feat: register custom ComputeLroErrorParser for Compute LROs

[nnicolee]

Overview

This is POC 2 that implements Phase 2 of Compute Engine's custom REST LRO error details propagation.

Instead of generating the parser class via code generation (which was the approach in POC 1), this POC introduces a manually written, package-private parser class in the Compute stub module and configures the code generator to register this parser during stub initialization. The parser class is protected from being wiped out during future Librarian code regeneration.

Key Changes

1. Handwritten Parser Class: Added a package-private parser implementation ComputeLroErrorParser.java inside the java-compute stub package. It extracts nested Compute LRO errors from Operation payloads and translates them into standard ErrorDetails (utilizing ErrorInfo).
2. Librarian Config: Updated librarian.yaml to include ComputeLroErrorParser.java in the keep block. This prevents the Librarian regeneration tool from deleting or overwriting the manual parser file.
3. Generator Settings Registration: Modified RetrySettingsComposer.java to automatically generate the registration of new ComputeLroErrorParser() inside the generated Compute stub settings (like AddressesStubSettings.java, NodeTemplatesStubSettings.java, etc.).
4. Integration Test Safety: Explicitly excluded the test package com.google.cloud.compute.v1small from parser registration inside RetrySettingsComposer.java. This keeps the integration test goldens untouched and ensures the test suite compiles and passes cleanly without requiring a mock parser.

[gemini-code-assist]

Code Review

This pull request introduces a custom LRO error parser (ComputeLroErrorParser) for the Google Cloud Compute Java client and updates the GAPIC generator (RetrySettingsComposer) to conditionally instantiate and pass this parser when generating LRO settings for com.google.cloud.compute.v1 services. The reviewer provided feedback on ComputeLroErrorParser to improve robustness: first, by conditionally adding message and location to the ErrorInfo metadata map only when they are non-empty; and second, by handling cases where code or message might be empty to prevent poorly formatted error messages (e.g., : message or code: ).

[gemini-code-assist]

Avoid adding empty strings to the ErrorInfo metadata map if message or location are not populated. We can conditionally add them only when they are non-empty to keep the metadata clean.

    List<Any> rawErrorMessages = new ArrayList<>();
    for (Errors error : operation.getError().getErrorsList()) {
      ErrorInfo.Builder errorInfoBuilder =
          ErrorInfo.newBuilder()
              .setReason(error.getCode())
              .setDomain("googleapis.com");
      if (!error.getMessage().isEmpty()) {
        errorInfoBuilder.putMetadata("message", error.getMessage());
      }
      if (!error.getLocation().isEmpty()) {
        errorInfoBuilder.putMetadata("location", error.getLocation());
      }
      rawErrorMessages.add(Any.pack(errorInfoBuilder.build()));
    }

[gemini-code-assist]

If either code or message is empty, appending them directly with : results in poorly formatted error messages like : message or code: . It is better to conditionally format the string based on which fields are present.

    StringBuilder sb = new StringBuilder();
    for (Errors error : operation.getError().getErrorsList()) {
      String code = error.getCode();
      String message = error.getMessage();
      if (code.isEmpty() && message.isEmpty()) {
        continue;
      }
      if (sb.length() > 0) {
        sb.append("; ");
      }
      if (!code.isEmpty() && !message.isEmpty()) {
        sb.append(code).append(": ").append(message);
      } else if (!code.isEmpty()) {
        sb.append(code);
      } else {
        sb.append(message);
      }
    }
    return sb.toString();

[sonarqubecloud]

Quality Gate failed for 'gapic-generator-java-root'

Failed conditions
26.1% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate failed for 'gapic-generator-java-root'

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud