Shared projects can't be found when using new slnx solution file

[oskarj]

Describe the bug

When migrating a .NET Lambda project that uses Native AOT to slnx, the build fails because the referenced shared project cannot be found.

https://devblogs.microsoft.com/dotnet/introducing-slnx-support-dotnet-cli/

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

I expected the project to build and the lambda to be deployed.

Output

Amazon Lambda Tools for .NET Core applications (5.13.0)
Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet

Found /etc/os-release
Found /etc/os-release
Executing publish command
Starting container for native AOT build using build image: public.ecr.aws/sam/build-dotnet8:latest-x86_64.
... invoking 'docker run --name tempLambdaBuildContainer-db2095a3-89aa-4a22-bf3e-37eb8e2657ee --rm --volume "/home/oskar/temp/BlogFunction":/tmp/source/ -i -u 1000:1000 -e DOTNET_CLI_HOME=/tmp/dotnet -e XDG_DATA_HOME=/tmp/xdg public.ecr.aws/sam/build-dotnet8:latest-x86_64 dotnet publish "/tmp/source/src/BlogFunction" --output "/tmp/source/src/BlogFunction/bin/Release/net8.0/publish" --configuration "Release" --framework "net8.0" /p:GenerateRuntimeConfigurationFiles=true --runtime linux-x64 --self-contained True /p:StripSymbols=true' from directory /home/oskar/temp/BlogFunction
... docker run: An issue was encountered verifying workloads. For more information, run "dotnet workload update".
... docker run: Determining projects to restore...
... docker run: Restored /tmp/source/src/BlogFunction.Shared/BlogFunction.Shared.csproj (in 2.48 sec).
... docker run: Restored /tmp/source/src/BlogFunction/BlogFunction.csproj (in 3.82 sec).
... docker run: BlogFunction.Shared -> /tmp/source/src/BlogFunction.Shared/bin/Release/net8.0/BlogFunction.Shared.dll

Current Behavior

The project fails to build

Output

Amazon Lambda Tools for .NET Core applications (5.13.0)
Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet

Found /etc/os-release
Found /etc/os-release
Executing publish command
Starting container for native AOT build using build image: public.ecr.aws/sam/build-dotnet8:latest-x86_64.
... invoking 'docker run --name tempLambdaBuildContainer-9b013d41-703c-4d77-aa3b-677a359793cd --rm --volume "/home/oskar/temp/BlogFunction/src/BlogFunction":/tmp/source/ -i -u 1000:1000 -e DOTNET_CLI_HOME=/tmp/dotnet -e XDG_DATA_HOME=/tmp/xdg public.ecr.aws/sam/build-dotnet8:latest-x86_64 dotnet publish "/tmp/source/" --output "/tmp/source/bin/Release/net8.0/publish" --configuration "Release" --framework "net8.0" /p:GenerateRuntimeConfigurationFiles=true --runtime linux-x64 --self-contained True /p:StripSymbols=true' from directory /home/oskar/temp/BlogFunction/src/BlogFunction
... docker run: An issue was encountered verifying workloads. For more information, run "dotnet workload update".
... docker run: Determining projects to restore...
... docker run: Skipping project "/tmp/BlogFunction.Shared/BlogFunction.Shared.csproj" because it was not found.
... docker run: Skipping project "/tmp/BlogFunction.Shared/BlogFunction.Shared.csproj" because it was not found.
... docker run: Restored /tmp/source/BlogFunction.csproj (in 3.61 sec).
... docker run: /var/lang/bin/sdk/8.0.414/Microsoft.Common.CurrentVersion.targets(2176,5): warning : The referenced project '../BlogFunction.Shared/BlogFunction.Shared.csproj' does not exist. [/tmp/source/BlogFunction.csproj]
... docker run: /tmp/source/Function.cs(2,20): error CS0234: The type or namespace name 'Shared' does not exist in the namespace 'BlogFunction' (are you missing an assembly reference?) [/tmp/source/BlogFunction.csproj]
ERROR: Container build returned 1

Reproduction Steps

Create a new lambda project with a shared library

dotnet new lambda.EmptyFunction --name BlogFunction --profile default --region us-east-2
cd BlogFunction
dotnet new sln
dotnet sln add src/BlogFunction/BlogFunction.csproj
dotnet sln add test/BlogFunction.Tests/BlogFunction.Tests.csproj
dotnet new classlib --framework "net8.0" -o src/BlogFunction.Shared
dotnet sln add src/BlogFunction.Shared/BlogFunction.Shared.csproj
dotnet reference add src/BlogFunction.Shared/BlogFunction.Shared.csproj --project src/BlogFunction/BlogFunction.csproj

Make sure that the lambda function is a AOT project edit BlogFunction.csproj to:

Exe net8.0 enable enable Lambda true true true partial

Verify that it works

cd src/BlogFunction/
dotnet lambda deploy-function

Output

Amazon Lambda Tools for .NET Core applications (5.13.0)
Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet

