Simplify feature-flag handling: collapse CSV dual-variant + skip filtering when no checker#2516
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SamMorrowDrums merged 8 commits intoMay 21, 2026
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Address review feedback on #2450: - Collapse the three near-identical sort helpers in pkg/inventory/filters.go into a generic sortByToolsetThenName so adding new inventory item types doesn't require copying the comparator. - Expand the doc comments on the three *WithoutFeatureFiltering helpers to spell out why they exist: HTTP mode builds a static (process-wide) inventory as an upper bound, but per-request feature flags from headers (X-MCP-Features, X-MCP-Insiders) are evaluated later, so feature-flagged variants must be preserved here. - Strengthen the doc comment on ResolveFeatureFlags to make the contract explicit: user-supplied flags are validated against AllowedFeatureFlags, but insiders expansion deliberately is not — InsidersFeatureFlags may include server-controlled flags that are not user-toggleable. CORS comments are intentionally left for the PR author. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Also add tests covering: - a user-toggleable flag (FeatureFlagIssuesGranular) that insiders does not turn on automatically - insiders mode not turning on user-only allowed flags Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
Refactors inventory sorting to use a single generic helper and clarifies (via doc comments) the intended contract/behavior around feature-flag filtering and feature-flag resolution, aligning with the post-#2450 feature-flag model.
Changes:
- Consolidated deterministic sorting for tools/resource templates/prompts into a generic
sortByToolsetThenNamehelper. - Expanded doc comments explaining why
Available*WithoutFeatureFilteringexists (static HTTP inventory must preserve feature-gated variants for per-request evaluation). - Strengthened
ResolveFeatureFlagsdocumentation to explicitly state that user-supplied flags are allowlisted while insiders expansion is not re-validated.
Show a summary per file
| File | Description |
|---|---|
| pkg/inventory/filters.go | Introduces generic deterministic sort helper and clarifies feature-flag deferral rationale for HTTP static inventories. |
| pkg/github/feature_flags.go | Documents the explicit contract for resolving user vs insiders feature flags. |
Copilot's findings
- Files reviewed: 3/3 changed files
- Comments generated: 1
Comment on lines
+110
to
116
| func sortByToolsetThenName[T any](items []T, toolsetID func(T) ToolsetID, name func(T) string) { | ||
| sort.Slice(items, func(i, j int) bool { | ||
| if toolsetID(items[i]) != toolsetID(items[j]) { | ||
| return toolsetID(items[i]) < toolsetID(items[j]) | ||
| } | ||
| return tools[i].Tool.Name < tools[j].Tool.Name | ||
| return name(items[i]) < name(items[j]) | ||
| }) |
…into StaticUpperBound The three parallel methods (AvailableToolsWithoutFeatureFiltering, AvailableResourceTemplatesWithoutFeatureFiltering, AvailablePromptsWithoutFeatureFiltering) were always called as a triple in exactly two places: HTTP buildStaticInventory and its test mirror. They exist because the dual-variant pattern (sibling tools with mirrored FeatureFlagEnable / FeatureFlagDisable on the same name, e.g. CSV output) makes feature filtering at static-build time impossible — both variants must be kept and resolved per-request. Replace the three with one method, Inventory.StaticUpperBound(ctx), that returns (tools, resources, prompts) and carries the rationale in its doc comment. Reduces API surface, eliminates the triplication, and makes the single "skip feature filtering" concept obvious to readers. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Two related simplifications, both about treating insiders as a meta flag that expands once at startup and then stops mattering: - Collapse CSV's dual-variant pattern into a single tool whose handler performs a runtime feature-flag check via deps.IsFeatureEnabled. CSV is a pure response-format toggle, not a schema change, so it does not need the dual-name pattern that genuine schema variants (granular issues/PRs) still use. - When no feature checker is installed, skip feature-flag filtering and return the full upper bound. The static HTTP inventory now uses plain AvailableTools/Resources/Prompts; the per-request inventory always installs a checker, so MCP registration (which serves a tool name once) always sees a deduplicated set. The bespoke StaticUpperBound helper and the isToolEnabledWithFeatureFlags split go away. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
SamMorrowDrums
changed the title
The mcp-diff matrix now includes:
- --insiders (and --insiders --read-only)
- one config per github.AllowedFeatureFlags entry, generated by
script/print-mcp-diff-configs so new user-controllable flags get
diffed automatically without editing the workflow
