`:quit` in the debugger should quit the whole program

(cherry picked from commit 2a8fe9a93837733e9dd9ed5c078734a35b203e14)
Change-Id: I71dadfef6b24d9272b206e9e2c408040559d8a1c

10 files changed, 111 insertions, 44 deletions

diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index bc5ff9525..ea2f4ebe6 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -49,6 +49,27 @@ extern "C" {
 
 namespace nix {
 
+/**
+ * Returned by `NixRepl::processLine`.
+ */
+enum class ProcessLineResult {
+    /**
+     * The user exited with `:quit`. The REPL should exit. The surrounding
+     * program or evaluation (e.g., if the REPL was acting as the debugger)
+     * should also exit.
+     */
+    QuitAll,
+    /**
+     * The user exited with `:continue`. The REPL should exit, but the program
+     * should continue running.
+     */
+    QuitOnce,
+    /**
+     * The user did not exit. The REPL should request another line of input.
+     */
+    Continue,
+};
+
 struct NixRepl
     : AbstractNixRepl
     #if HAVE_BOEHMGC
@@ -72,13 +93,13 @@ struct NixRepl
             std::function<AnnotatedValues()> getValues);
     virtual ~NixRepl();
 
-    void mainLoop() override;
+    ReplExitStatus mainLoop() override;
     void initEnv() override;
 
     StringSet completePrefix(const std::string & prefix);
     bool getLine(std::string & input, const std::string & prompt);
     StorePath getDerivationPath(Value & v);
-    bool processLine(std::string line);
+    ProcessLineResult processLine(std::string line);
 
     void loadFile(const Path & path);
     void loadFlake(const std::string & flakeRef);
@@ -243,7 +264,7 @@ static std::ostream & showDebugTrace(std::ostream & out, const PosTable & positi
 
 static bool isFirstRepl = true;
 
-void NixRepl::mainLoop()
+ReplExitStatus NixRepl::mainLoop()
 {
     if (isFirstRepl) {
         std::string_view debuggerNotice = "";
@@ -284,15 +305,25 @@ void NixRepl::mainLoop()
         // When continuing input from previous lines, don't print a prompt, just align to the same
         // number of chars as the prompt.
         if (!getLine(input, input.empty() ? "nix-repl> " : "          ")) {
-            // ctrl-D should exit the debugger.
+            // Ctrl-D should exit the debugger.
             state->debugStop = false;
-            state->debugQuit = true;
             logger->cout("");
-            break;
+            // TODO: Should Ctrl-D exit just the current debugger session or
+            // the entire program?
+            return ReplExitStatus::QuitAll;
         }
         logger->resume();
         try {
-            if (!removeWhitespace(input).empty() && !processLine(input)) return;
+            switch (processLine(input)) {
+                case ProcessLineResult::QuitAll:
+                    return ReplExitStatus::QuitAll;
+                case ProcessLineResult::QuitOnce:
+                    return ReplExitStatus::Continue;
+                case ProcessLineResult::Continue:
+                    break;
+                default:
+                    abort();
+            }
         } catch (ParseError & e) {
             if (e.msg().find("unexpected end of file") != std::string::npos) {
                 // For parse errors on incomplete input, we continue waiting for the next line of
@@ -479,10 +510,11 @@ void NixRepl::loadDebugTraceEnv(DebugTrace & dt)
     }
 }
 
-bool NixRepl::processLine(std::string line)
+ProcessLineResult NixRepl::processLine(std::string line)
 {
     line = trim(line);
-    if (line == "") return true;
+    if (line.empty())
+        return ProcessLineResult::Continue;
 
     _isInterrupted = false;
 
