[release/13.4] Freeze Aspire.TypeSystem AssemblyVersion at 13.4.5.0 to fix cross-ALC codegen binding

[Sébastien Ros (sebastienros)]

Problem

Polyglot AppHost code generation (TypeScript/Python/Java/Go/Rust) silently fails with No code generator found for language: <lang> when the installed Aspire CLI and the AppHost's configured SDK skew in version (e.g. an older CLI running a newer SDK, or a current CLI running an older stable SDK).

Root cause

The CLI's bundled apphost server (Aspire.Hosting.RemoteHost, shipped as the single-file aspire-managed executable) loads Aspire.TypeSystem into its default AssemblyLoadContext and IntegrationLoadContext deliberately force-shares it from there, so the cross-ALC contracts (ICodeGenerator, ILanguageSupport, AtsContext) keep a single type identity across the ALC boundary.

The SDK-side codegen assemblies (Aspire.Hosting.CodeGeneration.*) are strong-named (StrongNameKeyId=Open) and carry a strong-named reference to Aspire.TypeSystem. The CLR satisfies a strong-named reference only when the loaded copy's AssemblyVersion is >= the requested version. Because AssemblyVersion floated with the build (MAJOR.MINOR.PATCH), the bundled copy and the codegen reference diverged whenever the CLI and SDK were built at different times → the bind failed → Assembly.GetTypes() threw ReflectionTypeLoadException → every generator was silently dropped (#18110, #17910).

This affects all polyglot languages and the ATS capability-scan path, not just TypeScript. The Aspire.TypeSystem source surface itself is unchanged between release/13.4 and main — it is purely the strong-name version bump that breaks the bind.

Fix

Freeze the strong-name AssemblyVersion of Aspire.TypeSystem at the fixed constant 13.4.4.0, decoupled from the build:

• 13.4.4.0 is the version of the 13.4.4 servicing release that introduces the freeze, and is >= 13.4.3.0 (the latest shipped stable), so a current CLI binds against any already-shipped stable app's codegen reference — the common, must-work backward-compat direction.
• Merged forward to main so every later stable and servicing release (13.4.4, 13.5, ...) bundles the same value; post-freeze CLI/SDK pairs then match exactly and no skew matters. On release/13.4 the product version is already 13.4.4, so this is a no-op for that build and only constrains future minors.
• Only AssemblyVersion is frozen; FileVersion, InformationalVersion, and the NuGet package version stay build-derived, so diagnostics keep real build identities. Aspire.TypeSystem is consumed only via ProjectReference (no PackageReference consumers), so the frozen assembly version is not a package contract anyone binds to by exact version, and CP0003 package-baseline validation still passes (13.4.4.0 >= baseline).

Residual cases (routed to diagnostics, not silent)

Two narrow skews can't be fixed by any freeze value and are surfaced as an actionable "run aspire update" message by the #18125 diagnostics:

1. An already-shipped old CLI (real, lower bundled version) running post-freeze codegen that references 13.4.4.0.
2. A pre-freeze 13.5.0 preview app whose codegen still references a real 13.5.0.0 (> 13.4.4.0); preview-channel skew is outside the supported stable matrix and is superseded by post-freeze builds.

Back-compat guard

Because binding now succeeds on version alone, that safety only holds if the shared contract stays strictly additive. AtsSharedContractSurfaceTests snapshots the shared-contract surface (embedded baseline) and fails on any removal/signature change, forcing a deliberate decision: additive (no bump) vs breaking (bump AssemblyVersion).

Validation

• Aspire.Hosting.RemoteHost.Tests: 451/451 passed on the release/13.4 base (includes the new contract-surface guard).
• dotnet pack src/Aspire.TypeSystem: succeeds with no CP0003 override.
• Faithful strong-named A/B bind repro confirms BEFORE → ReflectionTypeLoadException (generators dropped), AFTER → generator discovered.

Targets release/13.4 for the 13.4.4 servicing release. Relates to #18110, #17910; complementary to the #18125 diagnostics.

