Add format() experimental function

[SteveL-MSFT]

PR Summary

Add experimental format() function. Use of this function will emit a warning as it doesn't currently support all the same format options as dotnet which is what ARM is based on.

Also updated versions of some crates.

PR Context

Fix #767

[Gijsreyn]

Just a question aside Steve, if this is experimental, should users toggle it on or off in the dsc.settings.json?

[SteveL-MSFT]

Just a question aside Steve, if this is experimental, should users toggle it on or off in the dsc.settings.json?

Good question. I don't think we need that since it's something you have to explicitly use.

[andyleejordan]

First basic round of testing is successful:

Logs:

2025-05-05T22:58:42.459120Z DEBUG dsc_lib::configure: 773: Invoke property expressions
2025-05-05T22:58:42.460693Z DEBUG dsc_lib::parser: 48: Parsing statement: [format('{0}\Themes\Personalize', variables('keyPathPrefix'))]
2025-05-05T22:58:42.470561Z DEBUG dsc_lib::parser: 84: Parsing expression
2025-05-05T22:58:42.471435Z DEBUG dsc_lib::parser::expressions: 43: Parsing function '{Node function (0, 1) - (0, 61)}'
2025-05-05T22:58:42.472362Z DEBUG dsc_lib::parser::expressions: 43: Parsing function '{Node function (0, 34) - (0, 60)}'
2025-05-05T22:58:42.473285Z DEBUG dsc_lib::parser::functions: 57: Function name: 'variables'
2025-05-05T22:58:42.474161Z DEBUG dsc_lib::parser::functions: 57: Function name: 'format'
2025-05-05T22:58:42.475071Z DEBUG dsc_lib::parser::functions: 80: Argument is a value: 'String("{0}\\Themes\\Personalize")'
2025-05-05T22:58:42.477017Z DEBUG dsc_lib::parser::functions: 75: Argument is an expression
2025-05-05T22:58:42.478129Z DEBUG dsc_lib::parser::functions: 80: Argument is a value: 'String("keyPathPrefix")'
2025-05-05T22:58:42.479103Z DEBUG dsc_lib::functions::variables: 28: variables function
2025-05-05T22:58:42.480001Z  WARN dsc_lib::functions::format: 99: `format()` function is experimental
2

Bicep:

var keyPathPrefix = 'HKCU\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion'

resource systemUsesLightTheme 'Microsoft.Windows/Registry@2025-04-07' = {
    name: 'SystemUsesLightTheme'
    properties: {
        keyPath: '${keyPathPrefix}\\Themes\\Personalize'
        valueName: 'SystemUsesLightTheme'
        valueData: {
          DWord: valueData
        }
    }
}

ARM:

  "variables": {
    "valueData": "[if(equals(parameters('colorMode'), 'light'), 1, 0)]",
    "keyPathPrefix": "HKCU\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion"
  },
  "resources": [
    {
      "type": "Microsoft.Windows/Registry",
      "apiVersion": "2025-04-07",
      "name": "SystemUsesLightTheme",
      "properties": {
        "keyPath": "[format('{0}\\Themes\\Personalize', variables('keyPathPrefix'))]",
        "valueName": "SystemUsesLightTheme",
        "valueData": {
          "DWord": "[variables('valueData')]"
        }
      }
    },

And this worked such that I didn't have to use Bicep's concat() any more (which throws a warning to use string interpolation). Would be happy to test some more, at least before release, but I liked the ample unit tests. Thing we'll have to worry about in general is bug-for-bug compatibility between Bicep (implemented in C#) and DSC (in Rust).

[andyleejordan]

This package seems reasonable enough, but I'll point out that it's last release was 3 years ago, and it has this note:

Is stable API a must-have? If so, you might consider the alternatives. This crate is still not at version 1.0, which means that the API is still not completely stable.

[andyleejordan]

Just something to consider, dyn-fmt appears more recently updated than the other two contenders (rt-format as above and the similarly named dynfmt last published 4 years ago).

[andyleejordan]

(I'm not saying it's better, I'm just looking into it.)

[SteveL-MSFT]

I was looking at the variety of options listed in the rt-format repository. Maybe will switch to dyn-fmt in the future. Since this is experimental, we can leave it as-is for now.