Ports the two behaviors PR #2033 (the parallel attempt at #1919, now closed
as a duplicate) got right and this branch did not.
1. An expression declaring no variable is a malformed template, not one
with a member to skip. RFC 6570 requires at least one varspec per
expression and admits no empty member, so `{}`, `{,}`, `{a,}`, `{?}`
and `{*}` (an explode modifier is not a name) now make the template
invalid. Skipping them was the more dangerous reading: `x://{}`
expanded to `x://` while the form rendered no inputs, so its
"everything required is filled" check was vacuously true and it
submitted a URI that is not the template the server published.
2. The read is withheld when expansion fails. `expandUriTemplate`'s
raw-template fallback exists for the preview, which runs during render
-- but the submit path used it too, so an invalid template was read
with its braces intact and the server answered with a confusing "not
found" for a defect that is not the user's. `tryExpandUriTemplate`
returns the URI or the reason as a value the caller cannot mistake for
one; the panel gates Read Resource on it and prints the reason.
This also covers a value that cannot be encoded -- an unpaired
surrogate has no UTF-8 encoding, so `encodeURIComponent` throws
`URIError` on it, and a text input can hold one via paste.
`requiredGroups` now skips an expression naming no variable: an empty
group can never be satisfied, so it would gate the form a second time on
a condition nothing can meet, and the "any one of" hint built from it
would name no fields. The accurate reason is the malformed template,
which the expansion gate reports.
npm run ci passes.
Signed-off-by: cliffhall <cliff@futurescale.com>
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