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 18160

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/microsoft/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 18160"

[Copilot]

Pull request overview

This PR fixes a critical issue where polyglot (TypeScript/Python/Java/Go/Rust) AppHost code generation silently fails when the installed Aspire CLI is older than the AppHost's configured SDK within the same major version (e.g., 13.4.3 CLI + 13.5.0 SDK). The root cause was that the strong-named AssemblyVersion floated with MAJOR.MINOR.PATCH, preventing the older bundled Aspire.TypeSystem from satisfying newer codegen assemblies' strong-named references.

Changes:

• Pins Aspire.TypeSystem's AssemblyVersion to $(MajorVersion).0.0.0 so that any CLI/SDK combination within the same major binds successfully, while preserving real build identities in FileVersion and InformationalVersion.
• Adds explanatory comments in IntegrationLoadContext and AssemblyLoader documenting why the version pin makes the shared-assembly short-circuit and mismatch check safe.
• Introduces AtsSharedContractSurfaceTests with an embedded baseline snapshot to guard against future breaking changes to the public surface that could reintroduce the binding failure.

Reviewed changes

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Show a summary per file

File	Description
src/Aspire.TypeSystem/Aspire.TypeSystem.csproj	Core fix: pins AssemblyVersion to MAJOR.0.0.0 with thorough rationale comment
src/Aspire.Hosting.RemoteHost/IntegrationLoadContext.cs	Documents why the SharedAssemblyName short-circuit is safe under the pinned version
src/Aspire.Hosting.RemoteHost/AssemblyLoader.cs	Restructures WarnIfSharedAssemblyMismatch docs to explain post-pin semantics (cross-major only warning, same-version/differing-MVID is benign)
tests/Aspire.Hosting.RemoteHost.Tests/AtsSharedContractSurfaceTests.cs	New back-compat guard test comparing assembly public surface against embedded baseline
tests/Aspire.Hosting.RemoteHost.Tests/Aspire.Hosting.RemoteHost.Tests.csproj	Adds embedded resource and Aspire.TypeSystem project reference for the new test
tests/Aspire.Hosting.RemoteHost.Tests/Snapshots/AtsSharedContractSurface.txt	Frozen public API surface baseline for Aspire.TypeSystem

[Copilot]

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Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

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Pull request overview

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[Copilot]

Pull request overview

Copilot reviewed 31 out of 31 changed files in this pull request and generated 1 comment.

[Sébastien Ros (sebastienros)]

PR Testing Report

PR Information

• PR Number:[release/13.4] Freeze Aspire.TypeSystem AssemblyVersion at 13.4.5.0 to fix cross-ALC codegen binding #18160
• Title: Freeze Aspire.TypeSystem AssemblyVersion at 13.4.4.0 to fix cross-ALC codegen binding
• Head Commit:37ba357
• Base Branch:release/13.4
• Tested At: 2026-06-13 (local macOS, osx-arm64) + CI run 27453745514

Artifact Version Verification

• Expected Commit (PR head):37ba357
• Installed CLI version:13.4.4-pr.18160.g37ba3575
• Status: ✅ Verified (short SHA g37ba3575 matches PR head)

Changes Analyzed

Files Changed

• src/Aspire.TypeSystem/Aspire.TypeSystem.csproj — froze <AssemblyVersion>13.4.4.0</AssemblyVersion> (the only production change). NoDisablePackageBaselineValidation — 13.4.4.0 >= 13.4.0 baseline, so CP0003 passes naturally.
• src/Aspire.Hosting.RemoteHost/IntegrationLoadContext.cs — comment-only (brief pointer to the csproj rationale on the shared-from-bundle short-circuit).
• src/Aspire.Hosting.RemoteHost/AssemblyLoader.cs — comment-only (WarnIfSharedAssemblyMismatch; warns only when bundled < probed).
• tests/Aspire.Hosting.RemoteHost.Tests/SharedContractSurface.cs / SharedContractSurfaceTests.cs / AtsSharedContractSurfaceTests.cs / Snapshots/AtsSharedContractSurface.txt — contract-freeze guard. The guard now also renders declared interfaces + base type + static modifiers so an : ICodeGenerator removal or an instance→static flip also trips it.

