readEnvironmentVariable() without a default value causes BCP338 linter error which is not configurable

[stewartadam]

Bicep version
Bicep CLI version 0.29.47 (132ade5)

Describe the bug
As described in #13994, when using readEnvironmentVariable() without a default value in a .bicepparams file, the value get underlined with an error.

This is confusing to the user as when just editing a file it's reasonable to expect users not to have every single deployment variable set with a real value just to edit the file. To make matters worse, this error cascades wherever that parameter is used (e.g. in a string template for another parameter) which can quickly litter your file with inactionable errors and obscure other errors.

#13994 was closed because details were added on how to export variables in PowerShell, but that's besides the point - users shouldn't have to supply every variable just to edit the file. Bicep already fails if it can't read the env variable when it's called to compile a template, and that should be enough.

To Reproduce
Steps to reproduce the behavior:

1. Generate a bicepparams file like so:

   param baseName = readEnvironmentVariable('BICEP_BASE_NAME', 'myapp')
   param environmentName = readEnvironmentVariable('BICEP_ENVIRONMENT_NAME')
   param uniqueSuffix = substring(uniqueString(readEnvironmentVariable('BICEP_RESOURCE_GROUP')), 0, 10)
   // ...
   param aiHubName = readEnvironmentVariable('BICEP_AI_HUB_NAME', '${baseName}-${environmentName}-aih')
   param aiProjectName = readEnvironmentVariable('BICEP_AI_PROJECT_NAME', '${baseName}-${environmentName}-aip')
   param appInsightsName = readEnvironmentVariable('BICEP_APP_INSIGHTS_NAME', '${baseName}-${environmentName}-appi')
   // ...
   

Additional context
BCP338 should be a configurable linter rule (side note, why are rules referenced by name only and only some are given names? every lint should be able to be enabled/disabled simply by its ID).

[jeskew]

Related to #11677

[hkaraoguz]

Hello,
Any updates about this issue?

[alex-frankel]

Adding back Triage label so that we can revisit if this should switch to a linter warning rather than a validation error, so that it can be disable/configured. It seems reasonable given there will be so many setups where the environment variables are not enabled locally, but are enabled in the CI environment.

[trylvis]

Any updates on this? Is there no way to ignore the error in bicepconfig.json?