Remove flake 'edition' field

Future editions of flakes or the Nix language can be supported by
renaming flake.nix (e.g. flake-v2.nix). This avoids a bootstrap
problem where we don't know which grammar to use to parse
flake*.nix. It also allows a project to support multiple flake
editions, in theory.

flake.nix

@@ -1,7 +1,7 @@
 {
   description = "The purely functional package manager";
 
-  edition = 201909;
+  edition = 201909; # FIXME: remove
 
   inputs.nixpkgs.uri = "nixpkgs/nixos-20.03-small";
 

src/libexpr/flake/call-flake.nix

@@ -19,7 +19,6 @@ let
           result = outputs // sourceInfo // { inherit inputs; inherit outputs; inherit sourceInfo; };
         in
           if node.flake or true then
-            assert flake.edition or flake.epoch or 0 == 201909;
             assert builtins.isFunction flake.outputs;
             result
           else

src/libexpr/flake/flake.cc

@@ -231,22 +231,14 @@ static Flake getFlake(
 
     expectType(state, tAttrs, vInfo, Pos(state.symbols.create(flakeFile), 0, 0));
 
-    auto sEdition = state.symbols.create("edition");
+    auto sEdition = state.symbols.create("edition"); // FIXME: remove soon
     auto sEpoch = state.symbols.create("epoch"); // FIXME: remove soon
 
-    auto edition = vInfo.attrs->get(sEdition);
-    if (!edition)
-        edition = vInfo.attrs->get(sEpoch);
-
-    if (edition) {
-        expectType(state, tInt, *edition->value, *edition->pos);
-        flake.edition = edition->value->integer;
-        if (flake.edition > 201909)
-            throw Error("flake '%s' requires unsupported edition %d; please upgrade Nix", lockedRef, flake.edition);
-        if (flake.edition < 201909)
-            throw Error("flake '%s' has illegal edition %d", lockedRef, flake.edition);
-    } else
-        throw Error("flake '%s' lacks attribute 'edition'", lockedRef);
+    if (vInfo.attrs->get(sEdition))
+        warn("flake '%s' has deprecated attribution 'edition'", lockedRef);
+
+    if (vInfo.attrs->get(sEpoch))
+        warn("flake '%s' has deprecated attribution 'epoch'", lockedRef);
 
     if (auto description = vInfo.attrs->get(state.sDescription)) {
         expectType(state, tString, *description->value, *description->pos);

src/libexpr/flake/flake.hh

@@ -34,7 +34,6 @@ struct Flake
     std::shared_ptr<const fetchers::Tree> sourceInfo;
     FlakeInputs inputs;
     Value * vOutputs; // FIXME: gc
-    unsigned int edition;
     ~Flake();
 };
 

src/nix/flake-template.nix

@@ -1,8 +1,6 @@
 {
   description = "A flake for building Hello World";
 
-  edition = 201909;
-
   outputs = { self, nixpkgs }: {
 
     packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hello;

src/nix/flake.cc

@@ -82,7 +82,6 @@ static void printFlakeInfo(const Store & store, const Flake & flake)
 {
     std::cout << fmt("Resolved URL:  %s\n", flake.resolvedRef.to_string());
     std::cout << fmt("Locked URL:    %s\n", flake.lockedRef.to_string());
-    std::cout << fmt("Edition:       %s\n", flake.edition);
     if (flake.description)
         std::cout << fmt("Description:   %s\n", *flake.description);
     std::cout << fmt("Path:          %s\n", store.printStorePath(flake.sourceInfo->storePath));
@@ -100,7 +99,6 @@ static nlohmann::json flakeToJson(const Store & store, const Flake & flake)
     nlohmann::json j;
     if (flake.description)
         j["description"] = *flake.description;
-    j["edition"] = flake.edition;
     j["originalUrl"] = flake.originalRef.to_string();
     j["original"] = attrsToJson(flake.originalRef.toAttrs());
     j["resolvedUrl"] = flake.resolvedRef.to_string();

tests/flakes.sh

@@ -35,8 +35,6 @@ done
 
 cat > $flake1Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   description = "Bla bla";
 
