New kinds of constraints

[baronfel]

Currently for .NET 7 we plan to support constraints based on

• Host OS
• Template Engine host
• Installed SDK Workloads
• Specific Project Properties

This discussion should serve as a space to talk about new kinds of constraints that users would like to see.

[michael-hawker]

Would this also be for things like limiting the length of the dotnet new <template> -n <name> name field length? Some build systems can run into issues if a value is too long after the template is generated. e.g. microsoft/microsoft-ui-xaml#7059

[baronfel]

Constraints are more about asking if the host environment meets a certain criteria than they are about validating set of input parameters. I don't think we have length validations on symbols, we could definitely consider it though!

[Jandini]

Is it possible to have no constraints at all? It broke my templates as they did not have "constraints" entry in template.json file.

This is the error I'm getting when try to create new project from my template which does not have any "constraints"

Template "Console Go" could not be created.
Failed to create template.
Details: Sequence contains no matching element

Jandini/Janda.Go#26

[vlada-shubina]

@Jandini The constraints are optional.

Could you please run the template with --diagnostics option to get verbose output? Also, could you please create an issue for your case? It doesn't seem to be related to the topic of this discussion. Thank you

[Jandini]

I am not sure if that is related to constrains. It was my first assumption as I saw this change the templating first. I can check it myself but were there any other changes to templating?

Here is the diagnostics run

[2022-11-24 16:31:50.462] [Debug] [Template Engine] => [Execute]: Execute started
[2022-11-24 16:31:50.598] [Debug] [Microsoft.TemplateEngine.Edge.TemplateConstraintManager] => [Execute]: Found 5 constraints factories, initializing.
[2022-11-24 16:31:50.599] [Debug] [Microsoft.TemplateEngine.Edge.TemplateConstraintManager] => [Execute]: Found 5 constraints factories, initializing.
[2022-11-24 16:31:50.602] [Debug] [MSBuildEvaluator] => [Execute]: Output directory is: C:\Temp\##.
[2022-11-24 16:31:50.602] [Debug] [MSBuildEvaluator] => [Execute]: Project full path is: <null>.
[2022-11-24 16:31:50.604] [Debug] [MSBuildEvaluator] => [Execute]: Found project files: .
[2022-11-24 16:31:50.604] [Debug] [MSBuildEvaluator] => [Execute]: No project found.
[2022-11-24 16:31:50.614] [Debug] [Template Engine] => [Execute] => [Template from config C:\Users\Matt\.templateengine\packages\Janda.Go.0.7.1-constraints.1.nupkg/content/src/Console/.template.config/template.json]: Template from config C:\Users\Matt\.templateengine\packages\Janda.Go.0.7.1-constraints.1.nupkg/content/src/Console/.template.config/template.json started
[2022-11-24 16:31:50.635] [Debug] [Template Engine] => [Execute] => [Template from config C:\Users\Matt\.templateengine\packages\Janda.Go.0.7.1-constraints.1.nupkg/content/src/Console/.template.config/template.json]: Template from config C:\Users\Matt\.templateengine\packages\Janda.Go.0.7.1-constraints.1.nupkg/content/src/Console/.template.config/template.json finished, took 21 ms
[2022-11-24 16:31:50.636] [Debug] [Microsoft.TemplateEngine.Edge.Template.TemplateCreator] => [Execute] => [Template content generation]: Template content generation started
[2022-11-24 16:31:50.692] [Debug] [Microsoft.TemplateEngine.Orchestrator.RunnableProjects.BindSymbolEvaluator] => [Execute] => [Template content generation]: Configured bind sources are: Environment variables(EnvironmentVariablesBindSource), Host defined parameters(HostParametersBindSource), Project context(ProjectContextSymbolSource).
[2022-11-24 16:31:50.693] [Debug] [Microsoft.TemplateEngine.Orchestrator.RunnableProjects.BindSymbolEvaluator] => [Execute] => [Template content generation]: Evaluating binding 'env:OS'.
[2022-11-24 16:31:50.693] [Debug] [Microsoft.TemplateEngine.Orchestrator.RunnableProjects.BindSymbolEvaluator] => [Execute] => [Template content generation]: The following sources match prefix 'env': Environment variables.
[2022-11-24 16:31:50.694] [Debug] [Template Engine] => [Execute] => [Template content generation]: [EnvironmentVariablesBindSource]: Retrieving bound value for 'OS'.
[2022-11-24 16:31:50.694] [Debug] [Template Engine] => [Execute] => [Template content generation]: [EnvironmentVariablesBindSource]: Retrieved bound value for 'OS': 'Windows_NT'.
[2022-11-24 16:31:50.698] [Debug] [Microsoft.TemplateEngine.Orchestrator.RunnableProjects.BindSymbolEvaluator] => [Execute] => [Template content generation]: 'Windows_NT' was retrieved for 'OS'.
[2022-11-24 16:31:50.698] [Debug] [Microsoft.TemplateEngine.Orchestrator.RunnableProjects.BindSymbolEvaluator] => [Execute] => [Template content generation]: Variable 'OS' was set to 'Windows_NT'.
[2022-11-24 16:31:50.701] [Debug] [Microsoft.TemplateEngine.Edge.Template.TemplateCreator] => [Execute] => [Template content generation]: Template content generation finished, took 65 ms
Template "Console Go" could not be created.
Failed to create template.                                                                                                                                                                                                                                                     
Details: Sequence contains no matching element      
[2022-11-24 16:31:50.790] [Debug] [NuGetLogger] => [Execute]: Searching for Janda.Go in https://api.nuget.org/v3/index.json.
[2022-11-24 16:31:50.832] [Debug] [NuGetLogger] => [Execute]:   GET https://api.nuget.org/v3/registration5-gz-semver2/janda.go/index.json
[2022-11-24 16:31:50.886] [Debug] [NuGetLogger] => [Execute]: Searching for Janda.Go in C:\Program Files (x86)\Microsoft SDKs\NuGetPackages\.
[2022-11-24 16:31:50.892] [Debug] [NuGetLogger] => [Execute]: Janda.Go is not found in NuGet feed C:\Program Files (x86)\Microsoft SDKs\NuGetPackages\.
[2022-11-24 16:31:51.422] [Debug] [NuGetLogger] => [Execute]:   OK https://api.nuget.org/v3/registration5-gz-semver2/janda.go/index.json 588ms
[2022-11-24 16:31:51.503] [Debug] [NuGetLogger] => [Execute]: Found 7 versions for Janda.Go in NuGet feed https://api.nuget.org/v3/index.json.
[2022-11-24 16:31:51.512] [Debug] [Template Engine] => [Execute]: Execute finished, took 1051 ms

[vlada-shubina]

The issue is caused by the fact that the template contains parameter name which is same as implicit parameter name. This case is not handled correctly in 7.0.1xx, but it was already fixed in 7.0.2xx and .NET 8.

Though error message is not correct, the root cause is template authoring issue. Please remove the name from parameter list and it will work in .NET 7. There is no need to have name parameter defined, having sourceName implicitly generates name parameter defined with same replacements.

I will create the issue to update documentation to explain that name parameter should not be used, as it is generated explicitly.