feat!(src/macros): Store allocation location in all strings

This makes it possible to automatically free the string in the correct
way expected by both c and rust.
Rust strings can now just be freed by the rust allocator, whilst c
strings are forgotten, so that the c allocator may free them.

BREAKING CHANGE: All usage of explicit mentions `std::string::String`
                 in your `handle_cmd` function will need to be replaced
                 by `trixy::types::newtypes::String`. Otherwise these
                 types should provide the same methods.

example/main/src/bin/main/main.rs

@@ -20,9 +20,10 @@
 * If not, see <https://www.gnu.org/licenses/>.
 */
 
-use std::{env, ffi::c_int, mem};
+use std::{env, ffi::c_int};
 
 use libloading::{Library, Symbol};
+use trixy::types::newtypes;
 
 use crate::dogs::{DogType, TrainedDog};
 
@@ -30,6 +31,7 @@ include!(concat!(env!("OUT_DIR"), "/api.rs"));
 
 // run `cargo run --bin api > ./src/bin/main/generated_api.rs` to output the generated api
 // mod generated_api;
+// pub use generated_api::*;
 
 fn handle_cmd(cmd: Commands) {
     match cmd {
@@ -38,9 +40,11 @@ fn handle_cmd(cmd: Commands) {
                 let output = format!("Hi {}!", name);
                 println!("(rust): {}", output);
                 trixy_output.send(output.into()).expect("Will work");
-                mem::forget(name);
             }
-            dogs::Dogs::train_dog { trixy_output, dog } => {
+            dogs::Dogs::train_dog {
+                trixy_output,
+                dog: _,
+            } => {
                 trixy_output
                     .send(
                         TrainedDog {
@@ -51,23 +55,19 @@ fn handle_cmd(cmd: Commands) {
                         .unwrap(),
                     )
                     .unwrap();
-                mem::forget(dog);
             }
             dogs::Dogs::guess_my_favourite_dog {
                 trixy_output,
                 callback,
             } => {
                 let fav_dog = callback("Frank".into(), 30);
-                let dog_name: String = fav_dog.name.clone().try_into().unwrap();
+                let dog_name: newtypes::String = fav_dog.name.clone().try_into().unwrap();
                 println!("(rust): They want a dog named: {}", dog_name);
                 trixy_output.send(DogType::Cat.into()).unwrap();
-
-                mem::forget(dog_name);
             }
         },
         Commands::outstanding { name } => {
             println!("(rust): {} is outstanding!", name);
-            mem::forget(name);
         }
     }
 }

src/macros/generate/convert/host/c/type/mod.rs

@@ -28,9 +28,6 @@ use crate::parser::command_spec::{Identifier, NamedType, Type};
 mod doc_named_type;
 mod named_type;
 
-// pub use doc_named_type::*;
-// pub use named_type::*;
-
 impl Type {
     pub fn to_c(&self) -> TokenStream2 {
         match self {
@@ -82,7 +79,7 @@ impl Type {
 
             let type_name = trixy_build_in_types
                 .first()
-                .expect("The names should not be dublicated, this should be the only value");
+                .expect("The names should not be duplicated, this should be the only value");
 
             match *type_name {
                 "Result" => {

src/macros/generate/convert/host/rust/function/mod.rs

@@ -26,7 +26,6 @@ use quote::quote;
 use crate::parser::command_spec::{Function, Identifier, NamedType, Type};
 
 impl Function {
-    // was called function_identifier_to_rust
     pub fn to_rust_identifier<F>(
         &self,
         input_fmt_fn: fn(&NamedType) -> TokenStream2,

src/macros/generate/convert/host/rust/type/mod.rs

@@ -61,16 +61,22 @@ impl Type {
         }
     }
     pub fn to_rust_typical(identifier: &Identifier, generic_args: &Vec<Type>) -> TokenStream2 {
+        match identifier {
+            Identifier { name, variant: _ } if name == "String" => {
+                // We wrap over the string to ensure that we know where it was allocated.
+                quote! {
+                    trixy::types::newtypes::String
+                }
+            }
+            _ => {
                 let ident = identifier.to_rust();
-        let namespaces_path = Variant::to_rust_path(&identifier.variant);
 
