[Analyzer] Route syntax analyzer

[JamesNK]

Background and Motivation

A route is a string that has a standard syntax. An invalid route string errors at runtime when parsed. This typically happens at app startup. We want to tighten the dev loop and tell people their route is invalid in the IDE.

Proposed API

An analyzer that inspects route strings for invalid content.

A route string is indicated by [StringSyntax("Route")] on the property, method argument, or constructor argument.

Usage Examples

public IEndpointConventionBuilder MapGet(
    IEndpointRouteBuilder builder,
    [StringSyntax("Route")] string pattern,
    Delegate delegate)
{
    // ...
}

endpoints.MapGet("{**slug?}", () => "hello world"); // <- invalid because parameter can't be catchall and optional
endpoints.MapGet("//login", () => "hello world"); // <- invalid because can't have consecutive forward slashes
endpoints.MapGet("{id}/{id}", () => "hello world"); // <- invalid because can't have duplicate parameter names

Alternative Designs

Risks

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• The PR contains changes to the reference-assembly that describe the API change. Or, you have included a snippet of reference-assembly-style code that illustrates the API change.
• The PR describes the impact to users, both positive (useful new APIs) and negative (breaking changes).
• Someone is assigned to "champion" this change in the meeting, and they understand the impact and design of the change.

[halter73]

API Review notes:

• Looks good! This would always cause a runtime error.

Category: Usage
Severity: Warning