From 160b974fb0623df436c9e834f6d4db62dfda02d2 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 17 Apr 2019 13:54:06 +0200
Subject: [PATCH] Fix mutability check

---
 src/libexpr/primops/flake.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/primops/flake.cc b/src/libexpr/primops/flake.cc
index 296db3f92..0bf666a98 100644
--- a/src/libexpr/primops/flake.cc
+++ b/src/libexpr/primops/flake.cc
@@ -193,10 +193,11 @@ static FlakeSourceInfo fetchFlake(EvalState & state, const FlakeRef flakeRef, bo
     FlakeRef fRef = lookupFlake(state, flakeRef,
         impureIsAllowed ? state.getFlakeRegistries() : std::vector<std::shared_ptr<FlakeRegistry>>());
 
+    if (evalSettings.pureEval && !impureIsAllowed && !fRef.isImmutable())
+        throw Error("requested to fetch mutable flake '%s' in pure mode", fRef.to_string());
+
     // This only downloads only one revision of the repo, not the entire history.
     if (auto refData = std::get_if<FlakeRef::IsGitHub>(&fRef.data)) {
-        if (evalSettings.pureEval && !impureIsAllowed && !fRef.isImmutable())
-            throw Error("requested to fetch FlakeRef '%s' purely, which is mutable", fRef.to_string());
 
         // FIXME: use regular /archive URLs instead? api.github.com
         // might have stricter rate limits.