Support trailing commas and comments in .slnf files

[Copilot]

The CreateFromFilteredSolutionFile method fails to parse solution filter files containing trailing commas or comments, despite MSBuild supporting both since dotnet/msbuild#6346.

Changes

• SlnFileFactory.cs: Pass JsonDocumentOptions to JsonDocument.Parse() with AllowTrailingCommas = true and CommentHandling = JsonCommentHandling.Skip
• Test coverage: Add TestAppWithTrailingCommaSlnf asset and tests validating both features work with dotnet solution list

Example

These .slnf files now parse correctly:

{
  // Filter for App projects only
  "solution": {
    "path": "App.sln",
    "projects": [
      "App\\App.csproj",
      "Lib\\Lib.csproj",  // trailing comma
    ]
  }
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Revise CreateFromFilteredSolutionFile implementation for trailing comma (and allowing comments)</issue_title>
<issue_description>The current implementation of this method doesn't seem to allow trailing commas (and comments).

MSBuild supported trailing commas (and comments) of slnf files in dotnet/msbuild#6346

sdk/src/Cli/dotnet/SlnFileFactory.cs

Line 92 in f578225

JsonElement root = JsonDocument.Parse(File.ReadAllText(filteredSolutionPath)).RootElement;

@baronfel @rainersigwald Another discrepancy due to not having a unified implementation/helper for how to parse solutions and solution filters. Not specific to test command this time :) </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Revise CreateFromFilteredSolutionFile implementation for trailing comma (and allowing comments) #51929

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