Support Microsoft.Build.Traversal projects in dotnet test (MTP) by Evangelink · Pull Request #55297 · dotnet/sdk

Evangelink · 2026-07-15T10:25:35Z

Summary

Draft / proof-of-concept that unblocks traversal project (dirs.proj) support for dotnet test with Microsoft.Testing.Platform. Fixes the scenario in #51316.

The approach treats a Microsoft.Build.Traversal project as a container that forwards to its ProjectReference items — the same mental model as a solution.

Root cause

Two independent problems both had to be fixed (a third surfaced while testing):

Build side — the _MTPBuild target (Microsoft.TestPlatform.ImportAfter.targets) only builds $(MSBuildProjectFullPath) when IsTestingPlatformApplication == true. A traversal project is not an MTP app, so nothing (including its referenced test projects) was built.
Evaluation side — the CLI treated the traversal project as a single, non-test project, found no test module, and errored out.
Arg parsing (found via testing) — .proj was not a recognized positional project extension, so dotnet test dirs.proj leaked dirs.proj to the test host as an invalid argument (MTP exit code 5).

Changes

File	Change
`SolutionAndProjectUtility.cs`	Special-case the `IsTraversal` property. When a project is a traversal project, expand it into its resolved `ProjectReference` items and evaluate each recursively (nested traversal). De-duplicates across the whole traversal graph (diamond references / cycle guard) via a threaded visited-set, and honors per-reference `Configuration`/`Platform` metadata (falling back to inherited values).
`MSBuildUtility.cs`	Recognize any `*proj` extension as a positional project (mirrors `ValidateProjectOrSolutionPath`), so the traversal path isn't forwarded to the test host as an argument.
`CliConstants.cs`	Added `IsTraversal` / `ProjectReference` names.
`Microsoft.TestPlatform.ImportAfter.targets`	`_MTPBuild` now forwards `_MTPBuild` to `@(ProjectReference)` when `IsTraversal == true`, so the referenced test projects actually build.
`TraversalTestProjects/` + test	Basic asset (`dirs.proj` + two MTP apps) and `RunTraversalProject_ShouldRunReferencedTestProjects`.
`TraversalTestProjectsNested/` + test	Nested/diamond asset and `RunNestedTraversalProjectWithDiamond_ShouldRunSharedProjectOnce`. Test apps drop a unique marker file per launch so the test deterministically asserts the shared (diamond) project runs exactly once and the leaf-only project (reachable solely via nested traversal) also runs — proving recursion + de-dup.

Validation

Full build succeeds (0 warnings / 0 errors).
New tests pass for both Debug and Release: referenced projects are discovered, built, and executed via the traversal; diamond de-dup and nested recursion are verified via marker files.
Related project/solution/positional-arg tests still pass (no regression).

Notes / open questions for reviewers

On "MSBuild APIs": no new public MSBuild API turned out to be strictly required for a working draft — the resolved ProjectReference items from evaluation are sufficient, and MSBuild already expands globs/conditions during evaluation. A cleaner long-term design would want a public traversal API to get the effective project set (analogous to SolutionFile.ProjectsInOrder) rather than relying on raw ProjectReference items — similar in spirit to the existing ProjectShouldBuild UnsafeAccessor workaround used for solutions (see MSBuild should publish a library that helps tools interact with Solution files and other container-ish project types msbuild#12711).
Per-reference metadata support currently covers Configuration/Platform; the P2P Set*/AdditionalProperties forms are not yet parsed (the Set* form uses a Name=Value string that would need parsing).
The _MTPBuild forwarding is intentionally minimal for this draft (no explicit BuildInParallel/property forwarding). The cross-targeting _MTPBuild variant is left unchanged since traversal projects are not cross-targeting.
Remaining test-coverage ideas: a traversal referencing a non-test project (should be skipped silently) and a mixed MTP + VSTest traversal (should hit the existing unsupported-VSTest error).

Closes #51316 (once finalized).

