Map enum tuple variants with no contents as unitary enum variants

cbindgen maps `enum A { V() }` with a `struct A_V_Body {}` which
has different size on C and C++ (0 and 1 bytes). While this is
fine if a different variant has non-0 size as the union will be
correctly sized. However, there isn't a lot of reason to rely on
this when we can just have a unitary variant as well.

diff --git a/c-bindings-gen/src/main.rs b/c-bindings-gen/src/main.rs
index 81f26bfa9ee3fce3da20931b431a90cfb91fee4b..c2ef30fbcf83a9e0c37204e1ee1b0f9466756ba4 100644 (file)
--- a/c-bindings-gen/src/main.rs
+++ b/c-bindings-gen/src/main.rs
@@ -1159,16 +1159,26 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
                        }
                        write!(w, "\t}}").unwrap();
                } else if let syn::Fields::Unnamed(fields) = &var.fields {
-                       needs_free = true;
-                       write!(w, "(").unwrap();
-                       for (idx, field) in fields.unnamed.iter().enumerate() {
-                               if export_status(&field.attrs) == ExportStatus::TestOnly { continue; }
-                               types.write_c_type(w, &field.ty, Some(&gen_types), false);
-                               if idx != fields.unnamed.len() - 1 {
-                                       write!(w, ",").unwrap();
+                       let mut empty_tuple_variant = false;
+                       if fields.unnamed.len() == 1 {
+                               let mut empty_check = Vec::new();
+                               types.write_c_type(&mut empty_check, &fields.unnamed[0].ty, Some(&gen_types), false);
+                               if empty_check.is_empty() {
+                                       empty_tuple_variant = true;
+                               }
+                       }
+                       if !empty_tuple_variant {
+                               needs_free = true;
+                               write!(w, "(").unwrap();
+                               for (idx, field) in fields.unnamed.iter().enumerate() {
+                                       if export_status(&field.attrs) == ExportStatus::TestOnly { continue; }
+                                       types.write_c_type(w, &field.ty, Some(&gen_types), false);
+                                       if idx != fields.unnamed.len() - 1 {
+                                               write!(w, ",").unwrap();
+                                       }
                                }
+                               write!(w, ")").unwrap();
                        }
-                       write!(w, ")").unwrap();
                }
                if var.discriminant.is_some() { unimplemented!(); }
                writeln!(w, ",").unwrap();
@@ -1180,6 +1190,7 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
                        writeln!(w, "\t#[allow(unused)]\n\tpub(crate) fn {} {{\n\t\tmatch {} {{", $fn_sig, if $to_c { "native" } else { "self" }).unwrap();
                        for var in e.variants.iter() {
                                write!(w, "\t\t\t{}{}::{} ", if $to_c { "native" } else { "" }, e.ident, var.ident).unwrap();
+                               let mut empty_tuple_variant = false;
                                if let syn::Fields::Named(fields) = &var.fields {
                                        write!(w, "{{").unwrap();
                                        for field in fields.named.iter() {
@@ -1188,12 +1199,21 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
                                        }
                                        write!(w, "}} ").unwrap();
                                } else if let syn::Fields::Unnamed(fields) = &var.fields {
-                                       write!(w, "(").unwrap();
-                                       for (idx, field) in fields.unnamed.iter().enumerate() {
-                                               if export_status(&field.attrs) == ExportStatus::TestOnly { continue; }
-                                               write!(w, "{}{}, ", if $ref { "ref " } else { "mut " }, ('a' as u8 + idx as u8) as char).unwrap();
+                                       if fields.unnamed.len() == 1 {
+                                               let mut empty_check = Vec::new();
+                                               types.write_c_type(&mut empty_check, &fields.unnamed[0].ty, Some(&gen_types), false);
+                                               if empty_check.is_empty() {
+                                                       empty_tuple_variant = true;
+                                               }
+                                       }
+                                       if !empty_tuple_variant || $to_c {
+                                               write!(w, "(").unwrap();
+                                               for (idx, field) in fields.unnamed.iter().enumerate() {
+                                                       if export_status(&field.attrs) == ExportStatus::TestOnly { continue; }
+                                                       write!(w, "{}{}, ", if $ref { "ref " } else { "mut " }, ('a' as u8 + idx as u8) as char).unwrap();
+                                               }
+                                               write!(w, ") ").unwrap();
                                        }
-                                       write!(w, ") ").unwrap();
                                }
                                write!(w, "=>").unwrap();
 
@@ -1233,7 +1253,9 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
                                } else if let syn::Fields::Unnamed(fields) = &var.fields {
                                        write!(w, " {{\n\t\t\t\t").unwrap();
                                        for (idx, field) in fields.unnamed.iter().enumerate() {
-                                               handle_field_a!(field, &format_ident!("{}", ('a' as u8 + idx as u8) as char));
+                                               if !empty_tuple_variant {
+                                                       handle_field_a!(field, &format_ident!("{}", ('a' as u8 + idx as u8) as char));
+                                               }
                                        }
                                } else { write!(w, " ").unwrap(); }
 
@@ -1268,12 +1290,14 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
                                        writeln!(w, "\n\t\t\t\t}}").unwrap();
                                        write!(w, "\t\t\t}}").unwrap();
                                } else if let syn::Fields::Unnamed(fields) = &var.fields {
-                                       write!(w, " (").unwrap();
-                                       for (idx, field) in fields.unnamed.iter().enumerate() {
-                                               write!(w, "\n\t\t\t\t\t").unwrap();
-                                               handle_field_b!(field, &format_ident!("{}", ('a' as u8 + idx as u8) as char));
+                                       if !empty_tuple_variant || !$to_c {
+                                               write!(w, " (").unwrap();
+                                               for (idx, field) in fields.unnamed.iter().enumerate() {
+                                                       write!(w, "\n\t\t\t\t\t").unwrap();
+                                                       handle_field_b!(field, &format_ident!("{}", ('a' as u8 + idx as u8) as char));
+                                               }
+                                               writeln!(w, "\n\t\t\t\t)").unwrap();
                                        }
-                                       writeln!(w, "\n\t\t\t\t)").unwrap();
                                        write!(w, "\t\t\t}}").unwrap();
                                }
                                writeln!(w, ",").unwrap();