/file,sha256:...,/file) # ... download a file from the Internet and expose it to the parser.
...
```
Be able to refer to different parsers:
```
# Built-in parsers
json
yaml
...
# Parsers installed on the local system
/path/to/my/parser
# Download parsers on demand
https://example.com/foo-parser
```
## Possible implementation
Use WASM runtimes:
* They already support capabilities.
* Parsers can be distributed as WASM blobs.
Maybe use [Extism](https://github.com/extism/extism) to implement.
## Motivating examples
### Declarative CI
`.github/workflows/workflow.yaml`:
```
#? https://jsonnet.org/jsonnet.wasm +load(https://jsonnetci.com/rust.libsonnet,sha256:...,/rust.libsonnet)
local rust = import '/rust.libsonnet';
rust.github({
'supported-archs': ['x86_64-unknown-linux-gnu', ...],
'attach-binaries-to-releases': true,
'upload-to-docsrs': true,
...
})
```
but also `.gitlab-ci.yml`:
```
#? https://jsonnet.org/jsonnet.wasm +load(https://jsonnetci.com/rust.libsonnet,sha256:...,/rust.libsonnet)
local rust = import '/rust.libsonnet';
rust.gitlab(...)
```
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