diff --git a/flake.nix b/flake.nix
index ab316c7c6..20ad2bc7e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -14,13 +14,22 @@
       nixpkgs = deps.nixpkgs;
     };
 
-    packages.nix = hydraJobs.build.x86_64-linux;
+    checks = {
+      binaryTarball = hydraJobs.binaryTarball.x86_64-linux;
+      perlBindings = hydraJobs.perlBindings.x86_64-linux;
+      inherit (hydraJobs.tests) remoteBuilds nix-copy-closure;
+      setuid = hydraJobs.tests.setuid.x86_64-linux;
+    };
+
+    packages = {
+      nix = hydraJobs.build.x86_64-linux;
+      nix-perl-bindings = hydraJobs.perlBindings.x86_64-linux;
+    };
 
     defaultPackage = packages.nix;
 
     devShell = import ./shell.nix {
       nixpkgs = deps.nixpkgs;
     };
-
   };
 }
diff --git a/shell.nix b/shell.nix
index 228a6685b..d7e63bad3 100644
--- a/shell.nix
+++ b/shell.nix
@@ -2,7 +2,7 @@
 , nixpkgs ? builtins.fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-19.03.tar.gz
 }:
 
-with import (builtins.fetchTarball https://github.com/NixOS/nixpkgs-channels/archive/nixos-19.03.tar.gz) { system = builtins.currentSystem or "x86_64-linux"; };
+with import nixpkgs { system = builtins.currentSystem or "x86_64-linux"; };
 
 with import ./release-common.nix { inherit pkgs; };
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 1e45bc1a8..46c6ea271 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -17,7 +17,10 @@ namespace nix {
 class Store;
 class EvalState;
 enum RepairFlag : bool;
+
+namespace flake {
 struct FlakeRegistry;
+}
 
 
 typedef void (* PrimOpFun) (EvalState & state, const Pos & pos, Value * * args, Value & v);
@@ -323,12 +326,12 @@ private:
 
 public:
 
-    const std::vector<std::shared_ptr<FlakeRegistry>> getFlakeRegistries();
+    const std::vector<std::shared_ptr<flake::FlakeRegistry>> getFlakeRegistries();
 
-    std::shared_ptr<FlakeRegistry> getGlobalFlakeRegistry();
+    std::shared_ptr<flake::FlakeRegistry> getGlobalFlakeRegistry();
 
 private:
-    std::shared_ptr<FlakeRegistry> _globalFlakeRegistry;
+    std::shared_ptr<flake::FlakeRegistry> _globalFlakeRegistry;
     std::once_flag _globalFlakeRegistryInit;
 };
 
diff --git a/src/libexpr/primops/flake.cc b/src/libexpr/primops/flake.cc
index 257b81887..0d762f2a1 100644
--- a/src/libexpr/primops/flake.cc
+++ b/src/libexpr/primops/flake.cc
@@ -14,6 +14,10 @@
 
 namespace nix {
 
+using namespace flake;
+
+namespace flake {
+
 /* Read a registry. */
 std::shared_ptr<FlakeRegistry> readRegistry(const Path & path)
 {
@@ -133,24 +137,6 @@ void writeLockFile(const LockFile & lockFile, const Path & path)
     writeFile(path, json.dump(4) + "\n"); // '4' = indentation in json file
 }
 
-std::shared_ptr<FlakeRegistry> EvalState::getGlobalFlakeRegistry()
-{
-    std::call_once(_globalFlakeRegistryInit, [&]() {
-        auto path = evalSettings.flakeRegistry;
-
-        if (!hasPrefix(path, "/")) {
-            CachedDownloadRequest request(evalSettings.flakeRegistry);
-            request.name = "flake-registry.json";
-            request.gcRoot = true;
-            path = getDownloader()->downloadCached(store, request).path;
-        }
-
-        _globalFlakeRegistry = readRegistry(path);
-    });
-
-    return _globalFlakeRegistry;
-}
-
 Path getUserRegistryPath()
 {
     return getHome() + "/.config/nix/registry.json";
@@ -170,17 +156,6 @@ std::shared_ptr<FlakeRegistry> getFlagRegistry(RegistryOverrides registryOverrid
     return flagRegistry;
 }
 
