elvish/0.17.0-release-notes.md

This is the draft release notes for 0.17.0, scheduled to be released on 2022-01-01.

Breaking changes

• Attempting to assign to a read-only variable (e.g. set nil = x) is now a compile-time error rather than an exception.

Deprecated features

Deprecated features will be removed in 0.18.0.

The following deprecated features trigger a warning whenever the code is parsed or compiled, even if it is not executed:

• The dir-history command is deprecated. Use store:dirs instead.

• The legacy assignment form is deprecated. Depending on whether the left-hand variable already exists or not, use var or set instead. Use the upgrader to migrate scripts.

• The lambda syntax that declares arguments and options within [] before { has been deprecated. The new syntax now declares arguments and options within a pair of |, after {. Use the upgrader to migrate scripts. See (#664).

• Use of the special namespace local: is deprecated.

  • If you are using local: to reference variables (e.g. echo $local:x), local: is never necessary in the first place since Elvish always resolves local variables first, so just remove it.

  • If you are using local: when assigning variables (e.g. local:x = foo), local: makes sure that a new variable is created; use the var special command instead.

• Use of the special namespace up: is deprecated.

  • If you are using up: to access a non-shadowed variable in an outer scope, up: is not necessary; just remove it.

  • If you are using up: to access a shadowed variable in an outer scope, rename the variables to have different names.

• Use of a leading empty namespace in a variable name (e.g. $:x) is deprecated. Since $:x is always equivalent to $x anyway, just remove the : prefix.

Notable new features

New features in the language:

• A new special command pragma. The only supported pragma now is unknown command; using pragma unknown command = disallow turns off the default behavior of treating unknown commands as external commands.

• A new special command coalesce.

New features in the interactive editor:

• Editor modes now form a stack, instead of being mutually exclusive. For example, it is now possible to start a minibuf mode within a completion mode, and vice versa.

New features in the standard library:

• The store: module now exposes all functionalities of Elvish's persistent store.

• New compare command to compare numbers, strings, and lists (#1347), in a consistent way as the order builtin.

• The range command now supports counting down.

Performance improvements:

• The overhead of executing pipelines consisting of a single form (i.e. a simple command with no pipes) has been reduced. A code chunk containing just nop command now executes 4 times as fast as before. Thanks to kolbycrouch for suggesting this optimization!