'dotnet lambda package' throws 'ArgumentNullException' when running for a project with multiple target frameworks

Description

When running dotnet lambda package for a csproj that has multitargetting enabled, a ArgumentNullException exception is throw and the process crashes.

Specifying the -f cmdline option with either netcoreapp3.1 or net5.0 works as expected.

I’d expect either it to work seamlessly, or to return a proper message saying that the target framework needs to be specified.

Reproduction Steps

1. Create an API lambda project targeting Net Core 3.1 and Net 5.0

Section of csproj:

<TargetFrameworks>netcoreapp3.1;net5.0</TargetFrameworks>

1. Run dotnet lambda package in the projects folder
2. Observe exception is quickly thrown

Logs

Amazon Lambda Tools for .NET Core applications (5.0.0) Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet

Unknown error executing command: Value cannot be null. Parameter name: paths at System.IO.Path.Combine(String[] paths) at Amazon.Lambda.Tools.LambdaPackager.CreateApplicationBundle(LambdaToolsDefaults defaults, IToolLogger logger, String workingDirectory, String projectLocation, String configuration, String targetFramework, String msbuildParameters, Boolean disableVersionCheck, LayerPackageInfo layerPackageInfo, String& publishLocation, String& zipArchivePath) in C:\codebuild\tmp\output\src845572623\src\src\Amazon.Lambda.Tools\LambdaPackager.cs:line 76 at Amazon.Lambda.Tools.Commands.PackageCommand.PerformActionAsync() at Amazon.Common.DotNetCli.Tools.Commands.BaseCommand`1.ExecuteAsync() in C:\codebuild\tmp\output\src845572623\src\src\Amazon.Common.DotNetCli.Tools\Commands\BaseCommand.cs:line 46

Environment

• OS Info: Windows 10
• Build Environment: Visual Studio 16.8.2 Developer Command Prompt, Amazon.Lambda.Tools 5.0.0
• Targeted .NET Platform: netcoreapp3.1 and net5.0

Resolution

• 👋 I can/would-like-to implement a fix for this problem myself

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This is a 🐛 bug-report

[ashishdhingra]

Ashish, after updating the tool, I’m now getting a proper validation message back:

PS C:\git\MyProject> dotnet lambda package Amazon Lambda Tools for .NET Core applications (5.0.1) Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet Missing required parameter: --framework

However, I’d suggest improving on the error message: the reason --framework becomes required is due to the project being a multi-target project, however the message could mislead developers into believing the parameter is always required.

Perhaps it would be better to be a bit more specific in the error message. Suggestion:

Missing required parameter for multi-target project: --framework

Having said that, the fact that we are not getting an exception anymore is great.

Hi @julealgon,

Good morning.

I had discussion with the development team and based on their findings, it would not be a simple change in the error message. The code is shared and refactoring it for the error message to include additional checks would impact the overall design and would not be feasible. While I cannot provide the specific details, but it’s good that exception is not thrown anymore for the mentioned scenario. Hence, closing this issue.

Thanks, Ashish

[normj]

Pull request out for prompting the user if tool doesn’t figure out the target framework. https://github.com/aws/aws-extensions-for-dotnet-cli/pull/151