D 2018-07-04T14:34:02.309
L config
N text/x-markdown
P 7487fe0092ccfa7199ac408dca5d2fb9282422b19e32f800efa5a8985cf78f80
U mario
W 4851
## # config:  {…}

The `config:` field is a list of entries describing feature- and
application-level settings.

    # config:
    #    { name: linky, type: bool, description: autolink urls }
    #    { name: xy.title, type: str, value: "blog title" }
    #    { name: perm, type: select, select: 3=USER|2=EX|1=SUP|0=KERN }

[PMD](wiki/Plugin+Meta+Data) is about uniform feature lookup. And
plugin handling goes hand in hand with configuration management.
However it requires a structured field to avoid bulky definitions, yet
support enough variation.

Usually `config:` contains multiple indented lines, each being a
<acronym title="JSON, but quotes optional">JSOL</acronym>-dictionary.

#### {

<table class="cnt-tbl">
<tr>
   <th><code>name:</code></th>
   <td>associates some variable/constant/expression to a setting.</td>
</tr>
<tr>
<th><code>type:</code></th>
<td> A few common types may cover 90% of configuration needs.
   <table>
    <tr>
       <th><code>bool</code></th>
       <td>would render as checkbox often.</td>
    </tr>
    <tr>
       <th><code>str</code></th>
       <td>for plain textual content.</td>
    </tr>
    <tr>
       <th><code>int</code></th>
       <td>verifies the value to be numeric.</td>
    </tr>
    <tr>
       <th><code>select</code></th>
       <td> defining a predefined list of defaults.</td>
    </tr>
   </table>
</td>
</tr>
<tr>
    <th><code>select:</code></tt>
      <td>With `select: "aaa┃bbb┃ccc"` being the alternatives attribute for
    combobox options.</td>
</tr>
<tr>
    <th><code>description:</code></th>
    <td>holds some elaboration on the key name.</td>
</tr>
<tr>
    <th><code>value:</code></th>
   <td>just sets a default</td>
</tr>
</table>

#### }



## `select:` alternatives

The syntax for `select:` is

 * preferrably `"alt|alt|alt"`
 * or with optional title `"1=title|2=alternative|3=…"`.
 * Though implementations may allow to use `,` comma and `|` dash.
 * Or allow both `:` and `=` to separate keys+values.


## Custom types

Apart from providing aliases for the base types, a plugin API might provide its own custom set of setting types:

| type | alias | usage |
------------------------
| `int` | `integer` / `numeric` | numbers |
| `bool` | `boolean` / `checkbox` | true/false |
| `str` | `string` / `numeric` | string |
| `select` | `multi` / `dropdown` | see select: alternatives |
| `text` | `textarea` / `long` | longer `string` type (= renders as textarea) |
| `color` | `rgb` | graphical color picker |
| `file` | `filechooser` | setting should be a valid filename | 
| `table`| `csv` / `list` | for supporting more complex (Excel-style) setting lists. |
| `dict` | `hashtable` | complex dictionary (Excel-style) setting field. |


## Other fields

Other per-config attributes migh encompass

| `category:` | grouping config options (else inherited from plugin) |
| `class:`       | either decoration or additional type qualifier |
| `arg:`          | declares a commandline argument instead of global app setting |
| `param:`   | plugin invocation argument instead of global app flag |

There's some paritiy with the main plugin meta fields. Except that config entries should not have a nested config: attribute, of course^^


## Storage and key `name:`

Notably this scheme just defines a list of available options. It does **not**
prescribe if they're stored in an `.ini`, `.json`, `xml` or code file, or a database
perhaps.  
Applications might utilize different stores even, and dispatch depending on
the `name:` syntax

  * For example `name: ALL_UPPERCASE` might become a code constant,
  * While `name: sectioned.feature.option` indicated an INI setting,
  * Or `name: "$cfg.plugins[after][]"` even a literal code target.

So names can be somewhat free-form. I'd avoid including the `$` sigil
however, or spaces obviously. Mostly-alphunumeric and dotted keys are
certainly most versatile.


## Regex tokenizer

You can get by with a somewhat simple regex extractor for this config
scheme. It's simply finding `{…}` pairs, then splitting key-value pairs,
and handling optional quoting.

  * Which allows syntax alternatives `[:=>]+` for key-value pairs.

  * Same as shortened/aliased type names add some user-friendliness.

Of course a stringent JSON-parser could be used. But that's obstructing
maintanability, and buys little performance-wise. (Plugin or option
management is rarely done during runtime; but confined to some admin
or installer UI.)


## Purpose

Once config options are easily parseable, it quickly pays off to implement
a centralized option/admin UI. And it sometimes can be combined with plugin
configuration itself. Which is why plugin meta data defines this simple
scheme.


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