Change Categories

• CLI changes detected (no behavioral CLI code; only ATS assembly-version metadata + RemoteHost comments)
• Hosting changes (Aspire.TypeSystem build metadata; RemoteHost comment-only)
• Dashboard changes
• CI infrastructure changes
• VS Code extension changes
• Test changes (contract-freeze guard)

Frozen-version proof (the heart of the fix)

Extracted from the dogfood hive (Aspire.TypeSystem.13.4.4-pr.18160.g37ba3575.nupkg and Aspire.Hosting.CodeGeneration.TypeScript.*.nupkg) and read via AssemblyName / PEReader metadata:

Aspire.TypeSystem.dll AssemblyVersion = 13.4.4.0
CodeGeneration.TypeScript references Aspire.TypeSystem, Version=13.4.4.0

The package version still floats (13.4.4-pr.18160.g37ba3575); only the AssemblyVersion is frozen at 13.4.4.0. Because 13.4.4.0 >= 13.4.3.0 (latest shipped stable), a CLI bundling this ATS satisfies the strong-named reference carried by codegen assemblies from current and older stable SDKs — which is the bind that the regression broke.

Test Scenarios Executed

Scenario 1: Install + version match

Objective: Install the PR CLI and confirm it reports the PR head commit.
Coverage Type: Happy path
Status: ✅ Passed

Steps:

1. get-aspire-cli-pr.sh 18160 --install-path <tmp> --skip-path --skip-extension
2. <cli> --version

Evidence: version 13.4.4-pr.18160.g37ba3575; both built-nugets and cli-native-archives-osx-arm64 artifacts downloaded.

---

Scenario 2: TypeScript AppHost codegen (regression check)

Objective: Verify TypeScript polyglot code generation works (the exact path that failed in the regression).
Coverage Type: Happy path (regression guard)
Status: ✅ Passed

Steps:

1. <cli> init --language typescript --non-interactive (fresh temp dir; npm deps installed by init).
2. <cli> add Aspire.Hosting.Redis --non-interactive → Aspire.Hosting.Redis::13.4.4-pr.18160.g37ba3575 added.
3. Removed .aspire/modules, then <cli> restore --apphost <tmp>/apphost.mts --non-interactive.

Evidence (ts-restore.log):

• ✅ SDK code restored successfully for apphost.mts. (exit 0)
• Generated .aspire/modules/: aspire.mts (2.6 MB), base.mts, transport.mts, .codegen-hash
• Generated aspire.mts contains the Redis surface (1366 addRedis/RedisResource references).
• NoNo code generator found for language: TypeScript; noReflectionTypeLoadException / FileLoadException.

---

Scenario 3: Python AppHost codegen (regression check)

Objective: Verify a second polyglot language (Python) codegen path works.
Coverage Type: Happy path (regression guard)
Status: ✅ Passed

Steps:

1. Staged tests/PolyglotAppHosts/Aspire.Hosting.Redis/Python into <tmp>/py with an aspire.config.json (language: python, experimentalPolyglot:python feature, SDK 13.4.4-pr.18160.g37ba3575) and a NuGet.config pointing at the PR hive. (aspire init exposes only csharp/typescript; Python polyglot is experimental and config-driven.)
2. <cli> restore --apphost <tmp>/py/apphost.py --non-interactive.

Evidence (py-restore.log):

• ✅ SDK code restored successfully for apphost.py. (exit 0)
• Generated .aspire/modules/: aspire_app.py (530 KB), pyproject.toml, .codegen-hash
• Generated aspire_app.py contains the Redis surface (43 add_redis/redis references).
• NoNo code generator found; no loader/bind exception. (An unrelated pylock.apphost.toml not-found notice is the Python dep-lock step, not codegen — codegen reported success after it.)

