move throw to preverve Error type; turn off debugger for tryEval

8 files changed, 361 insertions, 140 deletions

diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 3dd55e104..2e7974b5d 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -50,7 +50,7 @@ struct NixRepl
     ref<EvalState> state;
     Bindings * autoArgs;
 
-   const Error *debugError;
+    const Error *debugError;
     int debugTraceIndex;
 
     Strings loadedFiles;
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 9f6152561..0608d8378 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -528,14 +528,22 @@ std::string AttrCursor::getString()
                 debug("using cached string attribute '%s'", getAttrPathStr());
                 return s->first;
             } else
-                root->state.debug_throw(TypeError("'%s' is not a string", getAttrPathStr()));
+            {
+                auto e = TypeError("'%s' is not a string", getAttrPathStr());
+                root->state.debugLastTrace(e);
+                throw e;
+            }
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nString && v.type() != nPath)
-        root->state.debug_throw(TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type())));
+    {
+        auto e = TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type()));
+        root->state.debugLastTrace(e);
+        throw e;
+    }
 
     return v.type() == nString ? v.string.s : v.path;
 }
@@ -559,7 +567,11 @@ string_t AttrCursor::getStringWithContext()
                     return *s;
                 }
             } else
-                root->state.debug_throw(TypeError("'%s' is not a string", getAttrPathStr()));
+            {
+                auto e = TypeError("'%s' is not a string", getAttrPathStr());
+                root->state.debugLastTrace(e);
+                throw e;
+            }
         }
     }
 
@@ -571,7 +583,9 @@ string_t AttrCursor::getStringWithContext()
         return {v.path, {}};
     else
     {
-        root->state.debug_throw(TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type())));
+        auto e = TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type()));
+        root->state.debugLastTrace(e);
+        throw e;
         return {v.path, {}}; // should never execute
     }
 }
@@ -586,14 +600,22 @@ bool AttrCursor::getBool()
                 debug("using cached Boolean attribute '%s'", getAttrPathStr());
                 return *b;
             } else
-                root->state.debug_throw(TypeError("'%s' is not a Boolean", getAttrPathStr()));
+            {
+                auto e = TypeError("'%s' is not a Boolean", getAttrPathStr());
+                root->state.debugLastTrace(e);
+                throw e;
+            }
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nBool)
-        root->state.debug_throw(TypeError("'%s' is not a Boolean", getAttrPathStr()));
+    {
+        auto e = TypeError("'%s' is not a Boolean", getAttrPathStr());
+        root->state.debugLastTrace(e);
+        throw e;
+    }
 
     return v.boolean;
 }
@@ -608,14 +630,22 @@ std::vector<Symbol> AttrCursor::getAttrs()
                 debug("using cached attrset attribute '%s'", getAttrPathStr());
                 return *attrs;
             } else
-                root->state.debug_throw(TypeError("'%s' is not an attribute set", getAttrPathStr()));
+            {
+                auto e = TypeError("'%s' is not an attribute set", getAttrPathStr());
+                root->state.debugLastTrace(e);
+                throw e;
+            }
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nAttrs)
-        root->state.debug_throw(TypeError("'%s' is not an attribute set", getAttrPathStr()));
+    {
+        auto e = TypeError("'%s' is not an attribute set", getAttrPathStr());
+        root->state.debugLastTrace(e);
+        throw e;
+    }
 
     std::vector<Symbol> attrs;
     for (auto & attr : *getValue().attrs)
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 5ad7e546c..7d02222cf 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -833,15 +833,13 @@ LocalNoInlineNoReturn(void throwEvalError(const char * s, const std::string & s2
     throw error;
 }
 
-void EvalState::debug_throw(Error e) {
+void EvalState::debugLastTrace(Error & e) {
     // call this in the situation where Expr and Env are inaccessible.  The debugger will start in the last context
     // that's in the DebugTrace stack.
-
     if (debuggerHook && !debugTraces.empty()) {
         DebugTrace &last = debugTraces.front();
         debuggerHook(&e, last.env, last.expr);
     }
-    throw e;
 }
 
 LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const Suggestions & suggestions, const char * s, const std::string & s2, Env & env, Expr &expr))
@@ -865,10 +863,7 @@ LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const
         .errPos = pos
     });
 
-    if (debuggerHook && !evalState.debugTraces.empty()) {
-        DebugTrace &last = evalState.debugTraces.front();
-        debuggerHook(&error, last.env, last.expr);
-    }
+    evalState.debugLastTrace(error);
 
     throw error;
 }
@@ -906,10 +901,7 @@ LocalNoInlineNoReturn(void throwEvalError(const Pos & pos, const char * s, const
         .errPos = pos
     });
 
-    if (debuggerHook && !evalState.debugTraces.empty()) {
-        DebugTrace &last = evalState.debugTraces.front();
-        debuggerHook(&error, last.env, last.expr);
-    }
+    evalState.debugLastTrace(error);
 
     throw error;
 }
@@ -921,10 +913,7 @@ LocalNoInlineNoReturn(void throwEvalError(const char * s, const std::string & s2
         .errPos = noPos
     });
 
-    if (debuggerHook && !evalState.debugTraces.empty()) {
-        DebugTrace &last = evalState.debugTraces.front();
-        debuggerHook(&error, last.env, last.expr);
-    }
+    evalState.debugLastTrace(error);
 
     throw error;
 }
@@ -950,10 +939,7 @@ LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s, EvalS
         .errPos = pos
     });
 
-    if (debuggerHook && !evalState.debugTraces.empty()) {
-        DebugTrace &last = evalState.debugTraces.front();
-        debuggerHook(&error, last.env, last.expr);
-    }
+    evalState.debugLastTrace(error);
 
     throw error;
 }
@@ -972,8 +958,6 @@ LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s, const
     throw error;
 }
 
-// LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v));
-
 LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s, const ExprLambda & fun, const Symbol & s2, Env & env, Expr &expr))
 {
     auto error = TypeError({
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 2ced5bea9..11f5707a4 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -119,7 +119,7 @@ public:
     bool debugStop;
     bool debugQuit;
     std::list<DebugTrace> debugTraces;
-    void debug_throw(Error e);
+    void debugLastTrace(Error & e);
 
 private:
     SrcToStore srcToStore;
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 4182f36d5..ecfa5b7c2 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -783,14 +783,15 @@ Path EvalState::findFile(SearchPath & searchPath, const std::string_view path, c
     if (hasPrefix(path, "nix/"))
         return concatStrings(corepkgsPrefix, path.substr(4));
 
-    debug_throw(ThrownError({
+    auto e = ThrownError({
         .msg = hintfmt(evalSettings.pureEval
             ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
             : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
             path),
         .errPos = pos
-    }));
-    return Path();   // should never execute due to debug_throw above.
+    });
+    debugLastTrace(e);
+    throw e;
 }
 
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index c40c54247..b1d2f5f40 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -46,7 +46,11 @@ StringMap EvalState::realiseContext(const PathSet & context)
         auto [ctx, outputName] = decodeContext(*store, i);
         auto ctxS = store->printStorePath(ctx);
         if (!store->isValidPath(ctx))
-            debug_throw(InvalidPathError(store->printStorePath(ctx)));
+        {
+            auto e = InvalidPathError(store->printStorePath(ctx));
+            debugLastTrace(e);
+            throw e;
+        }
         if (!outputName.empty() && ctx.isDerivation()) {
             drvs.push_back({ctx, {outputName}});
         } else {
@@ -57,9 +61,13 @@ StringMap EvalState::realiseContext(const PathSet & context)
     if (drvs.empty()) return {};
 
     if (!evalSettings.enableImportFromDerivation)
-        debug_throw(Error(
+    {
+        auto e = Error(
             "cannot build '%1%' during evaluation because the option 'allow-import-from-derivation' is disabled",
-            store->printStorePath(drvs.begin()->drvPath)));
+            store->printStorePath(drvs.begin()->drvPath));
+        debugLastTrace(e);
+        throw e;
+    }
 
