diff options
| -rw-r--r-- | doc/manual/rl-next/nixversion-fake.md | 14 | ||||
| -rw-r--r-- | src/libexpr/primops.cc | 29 |
2 files changed, 29 insertions, 14 deletions
diff --git a/doc/manual/rl-next/nixversion-fake.md b/doc/manual/rl-next/nixversion-fake.md index 93f75611d..725b8e609 100644 --- a/doc/manual/rl-next/nixversion-fake.md +++ b/doc/manual/rl-next/nixversion-fake.md @@ -1,13 +1,17 @@ --- -synopsis: "`builtins.nixVersion` now returns a fixed value \"2.18.3-lix\"" -cls: 558 +synopsis: "`builtins.nixVersion` and `builtins.langVersion` return fixed values" +cls: [558, 1144] credits: jade category: Breaking Changes --- -`builtins.nixVersion` now returns a fixed value `"2.18.3-lix"`. This prevents -feature detection assuming that features that exist in Nix post-Lix-branch-off -might exist, even though the Lix version is greater than the Nix version. +`builtins.nixVersion` now returns a fixed value `"2.18.3-lix"`. + +`builtins.langVersion` returns a fixed value `6`, matching CppNix 2.18. + +This prevents feature detection assuming that features that exist in Nix +post-Lix-branch-off might exist, even though the Lix version is greater than +the Nix version. In the future, check for builtins for feature detection. If a feature cannot be detected by *those* means, please file a Lix bug. diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index 33a2688f1..e36b800c3 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -4355,10 +4355,13 @@ void EvalState::createBaseEnv() .doc = R"( Legacy version of Nix. Always returns "2.18.3-lix" on Lix. - To determine if features exist, Nix scripts should instead use direct - means of feature detection, such as checking for existence of - builtins they want to use. Doing so allows for much better compatibility - across implementations. + Code in the Nix language should use other means of feature detection + like detecting the presence of builtins, rather than trying to find + the version of the Nix implementation, as there may be other Nix + implementations with different feature combinations. + + If the feature you want to write compatibility code for cannot be + detected by any means, please file a Lix bug. )", }); @@ -4377,15 +4380,23 @@ void EvalState::createBaseEnv() )", }); - /* Language version. This should be increased every time a new - language feature gets added. It's not necessary to increase it - when primops get added, because you can just use `builtins ? - primOp' to check. */ + /* Legacy language version. + * This is fixed at 6, and will never change in the future on Lix. + * A better language versioning construct needs to be built instead. */ v.mkInt(6); addConstant("__langVersion", v, { .type = nInt, .doc = R"( - The current version of the Nix language. + The legacy version of the Nix language. Always is `6` on Lix, + matching Nix 2.18. + + Code in the Nix language should use other means of feature detection + like detecting the presence of builtins, rather than trying to find + the version of the Nix implementation, as there may be other Nix + implementations with different feature combinations. + + If the feature you want to write compatibility code for cannot be + detected by any means, please file a Lix bug. )", }); |