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Added a definition of {{StringContext}} extended attribute. #841

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Added a definition of {{StringContext}} extended attribute. #841

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238a0ad
Added a definition of {{StringContext}} extended attribute for
koto Feb 10, 2020
885ae1e
Mentioned that {{StringContext}} may apply only to regular operation …
koto Feb 14, 2020
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63 changes: 61 additions & 2 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -6353,8 +6353,10 @@ The following extended attributes are <dfn for="extended attributes">applicable
[{{AllowResizable}}],
[{{AllowShared}}],
[{{Clamp}}],
[{{EnforceRange}}], and
[{{LegacyNullToEmptyString}}].
[{{EnforceRange}}],
[{{LegacyNullToEmptyString}}] and
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Please bring back the Oxford comma.

[{{StringContext}}].


<div algorithm>
The <dfn for="IDL type" lt="extended attribute associated with|extended attributes associated with">extended attributes associated with</dfn>
Expand Down Expand Up @@ -7581,6 +7583,13 @@ value when its bit pattern is interpreted as an unsigned 64-bit integer.
A JavaScript value |V| is [=converted to an IDL value|converted=]
to an IDL {{DOMString}} value by running the following algorithm:

1. If the conversion is to an IDL type [=extended attribute associated with|associated with=] the
[{{StringContext}}] extended attribute, then set |V| to the result of [=validate the string in context=], passing
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validating*

[=this=], |V|, the {{StringContext}} extended attribute [=identifier=], and the [=identifier=]
of the [{{StringContext}}] extended attribute [=related construct=].
Comment on lines +7588 to +7589
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This has some extreme magic that I don't really understand.

As far as I know when we do type conversion there is no "this" and there is no access to something like a "related construct".

I'd like to hear what @domenic and @Ms2ger think, but it seems to me you have to patch algorithms such as https://webidl.spec.whatwg.org/#dfn-attribute-setter instead.

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I agree that this doesn't work with the layering as it currently exists.

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Yes, you cannot access "this" here. Some call sites don't have a "this".

Putting it in the appropriate call sites instead (e.g., the overload resolution algorithm and attribute setters) seems like the best approach.


Note: That algorithm may [=ECMAScript/throw=] a {{ECMAScript/TypeError}}.

1. If |V| is <emu-val>null</emu-val> and the conversion is to an IDL type
[=extended attribute associated with|associated with=] the [{{LegacyNullToEmptyString}}] extended
attribute, then return the {{DOMString}} value that represents the empty string.
Expand Down Expand Up @@ -10259,6 +10268,41 @@ that does specify [{{SecureContext}}].
</pre>
</div>

<h4 id="StringContext" extended-attribute lt="StringContext">[StringContext]</h4>

If the [{{StringContext}}] [=extended attribute=] appears on {{DOMString}} or {{USVString}}, it
modifies how the value is converted to the IDL type, causing additional value validation to
adhere to the context the string is used in.

The [{{StringContext}}] extended attribute must [=takes an identifier|take an identifier=]. The [=identifier=]
must be one of "<code>html</code>", "<code>script-url</code>" and "<code>script</code>".

[{{StringContext}}] extended attribute may only annotate a type of a [=regular attribute=] or
a [=regular operation=] argument. A type annotated with the [{{StringContext}}]
extended attribute must not appear in a [=read only=] attribute. The [=regular attribute=] or
a [=regular operation=] argument that the type annotated with the [{{StringContext}}] extended
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Suggested change
a [=regular operation=] argument that the type annotated with the [{{StringContext}}] extended
[=regular operation=] argument that the type annotated with the [{{StringContext}}] extended

attribute appears in is its <dfn>related construct</dfn>.

A type that is not {{DOMString}} or {{USVString}} must not be [=extended attributes associated with|associated with=]
the [{{StringContext}}] extended attribute.

See the rules for converting ECMAScript values to the IDL types in [[#es-DOMString]] and [[#es-USVString]]
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These two es-X references are fails in bikeshed which is breaking the preview

for the specific requirements that the use of [{{StringContext}}] entails.

<div class="example">

In the following [=IDL fragment=],
a [=variadic=] [=operation=] is declared
that uses the [{{StringContext}}] [=extended attribute=]
on all its arguments:

<pre highlight="webidl">
interface Document {
void write([StringContext=html] DOMString... text);
};
</pre>
</div>


<h4 id="Unscopable" extended-attribute lt="Unscopable">[Unscopable]</h4>

Expand Down Expand Up @@ -11056,6 +11100,21 @@ allowed. The security check takes the following three inputs:

Note: The HTML Standard defines how a security check is performed. [[!HTML]]

Certain algorithms in [[#es-type-mapping]] are defined to
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This es-X is likewise a bikeshed fail

<dfn id="dfn-validate-the-string-in-context" export>validate the string in context</dfn> on a given
value. This check is used to determine whether a given value
is appropriate for its {{StringContext}}. This validation takes the following four inputs:

1. the [=platform object=] on
which the operation invocation or attribute access is being done,
1. the value to validate,
1. the {{StringContext}} [=identifier=], and
1. the [=identifier=] of the operation or attribute.

The algorithm returns an ECMAScript String value, or [=ECMAScript/throws=] a {{ECMAScript/TypeError}}.
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Note that https://w3c.github.io/trusted-types/dist/spec/#html-validate-the-string-in-context doesn't necessarily return a string, and if it did, the conversion algorithm above does some unnecessary work.


Note: The HTML Standard defines how the validation is performed. [[!HTML]]


<h3 id="js-overloads" oldids="es-overloads">Overload resolution algorithm</h3>

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