[PrintAsClang] skip header maps when collecting include paths

Header map lookup is not handled when doing prefix checks for
textual header inclusion. Skip adding them to the list instead of
adding invalid paths for each header map.

lib/PrintAsClang/PrintAsClang.cpp

@@ -450,6 +450,11 @@ writeImports(raw_ostream &out, llvm::SmallPtrSetImpl<ImportModuleTy> &imports,
 
     for (auto searchDir = clangHeaderSearchInfo.search_dir_begin();
          searchDir != clangHeaderSearchInfo.search_dir_end(); ++searchDir) {
+      // Header map lookup is not supported for now, so don't add the hmap
+      // paths to the search list.
+      if (searchDir->isHeaderMap())
+          continue;
+
       // Ensure search directories end in / so that we don't prefix match
       // against a folder that starts with the same substring.
       auto path = normalizePath(searchDir->getName());

test/PrintAsObjC/emit-clang-header-nonmodular-includes-skip-header-maps.swift

@@ -0,0 +1,26 @@
+// REQUIRES: objc_interop
+
+// RUN: %empty-directory(%t)
+
+// Create a header map that maps header-regular.h to its real path.
+// RUN: echo '{"mappings": {"header-regular.h": "%/S/Inputs/custom-modules/header_subdirectory/header-regular.h"}}' > %t/hmap.json
+// RUN: %hmaptool write %t/hmap.json %t/headers.hmap
+
+// Compile with the header map as a search directory alongside a regular
+// include directory. The header map should be skipped when collecting include
+// paths for nonmodular includes.
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify -emit-objc-header-path %t/textual-imports.h -Xcc -fmodule-map-file=%S/Inputs/custom-modules/module.modulemap -Xcc -I%t/headers.hmap -Xcc -I%S/Inputs/custom-modules/header_subdirectory/ -emit-clang-header-nonmodular-includes %s
+// RUN: %FileCheck %s < %t/textual-imports.h
+
+import EmitClangHeaderNonmodularIncludesStressTest
+
+public class Bar : Baz {}
+
+// CHECK: @import EmitClangHeaderNonmodularIncludesStressTest;
+// CHECK-NEXT: #elif defined(__OBJC__)
+// CHECK-NEXT: #import <header-regular.h>
+// CHECK-NEXT: #import <header-symlink.h>
+// CHECK-NEXT: #else
+// CHECK-NEXT: #include <header-regular.h>
+// CHECK-NEXT: #include <header-symlink.h>
+// CHECK-NEXT: #endif