Fix TYPESPEC_NPM_REGISTRY forwarding during install

[Vivek JM (vivekjm)]

Summary

• forward TYPESPEC_NPM_REGISTRY to the npm process launched by tsp install
• preserve an existing npm registry configuration when no TypeSpec override is provided
• normalize case-insensitive npm registry environment keys before applying the override
• treat empty and whitespace-only TypeSpec overrides as unset

Fixes #11688.

Root cause

TypeSpec already used TYPESPEC_NPM_REGISTRY when it fetched package-manager metadata and archives. The later npm install subprocess inherited that TypeSpec-specific variable, but npm reads npm_config_registry instead, so project dependencies still came from npm's default configuration.

Testing

• pnpm setup:min
• pnpm --filter @typespec/compiler exec vitest run test/package-manager/npm-registry.test.ts — 6 tests passed
• pnpm --filter @typespec/compiler run build
• pnpm exec prettier --check packages/compiler/src/install/install.ts packages/compiler/src/package-manger/npm-registry.ts packages/compiler/test/package-manager/npm-registry.test.ts .chronus/changes/forward-typespec-npm-registry-2026-08-15.md
• pnpm --filter @typespec/compiler run lint
• git diff --check

Local setup note: I initially invoked the compiler tests before building the generated manifest and internal workspace packages, which produced bootstrap-related missing-module errors. After running the documented pnpm setup:min step, the focused tests and all checks above passed.

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR forwards the TYPESPEC_NPM_REGISTRY override to the npm process spawned by tsp install, ensuring installs use the same registry as manifest resolution.

Changes:

• Add getNpmRegistryEnvironment() to produce a child-process env with npm_config_registry set from TYPESPEC_NPM_REGISTRY.
• Update installer to use the new environment builder when invoking the package manager.
• Add unit tests covering forwarding behavior and preservation of existing npm registry env vars.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/compiler/test/package-manager/npm-registry.test.ts	Adds tests validating registry env forwarding and non-interference when no override is set.
packages/compiler/src/package-manger/npm-registry.ts	Introduces getNpmRegistryEnvironment() to map TypeSpec registry override to npm’s env convention.
packages/compiler/src/install/install.ts	Uses getNpmRegistryEnvironment() when spawning the package manager to apply the override.
.chronus/changes/forward-typespec-npm-registry-2026-08-15.md	Adds changelog entry documenting the fix.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

Suppressed comments (1)

packages/compiler/src/package-manger/npm-registry.ts:112

• This reads process.env[\"TYPESPEC_NPM_REGISTRY\"] (trimmed) in the guard, and then reads process.env again indirectly via getNpmRegistry() when setting npm_config_registry. To keep behavior consistent and easier to reason about, compute the effective registry once (e.g., a single const registry = ...) and use that value for both the guard and the assignment. This also avoids any chance of inconsistency if process.env were to change between the two reads.

export function getNpmRegistryEnvironment(): NodeJS.ProcessEnv {
  const environment = { ...process.env };
  if (!process.env["TYPESPEC_NPM_REGISTRY"]?.trim()) {
    return environment;
  }

  // Environment variable names are case-insensitive on Windows. Remove any
  // existing spelling so Node does not choose between duplicate keys.
  for (const name of Object.keys(environment)) {
    if (name.toLowerCase() === "npm_config_registry") {
      delete environment[name];
    }
  }
  environment["npm_config_registry"] = getNpmRegistry();
  return environment;

[iscai-msft]

thank you so much for your contribution Vivek JM (@vivekjm), Timothee Guerin (@timotheeguerin) can you take a look at this when you're back from vacation? Thanks!

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/compiler@11694

commit: bd08169

[github-actions]

All changed packages have been documented.

• ✅ @typespec/compiler

Show changes

@typespec/compiler - fix ✏️

Forward TYPESPEC_NPM_REGISTRY to the npm process launched by tsp install.