-// This always returns a vector with flakeReg, userReg, globalReg.
-// If one of them doesn't exist, the registry is left empty but does exist.
-const Registries EvalState::getFlakeRegistries()
-{
-    Registries registries;
-    registries.push_back(getFlagRegistry(registryOverrides));
-    registries.push_back(getUserRegistry());
-    registries.push_back(getGlobalFlakeRegistry());
-    return registries;
-}
-
 static FlakeRef lookupFlake(EvalState & state, const FlakeRef & flakeRef, const Registries & registries,
     std::vector<FlakeRef> pastSearches = {});
 
@@ -327,7 +302,9 @@ Flake getFlake(EvalState & state, const FlakeRef & flakeRef, bool impureIsAllowe
 
     state.forceAttrs(vInfo);
 
-    if (auto epoch = vInfo.attrs->get(state.symbols.create("epoch"))) {
+    auto sEpoch = state.symbols.create("epoch");
+
+    if (auto epoch = vInfo.attrs->get(sEpoch)) {
         flake.epoch = state.forceInt(*(**epoch).value, *(**epoch).pos);
         if (flake.epoch > 2019)
             throw Error("flake '%s' requires unsupported epoch %d; please upgrade Nix", flakeRef, flake.epoch);
@@ -342,14 +319,18 @@ Flake getFlake(EvalState & state, const FlakeRef & flakeRef, bool impureIsAllowe
     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"))) {
+    auto sRequires = state.symbols.create("requires");
+
+    if (auto requires = vInfo.attrs->get(sRequires)) {
         state.forceList(*(**requires).value, *(**requires).pos);
         for (unsigned int n = 0; n < (**requires).value->listSize(); ++n)
             flake.requires.push_back(FlakeRef(state.forceStringNoCtx(
                 *(**requires).value->listElems()[n], *(**requires).pos)));
     }
 
-    if (std::optional<Attr *> nonFlakeRequires = vInfo.attrs->get(state.symbols.create("nonFlakeRequires"))) {
+    auto sNonFlakeRequires = state.symbols.create("nonFlakeRequires");
+
+    if (std::optional<Attr *> nonFlakeRequires = vInfo.attrs->get(sNonFlakeRequires)) {
         state.forceAttrs(*(**nonFlakeRequires).value, *(**nonFlakeRequires).pos);
         for (Attr attr : *(*(**nonFlakeRequires).value).attrs) {
             std::string myNonFlakeUri = state.forceStringNoCtx(*attr.value, *attr.pos);
@@ -358,12 +339,25 @@ Flake getFlake(EvalState & state, const FlakeRef & flakeRef, bool impureIsAllowe
         }
     }
 
-    if (auto provides = vInfo.attrs->get(state.symbols.create("provides"))) {
+    auto sProvides = state.symbols.create("provides");
+
+    if (auto provides = vInfo.attrs->get(sProvides)) {
         state.forceFunction(*(**provides).value, *(**provides).pos);
         flake.vProvides = (**provides).value;
     } else
         throw Error("flake '%s' lacks attribute 'provides'", flakeRef);
 
+    for (auto & attr : *vInfo.attrs) {
+        if (attr.name != sEpoch &&
+            attr.name != state.sName &&
+            attr.name != state.sDescription &&
+            attr.name != sRequires &&
+            attr.name != sNonFlakeRequires &&
+            attr.name != sProvides)
+            throw Error("flake '%s' has an unsupported attribute '%s', at %s",
+                flakeRef, attr.name, *attr.pos);
+    }
+
     return flake;
 }
 
@@ -572,18 +566,11 @@ void callFlake(EvalState & state, const ResolvedFlake & resFlake, Value & v)
     v.attrs->sort();
 }
 
-// Return the `provides` of the top flake, while assigning to `v` the provides
-// of the dependencies as well.
-void makeFlakeValue(EvalState & state, const FlakeRef & flakeRef, HandleLockFile handle, Value & v)
-{
-    callFlake(state, resolveFlake(state, flakeRef, handle), v);
-}
-
 // This function is exposed to be used in nix files.
 static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
-    makeFlakeValue(state, state.forceStringNoCtx(*args[0], pos),
-        evalSettings.pureEval ? AllPure : UseUpdatedLockFile, v);
+    callFlake(state, resolveFlake(state, state.forceStringNoCtx(*args[0], pos),
+            evalSettings.pureEval ? AllPure : UseUpdatedLockFile), v);
 }
 
 static RegisterPrimOp r2("getFlake", 1, prim_getFlake);
@@ -618,3 +605,34 @@ void gitCloneFlake(FlakeRef flakeRef, EvalState & state, Registries registries,
 }
 
