add test for top-level decls of Clang submodules

Author: QuietMisdreavus

lib/ClangImporter/ClangImporter.cpp

@@ -3120,6 +3120,7 @@ class VectorDeclPtrConsumer : public swift::VisibleDeclConsumer {
 };
 } // unnamed namespace
 
+// FIXME: should submodules still be crawled for the symbol graph? (SR-15753)
 bool ClangModuleUnit::shouldCollectDisplayDecls() const { return isTopLevel(); }
 
 void ClangModuleUnit::getTopLevelDecls(SmallVectorImpl<Decl*> &results) const {

test/SymbolGraph/ClangImporter/Inputs/Submodules/Mixed.h

@@ -0,0 +1 @@
+double outerVar = 1.0;

test/SymbolGraph/ClangImporter/Inputs/Submodules/Submodule.h

@@ -0,0 +1 @@
+double innerVar = 2.0;

test/SymbolGraph/ClangImporter/Inputs/Submodules/module.modulemap

@@ -0,0 +1,9 @@
+module Mixed {
+  header "Mixed.h"
+  export *
+
+  explicit module Submodule {
+    header "Submodule.h"
+    export *
+  }
+}

test/SymbolGraph/ClangImporter/Submodules.swift

@@ -0,0 +1,11 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -I %S/Inputs/Submodules -emit-module-path %t/Submodules.swiftmodule -enable-objc-interop -module-name Submodules %s -emit-symbol-graph -emit-symbol-graph-dir %t
+
+// REQUIRES: objc_interop
+
+// Don't crash when a module declared an `@_exported import` for a Clang non-top-level module.
+
+@_exported import Mixed
+@_exported import Mixed.Submodule
+
+public func someFunc() {}