Program: Fix move of diagnostics.

Add test.

Change-Id: Ide47df8b3a946818ed9a8ffd62411284f568609b
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/42262
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>

src/program.cc

@@ -82,6 +82,7 @@ Program& Program::operator=(Program&& program) {
   ast_ = std::move(program.ast_);
   sem_ = std::move(program.sem_);
   symbols_ = std::move(program.symbols_);
+  diagnostics_ = std::move(program.diagnostics_);
   is_valid_ = program.is_valid_;
   return *this;
 }

src/program_test.cc

@@ -152,5 +152,22 @@ TEST_F(ProgramTest, IsValid_GeneratesError) {
   EXPECT_EQ(program.Diagnostics().begin()->message,
             "invalid program generated");
 }
+
+TEST_F(ProgramTest, DiagnosticsMove) {
+  Diagnostics().add_error("an error message");
+
+  Program program_a(std::move(*this));
+  EXPECT_FALSE(program_a.IsValid());
+  EXPECT_EQ(program_a.Diagnostics().count(), 1u);
+  EXPECT_EQ(program_a.Diagnostics().error_count(), 1u);
+  EXPECT_EQ(program_a.Diagnostics().begin()->message, "an error message");
+
+  Program program_b(std::move(program_a));
+  EXPECT_FALSE(program_b.IsValid());
+  EXPECT_EQ(program_b.Diagnostics().count(), 1u);
+  EXPECT_EQ(program_b.Diagnostics().error_count(), 1u);
+  EXPECT_EQ(program_b.Diagnostics().begin()->message, "an error message");
+}
+
 }  // namespace
 }  // namespace tint