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Adds a 'How feature flags are resolved' section covering:
- Insiders is a meta flag, like 'all'/'default' for toolsets
- User input -> allowlist filter -> insiders expansion ->
server-side fallback (remote only)
- AllowedFeatureFlags vs InsidersFeatureFlags are independent
- How to add a new feature flag, including the
TestGitHubPackageDoesNotReadInsidersMode guard
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Move tool feature-flag evaluation out of isToolEnabled and into a ToolFilter installed at the head of the pipeline by Build() when WithFeatureChecker received a non-nil checker. The 'no checker = no filtering' contract is now expressed structurally (the filter isn't installed) instead of by a runtime nil check inside the helper. Resources and prompts have no filter pipeline, so they call the now-pure featureFlagAllowed helper behind an explicit r.featureChecker != nil guard at the iteration site. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Avoid evaluating the extractor closures up to three times per comparison. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
RossTarrant
approved these changes
May 21, 2026
SamMorrowDrums
merged commit f59fce9
into
rosstarrant/add-csv-output-structure
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SamMorrowDrums
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May 21, 2026
#2450) * Add CSV output for list tools under insiders mode * fix: resolve rebase feature flag conflicts Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Simplify feature-flag handling: collapse CSV dual-variant + skip filtering when no checker (#2516) * refactor: generic toolset+name sort, clarify feature flag intent Address review feedback on #2450: - Collapse the three near-identical sort helpers in pkg/inventory/filters.go into a generic sortByToolsetThenName so adding new inventory item types doesn't require copying the comparator. - Expand the doc comments on the three *WithoutFeatureFiltering helpers to spell out why they exist: HTTP mode builds a static (process-wide) inventory as an upper bound, but per-request feature flags from headers (X-MCP-Features, X-MCP-Insiders) are evaluated later, so feature-flagged variants must be preserved here. - Strengthen the doc comment on ResolveFeatureFlags to make the contract explicit: user-supplied flags are validated against AllowedFeatureFlags, but insiders expansion deliberately is not — InsidersFeatureFlags may include server-controlled flags that are not user-toggleable. CORS comments are intentionally left for the PR author. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * docs(feature-flags): clarify allowed and insiders sets are independent Also add tests covering: - a user-toggleable flag (FeatureFlagIssuesGranular) that insiders does not turn on automatically - insiders mode not turning on user-only allowed flags Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * refactor(inventory): collapse three *WithoutFeatureFiltering helpers into StaticUpperBound The three parallel methods (AvailableToolsWithoutFeatureFiltering, AvailableResourceTemplatesWithoutFeatureFiltering, AvailablePromptsWithoutFeatureFiltering) were always called as a triple in exactly two places: HTTP buildStaticInventory and its test mirror. They exist because the dual-variant pattern (sibling tools with mirrored FeatureFlagEnable / FeatureFlagDisable on the same name, e.g. CSV output) makes feature filtering at static-build time impossible — both variants must be kept and resolved per-request. Replace the three with one method, Inventory.StaticUpperBound(ctx), that returns (tools, resources, prompts) and carries the rationale in its doc comment. Reduces API surface, eliminates the triplication, and makes the single "skip feature filtering" concept obvious to readers. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * refactor: simplify feature-flag handling Two related simplifications, both about treating insiders as a meta flag that expands once at startup and then stops mattering: - Collapse CSV's dual-variant pattern into a single tool whose handler performs a runtime feature-flag check via deps.IsFeatureEnabled. CSV is a pure response-format toggle, not a schema change, so it does not need the dual-name pattern that genuine schema variants (granular issues/PRs) still use. - When no feature checker is installed, skip feature-flag filtering and return the full upper bound. The static HTTP inventory now uses plain AvailableTools/Resources/Prompts; the per-request inventory always installs a checker, so MCP registration (which serves a tool name once) always sees a deduplicated set. The bespoke StaticUpperBound helper and the isToolEnabledWithFeatureFlags split go away. