From bc0d41e9baa19c10977dd38f4bb255c14bd6554d Mon Sep 17 00:00:00 2001
From: Ben Burdette <bburdette@protonmail.com>
Date: Thu, 2 Jun 2022 12:17:28 -0600
Subject: [PATCH] print message with exceptions in a try clause

---
 src/libexpr/eval.cc    | 12 ++++++++++--
 src/libexpr/eval.hh    |  1 +
 src/libexpr/primops.cc | 15 +++++++++++----
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index c35527992..60214453a 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -464,10 +464,11 @@ EvalState::EvalState(
     , emptyBindings(0)
     , store(store)
     , buildStore(buildStore ? buildStore : store)
-    , debugRepl(0)
+    , debugRepl(nullptr)
     , debugStop(false)
     , debugQuit(false)
     , ignoreTry(false)
+    , trylevel(0)
     , regexCache(makeRegexCache())
 #if HAVE_BOEHMGC
     , valueAllocCache(std::allocate_shared<void *>(traceable_allocator<void *>(), nullptr))
@@ -833,7 +834,14 @@ void EvalState::runDebugRepl(const Error * error, const Env & env, const Expr &
         : nullptr;
 
     if (error)
-        printError("%s\n\n" ANSI_BOLD "Starting REPL to allow you to inspect the current state of the evaluator.\n" ANSI_NORMAL, error->what());
+    {
+        printError("%s\n\n", error->what());
+
+        if (trylevel > 0 && error->info().level != lvlInfo)
+            printError("This exception occurred in a try clause. use " ANSI_GREEN "--ignore-try" ANSI_NORMAL " to skip these.\n");
+
+        printError(ANSI_BOLD "Starting REPL to allow you to inspect the current state of the evaluator.\n" ANSI_NORMAL, error->what());
+    }
 
     auto se = getStaticEnv(expr);
     if (se) {
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 3c3dddd1e..9aff77042 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -131,6 +131,7 @@ public:
     bool debugStop;
     bool debugQuit;
     bool ignoreTry;
+    int trylevel;
     std::list<DebugTrace> debugTraces;
     std::map<const Expr*, const std::shared_ptr<const StaticEnv>> exprEnvs;
     const std::shared_ptr<const StaticEnv> getStaticEnv(const Expr & expr) const
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 772898932..e4fd8f650 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -853,11 +853,15 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     auto attrs = state.buildBindings(2);
 
     void (* savedDebugRepl)(ref<EvalState> es, const ValMap & extraEnv) = nullptr;
-    if (state.debugRepl && state.ignoreTry)
+    if (state.debugRepl)
     {
-        // to prevent starting the repl from exceptions withing a tryEval, null it.
-        savedDebugRepl = state.debugRepl;
-        state.debugRepl = nullptr;
+        state.trylevel++;
+        if (state.ignoreTry)
+        {
+            // to prevent starting the repl from exceptions withing a tryEval, null it.
+            savedDebugRepl = state.debugRepl;
+            state.debugRepl = nullptr;
+        }
     }
 
     try {
@@ -873,6 +877,9 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     if (savedDebugRepl)
         state.debugRepl = savedDebugRepl;
 
+    if (state.debugRepl)
+        state.trylevel--;
+
     v.mkAttrs(attrs);
 }