 }
+
+std::shared_ptr<flake::FlakeRegistry> EvalState::getGlobalFlakeRegistry()
+{
+    std::call_once(_globalFlakeRegistryInit, [&]() {
+        auto path = evalSettings.flakeRegistry;
+
+        if (!hasPrefix(path, "/")) {
+            CachedDownloadRequest request(evalSettings.flakeRegistry);
+            request.name = "flake-registry.json";
+            request.gcRoot = true;
+            path = getDownloader()->downloadCached(store, request).path;
+        }
+
+        _globalFlakeRegistry = readRegistry(path);
+    });
+
+    return _globalFlakeRegistry;
+}
+
+// This always returns a vector with flakeReg, userReg, globalReg.
+// If one of them doesn't exist, the registry is left empty but does exist.
+const Registries EvalState::getFlakeRegistries()
+{
+    Registries registries;
+    registries.push_back(getFlagRegistry(registryOverrides));
+    registries.push_back(getUserRegistry());
+    registries.push_back(getGlobalFlakeRegistry());
+    return registries;
+}
+
+}
diff --git a/src/libexpr/primops/flake.hh b/src/libexpr/primops/flake.hh
index 0e2706e32..340b97c65 100644
--- a/src/libexpr/primops/flake.hh
+++ b/src/libexpr/primops/flake.hh
@@ -5,13 +5,15 @@
 
 namespace nix {
 
+struct Value;
+class EvalState;
+
+namespace flake {
+
 static const size_t FLAG_REGISTRY = 0;
 static const size_t USER_REGISTRY = 1;
 static const size_t GLOBAL_REGISTRY = 2;
 
-struct Value;
-class EvalState;
-
 struct FlakeRegistry
 {
     std::map<FlakeRef, FlakeRef> entries;
@@ -73,8 +75,6 @@ enum HandleLockFile : unsigned int
     , UseNewLockFile // `RecreateLockFile` without writing to file
     };
 
-void makeFlakeValue(EvalState &, const FlakeRef &, HandleLockFile, Value &);
-
 std::shared_ptr<FlakeRegistry> readRegistry(const Path &);
 
 void writeRegistry(const FlakeRegistry &, const Path &);
@@ -143,3 +143,5 @@ void updateLockFile(EvalState &, const FlakeRef & flakeRef, bool recreateLockFil
 void gitCloneFlake(FlakeRef flakeRef, EvalState &, Registries, const Path & destDir);
 
 }
+
+}
diff --git a/src/nix/command.hh b/src/nix/command.hh
index a841b879a..26c308331 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -12,7 +12,10 @@ struct Value;
 class Bindings;
 class EvalState;
 class Store;
+
+namespace flake {
 enum HandleLockFile : unsigned int;
+}
 
 /* A command that require a Nix store. */
 struct StoreCommand : virtual Command
@@ -71,7 +74,7 @@ struct MixFlakeOptions : virtual Args
 
     MixFlakeOptions();
 
-    HandleLockFile getLockFileMode();
+    flake::HandleLockFile getLockFileMode();
 };
 
 struct SourceExprCommand : virtual Args, EvalCommand, MixFlakeOptions
diff --git a/src/nix/flake.cc b/src/nix/flake.cc
index 7836f0cfe..872ec2849 100644
--- a/src/nix/flake.cc
+++ b/src/nix/flake.cc
@@ -3,13 +3,17 @@
 #include "shared.hh"
 #include "progress-bar.hh"
 #include "eval.hh"
+#include "eval-inline.hh"
 #include "primops/flake.hh"
+#include "get-drvs.hh"
+#include "store-api.hh"
 
 #include <nlohmann/json.hpp>
 #include <queue>
 #include <iomanip>
 
 using namespace nix;
+using namespace nix::flake;
 
 class FlakeCommand : virtual Args, public EvalCommand, public MixFlakeOptions
 {
@@ -33,12 +37,12 @@ public:
     Flake getFlake()
     {
         auto evalState = getEvalState();
-        return nix::getFlake(*evalState, getFlakeRef(), useRegistries);
+        return flake::getFlake(*evalState, getFlakeRef(), useRegistries);
     }
 
