Specifying interface in operation props causes emitter to crash

[shiron-dev]

Clear and concise description of the problem

When using “@typespec/openapi3”, specifying interface in operation props causes emitter to crash.
From a light reading of the implementation, it seems to me that it is not intended to specify an Interface in this ModelProperty section. In this case, why not make it an error message to the effect that “Interface cannot be specified in ModelProperty”?

Here is a simple example: both TestInterface1 and TestInterface2 generate the same error.
https://typespec.io/playground?c=aW50ZXJmYWNlIFRlc3RJyA4xIHsKICBnZXQxKHByb3A6zx4p0BE7Cn0KCtdMMiB7fQoKb3DETzLUTzLQTzI7Cg%3D%3D&e=%40typespec%2Fopenapi3&options=%7B%7D

Here is the current hard to understand error.

ExternalError: Emitter "@typespec/openapi3" crashed! This is a bug.
Please file an issue at https://github.com/microsoft/typespec/issues

Error: Unexpected non-code result from emit reference
    at OpenAPI3SchemaEmitter.modelPropertyLiteral (https://typespec.blob.core.windows.net/pkgs/@typespec/openapi3/0.56.0/index.js:3866:19)
    at https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17245:55
    at withTypeContext (https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17388:9)
    at invokeTypeEmitter (https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17235:9)
    at Object.emitModelProperty (https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17187:20)
    at OpenAPI3SchemaEmitter.modelProperties (https://typespec.blob.core.windows.net/pkgs/@typespec/openapi3/0.56.0/index.js:3825:41)
    at https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17245:55
    at withTypeContext (https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17388:9)
    at invokeTypeEmitter (https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17235:9)
    at Object.emitModelProperties (https://typespec.blob.core.windows.net/pkgs/@typespec/compiler/0.56.0/emitter-utils-Bonv920s.js:17178:25)

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[timotheeguerin]

This shouldn't crash but what would you expect this to do?

[markcowl]

• consider handling this in the emitter framework when operations are processed

[shiron-dev]

I want the error to be output in the following form. Note that the content of the message is tentative.

/Users/user/projects/typespec/packages/samples/scratch/main.tsp:7:9 - error @typespec/openapi3/model-property-non-code-result: 'Interface' cannot be specified in ModelProperty.
> 7 | op get2(prop: TestInterface2): TestInterface2;
    |         ^^^^
/Users/user/projects/typespec/packages/samples/scratch/main.tsp:2:8 - error @typespec/openapi3/model-property-non-code-result: 'Interface' cannot be specified in ModelProperty.
> 2 |   get1(prop: TestInterface1): TestInterface1;
    |        ^^^^

Found 2 errors.

This was reproduced by calling reportDiagnostic on the part that throws the original error (“Unexpected non-code result from emit reference”). Of course, if the syntax is not intended to specify an Interface in the ModelProperty in the first place, the framework should handle it.
If you are okay with this policy, please let me create a PR.

[timotheeguerin]

yep that's exactly what I would expect to happen, I was just wondering if you were expecting this to produce some OpenAPI3 output.
Looking forward to the PR