Map variables experiment

[pd93]

Warning

All experimental features are subject to breaking changes and/or removal at any time. We strongly recommend that you do not use these features in a production environment. They are intended for testing and feedback only.

Context

This experiment attempts to solve the problems originally described by #140. It is a follow-up to the "Any Variables" experiment (#1415) which was merged without support for maps.

Currently, all variable types are allowed except for maps. This is because there is some debate around the syntax that should be used to define them. The proposals for these syntaxes are described below.

Proposal 1

Warning

This experiment proposal breaks the following functionality:

• Dynamically defined variables (using the sh keyword)

Note

To enable this experiment, set the environment variable: TASK_X_MAP_VARIABLES=1. Check out [our guide to enabling experiments][enabling-experiments] for more information.

This proposal removes support for the sh keyword in favour of a new syntax for
dynamically defined variables, This allows you to define a map directly as you
would for any other type:

version: 3

tasks:
  foo:
    vars:
      FOO: {a: 1, b: 2, c: 3} # <-- Directly defined map on the `FOO` key
    cmds:
      - 'echo {{.FOO.a}}'

Migration

Taskfiles with dynamically defined variables via the sh subkey will no longer
work with this experiment enabled. In order to keep using dynamically defined
variables, you will need to migrate your Taskfile to use the new syntax.

Previously, you might have defined a dynamic variable like this:

version: 3

tasks:
  foo:
    vars:
      CALCULATED_VAR:
        sh: 'echo hello'
    cmds:
      - 'echo {{.CALCULATED_VAR}}'

With this experiment enabled, you will need to remove the sh subkey and define
your command as a string that begins with a $. This will instruct Task to
interpret the string as a command instead of a literal value and the variable
will be populated with the output of the command. For example:

version: 3

tasks:
  foo:
    vars:
      CALCULATED_VAR: '$echo hello'
    cmds:
      - 'echo {{.CALCULATED_VAR}}'

If your current Taskfile contains a string variable that begins with a $, you
will now need to escape the $ with a backslash (\) to stop Task from
executing it as a command.

Proposal 2

Note

To enable this experiment, set the environment variable: TASK_X_MAP_VARIABLES=2. Check out [our guide to enabling experiments][enabling-experiments] for more information.

This proposal maintains backwards-compatibility and the sh subkey and adds another new map subkey for defining map variables:

version: 3

tasks:
  foo:
    vars:
      FOO:
        map: {a: 1, b: 2, c: 3} # <-- Defined using the `map' subkey instead of directly on 'FOO'
      BAR: true # <-- Other types of variables are still defined directly on the key
      BAZ:
        sh: 'echo Hello Task' # <-- The `sh` subkey is still supported
    cmds:
      - 'echo {{.FOO.a}}'

Parsing JSON and YAML

In addition to the new map keyword, this proposal also adds support for the json and yaml keywords for parsing JSON and YAML strings into real objects/arrays. This is similar to the fromJSON template function, but means that you only have to parse the JSON/YAML once when you declare the variable,
instead of every time you want to access a value.

Before:

version: 3

tasks:
  foo:
    vars:
      FOO: '{"a": 1, "b": 2, "c": 3}' # <-- JSON string
    cmds:
      - 'echo {{(fromJSON .FOO).a}}' # <-- Parse JSON string every time you want to access a value
      - 'echo {{(fromJSON .FOO).b}}'

After:

version: 3

tasks:
  foo:
    vars:
      FOO:
        json: '{"a": 1, "b": 2, "c": 3}' # <-- JSON string parsed once
    cmds:
      - 'echo {{.FOO.a}}' # <-- Access values directly
      - 'echo {{.FOO.b}}'

Variables by reference

Lastly, this proposal adds support for defining and passing variables by reference. This is really important now that variables can be types other than a string.

Previously, to send a variable from one task to another, you would have to use the templating system. Unfortunately, the templater always outputs a string and operations on the passed variable may not have behaved as expected. With this proposal, you can now pass variables by reference using the ref subkey:

Before:

version: 3

tasks:
  foo:
    vars:
      FOO: [A, B, C] # <-- FOO is defined as an array
    cmds:
      - task: bar
        vars:
          FOO: '{{.FOO}}' # <-- FOO gets converted to a string when passed to bar
  bar:
    cmds:
      - 'echo {{index .FOO 0}}' # <-- FOO is a string so the task outputs '91' which is the ASCII code for '[' instead of the expected 'A'