   outputs = inputs: rec {
@@ -55,8 +53,6 @@ git -C $flake1Dir commit -m 'Initial'
 
 cat > $flake2Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   description = "Fnord";
 
   outputs = { self, flake1 }: rec {
@@ -70,8 +66,6 @@ git -C $flake2Dir commit -m 'Initial'
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   description = "Fnord";
 
   outputs = { self, flake2 }: rec {
@@ -246,8 +240,6 @@ rm $flake3Dir/flake.nix
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   description = "Fnord";
 
   outputs = { self, flake1, flake2 }: rec {
@@ -271,10 +263,6 @@ git -C $flake3Dir add flake.lock
 
 git -C $flake3Dir commit -m 'Add lockfile'
 
-# Unsupported editions should be an error.
-sed -i $flake3Dir/flake.nix -e s/201909/201912/
-nix build -o $TEST_ROOT/result $flake3Dir#sth 2>&1 | grep 'unsupported edition'
-
 # Test whether registry caching works.
 nix flake list --flake-registry file://$registry | grep -q flake3
 mv $registry $registry.tmp
@@ -300,8 +288,6 @@ rm $flake3Dir/flake.nix
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs = {
     flake1 = {};
     flake2 = {};
@@ -370,8 +356,6 @@ rm $flake3Dir/flake.nix
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs = {
     nonFlake = {
       url = "$nonFlakeDir";
@@ -428,8 +412,6 @@ nix flake clone flake1 --dest $TEST_ROOT/flake1-v2
 # More 'nix flake check' tests.
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { flake1, self }: {
     overlay = final: prev: {
     };
@@ -441,8 +423,6 @@ nix flake check $flake3Dir
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { flake1, self }: {
     overlay = finalll: prev: {
     };
@@ -454,8 +434,6 @@ EOF
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { flake1, self }: {
     nixosModules.foo = {
       a.b.c = 123;
@@ -469,8 +447,6 @@ nix flake check $flake3Dir
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { flake1, self }: {
     nixosModules.foo = {
       a.b.c = 123;
@@ -484,8 +460,6 @@ EOF
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { flake1, self }: {
     nixosModule = { config, pkgs, ... }: {
       a.b.c = 123;
@@ -498,8 +472,6 @@ nix flake check $flake3Dir
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { flake1, self }: {
     nixosModule = { config, pkgs }: {
       a.b.c = 123;
@@ -513,8 +485,6 @@ EOF
 # Test 'follows' inputs.
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.foo = {
     type = "indirect";
     id = "flake1";
@@ -531,8 +501,6 @@ nix flake update $flake3Dir
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.bar.follows = "flake2/flake1";
 
   outputs = { self, flake2, bar }: {
@@ -545,8 +513,6 @@ nix flake update $flake3Dir
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.bar.follows = "flake2";
 
   outputs = { self, flake2, bar }: {
@@ -560,8 +526,6 @@ nix flake update $flake3Dir
 # Test overriding inputs of inputs.
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.flake2.inputs.flake1 = {
     type = "git";
     url = file://$flake7Dir;
@@ -577,8 +541,6 @@ nix flake update $flake3Dir
 
 cat > $flake3Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.flake2.inputs.flake1.follows = "foo";
   inputs.foo.url = git+file://$flake7Dir;
 
@@ -596,8 +558,6 @@ hg init $flake5Dir
 
 cat > $flake5Dir/flake.nix <<EOF
 {
-  edition = 201909;
-
   outputs = { self, flake1 }: {
     defaultPackage.$system = flake1.defaultPackage.$system;
 
@@ -669,8 +629,6 @@ nix flake list-inputs $flake3Dir --json | jq .
 # Test circular flake dependencies.
 cat > $flakeA/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.b.url = git+file://$flakeB;
   inputs.b.inputs.a.follows = "/";
 
@@ -685,8 +643,6 @@ git -C $flakeA add flake.nix
 
 cat > $flakeB/flake.nix <<EOF
 {
-  edition = 201909;
-
   inputs.a.url = git+file://$flakeA;
 
   outputs = { self, nixpkgs, a }: {