     /* Build/substitute the context. */
     std::vector<DerivedPath> buildReqs;
@@ -71,8 +79,12 @@ StringMap EvalState::realiseContext(const PathSet & context)
         auto outputPaths = store->queryDerivationOutputMap(drvPath);
         for (auto & outputName : outputs) {
             if (outputPaths.count(outputName) == 0)
-                debug_throw(Error("derivation '%s' does not have an output named '%s'",
-                        store->printStorePath(drvPath), outputName));
+            {
+                auto e = Error("derivation '%s' does not have an output named '%s'",
+                        store->printStorePath(drvPath), outputName);
+                debugLastTrace(e);
+                throw e;
+            }
             res.insert_or_assign(
                 downstreamPlaceholder(*store, drvPath, outputName),
                 store->printStorePath(outputPaths.at(outputName))
@@ -318,17 +330,29 @@ void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
     if (!handle)
-        state.debug_throw(EvalError("could not open '%1%': %2%", path, dlerror()));
+    {
+        auto e = EvalError("could not open '%1%': %2%", path, dlerror());
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     dlerror();
     ValueInitializer func = (ValueInitializer) dlsym(handle, sym.c_str());
     if(!func) {
         char *message = dlerror();
         if (message)
-            state.debug_throw(EvalError("could not load symbol '%1%' from '%2%': %3%", sym, path, message));
+        {
+            auto e = EvalError("could not load symbol '%1%' from '%2%': %3%", sym, path, message);
+            state.debugLastTrace(e);
+            throw e;
+        }
         else
-            state.debug_throw(EvalError("symbol '%1%' from '%2%' resolved to NULL when a function pointer was expected",
-                sym, path));
+        {
+            auto e = EvalError("symbol '%1%' from '%2%' resolved to NULL when a function pointer was expected",
+                sym, path);
+            state.debugLastTrace(e);
+            throw e;
+        }
     }
 
     (func)(state, v);
@@ -344,10 +368,12 @@ void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
     auto elems = args[0]->listElems();
     auto count = args[0]->listSize();
     if (count == 0) {
-        state.debug_throw(EvalError({
+        auto e = EvalError({
             .msg = hintfmt("at least one argument to 'exec' required"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
     }
     PathSet context;
     auto program = state.coerceToString(pos, *elems[0], context, false, false).toOwned();
@@ -358,11 +384,13 @@ void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
     try {
         auto _ = state.realiseContext(context); // FIXME: Handle CA derivations
     } catch (InvalidPathError & e) {
-        state.debug_throw(EvalError({
+        auto ee = EvalError({
             .msg = hintfmt("cannot execute '%1%', since path '%2%' is not valid",
                 program, e.path),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(ee);
+        throw ee;
     }
 
     auto output = runProgram(program, true, commandArgs);
@@ -545,7 +573,11 @@ struct CompareValues
         if (v1->type() == nInt && v2->type() == nFloat)
             return v1->integer < v2->fpoint;
         if (v1->type() != v2->type())
-            state.debug_throw(EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2)));
+        {
+            auto e = EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2));
+            state.debugLastTrace(e);
+            throw e;
+        }
         switch (v1->type()) {
             case nInt:
                 return v1->integer < v2->integer;
@@ -567,8 +599,11 @@ struct CompareValues
                     }
                 }
             default:
-                state.debug_throw(EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2)));
-                return false;
+                {
+                    auto e = EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2));
+                    state.debugLastTrace(e);
+                    throw e;
+                }
         }
     }
 };
@@ -598,10 +633,12 @@ static Bindings::iterator getAttr(
 
