Document available wbformatvalue options

We’re about to declare other formatter options unsupported (change
Ifd1367eaff), so it stands to reason that the four validated options are
supported, part of the stable interface, and should be documented.

I first thought about putting this in docs/topics/, but I don’t think it
really fits there (and it would be confusing with the already existing
docs/topics/options.md). I think the parameter documentation works
pretty well (Special:ApiSandbox even makes the definition list
collapsable automatically), and there’s robust support for customizing
it and adding additional parameters (to avoid repeating the option names
– though they’re still part of the stable interface and can’t easily be
renamed, of course) both in ApiBase and in {{doc-apihelp-param}}.

Bug: T323778
Change-Id: I92931f3ddeef97ec22f89869c687f63f9fb596cc

repo/i18n/api/en.json

@@ -73,7 +73,7 @@
 	"apihelp-wbformatvalue-param-generate": "The desired output format to generate.",
 	"apihelp-wbformatvalue-param-datatype": "The value's data type. This is distinct from the value's type",
 	"apihelp-wbformatvalue-param-datavalue": "The data to format. This has to be the JSON serialization of a DataValue object.",
-	"apihelp-wbformatvalue-param-options": "The options the formatter should use. Provided as a JSON object.",
+	"apihelp-wbformatvalue-param-options": "The options the formatter should use. Provided as a JSON object.\n\nThe supported options are:\n; $1: The language in which the value should be formatted (a MediaWiki language code).\n; $2: Whether to apply rounding to the number. Can be a boolean (automatic / no rounding) or an integer (exponent of the last significant decimal digits). Only useful for quantity values.\n; $3: Whether to include the unit in the output (a boolean). Only useful for quantity values.\n; $4: Whether to show the calendar model. Can be a boolean (always / never show) or the string <code>\"auto\"</code> (automatically determine whether to show). Only useful for time values.",
 	"apihelp-wbformatvalue-param-property": "Property ID the data value belongs to, should be used instead of the <var>datatype</var> parameter.",
 	"apihelp-wbformatvalue-example-1": "Format a simple string value.",
 	"apihelp-wbformatvalue-example-2": "Format a string value as a URL in HTML.",

repo/i18n/api/qqq.json

@@ -96,7 +96,7 @@
 	"apihelp-wbformatvalue-param-generate": "{{doc-apihelp-param|wbformatvalue|generate}}",
 	"apihelp-wbformatvalue-param-datatype": "{{doc-apihelp-param|wbformatvalue|datatype}}",
 	"apihelp-wbformatvalue-param-datavalue": "{{doc-apihelp-param|wbformatvalue|datavalue}}",
-	"apihelp-wbformatvalue-param-options": "{{doc-apihelp-param|wbformatvalue|options}}",
+	"apihelp-wbformatvalue-param-options": "{{doc-apihelp-param|wbformatvalue|options|params=* $1, $2, $3, $4 - The names of the four supported options|paramstart=5}}",
 	"apihelp-wbformatvalue-param-property": "{{doc-apihelp-param|wbformatvalue|property}}",
 	"apihelp-wbformatvalue-example-1": "{{doc-apihelp-example|wbformatvalue}}",
 	"apihelp-wbformatvalue-example-2": "{{doc-apihelp-example|wbformatvalue}}",

repo/includes/Api/FormatSnakValue.php

@@ -362,6 +362,13 @@ protected function getAllowedParams(): array {
 			'options' => [
 				ParamValidator::PARAM_TYPE => 'text',
 				ParamValidator::PARAM_REQUIRED => false,
+				ApiBase::PARAM_HELP_MSG => [
+					'apihelp-wbformatvalue-param-options',
+					ValueFormatter::OPT_LANG,
+					QuantityFormatter::OPT_APPLY_ROUNDING,
+					QuantityFormatter::OPT_APPLY_UNIT,
+					ShowCalendarModelDecider::OPT_SHOW_CALENDAR,
+				],
 			],
 		];
 	}