Greater than 1 FromBody analyzer.

[mitchdenny]

This PR addresses #45382.

Detect when two or more [FromBody] attributes are used

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Description

This PR ads another diagnostic for when two [FromBody] attributes are used on a single handler function. It ads a diagnostic for each parameter which is decorated with [FromBody].

[ghost]

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[mitchdenny]

@halter73 waiting on your review. Based on @martincostello's feedback I also added support for scenarios where [AsParameters] is used. Because of this I wonder whether we should revisit the diagnostic message to make it cover that scenario as well. I would probably leave the title message alone, but expand the message with a bit more detail ... for example.

  <data name="Analyzer_MultipleFromBody_Message" xml:space="preserve">
    <value>Route handler has multiple parameters with the [FromBody] attribute or a parameter with an [AsParameters] attribute where the parameter type contains multiple members with [FromBody] attributes. Only one parameter can have a [FromBody] attribute.</value>
  </data>

[ghost]

/azp run

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[mitchdenny]

/azp run aspnetcore-ci

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Azure Pipelines successfully started running 1 pipeline(s).

[mitchdenny]

/azp run aspnetcore-components-e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mitchdenny]

/azp run aspnetcore-quarantined-pr

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[halter73]

This wouldn't fail if there's a single [FromBody] parameter and then another [AsParameter] parameter with a single [FromBody] property, right? Or multiple [AsParameter] parameters with a single [FromBody] property each? All of these should fail. Can we add test cases for these?

[halter73]

Because of this I wonder whether we should revisit the diagnostic message to make it cover that scenario as well. I would probably leave the title message alone, but expand the message with a bit more detail ... for example.

  <data name="Analyzer_MultipleFromBody_Message" xml:space="preserve">
    <value>Route handler has multiple parameters with the [FromBody] attribute or a parameter with an [AsParameters] attribute where the parameter type contains multiple members with [FromBody] attributes. Only one parameter can have a [FromBody] attribute.</value>
  </data>

I think the new message is good. I think the old message was good enough too. Hopefully it's obvious to the people using the feature that [AsParameters] properties count as parameters, but it doesn't hurt to be extra descriptive.