From ea792bcdc850c18e6785ff0d2c96d3ef1396bb80 Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Thu, 10 Jun 2021 09:11:47 +0200
Subject: [PATCH] Make nix search lazier

Only 4 evals left \o/
---
 src/libexpr/eval.cc | 25 ++++++++++++++++---------
 src/libexpr/eval.hh |  3 ++-
 src/nix/search.cc   |  5 +++--
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 2b7955bcb..e8130f93e 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1198,12 +1198,8 @@ EvalState::LazyValueType EvalState::lazyGetAttrField(Value & attrs, const std::v
     }
     auto [ cacheResult, resultingCursor ] = eval_cache.getValue(*this, selector, dest);
     updateCacheStats(cacheResult);
-    switch (cacheResult.returnCode) {
-        case ValueCache::CacheHit:
-            if (cacheResult.lastQueriedSymbolIfMissing)
-                return LazyValueType::Missing;
-            return LazyValueType::PlainValue;
-        case ValueCache::Forward: {
+
+    auto delayValue = [&](ValueCache & cursor) {
             auto recordAsVar = new ExprCastedVar(&attrs);
             auto accessExpr = new ExprSelect(pos, recordAsVar, selector);
             auto thunk = (Thunk*)allocBytes(sizeof(Thunk));
@@ -1212,10 +1208,21 @@ EvalState::LazyValueType EvalState::lazyGetAttrField(Value & attrs, const std::v
 
             dest.mkCachedThunk(
                 thunk,
-                new ValueCache(resultingCursor)
+                new ValueCache(cursor)
             );
-            return LazyValueType::DelayedAttrSet;
-                                  }
+    };
+
+    switch (cacheResult.returnCode) {
+        case ValueCache::CacheHit:
+            if (cacheResult.lastQueriedSymbolIfMissing)
+                return LazyValueType::Missing;
+            return LazyValueType::PlainValue;
+        case ValueCache::UnCacheable:
+            delayValue(resultingCursor);
+            return LazyValueType::DelayedUncacheable;
+        case ValueCache::Forward:
+            delayValue(resultingCursor);
+            return LazyValueType::DelayedAttr;
         default:
             if(getAttrField(attrs, selector, pos, dest))
                 return LazyValueType::PlainValue;
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 9d2ee2941..a19518913 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -359,7 +359,8 @@ public:
 
     enum struct LazyValueType {
         PlainValue,
-        DelayedAttrSet,
+        DelayedUncacheable,
+        DelayedAttr,
         Missing,
     };
 
diff --git a/src/nix/search.cc b/src/nix/search.cc
index f99faecdf..61bdba967 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -98,9 +98,10 @@ struct CmdSearch : InstallableCommand, MixJSON
                     attrPath2.push_back(attrName);
                     auto attrValue = state->allocValue();
                     auto value_ = allocRootValue(attrValue);
-                    state->lazyGetAttrField(current, {attrName}, noPos,
+                    auto childField = state->lazyGetAttrField(current, {attrName}, noPos,
                                             *attrValue);
-                    visit(*attrValue, attrPath2, false);
+                    if (childField != EvalState::LazyValueType::DelayedUncacheable)
+                        visit(*attrValue, attrPath2, false);
                   } catch (EvalError &e) {
                     if (!(attrPath.size() > 0 &&
                           attrPath[0] == "legacyPackages"))