Merge pull request #205 from DeterminateSystems/fix-debugger

Disable parallel eval if the debugger is enabled

Author: edolstra

src/libcmd/command.cc

@@ -125,6 +125,13 @@ ref<Store> EvalCommand::getEvalStore()
 ref<EvalState> EvalCommand::getEvalState()
 {
     if (!evalState) {
+        if (startReplOnEvalErrors && evalSettings.evalCores != 1U) {
+            // Disable parallel eval if the debugger is enabled, since
+            // they're incompatible at the moment.
+            warn("using the debugger disables multi-threaded evaluation");
+            evalSettings.evalCores = 1;
+        }
+
         evalState = std::allocate_shared<EvalState>(
             traceable_allocator<EvalState>(), lookupPath, getEvalStore(), fetchSettings, evalSettings, getStore());
 

src/libexpr/include/nix/expr/eval-settings.hh

@@ -377,6 +377,8 @@ struct EvalSettings : Config
           * Any evaluation that uses `builtins.parallel`
 
           The value `0` causes Nix to use all available CPU cores in the system.
+
+          Note that enabling the debugger (`--debugger`) disables multi-threaded evaluation.
         )"};
 };