feat(vars): add interactive prompting for required variables

[vmaerten]

Summary

fixes #2079

Add interactive prompting for missing required variables using Bubble Tea UI.

When interactive: true is set in .taskrc.yml or --interactive is passed, Task will prompt users for any missing required variables instead of failing with an error.

Note

I chose to bind this to requires.vars instead of defining it for each var because required vars already express the semantic of "this must be provided" so prompting is a natural fallback when they're missing.
Similar to Terraform's approach. If needed, we could add an interactive: false flag per var to opt-out, but I'm not sure it's necessary.

Features

Variable types supported

• Text input: For simple string variables
• Enum selection: For variables with predefined allowed values (with vim keybindings j/k)

tasks:
  deploy:
    requires:
      vars:
        - API_KEY                    # Text prompt
        - name: ENVIRONMENT          # Enum selector
          enum: [dev, staging, prod]

Bound to requires

Interactive prompting only applies to variables declared in requires.vars. Regular variables with defaults are not prompted.

Configuration

Enable in .taskrc.yml:

interactive: true

Or via CLI flag:

task deploy --interactive

Auto-detection of non-TTY environments

Task automatically detects non-TTY environments (CI, piped input, etc.) and skips prompts, failing with the standard missing variable error.

Design decisions

Hybrid approach: deps vs cmds

Task handles deps and cmds differently when it comes to prompting:

Dependencies (deps) - Upfront collection

Dependencies execute in parallel, which means multiple prompts could appear simultaneously:

? Enter value for VAR_A: >
? Select value for VAR_B:
❯ option1
? Enter value for VAR_C: >
    option2

To avoid this, we collect all required vars upfront before any execution begins:

1. Traverse the dependency tree recursively
2. Collect all missing required variables
3. Prompt for everything at once
4. Then execute all tasks with the collected values

? Select value for BUILD_MODE: release
? Select value for TEST_SUITE: all

task: [build] Building in release mode...
task: [test] Running all tests...

Commands (cmds) - Just-in-time prompting

Commands that call other tasks (task: foo) execute sequentially, so there's no risk of interleaved prompts. We prompt just-in-time when we encounter a task with missing variables:

pipeline:
  cmds:
    - task: setup      # Prompts for PROJECT_NAME when reached
    - task: build      # Prompts for BUILD_MODE when reached
    - task: deploy     # Prompts for ENVIRONMENT when reached

This approach is more natural for sequential workflows - users see prompts in context as the pipeline progresses.

Why this hybrid approach?

Aspect	Deps (parallel)	Cmds (sequential)
Execution	Concurrent	One at a time
Prompt timing	Must be upfront	Can be just-in-time
UX	All prompts together	Prompts in context

The hybrid approach gives the best of both worlds:

• Deps: No garbled output from parallel prompts
• Cmds: Natural flow where you answer questions as you reach each step

Variable caching

Once a variable is prompted, its value is cached in e.promptedVars. If the same variable is required by multiple tasks, the user is only prompted once.

Handling duplicate task calls with different vars

When the same task is called multiple times with different variables:

deps:
  - task: build
    vars: { TARGET: linux }   # TARGET provided
  - task: build
    vars: { MODE: release }   # TARGET missing!

The collection phase checks all calls, not just unique task names, ensuring we catch all missing variables.

Future considerations

Integration with if: on tasks

When the if: feature on tasks lands, we'll need to ensure that tasks with if: false (that would be skipped) are not prompted for their variables during the upfront collection phase. This will require evaluating the if condition before collecting vars from a task.

Test plan

• Run task pipeline in testdata/interactive_vars/ with interactive: true
• Verify deps prompts appear upfront before execution
• Verify cmds prompts appear just-in-time as tasks are reached
• Test enum selection with arrow keys and j/k vim bindings
• Verify --interactive=false disables prompts
• Verify prompts auto-skip in non-TTY (pipe output to file)
• Test task with nested deps requiring different variables
• Test full-deploy (deps + cmds combined)

[task-bot]

📦 Build artifacts ready!

Download binaries from this workflow run.

Available platforms: Linux, macOS, Windows (amd64, arm64)

[andreynering]

This looks a lot cooler in practice than I expected! Good job.

I liked that you added an interactive option to avoid this being a breaking change, and also that it works with enums!

You may also write a blog post for this if you want. (Or perhaps it could be a single post for this and #2564, as they'll likely be released together).

I'm holding the approve until you upgrade to Bubble Tea v2 RC, but otherwise this looks good!

[andreynering]

Change to import from charm.land/bubbletea/v2.

v2 is in release candidate and will be released soon!

[sashokbg]

Hello, @vmaerten great work!
I have a question, can the enum be replaced with a sh ? I worked on a similar feature and had implemented sh where it will split the newlines and present them as possible choices.
This way the select options can be fed from a script