for primops, enter the debugger at the last DebugTrace in the stack

4 files changed, 99 insertions, 85 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 79bdaff47..71a28bafa 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -437,7 +437,7 @@ EvalState::EvalState(
     , emptyBindings(0)
     , store(store)
     , buildStore(buildStore ? buildStore : store)
-    , debugStop(true)
+    , debugStop(false)
     , regexCache(makeRegexCache())
 #if HAVE_BOEHMGC
     , valueAllocCache(std::allocate_shared<void *>(traceable_allocator<void *>(), nullptr))
@@ -787,6 +787,17 @@ LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2, Eva
     throw error;
 }
 
+void EvalState::debug_throw(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 char * s, Env & env, Expr *expr))
 {
     auto error = EvalError({
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index a7d1207f2..1390c8885 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -118,6 +118,8 @@ public:
     bool debugStop;
     std::list<DebugTrace> debugTraces;
 
+    void debug_throw(Error e);
+
 private:
     SrcToStore srcToStore;
 
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 41ee92d27..e09bd9484 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -305,7 +305,7 @@ void ExprVar::bindVars(const std::shared_ptr<const StaticEnv> &env)
     if (withLevel == -1) 
     {
         throw UndefinedVarError({
-            .msg = hintfmt("undefined variable (ExprVar bindvars) '%1%'", name),
+            .msg = hintfmt("undefined variable '%1%'", name),
             .errPos = pos
         });
     }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 3b429f328..956c55e49 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -46,7 +46,7 @@ StringMap EvalState::realiseContext(const PathSet & context)
         auto [ctxS, outputName] = decodeContext(i);
         auto ctx = store->parseStorePath(ctxS);
         if (!store->isValidPath(ctx))
-            throw InvalidPathError(store->printStorePath(ctx));
+            debug_throw(InvalidPathError(store->printStorePath(ctx)));
         if (!outputName.empty() && ctx.isDerivation()) {
             drvs.push_back({ctx, {outputName}});
         } else {
@@ -57,9 +57,9 @@ StringMap EvalState::realiseContext(const PathSet & context)
     if (drvs.empty()) return {};
 
     if (!evalSettings.enableImportFromDerivation)
-        throw Error(
+        debug_throw(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)));
 
     /* Build/substitute the context. */
     std::vector<DerivedPath> buildReqs;
@@ -71,8 +71,8 @@ StringMap EvalState::realiseContext(const PathSet & context)
         auto outputPaths = store->queryDerivationOutputMap(drvPath);
         for (auto & outputName : outputs) {
             if (outputPaths.count(outputName) == 0)
-                throw Error("derivation '%s' does not have an output named '%s'",
-                        store->printStorePath(drvPath), outputName);
+                debug_throw(Error("derivation '%s' does not have an output named '%s'",
+                        store->printStorePath(drvPath), outputName));
             res.insert_or_assign(
                 downstreamPlaceholder(*store, drvPath, outputName),
                 store->printStorePath(outputPaths.at(outputName))
@@ -318,17 +318,17 @@ void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
     if (!handle)
-        throw EvalError("could not open '%1%': %2%", path, dlerror());
+        state.debug_throw(EvalError("could not open '%1%': %2%", path, dlerror()));
 
     dlerror();
     ValueInitializer func = (ValueInitializer) dlsym(handle, sym.c_str());
     if(!func) {
         char *message = dlerror();
         if (message)
-            throw EvalError("could not load symbol '%1%' from '%2%': %3%", sym, path, message);
+            state.debug_throw(EvalError("could not load symbol '%1%' from '%2%': %3%", sym, path, message));
         else
-            throw EvalError("symbol '%1%' from '%2%' resolved to NULL when a function pointer was expected",
-                sym, path);
+            state.debug_throw(EvalError("symbol '%1%' from '%2%' resolved to NULL when a function pointer was expected",
+                sym, path));
     }
 
