set lists tracking issue #3377

When set lists is enabled, values may be list of strings, as opposed to strings.

This enables a number of nice features, for example, with set list, quote() applies to each individual argument:

foo *args:
  echo {{ quote(args) }}

So foo a 'b c' will print 'a' 'b c', instead of 'a b c'.

set lists is unstable, both because it's a huge change, and because there are many contexts, mainly the built-in functions, where the ideal behavior of lists is still undecided. Currently, join_list() must be used wherever lists are used in contexts expecting a string.

open questions

• Should we provide TRUE and FALSE constants?
• Is show() the right name for the list formatting function?
• Should exporting [] set the environment variable to "" or skip setting it?
• Should a + b where a or b is [] be identity?

todo

• Write more comprehensive docs, including why lists
• Update built-in functions to work with lists
• for expression or list comprehension that evaluates to lists
• List indexing and slicing
• Argument options can be allowed to repeat
• * for cartesian product
• Support for match expressions #1990
• [feature request] Expand file lists with wildcards for Windows #2854

done

• Values are lists #3362
• Add set lists #3372
• Make absolute_path() distribute over lists #3374
• Map append() and prepend() over lists #3375
• Make all values lists of strings, instead of strings #2458
• Question: How to forward *args? #1988
• Dispatching variadic arguments to dependencies with splats #558
• Forwards lists to dependencies #3378
• Add list literals #3380
• [Feature request] Array variables #1889
• Reform booleans #3381
• Print lists in --evaluate #3382
• Add show() function #3383
• Use show() and --evaluate in list tests #3384
• Stabilize logical operators #3258
• Allow conditions to be used in arbitrary expressions #3387
• Allow chaining conditionals #2411
• and/or/compound boolean expressions if A and B or if A or B #2562
• Allow chaining conditions in if using &&/|| #3336
• Coalesce-like string function #2379
• Add negation operator ! #3389
• Add bool() function #3391
• Add flag [arg] attribute #3398
• Add example using [parallel] with mapped dependencies #3399
• Check structural equality in != and == #3402
• if without else evalutes to [] when false #3401
• Omitting "else" from an if statement #2002
• assert(condition) evaluates to condition #3405
• Make lists in string contexts an error #3406
• Join lists in interpolations #3407
• Load multiple .env files #3412
• Allow lists as regex operands of =~ and !~ #3414
• Make + and / work with lists #3415
• Make env() work with lists #3416
• env_var_or_default doesn't short circuit #1350
• Add split() function #3420
• Make which() require set lists #3418
• Organize lists readme section #3421
• Add ++ list concatenation operator #3427