Allow placeholders in `--report-trx-filename`

[Youssef1313]

Summary

Allow placeholders in --report-trx-filename. So, users can do --report-trx-filename MyFile_<target_framework>.trx

Background and Motivation

In VSTest, LogFilePrefix was supported. This is something we currently lack in MTP.

Proposed Feature

A more flexible solution, to allow placeholders in --report-trx-filename.

We can start with the following placeholders:

<assembly_name>
<target_framework>
<timestamp>
<process_id>

Alternative Designs

Add a new command-line option, --report-trx-file-prefix. Only one of --report-trx-filename and --report-trx-file-prefix can be used at the same time.
But placeholders can be more flexible.

[Youssef1313]

<target_framework> isn't super trivial. It doesn't seem easy (or possible at all?) to know net9.0 vs net9.0-windows for example. I don't want us to introduce something that's not accurate.

Maybe instead, we can expose <target_framework_identifier> (.NETFramework, .NETCoreApp, etc). And <target_framework_version>.

In that case, yes it will be the same for net9.0 and net9.0-windows, but that's what we expose and what the names refer to.

[nohwnd]

these two assembly level attributes have that info:

[assembly: TargetPlatform("Windows10.0.26100.0")]
[assembly: SupportedOSPlatform("Windows10.0.26100.0")]

When the value is Windows7.0 or 8.0, that is the -windows value. Otherwise the exact version is used.

The mapping is defined here: https://github.com/dotnet/sdk/blob/main/src/Layout/redist/targets/GenerateBundledVersions.targets#L1313-L1337

We already have some code that translates the TFM to short names, and this would be a good adition there, so we don't have to show .NETCoreApp,Version=7.0.0 to users, or whatever horrible name is in the framework identifier.

[nohwnd]

https://github.com/microsoft/testfx/blob/main/src/Platform/Microsoft.Testing.Platform/OutputDevice/TargetFrameworkParser.cs this is the code to show nice short names

[nohwnd]

Suggestion to further improve this, to choose the shortest names for the most used properties:

tfm -> net9.0
timestamp -> date + time with seconds accuracy in sortable format 2025-05-23T17-45-56
id / rng -> short random id like f0fJf that is just enough to guarantee that we don't get the conflict on seconds / minutes
assembly / project -> project name -> ContonsoTests

pid -> process id

date -> just date in sortable format
time -> just time in sortable format

repo_root -> place where there is .git or .sln ?
etc.

and then some other longer replacements: guid, precise_time, long_tfm based on the needs that we discover.

Also we should document when and where we take the values from, e.g. if we would rely on current folder, we should resolve it before the run and document that, to avoid leaving it after the run when tests can change the current folder etc.

[Evangelink]

Relates to #4130 for the format of placeholders.

Browsing the most common patterns in .NET, it seems we have:

• $(Variable) like MSBuild
• $var$ like templating engines (VS and dotnet)
• ${var} like most shell

@baronfel with your experience in SDK and your broad view over the products, is there a pattern you would recommend?

[baronfel]

I'd strongly encourage you to not do MSBuild-style placeholders - we don't expose MSBuild stuff anywhere else on the CLI directly. There is a small amount of prior art for the -bl flag in MSbuild - it accepts {} in the name and will expand it with the current timestamp formatted in a lexically-sortable way.

[RussKie]

Bumping the issue to reiterate the need for the customisation. Running dotnet test <name>.sln -- --results-directory "$(path)\TestsResults" --report-trx --report-trx-filename test_results.trx results in a trx from the last tested project, all others stomped over...