         Pos aPos = *attrSet->pos;
         if (aPos == noPos) {
-            state.debug_throw(TypeError({
+            auto e = TypeError({
                 .msg = errorMsg,
                 .errPos = pos,
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
         } else {
             auto e = TypeError({
                 .msg = errorMsg,
@@ -611,7 +648,8 @@ static Bindings::iterator getAttr(
             // Adding another trace for the function name to make it clear
             // which call received wrong arguments.
             e.addTrace(pos, hintfmt("while invoking '%s'", funcName));
-            state.debug_throw(e);
+            state.debugLastTrace(e);
+            throw e;
         }
     }
 
@@ -665,10 +703,14 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         Bindings::iterator key =
             e->attrs->find(state.sKey);
         if (key == e->attrs->end())
-            state.debug_throw(EvalError({
+        {
+            auto e = EvalError({
                 .msg = hintfmt("attribute 'key' required"),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
         state.forceValue(*key->value, pos);
 
         if (!doneKeys.insert(key->value).second) continue;
@@ -768,7 +810,11 @@ static RegisterPrimOp primop_abort({
     {
         PathSet context;
         auto s = state.coerceToString(pos, *args[0], context).toOwned();
-        state.debug_throw(Abort("evaluation aborted with the following error message: '%1%'", s));
+        {
+            auto e = Abort("evaluation aborted with the following error message: '%1%'", s);
+            state.debugLastTrace(e);
+            throw e;
+        }
     }
 });
 
@@ -786,7 +832,9 @@ static RegisterPrimOp primop_throw({
     {
       PathSet context;
       auto s = state.coerceToString(pos, *args[0], context).toOwned();
-      state.debug_throw(ThrownError(s));
+      auto e = ThrownError(s);
+      state.debugLastTrace(e);
+      throw e;
     }
 });
 
@@ -851,6 +899,8 @@ static RegisterPrimOp primop_floor({
 static void prim_tryEval(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     auto attrs = state.buildBindings(2);
+    auto saveDebuggerHook = debuggerHook;
+    debuggerHook = 0;
     try {
         state.forceValue(*args[0], pos);
         attrs.insert(state.sValue, args[0]);
@@ -859,6 +909,7 @@ static void prim_tryEval(EvalState & state, const Pos & pos, Value * * args, Val
         attrs.alloc(state.sValue).mkBool(false);
         attrs.alloc("success").mkBool(false);
     }
+    debuggerHook = saveDebuggerHook;
     v.mkAttrs(attrs);
 }
 
@@ -1041,37 +1092,53 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
             else
-                state.debug_throw(EvalError({
+            {
+                auto e = EvalError({
                     .msg = hintfmt("invalid value '%s' for 'outputHashMode' attribute", s),
                     .errPos = posDrvName
-                }));
+                });
+                state.debugLastTrace(e);
+                throw e;
+            }
         };
 
         auto handleOutputs = [&](const Strings & ss) {
             outputs.clear();
             for (auto & j : ss) {
                 if (outputs.find(j) != outputs.end())
-                    state.debug_throw(EvalError({
+                {
+                    auto e = EvalError({
                         .msg = hintfmt("duplicate derivation output '%1%'", j),
                         .errPos = posDrvName
-                    }));
+                    });
+                    state.debugLastTrace(e);
+                    throw e;
+                }
                 /* !!! Check whether j is a valid attribute
                    name. */
                 /* Derivations cannot be named ‘drv’, because
                    then we'd have an attribute ‘drvPath’ in
                    the resulting set. */
                 if (j == "drv")
-                    state.debug_throw(EvalError({
+                {
+                    auto e = EvalError({
                         .msg = hintfmt("invalid derivation output name 'drv'" ),
                         .errPos = posDrvName
-                    }));
+                    });
+                    state.debugLastTrace(e);
+                    throw e;
+                }
                 outputs.insert(j);
             }
             if (outputs.empty())
-                state.debug_throw(EvalError({
+            {
+                auto e = EvalError({
                     .msg = hintfmt("derivation cannot have an empty set of outputs"),
                     .errPos = posDrvName
-                }));
+                });
+                state.debugLastTrace(e);
+                throw e;
+            }
         };
 