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * ci(mcp-diff): add insiders + per-feature configs The mcp-diff matrix now includes: - --insiders (and --insiders --read-only) - one config per github.AllowedFeatureFlags entry, generated by script/print-mcp-diff-configs so new user-controllable flags get diffed automatically without editing the workflow Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * docs(insiders): explain feature-flag resolution for contributors Adds a 'How feature flags are resolved' section covering: - Insiders is a meta flag, like 'all'/'default' for toolsets - User input -> allowlist filter -> insiders expansion -> server-side fallback (remote only) - AllowedFeatureFlags vs InsidersFeatureFlags are independent - How to add a new feature flag, including the TestGitHubPackageDoesNotReadInsidersMode guard Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * refactor(inventory): make feature-flag gating a regular ToolFilter Move tool feature-flag evaluation out of isToolEnabled and into a ToolFilter installed at the head of the pipeline by Build() when WithFeatureChecker received a non-nil checker. The 'no checker = no filtering' contract is now expressed structurally (the filter isn't installed) instead of by a runtime nil check inside the helper. Resources and prompts have no filter pipeline, so they call the now-pure featureFlagAllowed helper behind an explicit r.featureChecker != nil guard at the iteration site. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * perf(inventory): cache extracted toolset IDs in sort comparator Avoid evaluating the extractor closures up to three times per comparison. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * fix: correct MCP features header in cors * docs: regenerate README for CSV output toolset Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * fix: remove duplicate MCPFeaturesHeader from CORS headers * ci(mcp-diff): add streamable-http job with header-based configs Adds a sibling mcp-diff-http job that exercises the streamable-http transport against a shared HTTP server, with per-config settings supplied via X-MCP-* request headers — mirroring how the remote server is invoked in production (server-side defaults + per-user header overrides). The config generator gains a -transport flag: - stdio (default, unchanged behaviour) - http-headers (emits headers-only configs targeting a shared server) Two new combined entries layer multiple headers together as a smoke test for header-merging regressions. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * docs: regenerate after merging main Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Sam Morrow <info@sam-morrow.com> Co-authored-by: sammorrowdrums <sammorrowdrums@github.com>
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Follow-up to #2450 addressing review feedback. Targets `rosstarrant/add-csv-output-structure` so it can be merged into that branch before the parent PR lands.
Background
The team agreement is that insiders is a meta feature flag, much like
allanddefaultare meta toolsets. It expands once at startup into a set of individual feature flags, and from that point on the rest of the codebase should be feature flags all the way down — no special-casing of insiders elsewhere (UA string is the only intentional exception).This PR pulls the implementation closer to that model.
Changes
Collapse CSV dual-variant pattern (
pkg/github/csv_output.go)withCSVOutputVariantsregistered eachlist_*default tool twice — once withFeatureFlagDisable=csv_output(JSON variant) and once withFeatureFlagEnable=csv_output(CSV variant). CSV is a pure response-format toggle: same name, same input schema, same output schema. It does not need the dual-name pattern.Replaced with
withCSVOutput, which wraps each tool's handler once and performs a runtimedeps.IsFeatureEnabled(ctx, FeatureFlagCSVOutput)check inside the wrapped handler. Granular issues/PRs tools, which genuinely change schemas under their flag, are intentionally untouched and still use the dual-variant pattern.Skip feature-flag filtering when no checker is installed (
pkg/inventory/filters.go,pkg/http/handler.go)Previously, an inventory built without a feature checker would treat every flag as off, and
pkg/httphad a bespokeStaticUpperBoundhelper that selectively skipped feature-flag filtering so that dual-name variants survived into the per-request inventory.The static HTTP inventory now just doesn't install a checker, and
isFeatureFlagAllowedshort-circuits to true in that case. Result:StaticUpperBound,isToolEnabledWithFeatureFlags, and the dedicatedWithFeatureCheckerargument tobuildStaticInventoryall go away.Documentation and minor refactors (earlier commits)
sortByToolsetThenName[T]to deduplicate the three sort wrappers.ResolveFeatureFlagsclarifying thatAllowedFeatureFlagsandInsidersFeatureFlagsare independent sets — user-passed flags are validated againstAllowedFeatureFlags, but insiders may expand to flags outside that set, andAllowedFeatureFlagsmay include flags that insiders does not turn on.feature_flags_test.gocovering both directions of that independence.Out of scope
MCPFeaturesHeaderis already incors.go:26.)Test plan
script/lint— clean (0 issues)script/test— passes