-        let nasp_path = if let Some(nasp_path) = Variant::to_rust_path(&identifier.variant) {
-            if nasp_path.is_empty() {
+                let nasp_path = if let Some(path) = &Variant::to_rust_path(&identifier.variant) {
+                    if path.is_empty() {
                         quote! {
                             crate ::
                         }
                     } else {
-                let path = namespaces_path;
                         quote! {
                             #path ::
                         }
@@ -84,10 +90,13 @@ impl Type {
                         #nasp_path #ident
                     }
                 } else {
-            let generics: Vec<TokenStream2> = generic_args.iter().map(Type::to_rust).collect();
+                    let generics: Vec<TokenStream2> =
+                        generic_args.iter().map(Type::to_rust).collect();
                     quote! {
                        #nasp_path #ident <#(#generics),*>
                     }
                 }
             }
         }
+    }
+}

src/types/mod.rs

@@ -24,6 +24,7 @@
 pub mod error;
 pub mod traits;
 pub mod types_list;
+pub mod newtypes;
 
 pub use types_list::*;
 

src/types/newtypes/mod.rs

@@ -0,0 +1,88 @@
+//! This module contains wrapper types for know rust types, where trixy needs to store additional
+//! information
+
+use std::{fmt::Display, mem, string};
+
+#[derive(Debug, Default, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct String {
+    pub(crate) data: Option<string::String>,
+    pub(crate) alloc_location: AllocLocation,
+}
+
+#[derive(Clone, Hash, Debug, Default, PartialEq, Eq, PartialOrd, Ord)]
+pub(crate) enum AllocLocation {
+    #[default]
+    Rust,
+    C,
+}
+
+impl From<&str> for String {
+    fn from(value: &str) -> Self {
+        Self {
+            // It's cloned here:
+            data: Some(value.to_owned()),
+            // The string is always allocated in rust, as we clone it above this comment
+            alloc_location: AllocLocation::Rust,
+        }
+    }
+}
+
+impl From<string::String> for String {
+    fn from(value: string::String) -> Self {
+        Self {
+            data: Some(value),
+            // We just assume that every std String is actually allocated in rust
+            alloc_location: AllocLocation::Rust,
+        }
+    }
+}
+
+impl Display for String {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+impl String {
+    pub fn as_str(&self) -> &str {
+        &self
+            .data
+            .as_ref()
+            .expect("The string should only be empty when it's dropped")
+    }
+    pub fn into_std_string(mut self) -> string::String {
+        match self.alloc_location {
+            AllocLocation::C => {
+                // Re-allocate the string in rust
+                let c_alloc_string = mem::take(&mut self.data).expect("It should only be Some");
+                let rust_alloc_string = c_alloc_string.clone();
+
+                // This is here because of the same reason as in the drop impl: we just can't free
+                // a string allocated in c.
+                mem::forget(c_alloc_string);
+
+                rust_alloc_string
+            }
+            AllocLocation::Rust => {
+                let string = mem::take(&mut self.data).expect("Will always be some");
+                string
+            }
+        }
+    }
+}
+
+impl Drop for String {
+    fn drop(&mut self) {
+        match self.alloc_location {
+            AllocLocation::C => {
+                let string = mem::take(&mut self.data);
+                // C needs to free it's strings by itself. We cannot do the job of the c allocator,
+                // thus just forget about it here
+                mem::forget(string)
+            }
+            AllocLocation::Rust => {
+                // A rust allocated string can be free normally. We don't need to do anything here.
+            }
+        }
+    }
+}

src/types/traits/try_from_impl.rs

@@ -20,32 +20,51 @@
 * If not, see <https://www.gnu.org/licenses/>.
 */
 
-use crate::types::String;
+use crate::types::{
+    newtypes::{self, AllocLocation},
+    types_list,
+};
 use std::ffi::CString;
 
 use super::convert_trait::Convertible;
 
-impl From<std::string::String> for String {
+impl From<std::string::String> for types_list::String {
     fn from(value: std::string::String) -> Self {
         let cstring =
             CString::new(value).expect("The input is a valid String, this always succeeds");
         let c_char = cstring.into_ptr();
-        String(c_char)
+        types_list::String(c_char)
     }
 }
 /// Plainly here for convenience
-impl From<&str> for String {
+impl From<&str> for types_list::String {
     fn from(value: &str) -> Self {
         value.to_owned().into()
     }
 }
 
-impl TryFrom<String> for std::string::String {
+impl From<newtypes::String> for types_list::String {
+    fn from(value: newtypes::String) -> Self {
+        // NOTE: This is not really performant, but necessary as we otherwise would need c to
+        // differentiate between c allocated strings (which are freed by `free`) and rust allocated strings
+        // (which are freed by `string_free`) <2024-05-04>
+        let value_string = value.into_std_string();
+        value_string.into()
+    }
+}
+
+impl TryFrom<types_list::String> for newtypes::String {
     type Error = crate::types::error::TypeConversionError;
 
-    fn try_from(value: String) -> Result<Self, Self::Error> {
+    fn try_from(value: types_list::String) -> Result<Self, Self::Error> {
         let cstring = CString::from_ptr(value.0)?;
         let string = cstring.into_string()?;
-        Ok(string)
+
+        Ok(newtypes::String {
+            data: Some(string),
+            // TODO: You could of course do a rust-only round trip, but I think it's reasonable to
+            // assume, that all types_list::String values come from C <2024-05-04>
+            alloc_location: AllocLocation::C,
+        })
     }
 }