         try {
@@ -1196,23 +1263,35 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 
     /* Do we have all required attributes? */
     if (drv.builder == "")
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("required attribute 'builder' missing"),
             .errPos = posDrvName
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     if (drv.platform == "")
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("required attribute 'system' missing"),
             .errPos = posDrvName
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     /* Check whether the derivation name is valid. */
     if (isDerivation(drvName))
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("derivation names are not allowed to end in '%s'", drvExtension),
             .errPos = posDrvName
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     if (outputHash) {
         /* Handle fixed-output derivations.
@@ -1220,10 +1299,14 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
            Ignore `__contentAddressed` because fixed output derivations are
            already content addressed. */
         if (outputs.size() != 1 || *(outputs.begin()) != "out")
-            state.debug_throw(Error({
+        {
+            auto e = Error({
                 .msg = hintfmt("multiple outputs are not supported in fixed-output derivations"),
                 .errPos = posDrvName
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
 
         auto h = newHashAllowEmpty(*outputHash, parseHashTypeOpt(outputHashAlgo));
 
@@ -1386,10 +1469,14 @@ static RegisterPrimOp primop_toPath({
 static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     if (evalSettings.pureEval)
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("'%s' is not allowed in pure evaluation mode", "builtins.storePath"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     PathSet context;
     Path path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context));
@@ -1398,10 +1485,14 @@ static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, V
        e.g. nix-push does the right thing. */
     if (!state.store->isStorePath(path)) path = canonPath(path, true);
     if (!state.store->isInStore(path))
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("path '%1%' is not in the Nix store", path),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
     auto path2 = state.store->toStorePath(path).first;
     if (!settings.readOnlyMode)
         state.store->ensurePath(path2);
@@ -1504,7 +1595,11 @@ static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Va
     auto path = realisePath(state, pos, *args[0]);
     auto s = readFile(path);
     if (s.find((char) 0) != std::string::npos)
-        state.debug_throw(Error("the contents of the file '%1%' cannot be represented as a Nix string", path));
+    {
+        auto e = Error("the contents of the file '%1%' cannot be represented as a Nix string", path);
+        state.debugLastTrace(e);
+        throw e;
+    }
     StorePathSet refs;
     if (state.store->isInStore(path)) {
         try {
@@ -1556,10 +1651,12 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
             auto rewrites = state.realiseContext(context);
             path = rewriteStrings(path, rewrites);
         } catch (InvalidPathError & e) {
-            state.debug_throw(EvalError({
+            auto ee = EvalError({
                 .msg = hintfmt("cannot find '%1%', since path '%2%' is not valid", path, e.path),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(ee);
+            throw ee;
         }
 
 
@@ -1583,10 +1680,14 @@ static void prim_hashFile(EvalState & state, const Pos & pos, Value * * args, Va
     auto type = state.forceStringNoCtx(*args[0], pos);
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
-        state.debug_throw(Error({
+    {
+        auto e = Error({
             .msg = hintfmt("unknown hash type '%1%'", type),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     auto path = realisePath(state, pos, *args[1]);
 
@@ -1823,13 +1924,17 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
 
     for (auto path : context) {
         if (path.at(0) != '/')
-            state.debug_throw(EvalError( {
+        {
+            auto e = EvalError( {
                 .msg = hintfmt(
                     "in 'toFile': the file named '%1%' must not contain a reference "
                     "to a derivation but contains (%2%)",
                     name, path),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
         refs.insert(state.store->parseStorePath(path));
     }
 
