Initial flake support

5 files changed, 205 insertions, 9 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 3891e8666..e3a264277 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -290,6 +290,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
     , sOutputHash(symbols.create("outputHash"))
     , sOutputHashAlgo(symbols.create("outputHashAlgo"))
     , sOutputHashMode(symbols.create("outputHashMode"))
+    , sDescription(symbols.create("description"))
     , repair(NoRepair)
     , store(store)
     , baseEnv(allocEnv(128))
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 60cf0f87f..674b08f45 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -72,7 +72,8 @@ public:
         sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
         sFile, sLine, sColumn, sFunctor, sToString,
         sRight, sWrong, sStructuredAttrs, sBuilder, sArgs,
-        sOutputHash, sOutputHashAlgo, sOutputHashMode;
+        sOutputHash, sOutputHashAlgo, sOutputHashMode,
+        sDescription;
     Symbol sDerivationNix;
 
     /* If set, force copying files to the Nix store even if they
@@ -311,6 +312,23 @@ private:
     friend struct ExprOpConcatLists;
     friend struct ExprSelect;
     friend void prim_getAttr(EvalState & state, const Pos & pos, Value * * args, Value & v);
+
+public:
+
+    struct FlakeRegistry
+    {
+        struct Entry
+        {
+            std::string uri;
+        };
+        std::map<std::string, Entry> entries;
+    };
+
+    const FlakeRegistry & getFlakeRegistry();
+
+private:
+    std::unique_ptr<FlakeRegistry> _flakeRegistry;
+    std::once_flag _flakeRegistryInit;
 };
 
 
diff --git a/src/libexpr/primops/fetchGit.cc b/src/libexpr/primops/fetchGit.cc
index b46d2f258..6b6ca08d1 100644
--- a/src/libexpr/primops/fetchGit.cc
+++ b/src/libexpr/primops/fetchGit.cc
@@ -1,3 +1,4 @@
+#include "fetchGit.hh"
 #include "primops.hh"
 #include "eval-inline.hh"
 #include "download.hh"
@@ -15,14 +16,6 @@ using namespace std::string_literals;
 
 namespace nix {
 
-struct GitInfo
-{
-    Path storePath;
-    std::string rev;
-    std::string shortRev;
-    uint64_t revCount = 0;
-};
-
 std::regex revRegex("^[0-9a-fA-F]{40}$");
 