Unblocks traversal (dirs.proj) support for 'dotnet test' with Microsoft.Testing.Platform (issue #51316). Three coordinated changes mirror how solutions are handled - the traversal project is a container that forwards to its ProjectReference items: - CLI evaluation: special-case the 'IsTraversal' MSBuild property in SolutionAndProjectUtility.GetProjectProperties. When a project is a traversal project, expand it into its resolved ProjectReference items and evaluate each recursively (so nested traversal projects work). - CLI arg parsing: recognize any '*proj' extension (not just .csproj/.vbproj/.fsproj) as a positional project in MSBuildUtility.GetPositionalArguments, matching ValidateProjectOrSolutionPath. Without this, 'dotnet test dirs.proj' leaked 'dirs.proj' to the test host as an invalid argument (MTP exit code 5). - Targets: the _MTPBuild target now forwards to @(ProjectReference) when IsTraversal is true, so the referenced test projects actually build. Adds a TraversalTestProjects test asset and RunTraversalProject_ShouldRunReferencedTestProjects test.

azure-pipelines · 2026-07-15T10:25:49Z

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…ata for traversal - De-duplicate referenced projects across the entire traversal graph (not just within a single traversal file) by threading a visited-set through the recursion. This prevents a project referenced by multiple traversal projects (a diamond) from being tested twice and guards against reference cycles. - Honor per-reference Configuration/Platform metadata on ProjectReference items, falling back to the values inherited from the traversal project. - Add a nested/diamond test asset (TraversalTestProjectsNested) and RunNestedTraversalProjectWithDiamond_ShouldRunSharedProjectOnce. The test apps drop a unique marker file per launch so the test deterministically asserts the shared project runs exactly once and the leaf-only project (reachable solely via nested traversal) also runs once.

Evangelink · 2026-07-15T10:54:37Z

@baronfel given there is no ETA or news for when transversal APIs will be available, I went ahead with doing some "hacks" as a simplified version which should give us a first support for dotnet test with traversal.

azure-pipelines · 2026-07-15T10:54:52Z

Azure Pipelines: Successfully started running 1 pipeline(s). 2 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

Copilot

Pull request overview

Adds draft traversal-project (Microsoft.Build.Traversal / dirs.proj) support to dotnet test when using Microsoft.Testing.Platform by expanding traversal containers into their referenced projects for evaluation and ensuring referenced projects get built.

Changes:

Teach MTP project evaluation to detect traversal projects and recursively expand their ProjectReference graph (with de-dup/cycle-guard).
Update argument parsing to treat any *proj file as a positional project so it isn’t forwarded to the test host.
Add MTP traversal test assets + tests, and update _MTPBuild to forward to @(ProjectReference) for traversal projects.

Show a summary per file

File	Description
src/Cli/dotnet/Commands/Test/MTP/SolutionAndProjectUtility.cs	Detects traversal projects and recursively evaluates referenced projects (incl. de-dup).
src/Cli/dotnet/Commands/Test/MTP/MSBuildUtility.cs	Broadens positional project detection to any extension ending in `proj`.
src/Cli/dotnet/Commands/Test/CliConstants.cs	Adds MSBuild property/item names used for traversal support.
src/Layout/redist/MSBuildImports/Current/Microsoft.Common.targets/ImportAfter/Microsoft.TestPlatform.ImportAfter.targets	For traversal projects, forwards `_MTPBuild` to referenced projects.
test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndRunsTests.cs	Adds tests covering traversal execution, nesting, and diamond de-dup.
test/TestAssets/TestProjects/TraversalTestProjects/global.json	Configures test assets to use Microsoft.Testing.Platform runner.
test/TestAssets/TestProjects/TraversalTestProjects/dirs.proj	Simple traversal project referencing two MTP test apps.
test/TestAssets/TestProjects/TraversalTestProjects/TestProject/TestProject.csproj	MTP “test app” project used by traversal asset.
test/TestAssets/TestProjects/TraversalTestProjects/TestProject/Program.cs	Minimal dummy MTP adapter app for traversal tests.
test/TestAssets/TestProjects/TraversalTestProjects/OtherTestProject/OtherTestProject.csproj	Second MTP “test app” project used by traversal asset.
test/TestAssets/TestProjects/TraversalTestProjects/OtherTestProject/Program.cs	Minimal dummy MTP adapter app for traversal tests.
test/TestAssets/TestProjects/TraversalTestProjectsNested/global.json	Configures nested traversal assets to use Microsoft.Testing.Platform runner.
test/TestAssets/TestProjects/TraversalTestProjectsNested/dirs.proj	Top-level traversal with nested traversal and a diamond reference.
test/TestAssets/TestProjects/TraversalTestProjectsNested/sub/dirs.proj	Nested traversal referencing shared + leaf MTP projects.
test/TestAssets/TestProjects/TraversalTestProjectsNested/SharedTestProject/SharedTestProject.csproj	Shared MTP “test app” used to validate diamond de-dup.
test/TestAssets/TestProjects/TraversalTestProjectsNested/SharedTestProject/Program.cs	Drops marker files to deterministically count runs for de-dup validation.
test/TestAssets/TestProjects/TraversalTestProjectsNested/LeafTestProject/LeafTestProject.csproj	Leaf-only MTP “test app” reachable only through nested traversal.
test/TestAssets/TestProjects/TraversalTestProjectsNested/LeafTestProject/Program.cs	Drops marker files to deterministically count runs for recursion validation.

