Return 0 when main falls off its end (#482)

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -429,6 +429,12 @@ void Converter::ConvertFunctionBody(clang::FunctionDecl *decl) {
     return;
   }
   auto compound = clang::dyn_cast<clang::CompoundStmt>(decl->getBody());
+  if (decl->isMain() && compound &&
+      (compound->body_empty() ||
+       !clang::isa<clang::ReturnStmt>(compound->body_back()))) {
+    StrCat('0');
+    return;
+  }
   if (!compound || compound->body_empty()) {
     return;
   }

tests/unit/empty_main.cpp

@@ -1 +1 @@
-int main(int, char **) { return 0; }
+int main(int, char **) {}

tests/unit/out/refcount/empty_main.rs

@@ -24,6 +24,6 @@ pub fn main() {
     ::std::process::exit(main_0(::std::env::args().len() as i32, argv.as_pointer()));
 }
 fn main_0(_a0: i32, _a1: Ptr<Ptr<i8>>) -> i32 {
-    return 0;
+    0
 }
 pub fn __cpp2rust_init_globals() {}

tests/unit/out/unsafe/empty_main.rs

@@ -23,6 +23,6 @@ pub fn main() {
     }
 }
 unsafe fn main_0(mut _a0: i32, mut _a1: *mut *mut libc::c_char) -> i32 {
-    return 0;
+    0
 }
 pub unsafe fn __cpp2rust_init_globals() {}