C++: add #pragma once to generated file

api/cpp/tests/multiple-includes/logic.cpp

@@ -3,6 +3,8 @@
 
 #include "logic.h"
 #include "appwindow.h"
+// Test that it's ok to include twice
+#include "appwindow.h"
 
 void setup_logic(const Logic &logic)
 {

internal/compiler/generator/cpp.rs

@@ -89,6 +89,8 @@ mod cpp_ast {
 
     impl Display for File {
         fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
+            writeln!(f, "// This file is auto-generated")?;
+            writeln!(f, "#pragma once")?;
             for i in &self.includes {
                 writeln!(f, "#include {}", i)?;
             }

tests/driver/cpp/cppdriver.rs

@@ -43,6 +43,12 @@ pub fn test(testcase: &test_driver_lib::TestCase) -> Result<(), Box<dyn Error>>
         return Err(vec.join("\n").into());
     }
 
+    // Remove the `#pragma once` as this is not going to be included and would produce a warning
+    // when compiling the generated code.
+    let hash_pos = generated_cpp.iter().position(|&b| b == b'#').unwrap();
+    assert_eq!(&generated_cpp[hash_pos..hash_pos + 12], b"#pragma once");
+    generated_cpp.drain(hash_pos..hash_pos + 12);
+
     generated_cpp.write_all(
         br"
 #ifdef NDEBUG