Copilot's findings

Files reviewed: 18/18 changed files
Comments generated: 3

…targets metadata forwarding Addresses three Copilot review comments on #55297: - Resolve ProjectReference 'FullPath' relative to the traversal project directory via Path.GetFullPath(fullPath, projectDirectory) instead of the process working directory. - Include Configuration/Platform in the traversal de-duplication key so the same project referenced with different Configuration/Platform is tested for each distinct combination, while true diamonds (same combination) are still de-duplicated. Introduces GetTraversalVisitKey and keys the traversal project's own visited entry the same way. - _MTPBuild now forwards per-reference Configuration/Platform metadata as global properties, consistent with the evaluation logic. Property assignments are precomputed in an ItemGroup so empty metadata never emits 'Configuration=' (which would clear the inherited global property); empty segments in Properties are ignored by MSBuild.

…-apis

The GetProjectProperties signature gained a FacadeLogger? parameter on main. Thread it through the recursive traversal call to resolve CS1503.

Evangelink · 2026-07-22T11:51:15Z

/ba-g

CI analysis: the failing check is unrelated flakiness (not this PR)

The only failing leg on the latest run (build 1517459) is Monitor Helix Jobs, which reports 1 failed work item out of 557: dotnet-watch.Tests.dll.3 (FullFramework: windows x64), exit code 7 (MTP hang-dump timeout). Every actual test run reports failedTests: 0 (the total vs passed gaps are skips), and this PR touches zero dotnet-watch files.

Failing test

Microsoft.DotNet.Watch.UnitTests.MobileHotReloadTests.HotReload_WithWebSocketCapability — the run shows 79 completed, 0 failed; only this one test wedges, then sits until MTP's 48-min hang-dump fires and kills the whole work item.

Root cause (two combining issues)

App-side WebSocket connect fails silently. dotnet watch starts a Kestrel WS server, launches the app, and the injected startup hook connects back via WebSocketTransport.SendAsync, where connectCts.CancelAfter(connectionTimeoutMS) uses the default 5000 ms from Transport.TryCreate. If that connect loses under CI load, the TimeoutException bubbles to Listener.Listen, which catches it, logs only through the off-by-default prefix logger, disposes the transport, and lets the app run normally. So the app prints Started but the server never logs "WebSocket client connected", and the watcher''s WaitForConnectionAsync waits forever. The test''s await App.WaitUntilOutputContains("WebSocket client connected") then never completes — with no diagnostic.
The test''s fast-fail timeout can never win. In AwaitableProcess, s_timeout = HELIX_WORK_ITEM_TIMEOUT - 10s. With TestWorkItemTimeout = 60min (test/UnitTests.proj), that''s ~59:50, but MTP''s hang-dump is 48:00 — so the hang-dump always fires before the per-wait Assert.Fail, turning a single wedged test into a work-item-nuking hang that loses results.

Already tracked as a Known Build Error: #55258, #55044, #53289.

Suggested fixes (belong in a separate dotnet-watch test-infra PR, not here)

Test infra: make AwaitableProcess.s_timeout a true per-wait cap well under the 48-min hang-dump (e.g. 5 min) so a wedged wait fails that one test fast with a useful message instead of nuking the work item.
Product: raise the 5s WS connect timeout and/or add retries, and surface the connect failure to stderr unconditionally (today it''s only logged when HotReloadDeltaClientLogMessages is set) so the hang becomes a visible, actionable error.

@tmat does this match your understanding of the WebSocket hot-reload hang? Happy to open the test-infra timeout fix separately if useful.

