From bb520d90b5782a2ad109a6c2e492882842aa07bd Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Fri, 22 Dec 2023 21:38:31 -0500
Subject: [PATCH] ppx: make sure to reconstruct backtraces

---
 README.md            |  8 ++++----
 ppx_trace.opam       |  2 +-
 src/ppx/ppx_trace.ml | 11 ++++++-----
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/README.md b/README.md
index 986f770..7f89707 100644
--- a/README.md
+++ b/README.md
@@ -100,11 +100,11 @@ let f x y z =
     do_sth y;
     begin
       let _trace_span = Trace_core.enter_span ~__FILE__ ~__LINE__ "sub-span" in
-      try
-        let _res = do_sth z in
+      match do_sth z with
+      | res ->
         Trace_core.exit_span _trace_span;
-        _res
-      with e ->
+        res
+      | exception e ->
         Trace_core.exit_span _trace_span
         raise e
     end;
diff --git a/ppx_trace.opam b/ppx_trace.opam
index 14992f3..b00d78c 100644
--- a/ppx_trace.opam
+++ b/ppx_trace.opam
@@ -9,7 +9,7 @@ tags: ["trace" "tracing" "observability" "profiling" "ppx"]
 homepage: "https://github.com/c-cube/ocaml-trace"
 bug-reports: "https://github.com/c-cube/ocaml-trace/issues"
 depends: [
-  "ocaml" {>= "4.08"}
+  "ocaml" {>= "4.12"}
   "ppxlib"
   "trace" {= version}
   "trace-tef" {= version & with-test}
diff --git a/src/ppx/ppx_trace.ml b/src/ppx/ppx_trace.ml
index e088cf9..8f59221 100644
--- a/src/ppx/ppx_trace.ml
+++ b/src/ppx/ppx_trace.ml
@@ -52,13 +52,14 @@ let expand_top_let ~ctxt rec_flag (vbs : _ list) =
           let _trace_span =
             Trace_core.enter_span ~__FILE__ ~__LINE__ __FUNCTION__
           in
-          try
-            let _trace_ppx_res = [%e e] in
+          match [%e e] with
+          | res ->
             Trace_core.exit_span _trace_span;
-            __trace_ppx_res
-          with exn ->
+            res
+          | exception exn ->
+            let bt = Printexc.get_raw_backtrace () in
             Trace_core.exit_span _trace_span;
-            raise exn]
+            Printexc.raise_with_backtrace exn bt]
     in
 
     let tr_vb (vb : value_binding) : value_binding =