Merge pull request #337 from DeterminateSystems/fix-302

builtins.getFlake fixes

Author: edolstra

src/libexpr/primops.cc

@@ -2360,6 +2360,23 @@ static RegisterPrimOp primop_hashFile({
     .fun = prim_hashFile,
 });
 
+static RegisterPrimOp primop_narHash({
+    .name = "__narHash",
+    .args = {"p"},
+    .doc = R"(
+      Return an SRI representation of the SHA-256 hash of the NAR serialisation of the path *p*.
+    )",
+    .fun =
+        [](EvalState & state, const PosIdx pos, Value ** args, Value & v) {
+            auto path = state.realisePath(pos, *args[0]);
+            auto hash =
+                fetchToStore2(state.fetchSettings, *state.store, path.resolveSymlinks(), FetchMode::DryRun).second;
+            v.mkString(hash.to_string(HashFormat::SRI, true), state.mem);
+        },
+    // FIXME: may be useful to expose to the user.
+    .internal = true,
+});
+
 static const Value & fileTypeToString(EvalState & state, SourceAccessor::Type type)
 {
     struct Constants

src/libexpr/primops/fetchTree.cc

@@ -30,12 +30,16 @@ void emitTreeAttrs(
 {
     auto attrs = state.buildBindings(100);
 
-    state.mkStorePathString(storePath, attrs.alloc(state.s.outPath));
+    auto & vStorePath = attrs.alloc(state.s.outPath);
+    state.mkStorePathString(storePath, vStorePath);
 
     // FIXME: support arbitrary input attributes.
 
     if (auto narHash = input.getNarHash())
         attrs.alloc("narHash").mkString(narHash->to_string(HashFormat::SRI, true), state.mem);
+    else
+        // Lazily compute the NAR hash for backward compatibility.
+        attrs.alloc("narHash").mkApp(*get(state.internalPrimOps, "narHash"), &vStorePath);
 
     if (input.getType() == "git")
         attrs.alloc("submodules").mkBool(fetchers::maybeGetBoolAttr(input.attrs, "submodules").value_or(false));

src/libflake/flake-primops.cc

@@ -35,8 +35,16 @@ namespace nix::flake::primops {
 PrimOp getFlake(const Settings & settings)
 {
     auto prim_getFlake = [&settings](EvalState & state, const PosIdx pos, Value ** args, Value & v) {
+        NixStringContext context;
         std::string flakeRefS(
-            state.forceStringNoCtx(*args[0], pos, "while evaluating the argument passed to builtins.getFlake"));
+            state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.getFlake"));
+        auto rewrites = state.realiseContext(context);
+        flakeRefS = state.devirtualize(rewriteStrings(flakeRefS, rewrites), context);
+        if (hasContext(context))
+            // FIXME: this should really be an error.
+            warn(
+                "In 'builtins.getFlake', the flakeref '%s' has string context, but that's not allowed. This may become a fatal error in the future.",
+                flakeRefS);
         auto flakeRef = nix::parseFlakeRef(state.fetchSettings, flakeRefS, {}, true);
         if (state.settings.pureEval && !flakeRef.input.isLocked(state.fetchSettings))
             throw Error(
@@ -125,7 +133,9 @@ static void prim_flakeRefToString(EvalState & state, const PosIdx pos, Value **
 {
     state.forceAttrs(*args[0], noPos, "while evaluating the argument passed to builtins.flakeRefToString");
     fetchers::Attrs attrs;
+    NixStringContext context;
     for (const auto & attr : *args[0]->attrs()) {
+        state.forceValue(*attr.value, attr.pos);
         auto t = attr.value->type();
         if (t == nInt) {
             auto intValue = attr.value->integer().value;
@@ -142,7 +152,9 @@ static void prim_flakeRefToString(EvalState & state, const PosIdx pos, Value **
         } else if (t == nBool) {
             attrs.emplace(state.symbols[attr.name], Explicit<bool>{attr.value->boolean()});
         } else if (t == nString) {
-            attrs.emplace(state.symbols[attr.name], std::string(attr.value->string_view()));
+            auto s = state.forceString(
+                *attr.value, context, attr.pos, "while evaluating an attribute in 'builtins.flakeRefToString'");
+            attrs.emplace(state.symbols[attr.name], std::string(s));
         } else {
             state
                 .error<EvalError>(
@@ -154,7 +166,7 @@ static void prim_flakeRefToString(EvalState & state, const PosIdx pos, Value **
         }
     }
     auto flakeRef = FlakeRef::fromAttrs(state.fetchSettings, attrs);
-    v.mkString(flakeRef.to_string(), state.mem);
+    v.mkString(flakeRef.to_string(), context, state.mem);
 }
 
 nix::PrimOp flakeRefToString({

tests/functional/flakes/get-flake.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+source ./common.sh
+
+createFlake1
+
+mkdir -p "$flake1Dir/subflake"
+cat > "$flake1Dir/subflake/flake.nix" <<EOF
+{
+  outputs = { self }:
+    let
+      parentFlake = builtins.getFlake (builtins.flakeRefToString { type = "path"; path = self.sourceInfo.outPath; narHash = self.narHash; });
+    in {
+      x = parentFlake.number;
+    };
+}
+EOF
+git -C "$flake1Dir" add subflake/flake.nix
+
+expectStderr 0 nix eval "$flake1Dir/subflake#x" | grepQuiet "This may become a fatal error in the future"
+[[ $(nix eval "$flake1Dir/subflake#x") = 123 ]]

tests/functional/flakes/meson.build

@@ -37,6 +37,7 @@ suites += {
     'build-time-flake-inputs.sh',
     'substitution.sh',
     'shallow.sh',
+    'get-flake.sh',
   ],
   'workdir' : meson.current_source_dir(),
 }