[Bug]: When main.tsp only contain minimal import, emitter fails

[allenjzhang]

Describe the bug

Right after tsp init with empty project that only, npx tsp compile . fails.

Emitter "@typespec/http-client-csharp" crashed! This is a bug.
Please file an issue at https://github.com/Microsoft/typespec/issues

Error: Root client not found
    at getRootApiVersions (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/http-client-csharp/dist/emitter/lib/client-model-builder.js:130:15)
    at createModel (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/http-client-csharp/dist/emitter/lib/client-model-builder.js:23:11)
    at Object.$onEmit [as emitFunction] (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/http-client-csharp/dist/emitter/emitter.js:44:22)
    at async runEmitter (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/compiler/dist/src/core/program.js:366:13)
    at async compile (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/compiler/dist/src/core/program.js:123:9)
    at async compileOnce (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/compiler/dist/src/core/cli/actions/compile/compile.js:36:25)
    at async compileAction (file:///C:/github/typespec-e2e-demo/sandbox/junk/node_modules/@typespec/compiler/dist/src/core/cli/actions/compile/compile.js:19:9)

main.tsp only contains following:

import "@typespec/http";
import "@typespec/rest";
import "@typespec/openapi3";

Reproduction

In E2E repo,

cd sandbox
md [project] && cd [project]
npx tsp init ../../tsptemplate.json
npm install
npx tsp compile .

Checklist

• Follow our Code of Conduct
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.

[ArthurMa1978]

We should verify if this issue exists in other languages too.

[rs-jayanth]

http-client-java compiles, but csharp and python client doesn't. There's an open issue - 5363

[msyyc]

For python, it was already fixed by #5200 so please try latest https://www.npmjs.com/package/@typespec/http-client-python.

[m-nash]

@allenjzhang what is the desired outcome here? A csproj with no cs files?

We should evaluate the assumptions we make and have cadl ranch tests for each of those.

• Is it valid to generate an sdk with no clients?
• Is it valid to generate an sdk with no models?
• Is it valid to generate an sdk with no operations?
• Is it valid to generate an sdk with none of those?
• etc

[allenjzhang]

The call stack is the one I would like to remove. It looked like an uncaught exception.

I tried with latest build, the result looks fine to me now with one line error:

Cannot generate CSharp SDK since no public root client is defined in typeSpec file.

BTW, nit, typespec should be TypeSpec. Once that fixed, you can close this issue. Thx

[JoshLove-msft]

Cannot generate CSharp SDK since no public root client is defined in typeSpec file.

Probably should be "C# library" and "TypeSpec". We should follow up to find out what PR actually fixed this as it still should have been part of our triage process.

[JoshLove-msft]

This was fixed in #5475

[m-nash]

I don't know if this was fixed would like to confirm with @allenjzhang what the expected result of an emitter should be if there are no clients or models in the spec? Should we throw an error or should we generate an empty library?

@srnagar , @joheredi , @lmazuel how are your languages handling this?

[JoshLove-msft]

As a general rule, we should not be throwing for "known" error cases. These should instead use error diagnostics. The only time we throw is for "unknown" cases. We should file an issue to scan the emitter to make sure we are following this rule.