Found /etc/os-release
Found /etc/os-release
Executing publish command
Starting container for native AOT build using build image: public.ecr.aws/sam/build-dotnet8:latest-x86_64.
... invoking 'docker run --name tempLambdaBuildContainer-db2095a3-89aa-4a22-bf3e-37eb8e2657ee --rm --volume "/home/oskar/temp/BlogFunction":/tmp/source/ -i -u 1000:1000 -e DOTNET_CLI_HOME=/tmp/dotnet -e XDG_DATA_HOME=/tmp/xdg public.ecr.aws/sam/build-dotnet8:latest-x86_64 dotnet publish "/tmp/source/src/BlogFunction" --output "/tmp/source/src/BlogFunction/bin/Release/net8.0/publish" --configuration "Release" --framework "net8.0" /p:GenerateRuntimeConfigurationFiles=true --runtime linux-x64 --self-contained True /p:StripSymbols=true' from directory /home/oskar/temp/BlogFunction
... docker run: An issue was encountered verifying workloads. For more information, run "dotnet workload update".
... docker run: Determining projects to restore...
... docker run: Restored /tmp/source/src/BlogFunction.Shared/BlogFunction.Shared.csproj (in 2.48 sec).
... docker run: Restored /tmp/source/src/BlogFunction/BlogFunction.csproj (in 3.82 sec).
... docker run: BlogFunction.Shared -> /tmp/source/src/BlogFunction.Shared/bin/Release/net8.0/BlogFunction.Shared.dll

Migrate to slnx

cd ../../
dotnet sln migrate
rm BlogFunction.sln
cd src/BlogFunction/
dotnet lambda deploy-function

Output

Amazon Lambda Tools for .NET Core applications (5.13.0)
Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet

Found /etc/os-release
Found /etc/os-release
Executing publish command
Starting container for native AOT build using build image: public.ecr.aws/sam/build-dotnet8:latest-x86_64.
... invoking 'docker run --name tempLambdaBuildContainer-9b013d41-703c-4d77-aa3b-677a359793cd --rm --volume "/home/oskar/temp/BlogFunction/src/BlogFunction":/tmp/source/ -i -u 1000:1000 -e DOTNET_CLI_HOME=/tmp/dotnet -e XDG_DATA_HOME=/tmp/xdg public.ecr.aws/sam/build-dotnet8:latest-x86_64 dotnet publish "/tmp/source/" --output "/tmp/source/bin/Release/net8.0/publish" --configuration "Release" --framework "net8.0" /p:GenerateRuntimeConfigurationFiles=true --runtime linux-x64 --self-contained True /p:StripSymbols=true' from directory /home/oskar/temp/BlogFunction/src/BlogFunction
... docker run: An issue was encountered verifying workloads. For more information, run "dotnet workload update".
... docker run: Determining projects to restore...
... docker run: Skipping project "/tmp/BlogFunction.Shared/BlogFunction.Shared.csproj" because it was not found.
... docker run: Skipping project "/tmp/BlogFunction.Shared/BlogFunction.Shared.csproj" because it was not found.
... docker run: Restored /tmp/source/BlogFunction.csproj (in 3.61 sec).
... docker run: /var/lang/bin/sdk/8.0.414/Microsoft.Common.CurrentVersion.targets(2176,5): warning : The referenced project '../BlogFunction.Shared/BlogFunction.Shared.csproj' does not exist. [/tmp/source/BlogFunction.csproj]
... docker run: /tmp/source/Function.cs(2,20): error CS0234: The type or namespace name 'Shared' does not exist in the namespace 'BlogFunction' (are you missing an assembly reference?) [/tmp/source/BlogFunction.csproj]
ERROR: Container build returned 1

Possible Solution

No response

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

Amazon Lambda Tools for .NET Core applications (5.13.0)
.NET SDK 8.0.415
Docker version 28.3.3, build 980b856

Targeted .NET Platform

NET 8.0

Operating System and version

Ubuntu 24.04.3 LTS

[oskarj]

After some investigations I found that the Lambda tools have moved here: https://github.com/aws/aws-extensions-for-dotnet-cli/

Please let me know if I should create the issue there.

A workaround is to create a symlink from .slnx to .sln
ln -s BlogFunction.slnx BlogFunction.sln

Also found this line of code that it should also contain a check for .slnx
https://github.com/aws/aws-extensions-for-dotnet-cli/blob/master/src/Amazon.Common.DotNetCli.Tools/Utilities.cs#L173

Are you accepting pull requests?

[muhammad-othman]

Thank you @oskarj for the detailed bug report and investigation.
I've transferred it issue to aws-extensions-for-dotnet-cli repository since that's where the Lambda tools are now maintained.
I agree that this is indeed a bug where the Lambda tools don't recognize the new .slnx solution file format introduced with .NET 9.
We do accept pull requests, If you're interested in contributing the fix, that would be greatly appreciated.