Detect model spread cycles without over-reporting recursive model-expression aliases

[Copilot]

Model-to-model spread cycles were not being validated correctly (Foo spreads Bar, Bar spreads Foo), which led to unresolved checker state instead of a proper diagnostic. At the same time, alias recursion through model expressions was being flagged too aggressively.

• Spread cycle validation

  • Adds explicit cycle detection for model spread chains in the checker.
  • Mutual spreads now surface the intended spread-model self-spread diagnostic instead of ending in pending-resolution failure.

• Alias recursion behavior

  • Narrows circular-alias handling for aliases whose value is a model expression.
  • Allows recursive object-shape aliases (via model expressions) to resolve without emitting circular-alias-type.

• Targeted test coverage

  • Unskips and enforces the mutual spread regression case in spread.test.ts.
  • Adds a regression case in alias.test.ts for recursive aliases through model expressions.

model Foo { ...Bar }
model Bar { ...Foo } // now diagnosed as spread-model self-spread

alias A = { a: B };
alias B = { a: A }; // now allowed (no circular-alias-type)

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• telemetry.astro.build
  • Triggering command: /opt/hostedtoolcache/node/22.22.2/x64/bin/node node /home/REDACTED/work/typespec/typespec/website/node_modules/.bin/../astro/bin/astro.mjs build node s/.b�� run --local de_modules/pnpm/dist/node-gyp-bin/node import @typespecsh --production reams/reference node sion�� build.json dotnet k/typespec/typespec/node_modules/.bin/node --no-emit node rsioning/referendoc sh (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/compiler@10684

commit: c5366f4

[timotheeguerin]

@copilot add changelog

[Copilot]

@copilot add changelog

Added in d5224a2: created a Chronus changelog entry for @typespec/compiler under .chronus/changes/copilot-fix-model-circular-references-2026-4-14-20-45-42.md.