     (func)(state, v);
@@ -344,10 +344,10 @@ 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) {
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("at least one argument to 'exec' required"),
             .errPos = pos
-        });
+        }));
     }
     PathSet context;
     auto program = state.coerceToString(pos, *elems[0], context, false, false).toOwned();
@@ -358,11 +358,11 @@ void prim_exec(EvalState & state, const Pos & pos, Value * * args, Value & v)
     try {
         auto _ = state.realiseContext(context); // FIXME: Handle CA derivations
     } catch (InvalidPathError & e) {
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("cannot execute '%1%', since path '%2%' is not valid",
                 program, e.path),
             .errPos = pos
-        });
+        }));
     }
 
     auto output = runProgram(program, true, commandArgs);
@@ -545,7 +545,7 @@ struct CompareValues
         if (v1->type() == nInt && v2->type() == nFloat)
             return v1->integer < v2->fpoint;
         if (v1->type() != v2->type())
-            throw EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2));
+            state.debug_throw(EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2)));
         switch (v1->type()) {
             case nInt:
                 return v1->integer < v2->integer;
@@ -567,7 +567,8 @@ struct CompareValues
                     }
                 }
             default:
-                throw EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2));
+                state.debug_throw(EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2)));
+                return false;
         }
     }
 };
@@ -597,10 +598,10 @@ static Bindings::iterator getAttr(
 
         Pos aPos = *attrSet->pos;
         if (aPos == noPos) {
-            throw TypeError({
+            state.debug_throw(TypeError({
                 .msg = errorMsg,
                 .errPos = pos,
-            });
+            }));
         } else {
             auto e = TypeError({
                 .msg = errorMsg,
@@ -610,7 +611,7 @@ 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));
-            throw e;
+            state.debug_throw(e);
         }
     }
 
@@ -664,10 +665,10 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
         Bindings::iterator key =
             e->attrs->find(state.sKey);
         if (key == e->attrs->end())
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("attribute 'key' required"),
                 .errPos = pos
-            });
+            }));
         state.forceValue(*key->value, pos);
 
         if (!doneKeys.insert(key->value).second) continue;
@@ -734,7 +735,7 @@ static RegisterPrimOp primop_abort({
     {
         PathSet context;
         string s = state.coerceToString(pos, *args[0], context).toOwned();
-        throw Abort("evaluation aborted with the following error message: '%1%'", s);
+        state.debug_throw(Abort("evaluation aborted with the following error message: '%1%'", s));
     }
 });
 
@@ -752,7 +753,7 @@ static RegisterPrimOp primop_throw({
     {
       PathSet context;
       string s = state.coerceToString(pos, *args[0], context).toOwned();
-      throw ThrownError(s);
+      state.debug_throw(ThrownError(s));
     }
 });
 
@@ -1006,37 +1007,37 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
             else
-                throw EvalError({
+                state.debug_throw(EvalError({
                     .msg = hintfmt("invalid value '%s' for 'outputHashMode' attribute", s),
                     .errPos = posDrvName
-                });
+                }));
         };
 
         auto handleOutputs = [&](const Strings & ss) {
             outputs.clear();
             for (auto & j : ss) {
                 if (outputs.find(j) != outputs.end())
-                    throw EvalError({
+                    state.debug_throw(EvalError({
                         .msg = hintfmt("duplicate derivation output '%1%'", j),
                         .errPos = posDrvName
-                    });
+                    }));
                 /* !!! 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")
-                    throw EvalError({
+                    state.debug_throw(EvalError({
                         .msg = hintfmt("invalid derivation output name 'drv'" ),
                         .errPos = posDrvName
-                    });
+                    }));
                 outputs.insert(j);
             }
             if (outputs.empty())
-                throw EvalError({
+                state.debug_throw(EvalError({
                     .msg = hintfmt("derivation cannot have an empty set of outputs"),
                     .errPos = posDrvName
-                });
+                }));
         };
 
         try {
@@ -1155,23 +1156,23 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 
     /* Do we have all required attributes? */
     if (drv.builder == "")
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("required attribute 'builder' missing"),
             .errPos = posDrvName
-        });
+        }));
 
     if (drv.platform == "")
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("required attribute 'system' missing"),
             .errPos = posDrvName
-        });
+        }));
 
