From bef40c29491ba9b31c85b9b89a5342979344f583 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 29 Jun 2021 21:09:48 +0200
Subject: [PATCH] Add --eval-store option

---
 src/libcmd/command.cc      | 32 ++++++++++++++++++++++++++++++++
 src/libcmd/command.hh      | 15 ++++++++++++---
 src/libcmd/installables.cc | 13 -------------
 src/libexpr/eval.cc        |  6 +++++-
 src/libexpr/eval.hh        |  9 ++++++++-
 5 files changed, 57 insertions(+), 18 deletions(-)

diff --git a/src/libcmd/command.cc b/src/libcmd/command.cc
index 6777b23be..93f20a8c3 100644
--- a/src/libcmd/command.cc
+++ b/src/libcmd/command.cc
@@ -54,6 +54,38 @@ void StoreCommand::run()
     run(getStore());
 }
 
+EvalCommand::EvalCommand()
+{
+    // FIXME: move to MixEvalArgs?
+    addFlag({
+        .longName = "eval-store",
+        .description = "The Nix store to use for evaluations.",
+        .labels = {"store-url"},
+        //.category = ...,
+        .handler = {&evalStoreUrl},
+    });
+}
+
+EvalCommand::~EvalCommand()
+{
+    if (evalState)
+        evalState->printStats();
+}
+
+ref<Store> EvalCommand::getEvalStore()
+{
+    if (!evalStore)
+        evalStore = evalStoreUrl ? openStore(*evalStoreUrl) : getStore();
+    return ref<Store>(evalStore);
+}
+
+ref<EvalState> EvalCommand::getEvalState()
+{
+    if (!evalState)
+        evalState = std::make_shared<EvalState>(searchPath, getEvalStore(), getStore());
+    return ref<EvalState>(evalState);
+}
+
 BuiltPathsCommand::BuiltPathsCommand(bool recursive)
     : recursive(recursive)
 {
diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
index 35b3a384b..3aba8f25f 100644
--- a/src/libcmd/command.hh
+++ b/src/libcmd/command.hh
@@ -45,11 +45,20 @@ private:
 
 struct EvalCommand : virtual StoreCommand, MixEvalArgs
 {
-    ref<EvalState> getEvalState();
-
-    std::shared_ptr<EvalState> evalState;
+    EvalCommand();
 
     ~EvalCommand();
+
+    ref<Store> getEvalStore();
+
+    ref<EvalState> getEvalState();
+
+private:
+    std::optional<std::string> evalStoreUrl;
+
+    std::shared_ptr<Store> evalStore;
+
+    std::shared_ptr<EvalState> evalState;
 };
 
 struct MixFlakeOptions : virtual Args, EvalCommand
diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 95327f958..66ec63da2 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -289,19 +289,6 @@ void completeFlakeRefWithFragment(
     completeFlakeRef(evalState->store, prefix);
 }
 
-ref<EvalState> EvalCommand::getEvalState()
-{
-    if (!evalState)
-        evalState = std::make_shared<EvalState>(searchPath, getStore());
-    return ref<EvalState>(evalState);
-}
-
-EvalCommand::~EvalCommand()
-{
-    if (evalState)
-        evalState->printStats();
-}
-
 void completeFlakeRef(ref<Store> store, std::string_view prefix)
 {
     if (prefix == "")
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index c3206a577..b3e952aaa 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -378,7 +378,10 @@ static Strings parseNixPath(const string & s)
 }
 
 
-EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
+EvalState::EvalState(
+    const Strings & _searchPath,
+    ref<Store> store,
+    std::shared_ptr<Store> buildStore)
     : sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
     , sDrvPath(symbols.create("drvPath"))
@@ -411,6 +414,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
     , sEpsilon(symbols.create(""))
     , repair(NoRepair)
     , store(store)
+    , buildStore(buildStore ? buildStore : store)
     , regexCache(makeRegexCache())
     , baseEnv(allocEnv(128))
     , staticBaseEnv(false, 0)
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index e3eaed6d3..a7aebb8ef 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -94,8 +94,12 @@ public:
 
     Value vEmptySet;
 
+    /* Store used to materialise .drv files. */
     const ref<Store> store;
 
+    /* Store used to build stuff. */
+    const ref<Store> buildStore;
+
 
 private:
     SrcToStore srcToStore;
@@ -128,7 +132,10 @@ private:
 
 public:
 
-    EvalState(const Strings & _searchPath, ref<Store> store);
+    EvalState(
+        const Strings & _searchPath,
+        ref<Store> store,
+        std::shared_ptr<Store> buildStore = nullptr);
     ~EvalState();
 
     void addToSearchPath(const string & s);