Evangelink · 2026-07-22T14:48:33Z

/backport to release/11.0.1xx-preview7

github-actions · 2026-07-22T14:48:42Z

Started backporting to release/11.0.1xx-preview7 (link to workflow run)

github-actions · 2026-07-22T14:49:17Z

@Evangelink backporting to release/11.0.1xx-preview7 failed, the patch most likely resulted in conflicts. Please backport manually!

git am output

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Draft: support Microsoft.Build.Traversal projects in dotnet test (MTP)
Applying: Add cross-graph de-dup and per-reference Configuration/Platform metadata for traversal
Using index info to reconstruct a base tree...
M	src/Cli/dotnet/Commands/Test/MTP/SolutionAndProjectUtility.cs
M	test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndRunsTests.cs
Falling back to patching base and 3-way merge...
Auto-merging src/Cli/dotnet/Commands/Test/MTP/SolutionAndProjectUtility.cs
Auto-merging test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndRunsTests.cs
CONFLICT (content): Merge conflict in test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndRunsTests.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0002 Add cross-graph de-dup and per-reference Configuration/Platform metadata for traversal
Error: The process '/usr/bin/git' failed with exit code 128

Link to workflow output

Evangelink marked this pull request as ready for review July 15, 2026 10:54

Evangelink requested a review from a team as a code owner July 15, 2026 10:54

Copilot AI review requested due to automatic review settings July 15, 2026 10:54

Copilot started reviewing on behalf of Evangelink July 15, 2026 10:55 View session

Copilot AI reviewed Jul 15, 2026

View reviewed changes

Comment thread src/Cli/dotnet/Commands/Test/MTP/SolutionAndProjectUtility.cs

Comment thread src/Cli/dotnet/Commands/Test/MTP/SolutionAndProjectUtility.cs Outdated

Comment thread ...orts/Current/Microsoft.Common.targets/ImportAfter/Microsoft.TestPlatform.ImportAfter.targets Outdated

Evangelink added 3 commits July 15, 2026 16:43

Merge branch 'main' into dev/amauryleve/dotnet-test-traversal-msbuild…

3863987

…-apis

Merge branch 'main' into dev/amauryleve/dotnet-test-traversal-msbuild…

074fc64

…-apis

This was referenced Jul 17, 2026

Template Engine SSL Connection Issue #51574

Open

Known Test Repository Issue Sometimes Misses Test Failures dotnet/dnceng#6411

Open

Evangelink added 2 commits July 20, 2026 09:18

Merge branch 'main' into dev/amauryleve/dotnet-test-traversal-msbuild…

07fc03d

…-apis

Fix build after merge: pass new FacadeLogger arg in traversal recursion

bc1ff37

The GetProjectProperties signature gained a FacadeLogger? parameter on main. Thread it through the recursive traversal call to resolve CS1503.

Evangelink enabled auto-merge July 20, 2026 10:52

Evangelink changed the title ~~[Draft] Support Microsoft.Build.Traversal projects in dotnet test (MTP)~~ Support Microsoft.Build.Traversal projects in dotnet test (MTP) Jul 22, 2026

drognanar approved these changes Jul 22, 2026

View reviewed changes

Evangelink merged commit 1958128 into main Jul 22, 2026
26 of 28 checks passed

Evangelink deleted the dev/amauryleve/dotnet-test-traversal-msbuild-apis branch July 22, 2026 12:27

MichaelSimons mentioned this pull request Jul 22, 2026

Microsoft.DotNet.Watch.UnitTests.LoggingTests.BinaryLogs: intermittent hang (test host hang-dump timeout, exit code 7) #55258

Open

This was referenced Jul 22, 2026

[dotnet-watch tests] Cap output-wait timeout below the MTP hang-dump #55406

Draft

Add deep-nested traversal e2e tests for dotnet test (MTP) #55407

Open

Evangelink mentioned this pull request Jul 22, 2026

[release/11.0.1xx-preview7] Support Microsoft.Build.Traversal projects in dotnet test (MTP) #55411

Merged

dotnet-maestro Bot mentioned this pull request Jul 22, 2026

[release/11.0.1xx-preview7] Source code updates from dotnet/sdk dotnet/dotnet#7912

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Support Microsoft.Build.Traversal projects in dotnet test (MTP)#55297

Support Microsoft.Build.Traversal projects in dotnet test (MTP)#55297
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Evangelink commented Jul 15, 2026 •

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Summary

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Notes / open questions for reviewers

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Evangelink commented Jul 22, 2026

CI analysis: the failing check is unrelated flakiness (not this PR)

Failing test

Root cause (two combining issues)

Suggested fixes (belong in a separate dotnet-watch test-infra PR, not here)

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Evangelink commented Jul 15, 2026 •

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