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lix/doc/manual/rl-next/deprecated-features.md
piegames 7c76053d93 libexpr: Undeprecate overriding __nixPath 
It being overridable was an intended feature with good use cases, and
should not have been removed. However, this feature is generally in a
bad state and needs revisiting in the future.

Fixup for 81d5f0a7d9
Fixes #599

Change-Id: I2d93e012caa65aa795bce3a71d8e56d7052ef9df
2024-12-10 19:02:41 +01:00

1.6 KiB
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Deprecated language features
fj#437
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Breaking Changes
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A system for deprecation (and then the planned removal) of undesired language features has been put into place. It is controlled via feature flags much like experimental features, except that the deprecations are enabled default, and can be disabled via the flags for backwards compatibility (opt-out with --extra-deprecated-features or the Nix configuration file).

  • url-literals: URL literals have long been obsolete and discouraged of use, and now they are officially deprecated. This means that all URLs must be properly put within quotes like all other strings.
  • rec-set-overrides: __overrides is an old arcane syntax which has not been in use for more than a decade. It is soft-deprecated with a warning only, with the plan to turn that into an error in a future release.
  • ancient-let: The old let syntax (let { body = …; … }) is soft-deprecated with a warning as well. Use the regular let … in instead.
  • shadow-internal-symbols: Arithmetic expressions like 5 - 3 internally expand to __sub 5 3, where __sub maps to a subtraction builtin. Shadowing such a symbols would affect the evaluation of such operations, but in a very inconsistent way, and is therefore deprecated now. Affected symbols are: __sub, __mul, __div, __lessThan, and __findFile. Note that these symbols may still be used as variable names as long as they do not shadow internal operations, so e.g. let __sub = x: y: x + y; in __sub 3 5 remains valid code.