[template-parser] Boolean attributes with invalid values throw inconsistent errors [should warn] #4732
Description
This throws:
<button autofocus="false"></button>
<button autofocus="true"></button>The errors are:
Error: LWC1037: To set a boolean attributes, try <button autofocus> instead of <button autofocus="true">.
If the attribute is present, its value must either be the empty string or a value that is an ASCII
case -insensitive match for the attribute's canonical name with no leading or trailing whitespace.
Error: LWC1036: To not set a boolean attribute, try <button> instead of <button autofocus="false">. To
represent a false value, the attribute has to be omitted altogether.
However, none of these throw:
<button autofocus="yolo"></button>
<button autofocus="FALSE"></button>
<button autofocus="TRUE"></button>Instead, these just render the attribute value as-is.
We should probably at least warn in cases where the attribute value is anything other than 1) the empty string, i.e. autofocus="", or 2) boolean true, i.e. autofocus (with no =) (these two are equivalent at parse time).
Edit: or 3) the attribute name itself as mentioned in the error message, e.g. autofocus="autofocus".
Problematic code:
lwc/packages/@lwc/template-compiler/src/parser/attribute.ts
Lines 93 to 107 in 641b740