     ResolvedFlake resolveFlake()
     {
-        return nix::resolveFlake(*getEvalState(), getFlakeRef(), getLockFileMode());
+        return flake::resolveFlake(*getEvalState(), getFlakeRef(), getLockFileMode());
     }
 };
 
@@ -195,6 +199,19 @@ struct CmdFlakeUpdate : FlakeCommand
     }
 };
 
+static void enumerateProvides(EvalState & state, Value & vFlake,
+    std::function<void(const std::string & name, Value & vProvide)> callback)
+{
+    state.forceAttrs(vFlake);
+
+    auto vProvides = (*vFlake.attrs->get(state.symbols.create("provides")))->value;
+
+    state.forceAttrs(*vProvides);
+
+    for (auto & attr : *vProvides->attrs)
+        callback(attr.name, *attr.value);
+}
+
 struct CmdFlakeInfo : FlakeCommand, MixJSON
 {
     std::string name() override
@@ -207,19 +224,133 @@ struct CmdFlakeInfo : FlakeCommand, MixJSON
         return "list info about a given flake";
     }
 
-    CmdFlakeInfo () { }
-
     void run(nix::ref<nix::Store> store) override
     {
         auto flake = getFlake();
         stopProgressBar();
-        if (json)
-            std::cout << flakeToJson(flake).dump() << std::endl;
-        else
+
+        if (json) {
+            auto json = flakeToJson(flake);
+
+            auto state = getEvalState();
+
+            auto vFlake = state->allocValue();
+            flake::callFlake(*state, flake, *vFlake);
+
+            auto provides = nlohmann::json::object();
+
+            enumerateProvides(*state,
+                *vFlake,
+                [&](const std::string & name, Value & vProvide) {
+                    auto provide = nlohmann::json::object();
+
+                    if (name == "checks" || name == "packages") {
+                        state->forceAttrs(vProvide);
+                        for (auto & aCheck : *vProvide.attrs)
+                            provide[aCheck.name] = nlohmann::json::object();
+                    }
+
+                    provides[name] = provide;
+                });
+
+            json["provides"] = std::move(provides);
+
+            std::cout << json.dump() << std::endl;
+        } else
             printFlakeInfo(flake);
     }
 };
 
+struct CmdFlakeCheck : FlakeCommand, MixJSON
+{
+    bool build = true;
+
+    CmdFlakeCheck()
+    {
+        mkFlag()
+            .longName("no-build")
+            .description("do not build checks")
+            .set(&build, false);
+    }
+
+    std::string name() override
+    {
+        return "check";
+    }
+
+    std::string description() override
+    {
+        return "check whether the flake evaluates and run its tests";
+    }
+
+    void run(nix::ref<nix::Store> store) override
+    {
+        settings.readOnlyMode = !build;
+
+        auto state = getEvalState();
+        auto flake = resolveFlake();
+
+        auto checkDerivation = [&](const std::string & attrPath, Value & v) {
+            try {
+                auto drvInfo = getDerivation(*state, v, false);
+                if (!drvInfo)
+                    throw Error("flake attribute '%s' is not a derivation", attrPath);
+                // FIXME: check meta attributes
+                return drvInfo->queryDrvPath();
+            } catch (Error & e) {
+                e.addPrefix(fmt("while checking flake attribute '" ANSI_BOLD "%s" ANSI_NORMAL "':\n", attrPath));
+                throw;
+            }
+        };
+
+        PathSet drvPaths;
+
+        {
+            Activity act(*logger, lvlInfo, actUnknown, "evaluating flake");
+
+            auto vFlake = state->allocValue();
+            flake::callFlake(*state, flake, *vFlake);
+
+            enumerateProvides(*state,
+                *vFlake,
+                [&](const std::string & name, Value & vProvide) {
+                    Activity act(*logger, lvlChatty, actUnknown,
+                        fmt("checking flake output '%s'", name));
+
+                    try {
+                        state->forceValue(vProvide);
+
+                        if (name == "checks") {
+                            state->forceAttrs(vProvide);
+                            for (auto & aCheck : *vProvide.attrs)
+                                drvPaths.insert(checkDerivation(
+                                        name + "." + (std::string) aCheck.name, *aCheck.value));
+                        }
+
+                        else if (name == "packages") {
+                            state->forceAttrs(vProvide);
+                            for (auto & aCheck : *vProvide.attrs)
+                                checkDerivation(
+                                    name + "." + (std::string) aCheck.name, *aCheck.value);
+                        }
+
+                        else if (name == "defaultPackage" || name == "devShell")
+                            checkDerivation(name, vProvide);
+
+                    } catch (Error & e) {
+                        e.addPrefix(fmt("while checking flake output '" ANSI_BOLD "%s" ANSI_NORMAL "':\n", name));
+                        throw;
+                    }
+                });
+        }
+
+        if (build) {
+            Activity act(*logger, lvlInfo, actUnknown, "running flake checks");
+            store->buildPaths(drvPaths);
+        }
+    }
+};
+
 struct CmdFlakeAdd : MixEvalArgs, Command
 {
     FlakeUri alias;
@@ -386,6 +517,7 @@ struct CmdFlake : virtual MultiCommand, virtual Command
         : MultiCommand({make_ref<CmdFlakeList>()
             , make_ref<CmdFlakeUpdate>()
             , make_ref<CmdFlakeInfo>()
+            , make_ref<CmdFlakeCheck>()
             , make_ref<CmdFlakeDeps>()
             , make_ref<CmdFlakeAdd>()
             , make_ref<CmdFlakeRemove>()
diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 4f9161666..ea12cd79c 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -32,8 +32,9 @@ MixFlakeOptions::MixFlakeOptions()
         .set(&useRegistries, false);
 }
 
