From 89e0b3e2d62f72e48bdda63b77a086c69b314113 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Sat, 30 May 2020 01:16:53 +0200
Subject: [PATCH] Move substitution into Input::fetch()

Closes #3520.
---
 src/libexpr/flake/flake.cc       | 30 ------------------------------
 src/libexpr/primops/fetchTree.cc | 25 -------------------------
 src/libfetchers/fetchers.cc      | 20 ++++++++++++++++++++
 3 files changed, 20 insertions(+), 55 deletions(-)

diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 9741d98c5..54282d40f 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -52,36 +52,6 @@ static std::tuple<fetchers::Tree, FlakeRef, FlakeRef> fetchOrSubstituteTree(
     bool allowLookup,
     FlakeCache & flakeCache)
 {
-    /* The tree may already be in the Nix store, or it could be
-       substituted (which is often faster than fetching from the
-       original source). So check that. */
-    if (originalRef.input.isDirect() && originalRef.input.isImmutable() && originalRef.input.hasAllInfo()) {
-        try {
-            auto storePath = originalRef.input.computeStorePath(*state.store);
-
-            state.store->ensurePath(storePath);
-
-            debug("using substituted/cached input '%s' in '%s'",
-                originalRef, state.store->printStorePath(storePath));
-
-            auto actualPath = state.store->toRealPath(storePath);
-
-            if (state.allowedPaths)
-                state.allowedPaths->insert(actualPath);
-
-            return {
-                Tree {
-                    .actualPath = actualPath,
-                    .storePath = std::move(storePath),
-                },
-                originalRef,
-                originalRef
-            };
-        } catch (Error & e) {
-            debug("substitution of input '%s' failed: %s", originalRef, e.what());
-        }
-    }
-
     auto resolvedRef = lookupInFlakeCache(flakeCache,
         maybeLookupFlake(state.store,
             lookupInFlakeCache(flakeCache, originalRef), allowLookup));
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index a1ad0a7b9..28f9cdb31 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -88,31 +88,6 @@ static void prim_fetchTree(EvalState & state, const Pos & pos, Value * * args, V
     if (evalSettings.pureEval && !input.isImmutable())
         throw Error("in pure evaluation mode, 'fetchTree' requires an immutable input, at %s", pos);
 
-    /* The tree may already be in the Nix store, or it could be
-       substituted (which is often faster than fetching from the
-       original source). So check that. */
-    if (input.hasAllInfo()) {
-        auto storePath = input.computeStorePath(*state.store);
-
-        try {
-            state.store->ensurePath(storePath);
-
-            debug("using substituted/cached input '%s' in '%s'",
-                input.to_string(), state.store->printStorePath(storePath));
-
-            auto actualPath = state.store->toRealPath(storePath);
-
-            if (state.allowedPaths)
-                state.allowedPaths->insert(actualPath);
-
-            emitTreeAttrs(state, fetchers::Tree { .actualPath = actualPath, .storePath = std::move(storePath) }, input, v);
-
-            return;
-        } catch (Error & e) {
-            debug("substitution of input '%s' failed: %s", input.to_string(), e.what());
-        }
-    }
-
     auto [tree, input2] = input.fetch(state.store);
 
     if (state.allowedPaths)
diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index aac8aa8c5..f0d8f72c8 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -103,6 +103,26 @@ std::pair<Tree, Input> Input::fetch(ref<Store> store) const
     if (!scheme)
         throw Error("cannot fetch unsupported input '%s'", attrsToJson(toAttrs()));
 
+    /* The tree may already be in the Nix store, or it could be
+       substituted (which is often faster than fetching from the
+       original source). So check that. */
+    if (hasAllInfo()) {
+        try {
+            auto storePath = computeStorePath(*store);
+
+            store->ensurePath(storePath);
+
+            debug("using substituted/cached input '%s' in '%s'",
+                to_string(), store->printStorePath(storePath));
+
+            auto actualPath = store->toRealPath(storePath);
+
+            return {fetchers::Tree { .actualPath = actualPath, .storePath = std::move(storePath) }, *this};
+        } catch (Error & e) {
+            debug("substitution of input '%s' failed: %s", to_string(), e.what());
+        }
+    }
+
     auto [tree, input] = scheme->fetch(store, *this);
 
     if (tree.actualPath == "")