From 333c558d78bd1c67f1a1b00a8706536e9a15cd81 Mon Sep 17 00:00:00 2001
From: Manish Goregaokar <manishsmail@gmail.com>
Date: Sat, 21 Jun 2025 15:20:25 -0700
Subject: [PATCH] [capi] expose error strings

---
 temporal_capi/bindings/c/TemporalError.d.h      |  1 +
 .../cpp/temporal_rs/TemporalError.d.hpp         |  2 ++
 .../bindings/cpp/temporal_rs/TemporalError.hpp  |  2 ++
 temporal_capi/src/error.rs                      | 17 ++++++++++++++++-
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/temporal_capi/bindings/c/TemporalError.d.h b/temporal_capi/bindings/c/TemporalError.d.h
index 9b2953996..3c37cf5f3 100644
--- a/temporal_capi/bindings/c/TemporalError.d.h
+++ b/temporal_capi/bindings/c/TemporalError.d.h
@@ -14,6 +14,7 @@
 
 typedef struct TemporalError {
   ErrorKind kind;
+  OptionStringView msg;
 } TemporalError;
 
 typedef struct TemporalError_option {union { TemporalError ok; }; bool is_ok; } TemporalError_option;
diff --git a/temporal_capi/bindings/cpp/temporal_rs/TemporalError.d.hpp b/temporal_capi/bindings/cpp/temporal_rs/TemporalError.d.hpp
index 2d59a55fd..05d57287e 100644
--- a/temporal_capi/bindings/cpp/temporal_rs/TemporalError.d.hpp
+++ b/temporal_capi/bindings/cpp/temporal_rs/TemporalError.d.hpp
@@ -21,6 +21,7 @@ namespace temporal_rs {
 namespace capi {
     struct TemporalError {
       temporal_rs::capi::ErrorKind kind;
+      diplomat::capi::OptionStringView msg;
     };
 
     typedef struct TemporalError_option {union { TemporalError ok; }; bool is_ok; } TemporalError_option;
@@ -31,6 +32,7 @@ namespace capi {
 namespace temporal_rs {
 struct TemporalError {
   temporal_rs::ErrorKind kind;
+  std::optional<std::string_view> msg;
 
   inline temporal_rs::capi::TemporalError AsFFI() const;
   inline static temporal_rs::TemporalError FromFFI(temporal_rs::capi::TemporalError c_struct);
diff --git a/temporal_capi/bindings/cpp/temporal_rs/TemporalError.hpp b/temporal_capi/bindings/cpp/temporal_rs/TemporalError.hpp
index 207949ac2..eb8dc32f7 100644
--- a/temporal_capi/bindings/cpp/temporal_rs/TemporalError.hpp
+++ b/temporal_capi/bindings/cpp/temporal_rs/TemporalError.hpp
@@ -27,12 +27,14 @@ namespace capi {
 inline temporal_rs::capi::TemporalError temporal_rs::TemporalError::AsFFI() const {
   return temporal_rs::capi::TemporalError {
     /* .kind = */ kind.AsFFI(),
+    /* .msg = */ msg.has_value() ? (diplomat::capi::OptionStringView{ { {msg.value().data(), msg.value().size()} }, true }) : (diplomat::capi::OptionStringView{ {}, false }),
   };
 }
 
 inline temporal_rs::TemporalError temporal_rs::TemporalError::FromFFI(temporal_rs::capi::TemporalError c_struct) {
   return temporal_rs::TemporalError {
     /* .kind = */ temporal_rs::ErrorKind::FromFFI(c_struct.kind),
+    /* .msg = */ c_struct.msg.is_ok ? std::optional(std::string_view(c_struct.msg.ok.data, c_struct.msg.ok.len)) : std::nullopt,
   };
 }
 
diff --git a/temporal_capi/src/error.rs b/temporal_capi/src/error.rs
index f385d459b..8e58bfbe3 100644
--- a/temporal_capi/src/error.rs
+++ b/temporal_capi/src/error.rs
@@ -1,7 +1,11 @@
+use alloc::borrow::Cow;
+
 #[diplomat::bridge]
 #[diplomat::abi_rename = "temporal_rs_{0}"]
 #[diplomat::attr(auto, namespace = "temporal_rs")]
 pub mod ffi {
+    use diplomat_runtime::{DiplomatOption, DiplomatUtf8StrSlice};
+
     #[diplomat::enum_convert(temporal_rs::error::ErrorKind)]
     pub enum ErrorKind {
         Generic,
@@ -14,6 +18,7 @@ pub mod ffi {
     // In the future we might turn this into an opaque type with a msg() field
     pub struct TemporalError {
         pub kind: ErrorKind,
+        pub msg: DiplomatOption<DiplomatUtf8StrSlice<'static>>,
     }
 
     impl TemporalError {
@@ -21,12 +26,14 @@ pub mod ffi {
         pub(crate) fn syntax() -> Self {
             TemporalError {
                 kind: ErrorKind::Syntax,
+                msg: None.into(),
             }
         }
 
         pub(crate) fn range() -> Self {
             TemporalError {
                 kind: ErrorKind::Range,
+                msg: None.into(),
             }
         }
     }
@@ -34,8 +41,16 @@ pub mod ffi {
 
 impl From<temporal_rs::TemporalError> for ffi::TemporalError {
     fn from(other: temporal_rs::TemporalError) -> Self {
+        let kind = other.kind().into();
+        let msg = other.into_message();
+        let msg = if let Cow::Borrowed(s) = msg {
+            Some(s)
+        } else {
+            None
+        };
         Self {
-            kind: other.kind().into(),
+            kind,
+            msg: msg.map(Into::into).into(),
         }
     }
 }