@@ -1986,7 +2091,11 @@ static void addPath(
                 ? state.store->computeStorePathForPath(name, path, method, htSHA256, filter).first
                 : state.store->addToStore(name, path, method, htSHA256, filter, state.repair, refs);
             if (expectedHash && expectedStorePath != dstPath)
-                state.debug_throw(Error("store path mismatch in (possibly filtered) path added from '%s'", path));
+            {
+                auto e = Error("store path mismatch in (possibly filtered) path added from '%s'", path);
+                state.debugLastTrace(e);
+                throw e;
+            }
             state.allowAndSetStorePathString(dstPath, v);
         } else
             state.allowAndSetStorePathString(*expectedStorePath, v);
@@ -2004,12 +2113,16 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
 
     state.forceValue(*args[0], pos);
     if (args[0]->type() != nFunction)
-        state.debug_throw(TypeError({
+    {
+        auto e = TypeError({
             .msg = hintfmt(
                 "first argument in call to 'filterSource' is not a function but %1%",
                 showType(*args[0])),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     addPath(state, pos, std::string(baseNameOf(path)), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
 }
@@ -2093,16 +2206,24 @@ static void prim_path(EvalState & state, const Pos & pos, Value * * args, Value
         else if (n == "sha256")
             expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
         else
-            state.debug_throw(EvalError({
+        {
+            auto e = EvalError({
                 .msg = hintfmt("unsupported argument '%1%' to 'addPath'", attr.name),
                 .errPos = *attr.pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
     }
     if (path.empty())
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("'path' required"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
     if (name.empty())
         name = baseNameOf(path);
 
@@ -2473,10 +2594,14 @@ static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args
         return;
     }
     if (!args[0]->isLambda())
-        state.debug_throw(TypeError({
+    {
+        auto e = TypeError({
             .msg = hintfmt("'functionArgs' requires a function"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     if (!args[0]->lambda.fun->hasFormals()) {
         v.mkAttrs(&state.emptyBindings);
@@ -2564,7 +2689,8 @@ static void prim_zipAttrsWith(EvalState & state, const Pos & pos, Value * * args
                 attrsSeen[attr.name].first++;
         } catch (TypeError & e) {
             e.addTrace(pos, hintfmt("while invoking '%s'", "zipAttrsWith"));
-            state.debug_throw(e);
+            state.debugLastTrace(e);
+            throw e;
         }
     }
 
@@ -2651,10 +2777,14 @@ static void elemAt(EvalState & state, const Pos & pos, Value & list, int n, Valu
 {
     state.forceList(list, pos);
     if (n < 0 || (unsigned int) n >= list.listSize())
-        state.debug_throw(Error({
+    {
+        auto e = Error({
             .msg = hintfmt("list index %1% is out of boundz", n),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
     state.forceValue(*list.listElems()[n], pos);
     v = *list.listElems()[n];
 }
@@ -2699,10 +2829,14 @@ static void prim_tail(EvalState & state, const Pos & pos, Value * * args, Value
 {
     state.forceList(*args[0], pos);
     if (args[0]->listSize() == 0)
-        state.debug_throw(Error({
+    {
+        auto e = Error({
             .msg = hintfmt("'tail' called on an empty list"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     state.mkList(v, args[0]->listSize() - 1);
     for (unsigned int n = 0; n < v.listSize(); ++n)
@@ -2937,10 +3071,14 @@ static void prim_genList(EvalState & state, const Pos & pos, Value * * args, Val
     auto len = state.forceInt(*args[1], pos);
 
     if (len < 0)
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("cannot create list of size %1%", len),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     state.mkList(v, len);
 
@@ -3149,7 +3287,8 @@ static void prim_concatMap(EvalState & state, const Pos & pos, Value * * args, V
             state.forceList(lists[n], lists[n].determinePos(args[0]->determinePos(pos)));
         } catch (TypeError &e) {
             e.addTrace(pos, hintfmt("while invoking '%s'", "concatMap"));
-            state.debug_throw(e);
+            state.debugLastTrace(e);
+            throw e;
         }
         len += lists[n].listSize();
     }
@@ -3244,10 +3383,14 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
 
