fetchTree: Do not re-fetch paths already present

1 files changed, 24 insertions, 4 deletions

diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index f3e3e70d8..ea416d2d9 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -185,6 +185,13 @@ static void prim_fetchTree(EvalState & state, const Pos & pos, Value * * args, V
 // FIXME: document
 static RegisterPrimOp primop_fetchTree("fetchTree", 1, prim_fetchTree);
 
+static void setStorePath(EvalState &state, const StorePath &storePath, Value &v) {
+    state.allowPath(storePath);
+
+    auto path = state.store->printStorePath(storePath);
+    v.mkString(path, PathSet({path}));
+}
+
 static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     const std::string & who, bool unpack, std::string name)
 {
@@ -203,6 +210,8 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
                 url = state.forceStringNoCtx(*attr.value, *attr.pos);
             else if (n == "sha256")
                 expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
+            else if (n == "narHash")
+                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, *attr.pos), htSHA256);
             else if (n == "name")
                 name = state.forceStringNoCtx(*attr.value, *attr.pos);
             else
@@ -230,6 +239,20 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     if (evalSettings.pureEval && !expectedHash)
         throw Error("in pure evaluation mode, '%s' requires a 'sha256' argument", who);
 
+    // early exit if pinned and already in the store
+    if (expectedHash && expectedHash->type == htSHA256) {
+        auto expectedPath =
+            unpack
+            ? state.store->makeFixedOutputPath(FileIngestionMethod::Recursive, *expectedHash, name, {})
+            : state.store->makeFixedOutputPath(FileIngestionMethod::Flat, *expectedHash, name, {});
+
+        auto validPaths = state.store->queryValidPaths({expectedPath}, NoSubstitute);
+        if (!validPaths.empty()) {
+            setStorePath(state, expectedPath, v);
+            return;
+        }
+    }
+
     auto storePath =
         unpack
         ? fetchers::downloadTarball(state.store, *url, name, (bool) expectedHash).first.storePath
@@ -244,10 +267,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
                 *url, expectedHash->to_string(Base32, true), hash.to_string(Base32, true));
     }
 
-    state.allowPath(storePath);
-
-    auto path = state.store->printStorePath(storePath);
-    v.mkString(path, PathSet({path}));
+    setStorePath(state, storePath, v);
 }
 
 static void prim_fetchurl(EvalState & state, const Pos & pos, Value * * args, Value & v)