Handle missing settings.json for Codespaces/Devcontainers

[mitchdenny]

… handle missing settings.json file.

Description

This pull request includes several changes to improve handling of what happens when the machine-wide settings.json file isn't present. The solution is to detect if the file exists and if it isn't - create it. This required a bunch of other collateral changes which are probably good long-term changes towards improving testability (although I still haven't tackled that yet).

I've also added Copilot to our contributing devcontainer since we would normally expect this to be present in our local VS installs - it's kinda helpful :)

Fixes #6873

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Is this introducing a breaking change?
      • Yes
        • Link to aspire-docs issue (please use this breaking-change template):
      • No
        • Link to aspire-docs issue (please use this doc-idea template):
  • No

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 suggestion.

Files not reviewed (1)

• .devcontainer/contributing/devcontainer.json: Language not supported

[Copilot]

Copilot reviewed 4 out of 5 changed files in this pull request and generated no suggestions.

Files not reviewed (1)

• .devcontainer/contributing/devcontainer.json: Language not supported

Comments skipped due to low confidence (2)

src/Aspire.Hosting/Devcontainers/DevcontainerSettingsWriter.cs:86

• [nitpick] The error message 'Codespaces or Devcontainer not detected.' could be more descriptive. Consider changing it to 'Neither Codespaces nor Devcontainer environment detected. Unable to determine the correct settings file path.'

throw new DistributedApplicationException("Codespaces or Devcontainer not detected.");

src/Aspire.Hosting/Devcontainers/DevcontainerSettingsWriter.cs:90

• Ensure that the new behavior introduced by 'EnsureSettingsFileExists' is covered by tests.

async Task EnsureSettingsFileExists(string path, CancellationToken cancellationToken)

[davidfowl]

I am gonna assume you tested this 😄

[mitchdenny]

I did. The race should be pretty rare as well. I was just being cautious.