From 55888633dd323c83cd1db3773d82dc954da34888 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Mon, 5 Jun 2023 11:37:41 +0200
Subject: [PATCH] makeContentAddressed: Add single path helper

---
 src/libexpr/primops/fetchClosure.cc    | 10 ++++------
 src/libstore/make-content-addressed.cc | 11 +++++++++++
 src/libstore/make-content-addressed.hh | 13 ++++++++++++-
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/src/libexpr/primops/fetchClosure.cc b/src/libexpr/primops/fetchClosure.cc
index 6d2271853..6a15c826f 100644
--- a/src/libexpr/primops/fetchClosure.cc
+++ b/src/libexpr/primops/fetchClosure.cc
@@ -94,14 +94,12 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
 
     if (enableRewriting) {
         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)
+            auto rewrittenPath = makeContentAddressed(*fromStore, *state.store, *fromPath);
+            if (toPath && *toPath != rewrittenPath)
                 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(rewrittenPath),
                         state.store->printStorePath(*toPath)),
                     .errPos = state.positions[pos]
                 });
@@ -111,7 +109,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
                         "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)),
+                        state.store->printStorePath(rewrittenPath)),
                     .errPos = state.positions[pos]
                 });
         }
diff --git a/src/libstore/make-content-addressed.cc b/src/libstore/make-content-addressed.cc
index 53fe04704..626a22480 100644
--- a/src/libstore/make-content-addressed.cc
+++ b/src/libstore/make-content-addressed.cc
@@ -80,4 +80,15 @@ std::map<StorePath, StorePath> makeContentAddressed(
     return remappings;
 }
 
+StorePath makeContentAddressed(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePath & fromPath)
+{
+    auto remappings = makeContentAddressed(srcStore, dstStore, StorePathSet { fromPath });
+    auto i = remappings.find(fromPath);
+    assert(i != remappings.end());
+    return i->second;
+}
+
 }
diff --git a/src/libstore/make-content-addressed.hh b/src/libstore/make-content-addressed.hh
index 2ce6ec7bc..60bb2b477 100644
--- a/src/libstore/make-content-addressed.hh
+++ b/src/libstore/make-content-addressed.hh
@@ -5,9 +5,20 @@
 
 namespace nix {
 
+/** Rewrite a closure of store paths to be completely content addressed.
+ */
 std::map<StorePath, StorePath> makeContentAddressed(
     Store & srcStore,
     Store & dstStore,
-    const StorePathSet & storePaths);
+    const StorePathSet & rootPaths);
+
+/** Rewrite a closure of a store path to be completely content addressed.
+ *
+ * This is a convenience function for the case where you only have one root path.
+ */
+StorePath makeContentAddressed(
+    Store & srcStore,
+    Store & dstStore,
+    const StorePath & rootPath);
 
 }