@@ -577,13 +609,13 @@ bool NixRepl::processLine(std::string line)
     else if (state->debugRepl && (command == ":s" || command == ":step")) {
         // set flag to stop at next DebugTrace; exit repl.
         state->debugStop = true;
-        return false;
+        return ProcessLineResult::QuitOnce;
     }
 
     else if (state->debugRepl && (command == ":c" || command == ":continue")) {
         // set flag to run to next breakpoint or end of program; exit repl.
         state->debugStop = false;
-        return false;
+        return ProcessLineResult::QuitOnce;
     }
 
     else if (command == ":a" || command == ":add") {
@@ -726,8 +758,7 @@ bool NixRepl::processLine(std::string line)
 
     else if (command == ":q" || command == ":quit") {
         state->debugStop = false;
-        state->debugQuit = true;
-        return false;
+        return ProcessLineResult::QuitAll;
     }
 
     else if (command == ":doc") {
@@ -788,7 +819,7 @@ bool NixRepl::processLine(std::string line)
         }
     }
 
-    return true;
+    return ProcessLineResult::Continue;
 }
 
 void NixRepl::loadFile(const Path & path)
@@ -919,7 +950,7 @@ std::unique_ptr<AbstractNixRepl> AbstractNixRepl::create(
 }
 
 
-void AbstractNixRepl::runSimple(
+ReplExitStatus AbstractNixRepl::runSimple(
     ref<EvalState> evalState,
     const ValMap & extraEnv)
 {
@@ -941,7 +972,7 @@ void AbstractNixRepl::runSimple(
     for (auto & [name, value] : extraEnv)
         repl->addVarToScope(repl->state->symbols.create(name), *value);
 
-    repl->mainLoop();
+    return repl->mainLoop();
 }
 
 }
diff --git a/src/libcmd/repl.hh b/src/libcmd/repl.hh
index 6d88883fe..21aa8bfc7 100644
--- a/src/libcmd/repl.hh
+++ b/src/libcmd/repl.hh
@@ -28,13 +28,13 @@ struct AbstractNixRepl
         const SearchPath & searchPath, nix::ref<Store> store, ref<EvalState> state,
         std::function<AnnotatedValues()> getValues);
 
-    static void runSimple(
+    static ReplExitStatus runSimple(
         ref<EvalState> evalState,
         const ValMap & extraEnv);
 
     virtual void initEnv() = 0;
 
-    virtual void mainLoop() = 0;
+    virtual ReplExitStatus mainLoop() = 0;
 };
 
 }
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index ba9fe9c65..e15781404 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -3,6 +3,7 @@
 #include "hash.hh"
 #include "primops.hh"
 #include "print-options.hh"
+#include "shared.hh"
 #include "types.hh"
 #include "util.hh"
 #include "store-api.hh"
@@ -391,7 +392,6 @@ EvalState::EvalState(
     , buildStore(buildStore ? buildStore : store)
     , debugRepl(nullptr)
     , debugStop(false)
-    , debugQuit(false)
     , trylevel(0)
     , regexCache(makeRegexCache())
 #if HAVE_BOEHMGC
@@ -798,7 +798,17 @@ void EvalState::runDebugRepl(const Error * error, const Env & env, const Expr &
     auto se = getStaticEnv(expr);
     if (se) {
         auto vm = mapStaticEnvBindings(symbols, *se.get(), env);
-        (debugRepl)(ref<EvalState>(shared_from_this()), *vm);
+        auto exitStatus = (debugRepl)(ref<EvalState>(shared_from_this()), *vm);
+        switch (exitStatus) {
+            case ReplExitStatus::QuitAll:
+                if (error)
+                    throw *error;
+                throw Exit(0);
+            case ReplExitStatus::Continue:
+                break;
+            default:
+                abort();
+        }
     }
 }
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 135e5fecb..5cdf34a47 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -11,6 +11,7 @@
 #include "experimental-features.hh"
 #include "input-accessor.hh"
 #include "search-path.hh"
+#include "repl-exit-status.hh"
 