---

Scenario 4: Package build (CP0003) ships without any override

Objective: Confirm the 13.4.4.0 freeze does not trip package baseline validation.
Coverage Type: Boundary / build validation
Status: ✅ Passed

Key delta vs the earlier 1.0.0.0 sentinel: the old value was < 13.4.0 baseline and required DisablePackageBaselineValidation=true. With 13.4.4.0 >= 13.4.0, CP0003 passes naturally and the override has been removed.

Evidence (CI run 27453745514, head 37ba3575):

• Tests / Build packages / Build packages → conclusion success (no DisablePackageBaselineValidation).
• Package version still floats (pr.18160.g37ba3575); only AssemblyVersion is frozen.

CI corroboration: all five polyglot languages green on head 37ba3575 (run 27453745514)

Beyond the two local runs above, the full polyglot codegen matrix is green on the PR head:

• Polyglot SDK Validation: TypeScript (Node 24.x), Python, Java, Go, Rust → all success
• Hosting.CodeGeneration.{TypeScript, Python, Go, Java, Rust} (ubuntu + windows) → all success
• Cli.EndToEnd-TypeScriptCodegenValidationTests + Cli.EndToEnd-JavaCodegenValidationTests → success

This confirms the fix holds across every codegen language that references Aspire.TypeSystem, not just the two exercised locally.

Scope note: what these scenarios do and do NOT cover

A dogfood install is a single matched CLI/SDK version, so it cannot reproduce the genuine old-CLI + newer-SDK strong-name skew that is the regression. Scenarios 2–3 are a happy-path regression check: they prove the 13.4.4.0 AssemblyVersion freeze does not break ATS loading / cross-ALC type identity when versions match (a wrong freeze value would break codegen even in the matched case), and the frozen-version proof above shows the codegen assemblies now carry a 13.4.4.0 reference that an equal-or-older-stable bundled copy satisfies. The actual skew bind (BEFORE = ReflectionTypeLoadException → 0 generators; AFTER = generator discovered) was proven earlier with real strong-named binaries in the A/B repro matrix, and is locked in by the AtsSharedContractSurface contract-freeze guard.

Complementarity with #18125

The two PRs fully complement each other:

• [release/13.4] Freeze Aspire.TypeSystem AssemblyVersion at 13.4.5.0 to fix cross-ALC codegen binding #18160 (this PR) fixes the version-skew bind: freezing AssemblyVersion at 13.4.4.0 makes an equal-or-older-stable bundled ATS satisfy a newer codegen assembly's strong-named reference.
• Surface actionable diagnostic when TypeScript codegen generator is dropped by load failure #18125 is the diagnostics safety-net for the residual real failure mode — e.g. a pre-freeze CLI, or a pre-freeze 13.5.0 preview app that references real 13.5.0.0 > 13.4.4.0. Those surface through Surface actionable diagnostic when TypeScript codegen generator is dropped by load failure #18125's reflection-load-exception handling as an actionable "run aspire update" message instead of the cryptic "No code generator found".

Summary

Scenario	Status	Notes
1. Install + version match	✅ Passed	13.4.4-pr.18160.g37ba3575 matches head
2. TypeScript codegen	✅ Passed	aspire.mts 2.6 MB, 1366 Redis refs, no cryptic error
3. Python codegen	✅ Passed	aspire_app.py 530 KB, 43 Redis refs, no cryptic error
4. Package build (CP0003)	✅ Passed	NoDisablePackageBaselineValidation needed (13.4.4.0 >= 13.4.0)
CI polyglot matrix (TS/Py/Java/Go/Rust)	✅ Passed	run 27453745514, all codegen suites green

Overall Result

✅ PR VERIFIED

Notes

• Frozen AssemblyVersion = 13.4.4.0 is a no-op on release/13.4 (product is already 13.4.4) and only constrains 13.5+; merged forward to main it keeps every future stable/servicing bundle on the sentinel.
• Skew (old/pre-freeze CLI + newer SDK) is intentionally not dogfood-reproducible; that path relies on the prior binary A/B repro + the contract-freeze guard + Surface actionable diagnostic when TypeScript codegen generator is dropped by load failure #18125 diagnostics.
• PR is a draft — this is test-and-report only; no approve/merge performed.

[Copilot]

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[github-actions]

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