Add utility method to construct new complex enums

This is incredibly useful for downstream languages eg Java as it
avoids having to manually implement constructors and can just use
common function-mapping logic.

diff --git a/c-bindings-gen/src/main.rs b/c-bindings-gen/src/main.rs
index cb7305bd7ee2356676326c30e8b699625d75b574..2f94e432e4f351c36e8f975cb531d1d57258f7ba 100644 (file)
--- a/c-bindings-gen/src/main.rs
+++ b/c-bindings-gen/src/main.rs
@@ -1170,6 +1170,23 @@ fn writeln_impl<W: std::io::Write>(w: &mut W, i: &syn::ItemImpl, types: &mut Typ
        }
 }
 
+/// Replaces upper case charachters with underscore followed by lower case except the first
+/// charachter and repeated upper case characthers (which are only made lower case).
+fn camel_to_snake_case(camel: &str) -> String {
+       let mut res = "".to_string();
+       let mut last_upper = -1;
+       for (idx, c) in camel.chars().enumerate() {
+               if c.is_uppercase() {
+                       if last_upper != idx as isize - 1 { res.push('_'); }
+                       res.push(c.to_lowercase().next().unwrap());
+                       last_upper = idx as isize;
+               } else {
+                       res.push(c);
+               }
+       }
+       res
+}
+
 
 /// Print a mapping of an enum. If all of the enum's fields are C-mapped in some form (or the enum
 /// is unitary), we generate an equivalent enum with all types replaced with their C mapped
@@ -1193,25 +1210,31 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
        assert!(gen_types.learn_generics(&e.generics, types));
 
        let mut needs_free = false;
+       let mut constr = Vec::new();
 
        writeln!(w, "#[must_use]\n#[derive(Clone)]\n#[repr(C)]\npub enum {} {{", e.ident).unwrap();
        for var in e.variants.iter() {
                assert_eq!(export_status(&var.attrs), ExportStatus::Export); // We can't partially-export a mirrored enum
                writeln_docs(w, &var.attrs, "\t");
                write!(w, "\t{}", var.ident).unwrap();
+               writeln!(&mut constr, "#[no_mangle]\n/// Utility method to constructs a new {}-variant {}", var.ident, e.ident).unwrap();
+               let constr_name = camel_to_snake_case(&format!("{}", var.ident));
+               write!(&mut constr, "pub extern \"C\" fn {}_{}(", e.ident, constr_name).unwrap();
+               let mut empty_tuple_variant = false;
                if let syn::Fields::Named(fields) = &var.fields {
                        needs_free = true;
                        writeln!(w, " {{").unwrap();
-                       for field in fields.named.iter() {
+                       for (idx, field) in fields.named.iter().enumerate() {
                                if export_status(&field.attrs) == ExportStatus::TestOnly { continue; }
                                writeln_field_docs(w, &field.attrs, "\t\t", types, Some(&gen_types), &field.ty);
                                write!(w, "\t\t{}: ", field.ident.as_ref().unwrap()).unwrap();
+                               write!(&mut constr, "{}{}: ", if idx != 0 { ", " } else { "" }, field.ident.as_ref().unwrap()).unwrap();
                                types.write_c_type(w, &field.ty, Some(&gen_types), false);
+                               types.write_c_type(&mut constr, &field.ty, Some(&gen_types), false);
                                writeln!(w, ",").unwrap();
                        }
                        write!(w, "\t}}").unwrap();
                } else if let syn::Fields::Unnamed(fields) = &var.fields {
-                       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);
@@ -1224,15 +1247,37 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
                                write!(w, "(").unwrap();
                                for (idx, field) in fields.unnamed.iter().enumerate() {
                                        if export_status(&field.attrs) == ExportStatus::TestOnly { continue; }
+                                       write!(&mut constr, "{}: ", ('a' as u8 + idx as u8) as char).unwrap();
                                        types.write_c_type(w, &field.ty, Some(&gen_types), false);
+                                       types.write_c_type(&mut constr, &field.ty, Some(&gen_types), false);
                                        if idx != fields.unnamed.len() - 1 {
                                                write!(w, ",").unwrap();
+                                               write!(&mut constr, ",").unwrap();
                                        }
                                }
                                write!(w, ")").unwrap();
                        }
                }
                if var.discriminant.is_some() { unimplemented!(); }
+               write!(&mut constr, ") -> {} {{\n\t{}::{}", e.ident, e.ident, var.ident).unwrap();
+               if let syn::Fields::Named(fields) = &var.fields {
+                       writeln!(&mut constr, " {{").unwrap();
+                       for field in fields.named.iter() {
+                               writeln!(&mut constr, "\t\t{},", field.ident.as_ref().unwrap()).unwrap();
+                       }
+                       writeln!(&mut constr, "\t}}").unwrap();
+               } else if let syn::Fields::Unnamed(fields) = &var.fields {
+                       if !empty_tuple_variant {
+                               write!(&mut constr, "(").unwrap();
+                               for idx in 0..fields.unnamed.len() {
+                                       write!(&mut constr, "{}, ", ('a' as u8 + idx as u8) as char).unwrap();
+                               }
+                               writeln!(&mut constr, ")").unwrap();
+                       } else {
+                               writeln!(&mut constr, "").unwrap();
+                       }
+               }
+               writeln!(&mut constr, "}}").unwrap();
                writeln!(w, ",").unwrap();
        }
        writeln!(w, "}}\nuse {}::{} as native{};\nimpl {} {{", types.module_path, e.ident, e.ident, e.ident).unwrap();
@@ -1373,6 +1418,7 @@ fn writeln_enum<'a, 'b, W: std::io::Write>(w: &mut W, e: &'a syn::ItemEnum, type
        writeln!(w, "pub extern \"C\" fn {}_clone(orig: &{}) -> {} {{", e.ident, e.ident, e.ident).unwrap();
        writeln!(w, "\torig.clone()").unwrap();
        writeln!(w, "}}").unwrap();
+       w.write_all(&constr).unwrap();
        write_cpp_wrapper(cpp_headers, &format!("{}", e.ident), needs_free, None);
 }