Allow variables to be used as part of a value in configuration.

[joeriddles]

Resolves: #5320

Based on #5544

Requires double dollar signs in strings to use variables (similar to using an environment variable in a Makefile). This solves @wallyqs's comment on the original pull request by preventing values like "$SYS" getting misinterpreted as a variable.

Note that using double dollar signs outside of string quotes is invalid. Existing parsing behavior of a single dollar sign outside of quotes remains unaffected.

Signed-off-by: Joseph Riddle joe@synadia.com

[MauriceVanVeen]

Thank you for getting this going 👍

In general I'd want to advocate for having both syntaxes work for the normal case. And instead of $$TOKEN I'd personally prefer the use of ${TOKEN} like was suggested here: #5320 (comment).

Then you'd be able to use the password: $TOKEN syntax that's supported normally but not for embedding. And then both password: ${TOKEN} should work and the embedded case of nats://user:${TOKEN}@localhost:6222.
That would allow someone to fully switch to the new syntax of ${TOKEN} also for the normal case, to keep the config consistent.

[MauriceVanVeen]

The test currently fails due to it not recognizing the TOKEN here. After removing the authorization block such that it can only fail on the embedded syntax, the test doesn't fail anymore and contains an unresolved nats://user:$$TOKEN@server.example.com:6222.

[MauriceVanVeen]

Should also add a test where password: is used with the other syntax. Currently if you try $$TOKEN here it fails.

[joeriddles]

@MauriceVanVeen I updated to use the brace syntax you and the commenter on the issue suggested. Also updated the tests based on the changes and your feedback. Thanks