     /* Check whether the derivation name is valid. */
     if (isDerivation(drvName))
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("derivation names are not allowed to end in '%s'", drvExtension),
             .errPos = posDrvName
-        });
+        }));
 
     if (outputHash) {
         /* Handle fixed-output derivations.
@@ -1179,10 +1180,10 @@ 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")
-            throw Error({
+            state.debug_throw(Error({
                 .msg = hintfmt("multiple outputs are not supported in fixed-output derivations"),
                 .errPos = posDrvName
-            });
+            }));
 
         std::optional<HashType> ht = parseHashTypeOpt(outputHashAlgo);
         Hash h = newHashAllowEmpty(*outputHash, ht);
@@ -1350,10 +1351,10 @@ static RegisterPrimOp primop_toPath({
 static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     if (evalSettings.pureEval)
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("'%s' is not allowed in pure evaluation mode", "builtins.storePath"),
             .errPos = pos
-        });
+        }));
 
     PathSet context;
     Path path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context));
@@ -1362,10 +1363,10 @@ 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))
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("path '%1%' is not in the Nix store", path),
             .errPos = pos
-        });
+        }));
     auto path2 = state.store->toStorePath(path).first;
     if (!settings.readOnlyMode)
         state.store->ensurePath(path2);
@@ -1468,7 +1469,7 @@ static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Va
     auto path = realisePath(state, pos, *args[0]);
     string s = readFile(path);
     if (s.find((char) 0) != string::npos)
-        throw Error("the contents of the file '%1%' cannot be represented as a Nix string", path);
+        state.debug_throw(Error("the contents of the file '%1%' cannot be represented as a Nix string", path));
     StorePathSet refs;
     if (state.store->isInStore(path)) {
         try {
@@ -1520,10 +1521,10 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
             auto rewrites = state.realiseContext(context);
             path = rewriteStrings(path, rewrites);
         } catch (InvalidPathError & e) {
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("cannot find '%1%', since path '%2%' is not valid", path, e.path),
                 .errPos = pos
-            });
+            }));
         }
 
 
@@ -1547,10 +1548,10 @@ 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)
-        throw Error({
+        state.debug_throw(Error({
             .msg = hintfmt("unknown hash type '%1%'", type),
             .errPos = pos
-        });
+        }));
 
     auto path = realisePath(state, pos, *args[1]);
 
@@ -1787,13 +1788,13 @@ static void prim_toFile(EvalState & state, const Pos & pos, Value * * args, Valu
 
     for (auto path : context) {
         if (path.at(0) != '/')
-            throw EvalError( {
+            state.debug_throw(EvalError( {
                 .msg = hintfmt(
                     "in 'toFile': the file named '%1%' must not contain a reference "
                     "to a derivation but contains (%2%)",
                     name, path),
                 .errPos = pos
-            });
+            }));
         refs.insert(state.store->parseStorePath(path));
     }
 
@@ -1951,7 +1952,7 @@ 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 != state.store->parseStorePath(dstPath))
-                throw Error("store path mismatch in (possibly filtered) path added from '%s'", path);
+                state.debug_throw(Error("store path mismatch in (possibly filtered) path added from '%s'", path));
         } else
             dstPath = state.store->printStorePath(*expectedStorePath);
 
@@ -1973,12 +1974,12 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
 
     state.forceValue(*args[0], pos);
     if (args[0]->type() != nFunction)
-        throw TypeError({
+        state.debug_throw(TypeError({
             .msg = hintfmt(
                 "first argument in call to 'filterSource' is not a function but %1%",
                 showType(*args[0])),
             .errPos = pos
-        });
+        }));
 
     addPath(state, pos, std::string(baseNameOf(path)), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
 }
@@ -2062,16 +2063,16 @@ 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
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("unsupported argument '%1%' to 'addPath'", attr.name),
                 .errPos = *attr.pos
-            });
+            }));
     }
     if (path.empty())
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("'path' required"),
             .errPos = pos
-        });
+        }));
     if (name.empty())
         name = baseNameOf(path);
 