-HandleLockFile MixFlakeOptions::getLockFileMode()
+flake::HandleLockFile MixFlakeOptions::getLockFileMode()
 {
+    using namespace flake;
     return
         useRegistries
         ? recreateLockFile
@@ -163,18 +164,20 @@ struct InstallableAttrPath : InstallableValue
     }
 };
 
-void makeFlakeClosureGCRoot(Store & store, const FlakeRef & origFlakeRef, const ResolvedFlake & resFlake)
+void makeFlakeClosureGCRoot(Store & store,
+    const FlakeRef & origFlakeRef,
+    const flake::ResolvedFlake & resFlake)
 {
     if (std::get_if<FlakeRef::IsPath>(&origFlakeRef.data)) return;
 
     /* Get the store paths of all non-local flakes. */
     PathSet closure;
 
-    std::queue<std::reference_wrapper<const ResolvedFlake>> queue;
+    std::queue<std::reference_wrapper<const flake::ResolvedFlake>> queue;
     queue.push(resFlake);
 
     while (!queue.empty()) {
-        const ResolvedFlake & flake = queue.front();
+        const flake::ResolvedFlake & flake = queue.front();
         queue.pop();
         if (!std::get_if<FlakeRef::IsPath>(&flake.flake.sourceInfo.resolvedRef.data))
             closure.insert(flake.flake.sourceInfo.storePath);
@@ -233,9 +236,9 @@ struct InstallableFlake : InstallableValue
 
         auto emptyArgs = state.allocBindings(0);
 
-        // As a convenience, look for the attribute in
-        // 'provides.packages'.
         if (searchPackages) {
+            // As a convenience, look for the attribute in
+            // 'provides.packages'.
             if (auto aPackages = *vProvides->attrs->get(state.symbols.create("packages"))) {
                 try {
                     auto * v = findAlongAttrPath(state, *attrPaths.begin(), *emptyArgs, *aPackages->value);
@@ -244,6 +247,17 @@ struct InstallableFlake : InstallableValue
                 } catch (AttrPathNotFound & e) {
                 }
             }
+
+            // As a temporary hack until Nixpkgs is properly converted
+            // to provide a clean 'packages' set, look in 'legacyPackages'.
+            if (auto aPackages = *vProvides->attrs->get(state.symbols.create("legacyPackages"))) {
+                try {
+                    auto * v = findAlongAttrPath(state, *attrPaths.begin(), *emptyArgs, *aPackages->value);
+                    state.forceValue(*v);
+                    return v;
+                } catch (AttrPathNotFound & e) {
+                }
+            }
         }
 
         // Otherwise, look for it in 'provides'.