 #include <map>
 #include <optional>
@@ -207,9 +208,8 @@ public:
     /**
      * Debugger
      */
-    void (* debugRepl)(ref<EvalState> es, const ValMap & extraEnv);
+    ReplExitStatus (* debugRepl)(ref<EvalState> es, const ValMap & extraEnv);
     bool debugStop;
-    bool debugQuit;
     int trylevel;
     std::list<DebugTrace> debugTraces;
     std::map<const Expr*, const std::shared_ptr<const StaticEnv>> exprEnvs;
@@ -753,7 +753,6 @@ struct DebugTraceStacker {
     DebugTraceStacker(EvalState & evalState, DebugTrace t);
     ~DebugTraceStacker()
     {
-        // assert(evalState.debugTraces.front() == trace);
         evalState.debugTraces.pop_front();
     }
     EvalState & evalState;
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 86db527f6..30933e191 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -754,15 +754,6 @@ static RegisterPrimOp primop_break({
 
             auto & dt = state.debugTraces.front();
             state.runDebugRepl(&error, dt.env, dt.expr);
-
-            if (state.debugQuit) {
-                // If the user elects to quit the repl, throw an exception.
-                throw Error(ErrorInfo{
-                    .level = lvlInfo,
-                    .msg = HintFmt("quit the debugger"),
-                    .pos = nullptr,
-                });
-            }
         }
 
         // Return the value we were passed.
@@ -873,7 +864,7 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     /* increment state.trylevel, and decrement it when this function returns. */
     MaintainCount trylevel(state.trylevel);
 
-    void (* savedDebugRepl)(ref<EvalState> es, const ValMap & extraEnv) = nullptr;
+    ReplExitStatus (* savedDebugRepl)(ref<EvalState> es, const ValMap & extraEnv) = nullptr;
     if (state.debugRepl && evalSettings.ignoreExceptionsDuringTry)
     {
         /* to prevent starting the repl from exceptions withing a tryEval, null it. */
diff --git a/src/libexpr/repl-exit-status.hh b/src/libexpr/repl-exit-status.hh
new file mode 100644
index 000000000..08299ff61
--- /dev/null
+++ b/src/libexpr/repl-exit-status.hh
@@ -0,0 +1,20 @@
+#pragma once
+
+namespace nix {
+
+/**
+ * Exit status returned from the REPL.
+ */
+enum class ReplExitStatus {
+    /**
+     * The user exited with `:quit`. The program (e.g., if the REPL was acting
+     * as the debugger) should exit.
+     */
+    QuitAll,
+    /**
+     * The user exited with `:continue`. The program should continue running.
+     */
+    Continue,
+};
+
+}
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 1b021d0b0..4ad1faec3 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -407,6 +407,4 @@ PrintFreed::~PrintFreed()
             showBytes(results.bytesFreed));
 }
 
-Exit::~Exit() { }
-
 }
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index 9415be78a..2b15d3368 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -6,6 +6,7 @@
 #include "common-args.hh"
 #include "path.hh"
 #include "derived-path.hh"
+#include "exit.hh"
 
 #include <signal.h>
 
@@ -14,15 +15,6 @@
 
 namespace nix {
 
-class Exit : public std::exception
-{
-public:
-    int status;
-    Exit() : status(0) { }
-    Exit(int status) : status(status) { }
-    virtual ~Exit();
-};
-
 int handleExceptions(const std::string & programName, std::function<void()> fun);
 
 /**
diff --git a/src/libutil/exit.cc b/src/libutil/exit.cc
new file mode 100644
index 000000000..73cd8b04e
--- /dev/null
+++ b/src/libutil/exit.cc
@@ -0,0 +1,7 @@
+#include "exit.hh"
+
+namespace nix {
+
+Exit::~Exit() {}
+
+}
diff --git a/src/libutil/exit.hh b/src/libutil/exit.hh
new file mode 100644
index 000000000..55f33e62f
--- /dev/null
+++ b/src/libutil/exit.hh
@@ -0,0 +1,19 @@
+#pragma once
+
+#include <exception>
+
+namespace nix {
+
+/**
+ * Exit the program with a given exit code.
+ */
+class Exit : public std::exception
+{
+public:
+    int status;
+    Exit() : status(0) { }
+    explicit Exit(int status) : status(status) { }
+    virtual ~Exit();
+};
+
+}