Linter diagnostics on library-defined model properties are dropped #12558

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   bugSomething isn't workingSomething isn't working

   compiler:coreIssues for @typespec/compilerIssues for @typespec/compiler

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   🎯 Issue Triage

   Linter diagnostics targeting properties declared in library models are discarded even when a project operation directly uses those properties. This creates a blind spot for rules that should report actionable diagnostics at the project use site.

   Category: Bug

   Area: compiler:core

   🔗 [Playground Reproduction]((typespec.io/redacted)

   📋 Reproduction code

   // lib.tsp
   model SharedQuery {
     @query
     top?: int32;
   }
   
   // main.tsp
   @route("/items")
   @get
   op list(...SharedQuery): string[];

   🔍 Analysis

   The affected component is the compiler's linter diagnostic pipeline. The likely cause is project/library filtering based only on the diagnostic target's declaration source: SharedQuery.top is classified as library-owned, so the diagnostic is dropped without relocating or associating it with the project operation that spreads the model.

   This is related to #1997's broader request to show library diagnostics at their use site. #11861 has similar symptoms but a distinct template-instantiation path; this report covers direct use of a non-template library model. The playground preserves the reported source shape, but reproducing the source-context filtering requires placing SharedQuery in an actual library package.

   📝 Suggested next steps

   • Add a compiler linter regression test with a library-defined non-template model spread into a project operation.
   • Determine the project use-site target or trace that should retain the diagnostic without exposing unrelated library-internal diagnostics.
   • Align the behavior with any shared solution for Linter System addition Show diagnostic in library at point of usage #1997 and ensure the template case in Linter silently drops diagnostics on library templates instantiated by the user project #11861 remains covered.

   Generated by Agentic Triage
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