When unidirectionally merging symbols, do so recursively

src/compiler/checker.ts

@@ -918,11 +918,12 @@ namespace ts {
                 addRange(target.declarations, source.declarations);
                 if (source.members) {
                     if (!target.members) target.members = createSymbolTable();
-                    mergeSymbolTable(target.members, source.members);
+                    mergeSymbolTable(target.members, source.members, unidirectional);
                 }
                 if (source.exports) {
                     if (!target.exports) target.exports = createSymbolTable();
-                    mergeSymbolTable(target.exports, source.exports);
+                    mergeSymbolTable(target.exports, source.exports, unidirectional
+                        );
                 }
                 if (!unidirectional) {
                     recordMergedSymbol(target, source);
@@ -993,10 +994,10 @@ namespace ts {
             return combined;
         }
 
-        function mergeSymbolTable(target: SymbolTable, source: SymbolTable) {
+        function mergeSymbolTable(target: SymbolTable, source: SymbolTable, unidirectional = false) {
             source.forEach((sourceSymbol, id) => {
                 const targetSymbol = target.get(id);
-                target.set(id, targetSymbol ? mergeSymbol(targetSymbol, sourceSymbol) : sourceSymbol);
+                target.set(id, targetSymbol ? mergeSymbol(targetSymbol, sourceSymbol, unidirectional) : sourceSymbol);
             });
         }
 

tests/baselines/reference/ambientDeclarationsPatterns_merging3.errors.txt

@@ -0,0 +1,18 @@
+tests/cases/conformance/ambient/test.ts(6,6): error TS2339: Property 'a' does not exist on type 'OhNo'.
+
+
+==== tests/cases/conformance/ambient/types.ts (0 errors) ====
+    declare module "*.foo" {
+      export interface OhNo { star: string }
+    }
+
+==== tests/cases/conformance/ambient/test.ts (1 errors) ====
+    declare module "a.foo" {
+      export interface OhNo { a: string }
+    }
+    import { OhNo } from "b.foo"
+    declare let ohno: OhNo;
+    ohno.a // oh no
+         ~
+!!! error TS2339: Property 'a' does not exist on type 'OhNo'.
+

tests/baselines/reference/ambientDeclarationsPatterns_merging3.js

@@ -0,0 +1,21 @@
+//// [tests/cases/conformance/ambient/ambientDeclarationsPatterns_merging3.ts] ////
+
+//// [types.ts]
+declare module "*.foo" {
+  export interface OhNo { star: string }
+}
+
+//// [test.ts]
+declare module "a.foo" {
+  export interface OhNo { a: string }
+}
+import { OhNo } from "b.foo"
+declare let ohno: OhNo;
+ohno.a // oh no
+
+
+//// [types.js]
+//// [test.js]
+"use strict";
+exports.__esModule = true;
+ohno.a; // oh no

tests/baselines/reference/ambientDeclarationsPatterns_merging3.symbols

@@ -0,0 +1,27 @@
+=== tests/cases/conformance/ambient/types.ts ===
+declare module "*.foo" {
+>"*.foo" : Symbol("*.foo", Decl(types.ts, 0, 0))
+
+  export interface OhNo { star: string }
+>OhNo : Symbol(OhNo, Decl(types.ts, 0, 24))
+>star : Symbol(OhNo.star, Decl(types.ts, 1, 25))
+}
+
+=== tests/cases/conformance/ambient/test.ts ===
+declare module "a.foo" {
+>"a.foo" : Symbol("a.foo", Decl(test.ts, 0, 0), Decl(types.ts, 0, 0))
+
+  export interface OhNo { a: string }
+>OhNo : Symbol(OhNo, Decl(test.ts, 0, 24), Decl(types.ts, 0, 24))
+>a : Symbol(OhNo.a, Decl(test.ts, 1, 25))
+}
+import { OhNo } from "b.foo"
+>OhNo : Symbol(OhNo, Decl(test.ts, 3, 8))
+
+declare let ohno: OhNo;
+>ohno : Symbol(ohno, Decl(test.ts, 4, 11))
+>OhNo : Symbol(OhNo, Decl(test.ts, 3, 8))
+
+ohno.a // oh no
+>ohno : Symbol(ohno, Decl(test.ts, 4, 11))
+

tests/baselines/reference/ambientDeclarationsPatterns_merging3.types

@@ -0,0 +1,26 @@
+=== tests/cases/conformance/ambient/types.ts ===
+declare module "*.foo" {
+>"*.foo" : typeof import("*.foo")
+
+  export interface OhNo { star: string }
+>star : string
+}
+
+=== tests/cases/conformance/ambient/test.ts ===
+declare module "a.foo" {
+>"a.foo" : typeof import("a.foo")
+
+  export interface OhNo { a: string }
+>a : string
+}
+import { OhNo } from "b.foo"
+>OhNo : any
+
+declare let ohno: OhNo;
+>ohno : OhNo
+
+ohno.a // oh no
+>ohno.a : any
+>ohno : OhNo
+>a : any
+