Remove special-casing of string enumerables in McpServerTool #699
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We special-case string enumerables, translating them to an array of text content blocks, but other enumerables just get serialized, and there's a reasonable expectation that returning a string[] would produce a JSON array of strings. Just delete the special-casing.
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Yeah, agree. One downside is that it's no longer possible to return multiple text blocks by using string array as the return type. And it's a valid signature for tools (can make sense in some cases, as it's different schema wise at the LLM api level). I can't recall if it's possible to return this via array of text AIContent. If so, nothing lost. |
You can return an AIContent[], a TextContentBlock[], or even a CallToolResult. |
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halter73
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…7897) Updated [ModelContextProtocol](https://github.com/modelcontextprotocol/csharp-sdk) from 0.3.0-preview.2 to 0.3.0-preview.4. <details> <summary>Release notes</summary> _Sourced from [ModelContextProtocol's releases](https://github.com/modelcontextprotocol/csharp-sdk/releases)._ ## 0.3.0-preview.4 ## What's Changed * Respect HandleResponse() and SkipHandler() calls in OnResourceMetadataRequest by @halter73 in modelcontextprotocol/csharp-sdk#607 * UnreferenceDisposable made slimmer by @Scooletz in modelcontextprotocol/csharp-sdk#627 * IdleTracking uses lists instead of SortedSet by @Scooletz in modelcontextprotocol/csharp-sdk#629 * Fix ResourceLinkBlock deserialization by adding missing "name" case by @Copilot in modelcontextprotocol/csharp-sdk#645 * Add an in-memory transport sample by @stephentoub in modelcontextprotocol/csharp-sdk#664 * Remove 'Sse' from AspNetCoreSseServer sample name by @halter73 in modelcontextprotocol/csharp-sdk#665 * Fix NotSupportedException when returning IEnumerable<ContentBlock> by @Copilot in modelcontextprotocol/csharp-sdk#675 * Enhance HTTP and MCP session logging by @theojiang25 in modelcontextprotocol/csharp-sdk#608 * Remove special-casing of string enumerables in McpServerTool by @stephentoub in modelcontextprotocol/csharp-sdk#699 * Prune idle sessions before starting new ones by @halter73 in modelcontextprotocol/csharp-sdk#701 * Add framework for conceptual docs by @mikekistler in modelcontextprotocol/csharp-sdk#708 ## New Contributors * @Scooletz made their first contribution in modelcontextprotocol/csharp-sdk#627 * @Copilot made their first contribution in modelcontextprotocol/csharp-sdk#645 * @theojiang25 made their first contribution in modelcontextprotocol/csharp-sdk#608 **Full Changelog**: modelcontextprotocol/csharp-sdk@v0.3.0-preview.3...v0.3.0-preview.4 ## 0.3.0-preview.3 ## What's Changed * Enable netfx testing. by @eiriktsarpalis in modelcontextprotocol/csharp-sdk#588 * fix: Prevent crash when Options.ResourceMetadata is null but handled by event by @DavidParks8 in modelcontextprotocol/csharp-sdk#603 * Update to M.E.AI 9.7.0 by @stephentoub in modelcontextprotocol/csharp-sdk#602 * Ensure IsExternalInit is type forwarded on NET builds by @stephentoub in modelcontextprotocol/csharp-sdk#619 * Flow ExecutionContext with JsonRpcMessage by @halter73 in modelcontextprotocol/csharp-sdk#616 * Update MEAI version and add regression test for #601. by @eiriktsarpalis in modelcontextprotocol/csharp-sdk#628 ## New Contributors * @DavidParks8 made their first contribution in modelcontextprotocol/csharp-sdk#603 **Full Changelog**: modelcontextprotocol/csharp-sdk@v0.3.0-preview.2...v0.3.0-preview.3 Commits viewable in [compare view](modelcontextprotocol/csharp-sdk@v0.3.0-preview.2...v0.3.0-preview.4). </details> [](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- <details> <summary>Dependabot commands and options</summary> <br /> You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot merge` will merge this PR after your CI passes on it - `@dependabot squash and merge` will squash and merge this PR after your CI passes on it - `@dependabot cancel merge` will cancel a previously requested merge and block automerging - `@dependabot reopen` will reopen this PR if it is closed - `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually - `@dependabot show <dependency name> ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself) </details> ###### Microsoft Reviewers: [Open in CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/Azure/bicep/pull/17897) Signed-off-by: dependabot[bot] <[email protected]> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
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…ntextprotocol#699) We special-case string enumerables, translating them to an array of text content blocks, but other enumerables just get serialized, and there's a reasonable expectation that returning a string[] would produce a JSON array of strings. Just delete the special-casing.
This was referenced Aug 26, 2025
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We special-case string enumerables, translating them to an array of text content blocks, but other enumerables just get serialized, and there's a reasonable expectation that returning a string[] would produce a JSON array of strings. Just delete the special-casing.
Fixes #698
cc: @AArnott