 GitInfo exportGit(ref<Store> store, const std::string & uri,
diff --git a/src/libexpr/primops/fetchGit.hh b/src/libexpr/primops/fetchGit.hh
new file mode 100644
index 000000000..23ab2fae9
--- /dev/null
+++ b/src/libexpr/primops/fetchGit.hh
@@ -0,0 +1,23 @@
+#pragma once
+
+#include "store-api.hh"
+
+#include <regex>
+
+namespace nix {
+
+struct GitInfo
+{
+    Path storePath;
+    std::string rev;
+    std::string shortRev;
+    uint64_t revCount = 0;
+};
+
+GitInfo exportGit(ref<Store> store, const std::string & uri,
+    std::experimental::optional<std::string> ref, std::string rev,
+    const std::string & name);
+
+extern std::regex revRegex;
+
+}
diff --git a/src/libexpr/primops/flake.cc b/src/libexpr/primops/flake.cc
new file mode 100644
index 000000000..457c30948
--- /dev/null
+++ b/src/libexpr/primops/flake.cc
@@ -0,0 +1,161 @@
+#include "primops.hh"
+#include "eval-inline.hh"
+#include "fetchGit.hh"
+#include "download.hh"
+
+#include <queue>
+#include <nlohmann/json.hpp>
+
+namespace nix {
+
+const EvalState::FlakeRegistry & EvalState::getFlakeRegistry()
+{
+    std::call_once(_flakeRegistryInit, [&]()
+    {
+        _flakeRegistry = std::make_unique<FlakeRegistry>();
+
+        if (!evalSettings.pureEval) {
+
+            auto registryUri = "file:///home/eelco/Dev/gists/nix-flakes/registry.json";
+
+            auto registryFile = getDownloader()->download(DownloadRequest(registryUri));
+
+            auto json = nlohmann::json::parse(*registryFile.data);
+
+            auto version = json.value("version", 0);
+            if (version != 1)
+                throw Error("flake registry '%s' has unsupported version %d", registryUri, version);
+
+            auto flakes = json["flakes"];
+            for (auto i = flakes.begin(); i != flakes.end(); ++i) {
+                FlakeRegistry::Entry entry;
+                entry.uri = i->value("uri", "");
+                if (entry.uri.empty())
+                    throw Error("invalid flake registry entry");
+                _flakeRegistry->entries.emplace(i.key(), entry);
+            }
+        }
+    });
+
+    return *_flakeRegistry;
+}
+
+static void prim_flakeRegistry(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    auto registry = state.getFlakeRegistry();
+
+    state.mkAttrs(v, registry.entries.size());
+
+    for (auto & entry : registry.entries) {
+        auto vEntry = state.allocAttr(v, entry.first);
+        state.mkAttrs(*vEntry, 2);
+        mkString(*state.allocAttr(*vEntry, state.symbols.create("uri")), entry.second.uri);
+        vEntry->attrs->sort();
+    }
+
+    v.attrs->sort();
+}
+
+static RegisterPrimOp r1("__flakeRegistry", 0, prim_flakeRegistry);
+
+struct Flake
+{
+    std::string name;
+    std::string description;
+    Path path;
+    std::set<std::string> requires;
+    Value * vProvides; // FIXME: gc
+};
+
+static Flake fetchFlake(EvalState & state, const std::string & flakeUri)
+{
+    Flake flake;
+
+    auto gitInfo = exportGit(state.store, flakeUri, {}, "", "source");
+
+    state.store->assertStorePath(gitInfo.storePath);
+
+    Value vInfo;
+    state.evalFile(gitInfo.storePath + "/flake.nix", vInfo);
+
+    state.forceAttrs(vInfo);
+
+    if (auto name = vInfo.attrs->get(state.sName))
+        flake.name = state.forceStringNoCtx(*(**name).value, *(**name).pos);
+    else
+        throw Error("flake lacks attribute 'name'");
+
+    if (auto description = vInfo.attrs->get(state.sDescription))
+        flake.description = state.forceStringNoCtx(*(**description).value, *(**description).pos);
+
+    if (auto requires = vInfo.attrs->get(state.symbols.create("requires"))) {
+        state.forceList(*(**requires).value, *(**requires).pos);
+        for (unsigned int n = 0; n < (**requires).value->listSize(); ++n)
+            flake.requires.insert(state.forceStringNoCtx(
+                    *(**requires).value->listElems()[n], *(**requires).pos));
+    }
+
+    if (auto provides = vInfo.attrs->get(state.symbols.create("provides"))) {
+        state.forceFunction(*(**provides).value, *(**provides).pos);
+        flake.vProvides = (**provides).value;
+    } else
+        throw Error("flake lacks attribute 'provides'");
+
+    return flake;
+}
+
+static std::map<std::string, Flake> resolveFlakes(EvalState & state, const StringSet & flakeUris)
+{
+    auto registry = state.getFlakeRegistry();
+
+    std::map<std::string, Flake> done;
+    std::queue<std::string> todo;
+    for (auto & i : flakeUris) todo.push(i);
+
+    while (!todo.empty()) {
+        auto flakeUri = todo.front();
+        todo.pop();
+        if (done.count(flakeUri)) continue;
+
+        auto flake = fetchFlake(state, flakeUri);
+
+        for (auto & require : flake.requires) {
+            auto i = registry.entries.find(require);
+            if (i == registry.entries.end())
+                throw Error("unknown flake '%s'", require);
+            todo.push(i->second.uri);
+        }
+
+        done.emplace(flake.name, flake);
+    }
+
+    return done;
+}
+
+static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Value & v)
+{
+    std::string flakeUri = state.forceStringNoCtx(*args[0], pos);
+
+    auto flakes = resolveFlakes(state, {flakeUri});
+
+    auto vResult = state.allocValue();
+
+    state.mkAttrs(*vResult, flakes.size());
+
+    for (auto & flake : flakes) {
+        auto vFlake = state.allocAttr(*vResult, flake.second.name);
+        state.mkAttrs(*vFlake, 2);
+        mkString(*state.allocAttr(*vFlake, state.sDescription), flake.second.description);
+        auto vProvides = state.allocAttr(*vFlake, state.symbols.create("provides"));
+        mkApp(*vProvides, *flake.second.vProvides, *vResult);
+        vFlake->attrs->sort();
+    }
+
+    vResult->attrs->sort();
+
+    v = *vResult;
+}
+
+static RegisterPrimOp r2("getFlake", 1, prim_getFlake);
+
+}