After:

version: 3

tasks:
  foo:
    vars:
      FOO: [A, B, C] # <-- FOO is defined as an array
    cmds:
      - task: bar
        vars:
          FOO:
            ref: .FOO # <-- FOO gets passed by reference to bar and maintains its type
  bar:
    cmds:
      - 'echo {{index .FOO 0}}' # <-- FOO is still a map so the task outputs 'A' as expected

This means that the type of the variable is maintained when it is passed to another Task. This also works the same way when calling deps and when defining a variable and can be used in any combination:

version: 3

tasks:
  foo:
    vars:
      FOO: [A, B, C] # <-- FOO is defined as an array
      BAR:
        ref: .FOO # <-- BAR is defined as a reference to FOO
    deps:
      - task: bar
        vars:
          BAR:
            ref: .BAR # <-- BAR gets passed by reference to bar and maintains its type
  bar:
    cmds:
      - 'echo {{index .BAR 0}}' # <-- BAR still refers to FOO so the task outputs 'A'

All references use the same templating syntax as regular templates, so in
addition to simply calling .FOO, you can also pass subkeys (.FOO.BAR) or
indexes (index .FOO 0) and use functions (len .FOO):

version: 3

tasks:
  foo:
    vars:
      FOO: [A, B, C] # <-- FOO is defined as an array
    cmds:
      - task: bar
        vars:
          FOO:
            ref: index .FOO 0 # <-- The element at index 0 is passed by reference to bar
  bar:
    cmds:
      - 'echo {{.MYVAR}}' # <-- FOO is just the letter 'A'

Looping over maps (Both proposals)

This experiment also adds support for looping over maps using the for keyword, just like arrays. In addition to the {{.ITEM}} variable being populated when looping over a map, we also make an additional {{.KEY}} variable available that holds the string value of the map key.

Proposal 1

version: 3

tasks:
  foo:
    vars:
      MAP: {a: 1, b: 2, c: 3}
    cmds:
      - for:
          var: MAP
        cmd: 'echo "{{.KEY}}: {{.ITEM}}"'

Proposal 2

version: 3

tasks:
  foo:
    vars:
      map:
        MAP: {a: 1, b: 2, c: 3}
    cmds:
      - for:
          var: MAP
        cmd: 'echo "{{.KEY}}: {{.ITEM}}"'

Note

Remember that maps are unordered, so the order in which the items are looped over is random.

[task-bot]

This issue has been marked as an experiment proposal! 🧪 It will now enter a period of consultation during which we encourage the community to provide feedback on the proposed design. Please see the experiment workflow documentation for more information on how we release experiments.

[simonrouse9461]

Is there a way to do templating in map variables?
For example,

version: 3

tasks:
  foo:
    vars:
      PREFIX: prefix_
      MAP:
        map: 
          a: '{{.PREFIX}}1'
          b: '{{.PREFIX}}2'
          c: '{{.PREFIX}}3'
    cmds:
      - echo {{index .MAP "a"}}

This will print {{.PREFIX}}1 instead of prefix_1.

[pd93]

@simonrouse9461 See #1526 and #1544. Your example works in the latest release. Also worth noting that TASK_X_MAP_VARIABLES won't replace TASK_X_ANY_VARIABLES until the next release.

[simonrouse9461]

@pd93 Thanks! Upgrading to the latest release solved the problem.

[simonrouse9461]

Suggestion:
For the ref variables, is it possible to reuse the template engine syntax? For example,

version: 3

tasks:
  foo:
    requires:
      vars: [VAR_NAME]
    vars:
      VAR_MAP: 
        map:
          FOO: [1, 2, 3]
          BAR: [4, 5, 6]
    cmds:
      - task: bar
        vars:
          VAR:
            ref: index .VAR_MAP .VAR_NAME
  bar:
    cmds:
      - echo {{index .VAR 0}}

Then,

• task foo VAR_NAME=FOO will print 1
• task foo VAR_NAME=BAR will print 4

This will make things more flexible and programmable.

[pd93]

is it possible to reuse the template engine syntax

@simonrouse9461 I was initially going to reply saying that this is quite difficult as the text/template package doesn't surface the ability to resolve references without converting the result to a string. However, after some thought, I have created #1612 to solve this.

[task-bot]

This experiment has been marked as a draft! ✨ This means that an initial implementation has been added to the latest release of Task! You can find information about this experiment and how to enable it in our experiments documentation. Please see the experiment workflow documentation for more information on how we release experiments.