Elvish script upgrader for 0.17

What this does

Rewriting legacy assignment forms

This program rewrites legacy assignment forms to equivalent var or set forms:

a = foo
# becomes:
var a = foo

# but when $a is already defined...
a = foo
# becomes:
set a = foo

If the assignment form contains a mix of existing and new variables, it is rewritten to a var form that declares the non-existing variables and a set form:

a = foo
a b = lorem ipsum
# becomes
var a = foo
var b; set a b = lorem ipsum

The version of the set command in 0.15.x and 0.16.x contained a bug where it could also create variables. This program also rewrites such uses of set by declaring those variables with var first:

set a = foo
set a b = lorem ipsum
# becomes
var a; set a = foo
var b; set a b = lorem ipsum

Rewriting legacy lambda syntax

This program also rewrites legacy lambda syntax to the new syntax, moving arguments and options within [...] before { to within |...| after {.

x = [a b &k=v]{ ... }
# becomes
x = {|a b &k=v| ... }

The new lambda syntax is supported since 0.17.0. If your script still needs to support older versions, you can turn off lambda rewrite with -lambda=false.

What this doesn't do

This program does not handle any other changes introduced in 0.17.

Known limitations

In the legacy assignment form, the RHS may refer to the just declared variable, such as:

m = [&x={ put $m }]

This will get rewritten to the following, which doesn't work since the var form now evaluates the RHS before declaring the variable:

var m = [&x={ put $m }]

You will need to manually rewrite this to:

var m
set m = [&x={ put $m }]

How to use

Build this program:

go install github.com/elves/upgrade-scripts-for-0.17@main

This will install the program to ~/go/bin by default. Add ~/go/bin to your PATH, or copy the program to somewhere already on PATH.

Command line invocation works like gofmt - there are 3 modes:

upgrade-scripts-for-0.17 # no arguments; rewrite stdin to stdout
upgrade-scripts-for-0.17 a.elv b.elv # rewrites script to stdout
upgrade-scripts-for-0.17 -w a.elv b.elv # rewrites script in place

If you're invoking it from Elvish, use the following to rewrite all Elvish scripts in the current directory recursively:

upgrade-scripts-for-0.17 -w **[type:regular].elv

Remember to back up the files, or make sure that they are in version control, just in case this program has bugs and renders your scripts unusable.