GN: Check if targets with precompiled headers use unsupported toolchains.

tools/gn/target_unittest.cc

Index: tools/gn/target_unittest.cc
diff --git a/tools/gn/target_unittest.cc b/tools/gn/target_unittest.cc
index 9bfeed5c32ebb7873f95142508c84b8949684d92..9b413ef8e1d72c5497da7dac15d50157c3bc6190 100644
--- a/tools/gn/target_unittest.cc
+++ b/tools/gn/target_unittest.cc
@@ -869,6 +869,39 @@ TEST(Target, ResolvePrecompiledHeaders) {
       err.help_text());
 }
 
+TEST(Target, PrecompiledHeaderSupport) {
+  TestWithScope setup;
+  Err err;
+
+  std::string pch_1("pch.h");
+  SourceFile pcs_1("//pcs.cc");
+
+  // No source files, so it doesn't matter
+  TestTarget a(setup, "//a", Target::SOURCE_SET);
+  a.config_values().set_precompiled_header(pch_1);
+  a.config_values().set_precompiled_source(pcs_1);
+  ASSERT_TRUE(a.OnResolved(&err));
+
+  // TestWithScope toolchain doesn't support precompiled headers.
+  TestTarget b(setup, "//b", Target::SOURCE_SET);
+  b.config_values().set_precompiled_header(pch_1);
+  b.config_values().set_precompiled_source(pcs_1);
+  b.sources().push_back(SourceFile("//foo/b1.c"));
+  ASSERT_FALSE(b.OnResolved(&err));
+
+  Tool* cxx = setup.toolchain()->GetTool(Toolchain::TYPE_CXX);
+  ASSERT_NE(nullptr, cxx);
+
+  cxx->set_precompiled_header_type(Tool::PCH_GCC);
+
+  // CXX tool now supports PCHs.
+  TestTarget c(setup, "//c", Target::SOURCE_SET);
+  c.config_values().set_precompiled_header(pch_1);
+  c.config_values().set_precompiled_source(pcs_1);
+  c.sources().push_back(SourceFile("//foo/c1.cpp"));
+  ASSERT_TRUE(c.OnResolved(&err));
+}
+
 TEST(Target, AssertNoDeps) {
   TestWithScope setup;
   Err err;