Invalid AspireCliInvocationMode values are silently ignored

[afscrome]

Description

AspireCliInvocationMode accepts invalid values silently. A misspelled or unsupported value is ignored/falls back to Aspire CLI resolution without any warning or error.

This makes configuration mistakes difficult to spot. For example, DnxPinnedd or DefinitelyInvalid does not fail validation and does not emit a warning; the SDK simply resolves the normal Aspire CLI path instead of DNX.

This is separate from explicit AspireCliPath precedence. The behavior below was confirmed with AspireCliPath cleared both as an environment variable and as an MSBuild property.

Reproduction

In a generic AppHost project using Aspire.AppHost.Sdk/13.5.1, set or pass an invalid invocation mode:

$env:AspireCliPath = ''
$env:ASPIRE_CLI_PATH = ''

dotnet msbuild app/Sample.AppHost/Sample.AppHost.csproj `
  /t:_ResolveAspireCliInvocation `
  /v:diag `
  /p:AspireUseCliBundle=true `
  /p:AspireCliInvocationMode=DefinitelyInvalid `
  /p:AspireCliPath= `
  /nologo |
  Select-String -Pattern 'AspireCliInvocationMode=|AspireCliPath=|Aspire CLI invocation selection:'

Observed result:

Task Parameter:AspireCliInvocationMode=DefinitelyInvalid
Aspire CLI invocation selection: Aspire (aspire: C:\Users\<user>\.aspire\bin\aspire.exe, dnx: C:\Program Files\dotnet\dnx.cmd)

Running the validation target also succeeds:

$env:AspireCliPath = ''
$env:ASPIRE_CLI_PATH = ''

dotnet msbuild app/Sample.AppHost/Sample.AppHost.csproj `
  /t:_ValidateAspireCliDnxInvocationMode `
  /v:normal `
  /p:AspireUseCliBundle=true `
  /p:AspireCliInvocationMode=DefinitelyInvalid `
  /p:AspireCliPath= `
  /nologo

Observed result:

Build succeeded.
    0 Warning(s)
    0 Error(s)

Diagnostic output confirms the invalid property value was present:

AspireCliInvocationMode = DefinitelyInvalid

Expected behavior

The SDK should warn or error when AspireCliInvocationMode is set to an unsupported value.

For example, if the supported values are Path, Dnx, and DnxPinned, then a value like DefinitelyInvalid should produce a diagnostic explaining the accepted values.

Actual behavior

Invalid values are accepted silently. They do not produce a warning, error, or validation diagnostic, and resolution falls back to Aspire CLI mode.

Environment

• OS: Windows
• .NET SDK: 10.0.303
• AppHost SDK: Aspire.AppHost.Sdk/13.5.1

[joperezr]

🤖 Aspire triage pass — 2026-08-26 17:58 UTC

Area: area-cli
Kind: bug
Repro: yes-minimal — see the "Reproduction" section of the issue body (msbuild _ResolveAspireCliInvocation / _ValidateAspireCliDnxInvocationMode invocations)
Affected version(s): Aspire.AppHost.Sdk 13.5.1 (latest line: 13.5.x servicing; vNext 13.6)
Severity: S4 — missing validation diagnostic; valid values still resolve correctly, no functional breakage, workaround is to use a supported value

Urgency: ⚪ backlog — no milestone
Reason: diagnostics/validation gap in the AppHost SDK invocation-mode resolution; not a regression and a clear workaround exists (use a valid mode value).

Suggested owner(s): Mitch Denny (@mitchdenny) (CLI SDK / CLI-bundle owner), backup James Newton-King (@JamesNK)
Evidence:

• CODEOWNERS lists Mitch Denny (@mitchdenny) for /src/Aspire.Cli
• Mitch Denny (@mitchdenny) merged recent area-cli PRs Exclude unused hex1bpty.exe from published CLI archives #19554, Persist CLI channel across installs and self-updates #19469, [release/13.5] Fix mixed-quality staging package discovery #19427, Fix mixed-quality staging package discovery #19426 and closed aspire add / integration search over-filters in polyglot hosts: zero compatible integrations returned in a TypeScript AppHost #19161 as completed
• James Newton-King (@JamesNK) is the highest-volume recent area-cli contributor (e.g. merged Remove flaky duplicate child log path test #19538, Preserve CLI status messages without interactive spinners #19272, Resolve dotnet paths in doctor checks #19232; closed [13.5] Trace logging on aspire doctor causes weird indentation #19017, [main] aspire doctor taking 15 secs to run #19016, Use resolved dotnet paths in aspire doctor #19003 as completed)

Confidence: medium
Needs human?: no