@@ -2442,10 +2443,10 @@ static void prim_functionArgs(EvalState & state, const Pos & pos, Value * * args
         return;
     }
     if (!args[0]->isLambda())
-        throw TypeError({
+        state.debug_throw(TypeError({
             .msg = hintfmt("'functionArgs' requires a function"),
             .errPos = pos
-        });
+        }));
 
     if (!args[0]->lambda.fun->hasFormals()) {
         v.mkAttrs(&state.emptyBindings);
@@ -2620,10 +2621,10 @@ 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())
-        throw Error({
-            .msg = hintfmt("list index %1% is out of bounds", n),
+        state.debug_throw(Error({
+            .msg = hintfmt("list index %1% is out of boundz", n),
             .errPos = pos
-        });
+        }));
     state.forceValue(*list.listElems()[n], pos);
     v = *list.listElems()[n];
 }
@@ -2668,10 +2669,10 @@ static void prim_tail(EvalState & state, const Pos & pos, Value * * args, Value
 {
     state.forceList(*args[0], pos);
     if (args[0]->listSize() == 0)
-        throw Error({
+        state.debug_throw(Error({
             .msg = hintfmt("'tail' called on an empty list"),
             .errPos = pos
-        });
+        }));
 
     state.mkList(v, args[0]->listSize() - 1);
     for (unsigned int n = 0; n < v.listSize(); ++n)
@@ -2906,10 +2907,10 @@ static void prim_genList(EvalState & state, const Pos & pos, Value * * args, Val
     auto len = state.forceInt(*args[1], pos);
 
     if (len < 0)
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("cannot create list of size %1%", len),
             .errPos = pos
-        });
+        }));
 
     state.mkList(v, len);
 
@@ -3213,10 +3214,10 @@ static void prim_div(EvalState & state, const Pos & pos, Value * * args, Value &
 
     NixFloat f2 = state.forceFloat(*args[1], pos);
     if (f2 == 0)
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("division by zero"),
             .errPos = pos
-        });
+        }));
 
     if (args[0]->type() == nFloat || args[1]->type() == nFloat) {
         v.mkFloat(state.forceFloat(*args[0], pos) / state.forceFloat(*args[1], pos));
@@ -3225,10 +3226,10 @@ 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)
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("overflow in integer division"),
                 .errPos = pos
-            });
+            }));
 
         v.mkInt(i1 / i2);
     }
@@ -3356,10 +3357,10 @@ static void prim_substring(EvalState & state, const Pos & pos, Value * * args, V
     auto s = state.coerceToString(pos, *args[2], context);
 
     if (start < 0)
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("negative start position in 'substring'"),
             .errPos = pos
-        });
+        }));
 
     v.mkString((unsigned int) start >= s->size() ? "" : s->substr(start, len), context);
 }
@@ -3407,10 +3408,10 @@ 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)
-        throw Error({
+        state.debug_throw(Error({
             .msg = hintfmt("unknown hash type '%1%'", type),
             .errPos = pos
-        });
+        }));
 
     PathSet context; // discarded
     auto s = state.forceString(*args[1], context, pos);
@@ -3480,15 +3481,15 @@ 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++
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("memory limit exceeded by regular expression '%s'", re),
                 .errPos = pos
-            });
+            }));
         } else {
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("invalid regular expression '%s'", re),
                 .errPos = pos
-            });
+            }));
         }
     }
 }
@@ -3585,15 +3586,15 @@ 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++
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("memory limit exceeded by regular expression '%s'", re),
                 .errPos = pos
-            });
+            }));
         } else {
-            throw EvalError({
+            state.debug_throw(EvalError({
                 .msg = hintfmt("invalid regular expression '%s'", re),
                 .errPos = pos
-            });
+            }));
         }
     }
 }
@@ -3670,10 +3671,10 @@ 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())
-        throw EvalError({
+        state.debug_throw(EvalError({
             .msg = hintfmt("'from' and 'to' arguments to 'replaceStrings' have different lengths"),
             .errPos = pos
-        });
+        }));
 
     vector<string> from;
     from.reserve(args[0]->listSize());