From 7ffda0af6effbf32c8668f34cc3f0448c58bc3c1 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 22 Mar 2022 22:01:20 +0100
Subject: fetchClosure: Skip makeContentAddressed() if toPath is already valid

---
 src/libexpr/primops/fetchClosure.cc | 42 +++++++++++++++++++------------------
 1 file changed, 22 insertions(+), 20 deletions(-)

diff --git a/src/libexpr/primops/fetchClosure.cc b/src/libexpr/primops/fetchClosure.cc
index 56fd53ed5..c3f07b6d6 100644
--- a/src/libexpr/primops/fetchClosure.cc
+++ b/src/libexpr/primops/fetchClosure.cc
@@ -54,26 +54,28 @@ static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args
     auto fromStore = openStore(*fromStoreUrl);
 
     if (toCA) {
-        auto remappings = makeContentAddressed(*fromStore, *state.store, { *fromPath });
-        auto i = remappings.find(*fromPath);
-        assert(i != remappings.end());
-        if (toPath && *toPath != i->second)
-            throw Error({
-                .msg = hintfmt("rewriting '%s' to content-addressed form yielded '%s', while '%s' was expected",
-                    state.store->printStorePath(*fromPath),
-                    state.store->printStorePath(i->second),
-                    state.store->printStorePath(*toPath)),
-                .errPos = pos
-            });
-        if (!toPath)
-            throw Error({
-                .msg = hintfmt(
-                    "rewriting '%s' to content-addressed form yielded '%s'; "
-                    "please set this in the 'toPath' attribute passed to 'fetchClosure'",
-                    state.store->printStorePath(*fromPath),
-                    state.store->printStorePath(i->second)),
-                .errPos = pos
-            });
+        if (!toPath || !state.store->isValidPath(*toPath)) {
+            auto remappings = makeContentAddressed(*fromStore, *state.store, { *fromPath });
+            auto i = remappings.find(*fromPath);
+            assert(i != remappings.end());
+            if (toPath && *toPath != i->second)
+                throw Error({
+                    .msg = hintfmt("rewriting '%s' to content-addressed form yielded '%s', while '%s' was expected",
+                        state.store->printStorePath(*fromPath),
+                        state.store->printStorePath(i->second),
+                        state.store->printStorePath(*toPath)),
+                    .errPos = pos
+                });
+            if (!toPath)
+                throw Error({
+                    .msg = hintfmt(
+                        "rewriting '%s' to content-addressed form yielded '%s'; "
+                        "please set this in the 'toPath' attribute passed to 'fetchClosure'",
+                        state.store->printStorePath(*fromPath),
+                        state.store->printStorePath(i->second)),
+                    .errPos = pos
+                });
+        }
     } else {
         copyClosure(*fromStore, *state.store, RealisedPath::Set { *fromPath });
         toPath = fromPath;
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