github/github-mcp-server · warning

failed to marshal discussion categories: %w

Error message

failed to marshal discussion categories: %w

What it means

list_discussion_categories marshals a response map of the categories slice, pageInfo (bools and cursor strings), and totalCount int after a successful GraphQL query. All values are primitives derived from GraphQL scalars, so json.Marshal's failure modes (unsupported types, cycles, NaN) are not reachable; the branch guards against future type regressions in the response construction.

Source

Thrown at pkg/github/discussions.go:1098

					"name": string(c.Name),
				})
			}

			// Create response with pagination info
			response := map[string]any{
				"categories": categories,
				"pageInfo": map[string]any{
					"hasNextPage":     q.Repository.DiscussionCategories.PageInfo.HasNextPage,
					"hasPreviousPage": q.Repository.DiscussionCategories.PageInfo.HasPreviousPage,
					"startCursor":     string(q.Repository.DiscussionCategories.PageInfo.StartCursor),
					"endCursor":       string(q.Repository.DiscussionCategories.PageInfo.EndCursor),
				},
				"totalCount": q.Repository.DiscussionCategories.TotalCount,
			}

			out, err := json.Marshal(response)
			if err != nil {
				return nil, nil, fmt.Errorf("failed to marshal discussion categories: %w", err)
			}
			result := utils.NewToolResultText(string(out))
			// Discussion categories are repo-defined structural metadata
			// (trusted); confidentiality follows repo visibility.
			result = attachRepoVisibilityIFCLabelLazy(ctx, deps, owner, repo, result, ifc.LabelRepoMetadata)
			return result, nil, nil
		},
	)
}

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Project categories into maps of string/int before insertion into the response
2. Add a golden-file test for the categories response JSON
3. On occurrence, inspect element types of the categories slice — the defect is in this handler's projection, not the API call
4. Do not retry the tool: the query already succeeded and marshal outcome is deterministic per input

out, err := json.Marshal(response)
if err != nil {
	return nil, nil, fmt.Errorf("failed to marshal discussion categories: %w", err)
}

When it happens

Trigger: A refactor moving raw githubv4 category objects into the categories slice without projecting to plain maps; addition of float fields that could be NaN; cyclic structures from embedding. Current GitHub category data (ids, names, cursors) cannot trip it.

Common situations: Forks adding category description/emoji fields as typed objects; library upgrades changing embedded struct shapes; test doubles with unmarshalable fields.

Related errors

• failed to marshal discussions: %w
• failed to marshal discussion: %w
• failed to marshal comments: %w
• failed to marshal comment: %w
• failed to marshal response: %w

AI-assisted analysis of github/github-mcp-server@0ea1f775a7 (2026-08-15). Data as JSON: /api/errors/a090eb4fa7c5a2d4. Report an issue: GitHub.