libproc_macro: Make Ident ffi-safe

Make the Ident rust type ffi-safe. This involved a rework of the
structure construction/destroy which will be delagated to the cpp part.

ChangeLog:

	* librust/proc_macro/rust/bridge/ident.rs: Make Ident ffi-safe.
	* librust/proc_macro/rust/ident.rs: Refactor display trait.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

2 files changed, 37 insertions, 21 deletions

diff --git a/librust/proc_macro/rust/bridge/ident.rs b/librust/proc_macro/rust/bridge/ident.rs
index b6e4719..880cf77 100644
--- a/librust/proc_macro/rust/bridge/ident.rs
+++ b/librust/proc_macro/rust/bridge/ident.rs
@@ -1,26 +1,29 @@
 use bridge::span::Span;
-use std::ffi::CString;
+use std::ffi::{c_char, CStr, CString};
+use std::fmt;
+
+extern "C" {
+    fn Ident__new(string: *const c_char) -> Ident;
+    fn Ident__new_raw(string: *const c_char) -> Ident;
+    fn Ident__drop(ident: *const Ident);
+}
 
 #[repr(C)]
 #[derive(Clone, Debug)]
 pub struct Ident {
     pub(crate) is_raw: bool,
-    pub(crate) val: CString,
+    pub(crate) val: *const c_char,
 }
 
 impl Ident {
     pub fn new(string: &str, _span: Span) -> Self {
-        Ident {
-            is_raw: false,
-            val: CString::new(string).expect("Cannot create CString from rust String"),
-        }
+        let string = CString::new(string).expect("Cannot convert to CString");
+        unsafe { Ident__new(string.as_ptr()) }
     }
 
     pub fn new_raw(string: &str, _span: Span) -> Self {
-        Ident {
-            is_raw: true,
-            val: CString::new(string).expect("Cannot create CString from rust String"),
-        }
+        let string = CString::new(string).expect("Cannot convert to CString");
+        unsafe { Ident__new_raw(string.as_ptr()) }
     }
 
     pub fn span(&self) -> Span {
@@ -31,3 +34,26 @@ impl Ident {
         let _ = span;
     }
 }
+
+impl Drop for Ident {
+    fn drop(&mut self) {
+        unsafe { Ident__drop(self as *const Ident) }
+    }
+}
+
+impl fmt::Display for Ident {
+    /// Display as lossless converted string.
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_raw {
+            f.write_str("r#")?;
+        }
+        fmt::Display::fmt(
+            unsafe {
+                CStr::from_ptr(self.val)
+                    .to_str()
+                    .expect("Cannot convert back to rust string")
+            },
+            f,
+        )
+    }
+}
diff --git a/librust/proc_macro/rust/ident.rs b/librust/proc_macro/rust/ident.rs
index cc85ea5..809c993 100644
--- a/librust/proc_macro/rust/ident.rs
+++ b/librust/proc_macro/rust/ident.rs
@@ -56,17 +56,7 @@ impl Ident {
 impl fmt::Display for Ident {
     /// Display as lossless converted string.
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        if self.0.is_raw {
-            f.write_str("r#")?;
-        }
-        fmt::Display::fmt(
-            &self
-                .0
-                .val
-                .to_str()
-                .expect("Cannot convert back to rust string"),
-            f,
-        )
+        self.0.fmt(f)
     }
 }