Rename 'epoch' -> 'edition'

doc/flakes/design.md

@@ -65,7 +65,7 @@ Upcoming but not yet implemented:
   NixOS configuration can be reproduced unambiguously from the top-level flake.
 
 * Nix code can query flake metadata such as `commitHash` (the Git revision) or
-  `epoch` (the date of the last commit). This is useful for NixOS to compute
+  `edition` (the date of the last commit). This is useful for NixOS to compute
   the NixOS version string (which will be the revision of the top-level
   configuration flake, uniquely identifying the configuration).
 
@@ -85,9 +85,9 @@ repository that provides a single package and a single NixOS module.
   # The flake identifier.
   name = "dwarffs";
 
-  # The epoch may be used in the future to determine how Nix
+  # The edition may be used in the future to determine how Nix
   # expressions inside this flake are to be parsed.
-  epoch = 201906;
+  edition = 201906;
 
   # Some other metadata.
   description = "A filesystem that fetches DWARF debug info from the Internet on demand";
@@ -162,7 +162,7 @@ Similarly, a minimal `flake.nix` for Nixpkgs:
 {
   name = "nixpkgs";
 
-  epoch = 201906;
+  edition = 201906;
 
   description = "A collection of packages for the Nix package manager";
 
@@ -449,7 +449,7 @@ flakes in (local) Git repositories.
 {
   name = "my-system";
 
-  epoch = 201906;
+  edition = 201906;
 
   inputs =
     [ "nixpkgs/nixos-18.09"

src/libexpr/flake/flake.cc

@@ -223,16 +223,21 @@ Flake getFlake(EvalState & state, const FlakeRef & flakeRef)
 
     state.forceAttrs(vInfo);
 
-    auto sEpoch = state.symbols.create("epoch");
+    auto sEdition = state.symbols.create("edition");
+    auto sEpoch = state.symbols.create("epoch"); // FIXME: remove soon
 
-    if (auto epoch = vInfo.attrs->get(sEpoch)) {
-        flake.epoch = state.forceInt(*(**epoch).value, *(**epoch).pos);
-        if (flake.epoch < 201906)
-            throw Error("flake '%s' has illegal epoch %d", flakeRef, flake.epoch);
-        if (flake.epoch > 201906)
-            throw Error("flake '%s' requires unsupported epoch %d; please upgrade Nix", flakeRef, flake.epoch);
+    auto edition = vInfo.attrs->get(sEdition);
+    if (!edition)
+        edition = vInfo.attrs->get(sEpoch);
+
+    if (edition) {
+        flake.edition = state.forceInt(*(**edition).value, *(**edition).pos);
+        if (flake.edition < 201906)
+            throw Error("flake '%s' has illegal edition %d", flakeRef, flake.edition);
+        if (flake.edition > 201906)
+            throw Error("flake '%s' requires unsupported edition %d; please upgrade Nix", flakeRef, flake.edition);
     } else
-        throw Error("flake '%s' lacks attribute 'epoch'", flakeRef);
+        throw Error("flake '%s' lacks attribute 'edition'", flakeRef);
 
     if (auto name = vInfo.attrs->get(state.sName))
         flake.id = state.forceStringNoCtx(*(**name).value, *(**name).pos);
@@ -271,7 +276,8 @@ Flake getFlake(EvalState & state, const FlakeRef & flakeRef)
         throw Error("flake '%s' lacks attribute 'outputs'", flakeRef);
 
     for (auto & attr : *vInfo.attrs) {
-        if (attr.name != sEpoch &&
+        if (attr.name != sEdition &&
+            attr.name != sEpoch &&
             attr.name != state.sName &&
             attr.name != state.sDescription &&
             attr.name != sInputs &&

src/libexpr/flake/flake.hh

@@ -67,7 +67,7 @@ struct Flake
     std::vector<FlakeRef> inputs;
     std::map<FlakeAlias, FlakeRef> nonFlakeInputs;
     Value * vOutputs; // FIXME: gc
-    unsigned int epoch;
+    unsigned int edition;
 
     Flake(const FlakeRef & origRef, const SourceInfo & sourceInfo)
         : originalRef(origRef), sourceInfo(sourceInfo) {};

src/nix/flake.cc

@@ -105,7 +105,7 @@ static void printFlakeInfo(const Flake & flake)
 {
     std::cout << fmt("ID:            %s\n", flake.id);
     std::cout << fmt("Description:   %s\n", flake.description);
-    std::cout << fmt("Epoch:         %s\n", flake.epoch);
+    std::cout << fmt("Edition:       %s\n", flake.edition);
     printSourceInfo(flake.sourceInfo);
 }
 
@@ -114,7 +114,7 @@ static nlohmann::json flakeToJson(const Flake & flake)
     nlohmann::json j;
     j["id"] = flake.id;
     j["description"] = flake.description;
-    j["epoch"] = flake.epoch;
+    j["edition"] = flake.edition;
     sourceInfoToJson(flake.sourceInfo, j);
     return j;
 }