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Add MCP compile_route tool#92951

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Add MCP compile_route tool#92951
lukesandberg wants to merge 7 commits intoeviction_semantics_for_real_this_timefrom
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@lukesandberg lukesandberg commented Apr 17, 2026 •
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What?

Adds a compile_route MCP tool that triggers on-demand compilation of a specific route (app or pages) without issuing an HTTP request, and returns any compilation issues.

Why?

Coding agents and benchmarking workflows need a way to warm the module graph or measure compile time for a route without standing up a live backend to satisfy the request. The existing path — hitting the URL — requires the route's runtime dependencies to be available and couples compile timing to request handling.

How?

  • New tool mcp/compile_route registered in get-or-create-mcp-server.ts, backed by a compileRoute({ page, clientOnly }) callback plumbed from both the Turbopack and webpack hot reloaders.
  • Reuses the dev server's existing on-demand entry path (ensurePage / handleRouteType), so the call path matches a first navigation.
  • Adds a subscribeToChanges opt-out on ensurePage and threads it through handleRouteType / handlePagesErrorRoute. One-shot MCP compilations skip HMR subscription wiring — without this, each call would leak a subscription that fires on every subsequent file change for the life of the dev server.
  • Telemetry: registers mcp/compile_route in the McpToolName union.
  • Error 1172 reserved for "compilation failed but no issues were recorded".
  • e2e test in test/development/mcp-server/mcp-server-compile-route.test.ts.

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lukesandberg commented Apr 17, 2026

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@lukesandberg lukesandberg mentioned this pull request Apr 17, 2026
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@lukesandberg lukesandberg changed the title compile route mcsp handler Add MCP compile_route tool Apr 17, 2026
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nextjs-bot commented Apr 17, 2026 •
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Tests Passed

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lukesandberg commented Apr 17, 2026
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@nextjs-bot nextjs-bot added the Documentation Related to Next.js' official documentation. label Apr 18, 2026
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nextjs-bot commented Apr 18, 2026

Stats from current PR

🔴 1 regression

Metric Canary PR Change Trend
node_modules Size 494 MB 494 MB 🔴 +87.8 kB (+0%) ████▁
📊 All Metrics
📖 Metrics Glossary

Dev Server Metrics:

  • Listen = TCP port starts accepting connections
  • First Request = HTTP server returns successful response
  • Cold = Fresh build (no cache)
  • Warm = With cached build artifacts

Build Metrics:

  • Fresh = Clean build (no .next directory)
  • Cached = With existing .next directory

Change Thresholds:

  • Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
  • Size: Changes < 1KB AND < 1% are insignificant
  • All other changes are flagged to catch regressions

⚡ Dev Server

Metric Canary PR Change Trend
Cold (Listen) 455ms 455ms ✓ ▁▁▅▅▅
Cold (Ready in log) 440ms 440ms ✓ ▇▂▅▅▆
Cold (First Request) 827ms 822ms ✓ ▁█▁█▁
Warm (Listen) 456ms 456ms ✓ ▅▅▅█▅
Warm (Ready in log) 439ms 439ms ✓ ▃▃▁▄▁
Warm (First Request) 340ms 338ms ✓ ▅▇▂▇▁
📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric Canary PR Change Trend
Cold (Listen) 456ms 456ms ✓ ▁▅▅▅▁
Cold (Ready in log) 438ms 438ms ✓ ▇▁▃▅▁
Cold (First Request) 1.867s 1.871s ✓ █▆▆█▆
Warm (Listen) 455ms 455ms ✓ █▁▅▅▅
Warm (Ready in log) 437ms 437ms ✓ ▆▂▃▅▂
Warm (First Request) 1.881s 1.856s ✓ ▇▆▆█▆

⚡ Production Builds

Metric Canary PR Change Trend
Fresh Build 4.006s 4.006s ✓ ▇▃▅▂█
Cached Build 4.002s 3.986s ✓ █▂▄▁█
📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric Canary PR Change Trend
Fresh Build 14.423s 14.409s ✓ █▂▃█▃
Cached Build 14.537s 14.520s ✓ █▄▁▆▁
node_modules Size 494 MB 494 MB 🔴 +87.8 kB (+0%) ████▁
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Server

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📎 Tarball URL 
https://vercel-packages.vercel.app/next/commits/2c18328be3b24216906fa3685cddf39c186938c3/next

@lukesandberg lukesandberg marked this pull request as ready for review April 20, 2026 20:49
@lukesandberg lukesandberg marked this pull request as draft April 20, 2026 20:49
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codspeed-hq Bot commented Apr 20, 2026 •
edited
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Merging this PR will degrade performance by 3.48%

❌ 2 regressed benchmarks
✅ 15 untouched benchmarks
⏩ 3 skipped benchmarks1

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

Mode Benchmark BASE HEAD Efficiency
❌ Simulation packages-bundle.js[full] 949.3 ms 982.2 ms -3.35%
❌ Simulation app-page-turbo.runtime.prod.js[full] 621.2 ms 643.6 ms -3.48%

Comparing followups (ca35fb9) with eviction_semantics_for_real_this_time (bc661cd)

Open in CodSpeed

Footnotes

  1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

lukesandberg
lukesandberg commented Apr 20, 2026
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Comment thread packages/next/src/server/dev/hot-reloader-turbopack.ts Outdated
lukesandberg
lukesandberg commented Apr 20, 2026
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Comment thread packages/next/src/server/dev/turbopack-utils.ts Outdated
@lukesandberg lukesandberg force-pushed the eviction_semantics_for_real_this_time branch from bc661cd to 852ab00 Compare April 21, 2026 17:50
@lukesandberg lukesandberg force-pushed the eviction_semantics_for_real_this_time branch from 852ab00 to 765be4f Compare April 21, 2026 23:48
@lukesandberg lukesandberg force-pushed the followups branch 2 times, most recently from 6910f57 to 9d239e3 Compare April 21, 2026 23:52
@lukesandberg lukesandberg force-pushed the eviction_semantics_for_real_this_time branch from 765be4f to c5f0530 Compare April 21, 2026 23:52
@lukesandberg lukesandberg force-pushed the eviction_semantics_for_real_this_time branch 2 times, most recently from 8b16ef4 to 6ba65cc Compare April 24, 2026 23:04
@github-actions github-actions Bot added the Turbopack Related to Turbopack with Next.js. label Apr 24, 2026
@lukesandberg lukesandberg force-pushed the eviction_semantics_for_real_this_time branch from 6ba65cc to 46b10ce Compare April 24, 2026 23:06
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github-actions Bot commented Apr 24, 2026

Failing CI jobs

Commit: 398e84e | About building and testing Next.js

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