Merge "builtins: fix builtins.langVersion docs to state it's deprecated" into main
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commit
9322a1cbe7
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@ -1,13 +1,17 @@
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---
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synopsis: "`builtins.nixVersion` now returns a fixed value \"2.18.3-lix\""
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cls: 558
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synopsis: "`builtins.nixVersion` and `builtins.langVersion` return fixed values"
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cls: [558, 1144]
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credits: jade
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category: Breaking Changes
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---
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`builtins.nixVersion` now returns a fixed value `"2.18.3-lix"`. This prevents
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feature detection assuming that features that exist in Nix post-Lix-branch-off
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might exist, even though the Lix version is greater than the Nix version.
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`builtins.nixVersion` now returns a fixed value `"2.18.3-lix"`.
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`builtins.langVersion` returns a fixed value `6`, matching CppNix 2.18.
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This prevents feature detection assuming that features that exist in Nix
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post-Lix-branch-off might exist, even though the Lix version is greater than
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the Nix version.
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In the future, check for builtins for feature detection. If a feature cannot be
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detected by *those* means, please file a Lix bug.
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@ -4355,10 +4355,13 @@ void EvalState::createBaseEnv()
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.doc = R"(
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Legacy version of Nix. Always returns "2.18.3-lix" on Lix.
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To determine if features exist, Nix scripts should instead use direct
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means of feature detection, such as checking for existence of
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builtins they want to use. Doing so allows for much better compatibility
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across implementations.
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Code in the Nix language should use other means of feature detection
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like detecting the presence of builtins, rather than trying to find
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the version of the Nix implementation, as there may be other Nix
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implementations with different feature combinations.
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If the feature you want to write compatibility code for cannot be
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detected by any means, please file a Lix bug.
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)",
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});
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@ -4377,15 +4380,23 @@ void EvalState::createBaseEnv()
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)",
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});
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/* Language version. This should be increased every time a new
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language feature gets added. It's not necessary to increase it
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when primops get added, because you can just use `builtins ?
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primOp' to check. */
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/* Legacy language version.
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* This is fixed at 6, and will never change in the future on Lix.
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* A better language versioning construct needs to be built instead. */
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v.mkInt(6);
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addConstant("__langVersion", v, {
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.type = nInt,
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.doc = R"(
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The current version of the Nix language.
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The legacy version of the Nix language. Always is `6` on Lix,
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matching Nix 2.18.
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Code in the Nix language should use other means of feature detection
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like detecting the presence of builtins, rather than trying to find
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the version of the Nix implementation, as there may be other Nix
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implementations with different feature combinations.
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If the feature you want to write compatibility code for cannot be
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detected by any means, please file a Lix bug.
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)",
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});
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