java: enforce non-blank @CopilotToolParam description at compile time

[rinceyuan]

Closes #1836

Summary

Adds compile-time validation in CopilotToolProcessor to reject @CopilotToolParam annotations with blank value() (description). Without a meaningful description, the LLM cannot reliably select and invoke tools.

Changes

CopilotToolProcessor.java

• Added blank-description check after the single-record wrapper validation block
• Checks paramAnnotation.value().isBlank() (catches both empty and whitespace-only)
• Single-record wrapper parameters are exempt (as specified in the issue)
• Error message identifies the parameter name, enclosing method, and class

CopilotToolProcessorTest.java (5 new tests)

1. Blank value — @CopilotToolParam("") produces compile error
2. Whitespace-only value — @CopilotToolParam(" ") produces compile error
3. Valid value — @CopilotToolParam("Search query") compiles without error
4. No annotation — unannotated parameter compiles without error
5. Record wrapper exemption — @CopilotToolParam on single-record wrapper is exempt

Error message example

error: @CopilotToolParam on parameter 'query' in 'BlankDescTools.searchItems' has a blank value (description).
Descriptions are required so the LLM can correctly select and invoke the tool

Testing

• mvn test -Dtest=CopilotToolProcessorTest — 39 tests pass (0 failures)
• All existing tests pass with no regressions
• Local JDK is 17; CI will run the full mvn verify with JDK 25+

[rinceyuan]

@microsoft-github-policy-service agree company=Microsoft

[rinceyuan]

@edburns Hi! This implements #1836 — compile-time validation for blank @CopilotToolParam descriptions in the annotation processor. 5 new tests, all passing. Would appreciate your review. Thanks!

[rinceyuan]

@stephentoub Gentle ping — this implements the spec from #1836 (blank @CopilotToolParam description validation). 2 files, 5 new tests, all passing. Happy to address any feedback!

[rinceyuan]

@edburns @stephentoub Friendly follow-up — this PR has been open for 6 days with no review. It's a small change (18 lines in the processor + 5 tests) implementing the spec from #1836. Happy to rebase or address any concerns. Is there anything blocking review?

[Copilot]

Pull request overview

Adds compile-time enforcement for non-blank @CopilotToolParam descriptions while exempting record-wrapper parameters.

Changes:

• Validates empty and whitespace-only descriptions with contextual errors.
• Adds tests for invalid, valid, unannotated, and exempt parameters.

Show a summary per file

File	Description
CopilotToolProcessor.java	Implements description validation.
CopilotToolProcessorTest.java	Covers validation and exemption behavior.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Medium

[edburns]

CI Failure Analysis

The CI failure in this run is unrelated to this PR's changes.

Root cause

CopilotSessionTest.testShouldAbortSession timed out after 60s — a flaky E2E test with no connection to the tool processor validation added here.

Local verification

• ✅ mvn spotless:apply — no formatting changes needed (307 files already clean)
• ✅ All 5 new tests pass locally (blank param description validation)
• ✅ Checkstyle: 0 violations
• ✅ Compilation succeeds on JDK 25

Recommendation

Re-run CI — the timeout is transient and not caused by this PR.