ffi: Add new error-pointer-based error handling.

  - Express existing context-based error handling using the new set of
    macros.

2 files changed, 20 insertions, 2 deletions

diff --git a/ffi/src/core.rs b/ffi/src/core.rs
index ae614ed4..d1b74437 100644
--- a/ffi/src/core.rs
+++ b/ffi/src/core.rs
@@ -64,6 +64,10 @@ impl Context {
         Context{c: c, e: ptr::null_mut()}
     }
 
+    pub(crate) fn errp(&mut self) -> &mut *mut failure::Error {
+        &mut self.e
+    }
+
     pub(crate) fn set_error(&mut self, e: failure::Error) {
         if ! self.e.is_null() {
             unsafe {
diff --git a/ffi/src/lib.rs b/ffi/src/lib.rs
index 2085521c..f7202cc7 100644
--- a/ffi/src/lib.rs
+++ b/ffi/src/lib.rs
@@ -265,6 +265,16 @@ macro_rules! ffi_return_maybe_string {
 /// to store complex errors.
 macro_rules! ffi_make_fry_from_ctx {
     ($ctx:ident) => {
+        ffi_make_fry_from_errp!(Some($ctx.errp()))
+    }
+}
+
+/* Error handling with implicit error return argument.  */
+
+/// Emits local macros for error handling that use the given context
+/// to store complex errors.
+macro_rules! ffi_make_fry_from_errp {
+    ($errp:expr) => {
         /// Like try! for ffi glue.
         ///
         /// Evaluates the given expression.  On success, evaluate to
@@ -277,7 +287,9 @@ macro_rules! ffi_make_fry_from_ctx {
                     Ok(_) => Status::Success,
                     Err(e) => {
                         let status = Status::from(&e);
-                        $ctx.set_error(e);
+                        if let Some(errp) = $errp {
+                            *errp = box_raw!(e);
+                        }
                         status
                     },
                 }
@@ -294,7 +306,9 @@ macro_rules! ffi_make_fry_from_ctx {
                 match $expr {
                     Ok(v) => v,
                     Err(e) => {
-                        $ctx.set_error(e);
+                        if let Some(errp) = $errp {
+                            *errp = box_raw!(e);
+                        }
                         return $or;
                     },
                 }