     NixFloat f2 = state.forceFloat(*args[1], pos);
     if (f2 == 0)
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("division by zero"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     if (args[0]->type() == nFloat || args[1]->type() == nFloat) {
         v.mkFloat(state.forceFloat(*args[0], pos) / state.forceFloat(*args[1], pos));
@@ -3256,10 +3399,14 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
         NixInt i2 = state.forceInt(*args[1], pos);
         /* Avoid division overflow as it might raise SIGFPE. */
         if (i1 == std::numeric_limits<NixInt>::min() && i2 == -1)
-            state.debug_throw(EvalError({
+        {
+            auto e = EvalError({
                 .msg = hintfmt("overflow in integer division"),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
 
         v.mkInt(i1 / i2);
     }
@@ -3387,10 +3534,14 @@ static void prim_substring(EvalState & state, const Pos & pos, Value * * args, V
     auto s = state.coerceToString(pos, *args[2], context);
 
     if (start < 0)
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("negative start position in 'substring'"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     v.mkString((unsigned int) start >= s->size() ? "" : s->substr(start, len), context);
 }
@@ -3438,10 +3589,14 @@ static void prim_hashString(EvalState & state, const Pos & pos, Value * * args,
     auto type = state.forceStringNoCtx(*args[0], pos);
     std::optional<HashType> ht = parseHashType(type);
     if (!ht)
-        state.debug_throw(Error({
+    {
+        auto e = Error({
             .msg = hintfmt("unknown hash type '%1%'", type),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     PathSet context; // discarded
     auto s = state.forceString(*args[1], context, pos);
@@ -3511,15 +3666,19 @@ void prim_match(EvalState & state, const Pos & pos, Value * * args, Value & v)
     } catch (std::regex_error &e) {
         if (e.code() == std::regex_constants::error_space) {
             // limit is _GLIBCXX_REGEX_STATE_LIMIT for libstdc++
-            state.debug_throw(EvalError({
+            auto e = EvalError({
                 .msg = hintfmt("memory limit exceeded by regular expression '%s'", re),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
         } else {
-            state.debug_throw(EvalError({
+            auto e = EvalError({
                 .msg = hintfmt("invalid regular expression '%s'", re),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
         }
     }
 }
@@ -3616,15 +3775,19 @@ void prim_split(EvalState & state, const Pos & pos, Value * * args, Value & v)
     } catch (std::regex_error &e) {
         if (e.code() == std::regex_constants::error_space) {
             // limit is _GLIBCXX_REGEX_STATE_LIMIT for libstdc++
-            state.debug_throw(EvalError({
+            auto e = EvalError({
                 .msg = hintfmt("memory limit exceeded by regular expression '%s'", re),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
         } else {
-            state.debug_throw(EvalError({
+            auto e = EvalError({
                 .msg = hintfmt("invalid regular expression '%s'", re),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
         }
     }
 }
@@ -3701,10 +3864,14 @@ static void prim_replaceStrings(EvalState & state, const Pos & pos, Value * * ar
     state.forceList(*args[0], pos);
     state.forceList(*args[1], pos);
     if (args[0]->listSize() != args[1]->listSize())
-        state.debug_throw(EvalError({
+    {
+        auto e = EvalError({
             .msg = hintfmt("'from' and 'to' arguments to 'replaceStrings' have different lengths"),
             .errPos = pos
-        }));
+        });
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     std::vector<std::string> from;
     from.reserve(args[0]->listSize());
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index bae0fb1e4..131cc87dc 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -108,16 +108,25 @@ static void fetchTree(
 
         if (auto aType = args[0]->attrs->get(state.sType)) {
             if (type)
-                state.debug_throw(EvalError({
+            {
+                auto e = EvalError({
                     .msg = hintfmt("unexpected attribute 'type'"),
                     .errPos = pos
-                }));
+                });
+                state.debugLastTrace(e);
+                throw e;
+
+            }
             type = state.forceStringNoCtx(*aType->value, *aType->pos);
         } else if (!type)
-            state.debug_throw(EvalError({
+        {
+            auto e = EvalError({
                 .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
 
         attrs.emplace("type", type.value());
 
