Add warning for unused client initialization parameters #3763

Copilot · 2026-01-13T19:53:39Z

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This section details on the original issue you should resolve

<issue_title>[Bug]: no warning on unused client initializer param(s)</issue_title>
<issue_description>### Describe the bug

If clientInitialization.parameters contains values that aren't used in any routes (client or its sub-clients), a diagnostic warning should be produced (maybe even an error as this seems like an authoring mistake).

Reproduction

tcgc version 0.54.0

Checklist

Follow our Code of Conduct

Check that this issue is about the Azure libraries for typespec. For bug in the typespec language or core libraries file it in the TypeSpec repo

Check that there isn't already an issue that request the same bug to avoid creating a duplicate.

The provided reproduction is a minimal reproducible example of the bug.</issue_description>

<agent_instructions>1. Add a linter rule warning definition here https://github.com/Azure/typespec-azure/blob/main/packages/typespec-client-generator-core/src/lib.ts
2. Add verification checks here https://github.com/Azure/typespec-azure/blob/main/packages/typespec-client-generator-core/src/decorators.ts#L1007. If this doesn't work with the test cases later, then add it once the whole client hierarchy is set up
3. Add tests like the one here to check whether a warning is raised https://github.com/Azure/typespec-azure/blob/main/packages/typespec-client-generator-core/test/decorators/alternate-type.test.ts#L199
4. Make sure this works with the @client, @operationGroup, and @clientLocation decorator. For example, make sure the code works if we use @operationGroup decorators to make something a sub client and it has those parameters, that we don't raise a warning.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes [Bug]: no warning on unused client initializer param(s) #2549

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

…parameters Co-authored-by: iscai-msft <[email protected]>

Co-authored-by: iscai-msft <[email protected]>

iscai-msft · 2026-01-13T20:43:51Z

@copilot fix build failures

Co-authored-by: iscai-msft <[email protected]>

Copilot · 2026-01-13T21:14:59Z

@copilot fix build failures

Fixed in commit 3a28190. The build failures were caused by:

TypeScript compilation error: validation function was returning readonly Diagnostic[] instead of being integrated with the existing diagnostic reporting mechanism
Invalid method kind check: attempted to check for "clientaccessor" which doesn't exist in the SdkMethod type union
Diagnostics not being reported to the program, so tests couldn't see them

Changes made:

Switched from createDiagnostic to reportDiagnostic to properly report diagnostics to the program
Removed invalid clientaccessor kind check
Fixed validation logic to only validate at top-level clients (not recursively) to avoid duplicate warnings for inherited parameters

All 1098 tests now pass including the 8 new tests for unused client initialization parameter warnings.

…opilot/fix-unused-client-params-warning

pkg-pr-new · 2026-01-26T20:32:56Z

Open in StackBlitz

npm i https://pkg.pr.new/Azure/typespec-azure/@azure-tools/typespec-client-generator-core@3763

commit: 3169c5a

azure-sdk · 2026-01-26T21:02:13Z

All changed packages have been documented.

✅ @azure-tools/typespec-client-generator-core

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`@azure-tools/typespec-client-generator-core` - feature ✏️

Add warning diagnostic for unused client initialization parameters. If clientInitialization.parameters contains values that aren't used in any routes (client or its sub-clients), a diagnostic warning is now produced.

azure-sdk · 2026-01-26T21:11:37Z

You can try these changes here

🛝 Playground	🌐 Website

tadelesh

The validation should not apply to all clients since the parameter gathering iteration will cause perf issue. We should check it only when there is customized client initialization parameter. Another problem for this PR is it does not take @paramAlias into account.

tadelesh · 2026-01-28T05:48:25Z

packages/typespec-client-generator-core/src/package.ts

+>(context: TCGCContext, client: SdkClientType<TServiceOperation>): void {
+  // Only validate when there's a customized @clientInitialization decorator with parameters
+  // Skip validation for default/auto-generated client initialization
+  if (!client.clientInitialization.__raw) {


Oh, I just found a problem for this skip. This will also skip the check for nested clients with client initialization customization.

tadelesh

@iscai-msft I missed some comments when approval. I could not fine the dismiss button. So, please check my new comments before merge. Thanks.

tadelesh · 2026-01-28T05:50:47Z

packages/typespec-client-generator-core/src/package.ts

+          for (const path of param.methodParameterSegments) {
+            for (const methodParam of path) {
+              if (methodParam.kind === "method" && methodParam.onClient) {
+                parameterNames.add(methodParam.name);


You should not add name, but just add instance.

tadelesh · 2026-01-28T05:51:32Z

packages/typespec-client-generator-core/src/package.ts

+  // Check each custom client initialization parameter
+  for (const param of customParams) {
+    // Check if this parameter is used in any operation
+    if (!allOperationParameterNames.has(param.name)) {


You could use instance check directly since the methodParameterSegments stores the direct reference, which could resolve potential naming and alias issue.

Copilot AI self-assigned this Jan 13, 2026

Initial plan

fff6923

Copilot AI assigned iscai-msft Jan 13, 2026

Copilot started work on behalf of iscai-msft January 13, 2026 19:54 View session

Copilot AI and others added 2 commits January 13, 2026 20:07

Add diagnostic and validation logic for unused client initialization …

be839f8

…parameters Co-authored-by: iscai-msft <[email protected]>

Add changeset for unused client initialization parameter warning

206ed72

Co-authored-by: iscai-msft <[email protected]>

Copilot AI changed the title ~~[WIP] Fix no warning on unused client initializer parameters~~ Add warning for unused client initialization parameters Jan 13, 2026

Copilot AI requested a review from iscai-msft January 13, 2026 20:11

Copilot finished work on behalf of iscai-msft January 13, 2026 20:11

Copilot started work on behalf of iscai-msft January 13, 2026 20:44 View session

Fix build failures: use reportDiagnostic and fix validation logic

3a28190

Co-authored-by: iscai-msft <[email protected]>

Copilot finished work on behalf of iscai-msft January 13, 2026 21:15

iscai-msft added 2 commits January 26, 2026 15:19

Merge branch 'main' of https://github.com/Azure/typespec-azure into c…

ccc9422

…opilot/fix-unused-client-params-warning

update tests

3dbc1f6

microsoft-github-policy-service bot added the lib:tcgc Issues for @azure-tools/typespec-client-generator-core library label Jan 26, 2026

iscai-msft marked this pull request as ready for review January 26, 2026 20:59

iscai-msft requested review from bterlson, joheredi, lmazuel, m-nash, markcowl, srnagar and timotheeguerin as code owners January 26, 2026 20:59

use methodParameterSegments instead

5a2c0bb

iscai-msft enabled auto-merge January 26, 2026 21:16

tadelesh reviewed Jan 27, 2026

View reviewed changes

only check for client init params and add verification for

3169c5a

tadelesh approved these changes Jan 28, 2026

View reviewed changes

tadelesh reviewed Jan 28, 2026

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tadelesh disabled auto-merge January 28, 2026 05:52

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Add warning for unused client initialization parameters #3763

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`@azure-tools/typespec-client-generator-core` - feature ✏️

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@azure-tools/typespec-client-generator-core - feature ✏️

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`@azure-tools/typespec-client-generator-core` - feature ✏️