Warn when dab validate finds zero entities in the config

[aaronburtle]

Why make this change?

Closes #3267

What is this change?

Add a method to check and log a warning when entities are empty when running dab validate.
Added a test case to cover this new behavior.

How was this tested?

New test case covers change in behavior, manually tested with dab validate against zero entities.

[Copilot]

Pull request overview

Adds a CLI validation-time warning to help users detect “valid” configs that define no entities (and have no autoentities / multi-config datasource files), aligning dab validate behavior with Issue #3267.

Changes:

• Adds a WarnIfNoEntitiesDefined(RuntimeConfig) helper and invokes it during dab validate.
• Refactors IsConfigValid to log the new structural warning regardless of overall validation outcome.
• Adds a CLI unit test that verifies the warning is logged for a minimal config with zero entities.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Cli/ConfigGenerator.cs	Introduces and invokes the new “zero entities” warning helper during dab validate.
src/Cli.Tests/ValidateConfigTests.cs	Adds a unit test verifying the warning is emitted for an empty-entities config.

[anushakolan]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 6 pipeline(s).

[anushakolan]

LGTM, Apart from the minor comment left.

[Aniruddh25]

if there are 0 entities, or autoentities, it is still a valid configuration.

But do we still need to check whether any entity has missing fields when MCP is enabled - i.e. perform the below validation?

We should still Warn if Unauthenticated provider is used with authenticated or custom roles

[aaronburtle]

If there are no entities, then the for loop below iterates zero times and this is a no-op, so there wont really be any validation happening; there is nothing to validate. On the other hand, if validation fails for some other reason the user wont see any "missing fields with MCP" warnings, which may be an enhancement we want to add, but shouldn't be scoped to this PR.

[aaronburtle]

Similar to unauthenticated provider with non-anonymous roles. Since it is inside if(isValid) it only fires when everything else passes. If we move it outside then it would always run, but with 0 entities, the warning can never trigger.

[Aniruddh25]

Instead of directly calling the WarnIfNoEntitiesDefined function, test the scenario for which the bug is identified.
In this case, can we call IsConfigValid and verify the warning is printed?

[Aniruddh25]

Left few comments

[Aniruddh25]

Could you please clarify with @JerryNixon, if it is a config validation error or warning in case:

1. entities/autoentities both sections are completely missing - i.e. null from the config -> we error out today on this case.
2. entities/autoentities - either is present but count is 0 - no validation error - but warning emitted as per this PR.

[JerryNixon]

Config rules

Level 1. Root config (top level (has a child))

Root rules:

- if data-source-files is empty array, this is a non-Root.
- if data-source-files is NOT empty array, 
    data-source+entities is optional. 

Level 1.1. Non-Root A (including grandchildren)

Non-Root rules:

- must have data source and must have entities (or found entities if auto-entities is configured)
- if has children, same rules as above, must have ds and entities

When to warn

if (IsRoot) // at this point we know it has children
{
    if (has-data-source) // if you have a data source you must have entities
    {
        ValidateItHasEntities();
    }
    else if (!has-data-source && (has-any-entities || has-any-auto-entities-definitions))
    {
        Error("Entities found but no data source defined.");
    }
    else
    {
        Valid();
    }
}
else if (!IsRoot) // non-root/child
{
    ValidateItHasEntities();
}

ValidateItHasEntities()
{
    foreach (var definition in auto-entities-definitions)
    {
        if (definition has no entities)
        {
            Warning($"Auto-entities definition '{definition.Name}' but no entities found.");
        }
    }

    var entityCountFromAutoEntityDefinitions = 123; // count of all autoentities

    if (entityCountFromAutoEntityDefinitions == 0
        && entityCountFromEntities == 0)
    {
        Error("Data source defined but no entities found.");
    }

    Valid();
}