@@ -138,16 +147,24 @@ static void fetchTree(
             else if (attr.value->type() == nInt)
                 attrs.emplace(attr.name, uint64_t(attr.value->integer));
             else
-                state.debug_throw(TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
-                    attr.name, showType(*attr.value)));
+            {
+                auto e = TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
+                    attr.name, showType(*attr.value));
+                state.debugLastTrace(e);
+                throw e;
+            }
         }
 
         if (!params.allowNameArgument)
             if (auto nameIter = attrs.find("name"); nameIter != attrs.end())
-                state.debug_throw(EvalError({
+            {
+                auto e = EvalError({
                     .msg = hintfmt("attribute 'name' isn’t supported in call to 'fetchTree'"),
                     .errPos = pos
-                }));
+                });
+                state.debugLastTrace(e);
+                throw e;
+            }
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
@@ -167,7 +184,11 @@ static void fetchTree(
         input = lookupInRegistries(state.store, input).first;
 
     if (evalSettings.pureEval && !input.isLocked())
-        state.debug_throw(EvalError("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", pos));
+    {
+        auto e = EvalError("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", pos);
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     auto [tree, input2] = input.fetch(state.store);
 
@@ -205,18 +226,25 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
                 expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
             else if (n == "name")
                 name = state.forceStringNoCtx(*attr.value, *attr.pos);
-            else
-                state.debug_throw(EvalError({
-                    .msg = hintfmt("unsupported argument '%s' to '%s'", attr.name, who),
-                    .errPos = *attr.pos
-                }));
+            else {
+                    auto e = EvalError({
+                        .msg = hintfmt("unsupported argument '%s' to '%s'", attr.name, who),
+                        .errPos = *attr.pos
+                    });
+                    state.debugLastTrace(e);
+                    throw e;
             }
+        }
 
         if (!url)
-            state.debug_throw(EvalError({
+        {
+            auto e = EvalError({
                 .msg = hintfmt("'url' argument required"),
                 .errPos = pos
-            }));
+            });
+            state.debugLastTrace(e);
+            throw e;
+        }
     } else
         url = state.forceStringNoCtx(*args[0], pos);
 
@@ -228,7 +256,11 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
         name = baseNameOf(*url);
 
     if (evalSettings.pureEval && !expectedHash)
-        state.debug_throw(EvalError("in pure evaluation mode, '%s' requires a 'sha256' argument", who));
+    {
+        auto e = EvalError("in pure evaluation mode, '%s' requires a 'sha256' argument", who);
+        state.debugLastTrace(e);
+        throw e;
+    }
 
     // early exit if pinned and already in the store
     if (expectedHash && expectedHash->type == htSHA256) {
@@ -255,8 +287,12 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
             ? state.store->queryPathInfo(storePath)->narHash
             : hashFile(htSHA256, state.store->toRealPath(storePath));
         if (hash != *expectedHash)
-            state.debug_throw(EvalError((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
-                *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true)));
+        {
+            auto e = EvalError((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n  specified: %s\n  got:       %s",
+                *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true));
+            state.debugLastTrace(e);
+            throw e;
+        }
     }
 
     state.allowAndSetStorePathString(storePath, v);
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index d8bf73cd5..2f34feb1f 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -85,7 +85,8 @@ void printValueAsJSON(EvalState & state, bool strict,
                 .errPos = v.determinePos(pos)
             });
             e.addTrace(pos, hintfmt("message for the trace"));
-            state.debug_throw(e);
+            state.debugLastTrace(e);
+            throw e;
     }
 }
 
@@ -99,7 +100,9 @@ void printValueAsJSON(EvalState & state, bool strict,
 void ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
     JSONPlaceholder & out, PathSet & context) const
 {
-    state.debug_throw(TypeError("cannot convert %1% to JSON", showType()));
+    auto e = TypeError("cannot convert %1% to JSON", showType());
+    state.debugLastTrace(e);
+    throw e;
 }