From a865049c4f39cb7773f97a67cfa12f5b650a86ee Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 20 Mar 2024 23:06:23 +0100
Subject: [PATCH] tryEval: Allocate true and false once

---
 src/libexpr/eval.cc    |  2 ++
 src/libexpr/eval.hh    | 18 +++++++++++++++++-
 src/libexpr/primops.cc |  7 ++++---
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index a6e8a4a8b..a62cee299 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -437,6 +437,8 @@ EvalState::EvalState(
 
     vEmptyList.mkList(buildList(0));
     vNull.mkNull();
+    vTrue.mkBool(true);
+    vFalse.mkBool(false);
     vStringRegular.mkString("regular");
     vStringDirectory.mkString("directory");
     vStringSymlink.mkString("symlink");
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index a405888c1..eac83fe34 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -187,10 +187,26 @@ public:
     Value vEmptyList;
 
     /**
-     * Null constant.
+     * `null` constant.
+     *
+     * This is _not_ a singleton. Pointer equality is _not_ sufficient.
      */
     Value vNull;
 
+    /**
+     * `true` constant.
+     *
+     * This is _not_ a singleton. Pointer equality is _not_ sufficient.
+     */
+    Value vTrue;
+
+    /**
+     * `true` constant.
+     *
+     * This is _not_ a singleton. Pointer equality is _not_ sufficient.
+     */
+    Value vFalse;
+
     /** `"regular"` */
     Value vStringRegular;
     /** `"directory"` */
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 2022f6dcf..0f2aaa83f 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -896,10 +896,11 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     try {
         state.forceValue(*args[0], pos);
         attrs.insert(state.sValue, args[0]);
-        attrs.alloc("success").mkBool(true);
+        attrs.insert(state.symbols.create("success"), &state.vTrue);
     } catch (AssertionError & e) {
-        attrs.alloc(state.sValue).mkBool(false);
-        attrs.alloc("success").mkBool(false);
+        // `value = false;` is unfortunate but removing it is a breaking change.
+        attrs.insert(state.sValue, &state.vFalse);
+        attrs.insert(state.symbols.create("success"), &state.vFalse);
     }
 
     // restore the debugRepl pointer if we saved it earlier.