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+# Nix language version history
+
+The Nix language (“Nix”) has its own versioning mechanism independent from its
+most popular implementation (“C++ Nix”): `builtins.langVersion`. It has been
+increased whenever the language has changed syntactically or semantically in a
+way that would not be introspectable otherwise. In particular, this does not
+include addition (or removal) of `builtins`, as this can be introspected using
+standard attribute set operations.
+
+Changes to `builtins.langVersion` are best found by viewing the git history of
+C++ Nix using `git log -G 'mkInt\\(v, [0-9]\\)'` for `builtins.langVersion` < 7.
+After that point `git log -G 'v\\.mkInt\\([0-9]+\\)'` should work. To reduce the
+amount of false positives, specify the version number you are interested in
+explicitly.
+
+## 1
+
+The first version of the Nix language is its state at the point when
+`builtins.langVersion` was added in [8b8ee53] which was first released
+as part of C++ Nix 1.2.
+
+## 2
+
+Nix version 2 changed the behavior of `builtins.storePath`: It would now [try to
+substitute the given path if missing][storePath-substitute], instead of creating
+an evaluation failure. `builtins.langVersion` was increased in [e36229d].
+
+## 3
+
+Nix version 3 changed the behavior of the `==` behavior. Strings would now be
+considered [equal even if they had differing string context][equal-no-ctx].
+
+## 4
+
+Nix version 4 [added the float type][float] to the language.
+
+## 5
+
+The [increase of `builtins.langVersion` to 5][langVersion-5] did not signify a
+language change, but added support for structured attributes to the Nix daemon.
+Eelco Dolstra writes as to what changed:
+
+> The structured attributes support. Unfortunately that's not so much a language
+> change as a build.cc (i.e. daemon) change, but we don't really have a way to
+> express that...
+
+Probably `builtins.nixVersion` (which was added in version 1) should have been
+used instead.
+
+## 6
+
+Nix version 6 added support for [comparing two lists][list-comparison].
+
+[8b8ee53]: https://github.com/nixos/nix/commit/8b8ee53bc73769bb25d967ba259dabc9b23e2e6f
+[storePath-substitute]: https://github.com/nixos/nix/commit/22d665019a3770148929b7504c73bcdbe025ec12
+[e36229d]: https://github.com/nixos/nix/commit/e36229d27f9ab508e0abf1892f3e8c263d2f8c58
+[equal-no-ctx]: https://github.com/nixos/nix/commit/ee7fe64c0ac00f2be11604a2a6509eb86dc19f0a
+[float]: https://github.com/nixos/nix/commit/14ebde52893263930cdcde1406cc91cc5c42556f
+[langVersion-5]: https://github.com/nixos/nix/commit/8191992c83bf4387b03c5fdaba818dc2b520462d
+[list-comparison]: https://github.com/nixos/nix/commit/09471d2680292af48b2788108de56a8da755d661