findAllReferences: Type parameter is not globally visible (#16419)

* findAllReferences: Type parameter is not globally visible

* Add test for merged interface

* Clean up comment

src/services/findAllReferences.ts

@@ -652,10 +652,15 @@ namespace ts.FindAllReferences.Core {
             return undefined;
         }
 
-        // If the symbol has a parent, it's globally visible.
-        // Unless that parent is an external module, then we should only search in the module (and recurse on the export later).
-        // But if the parent is a module that has `export as namespace`, then the symbol *is* globally visible.
-        if (parent && !((parent.flags & SymbolFlags.Module) && isExternalModuleSymbol(parent) && !parent.globalExports)) {
+        /*
+        If the symbol has a parent, it's globally visible unless:
+        - It's a private property (handled above).
+        - It's a type parameter.
+        - The parent is an external module: then we should only search in the module (and recurse on the export later).
+          - But if the parent has `export as namespace`, the symbol is globally visible through that namespace.
+        */
+        const exposedByParent = parent && !(symbol.flags & SymbolFlags.TypeParameter);
+        if (exposedByParent && !((parent.flags & SymbolFlags.Module) && isExternalModuleSymbol(parent) && !parent.globalExports)) {
             return undefined;
         }
 
@@ -682,7 +687,7 @@ namespace ts.FindAllReferences.Core {
         //     declare module "a" { export type T = number; }
         //     declare module "b" { import { T } from "a"; export const x: T; }
         // So we must search the whole source file. (Because we will mark the source file as seen, we we won't return to it when searching for imports.)
-        return parent ? scope.getSourceFile() : scope;
+        return exposedByParent ? scope.getSourceFile() : scope;
     }
 
     function getPossibleSymbolReferencePositions(sourceFile: SourceFile, symbolName: string, container: Node = sourceFile): number[] {

tests/cases/fourslash/findAllRefsTypeParameterInMergedInterface.ts

@@ -0,0 +1,6 @@
+/// <reference path='fourslash.ts' />
+
+////interface I<[|{| "isWriteAccess": true, "isDefinition": true |}T|]> { a: [|T|] }
+////interface I<[|{| "isWriteAccess": true, "isDefinition": true |}T|]> { b: [|T|] }
+
+verify.singleReferenceGroup("(type parameter) T in I<T>");