Port #60195: Allow reusing type nodes that resolve to error types

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,32 @@
+name: 'Copilot Setup Steps'
+
+on: workflow_dispatch
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      # If you want to clone the repository as part of your setup steps, for example to install dependencies, you'll need the `contents: read` permission. If you don't clone the repository in your setup steps, Copilot will do this for you automatically after the steps complete.
+      contents: read
+
+    # You can define any steps you want, and they will run before the agent starts.
+    # If you do not check out your code, Copilot will do this for you.
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          submodules: true
+      - run: |
+          cd _submodules/TypeScript
+          git config remote.origin.fetch "+refs/heads/*:refs/remotes/origin/*"
+          git fetch origin --unshallow
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+      - uses: dtolnay/rust-toolchain@fcf085fcb4b4b8f63f96906cd713eb52181b5ea4 # stable
+      - uses: ./.github/actions/setup-go
+        with:
+          cache-name: copilot-setup-steps
+      - run: npm ci
+      - run: npx hereby build

internal/checker/nodebuilderimpl.go

@@ -304,6 +304,12 @@ func (b *nodeBuilderImpl) tryReuseExistingNonParameterTypeNode(existing *ast.Typ
 	if annotationType == nil {
 		annotationType = b.getTypeFromTypeNode(existing, true)
 	}
+	if annotationType != nil && b.ch.isErrorType(annotationType) {
+		// allow "reusing" type nodes that resolve to error types
+		// those can't truly be reused but it prevents cascading errors in isolatedDeclarations
+		// for source with errors there is no guarantee to emit correct code anyway
+		return b.tryReuseExistingTypeNodeHelper(existing)
+	}
 	if annotationType != nil && b.typeNodeIsEquivalentToType(host, t, annotationType) && b.existingTypeNodeIsNotReferenceOrIsReferenceWithCompatibleTypeArgumentCount(existing, t) {
 		result := b.tryReuseExistingTypeNodeHelper(existing)
 		if result != nil {