encoding/jsonschema: patternProperties does not quote field names in regexp pattern

[rogpeppe]

What version of CUE are you using (cue version)?

deed7d5c

Does this issue reproduce with the latest stable release?

Yes (v0.10.0)

What did you do?

exec cue mod init
exec cue import -p main schema.json
! exec cue vet . data.json
-- data.json --
{
    "cue": 123
}
-- schema.json --
{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "type": "object",
    "properties": {
        "c.e": {
            "type": "boolean"
        }
    },
    "patternProperties": {
        ".*": {
            "type": "string"
        }
    }
}

What did you expect to see?

A passing test. The patternProperties keyword applies only to properties that aren't
explicitly defined. The jsonschema logic tries to work around the lack of support
for ... T in structs (c.f. the "Types for all elements versus remaining elements" section
in #165) by including the other field names in a regexp, but it does not quote metacharacters
in their names, so the field name cue, which should come under the auspices of
patternProperties in this example, doesn't get checked at all.

What did you see instead?

> exec cue mod init
> exec cue import -p main schema.json
> exec cat schema.cue
[stdout]
package main

@jsonschema(schema="http://json-schema.org/draft-07/schema#")
"c.e"?: bool

{[=~".*" & !~"^(c.e)$"]: string}
...
> ! exec cue vet . data.json
FAIL: /tmp/z.txtar:4: unexpected command success