KCL Composition Validator

When This Skill Activates

This skill automatically activates when:

• Modifying files in infrastructure/base/crossplane/configuration/kcl/
• Working with KCL compositions or Crossplane resources
• User mentions "kcl", "crossplane", "composition", or "validate"
• Before committing changes that include .k files
• When running pre-commit validation

Critical: Why This Matters

The CI enforces strict KCL formatting and will fail your commit if validation doesn't pass.

Common issues this skill prevents:

• Formatting violations that fail CI
• Syntax errors in KCL code
• Resource mutation causing duplicate resources (issue #285)
• Rendering failures in composition pipeline

Three-Stage Validation Process

Stage 1: KCL Formatting (CRITICAL - CI Enforced)

Purpose: Ensure code follows strict formatting standards that CI will check.

What to check:

• Single-line list comprehensions (NOT multi-line)
• No trailing blank lines between sections
• Proper indentation and spacing

How to validate:

cd infrastructure/base/crossplane/configuration/kcl/<module>
kcl fmt .

Check for changes:

git diff --quiet . || echo "Files were reformatted - review changes"

If kcl fmt made changes, the formatting was incorrect. Review the diff and commit the formatted version.

Stage 2: KCL Syntax and Logic Validation

Purpose: Test KCL code executes without errors using example settings.

How to validate:

cd infrastructure/base/crossplane/configuration/kcl/<module>
kcl run . -Y settings-example.yaml

What this catches:

• Syntax errors in KCL code
• Logic errors in conditionals
• Type mismatches
• Reference errors

Stage 3: Crossplane Render Validation

Purpose: Test the complete composition pipeline end-to-end.

Comprehensive validation script:

# From repository root
./scripts/validate-kcl-compositions.sh

This script validates ALL compositions through all three stages automatically.

Manual validation (for specific compositions):

cd infrastructure/base/crossplane/configuration

# Test basic example
crossplane render examples/app-basic.yaml app-composition.yaml functions.yaml \
  --extra-resources examples/environmentconfig.yaml > /tmp/rendered.yaml

# Test complete example
crossplane render examples/app-complete.yaml app-composition.yaml functions.yaml \
  --extra-resources examples/environmentconfig.yaml > /tmp/rendered.yaml

Tested compositions:

• app: app-basic.yaml, app-complete.yaml
• cloudnativepg (SQLInstance): sqlinstance-basic.yaml, sqlinstance-complete.yaml
• eks-pod-identity: epi.yaml

Critical KCL Rules

Rule 1: NEVER MUTATE RESOURCES (Issue #285)

Background: https://github.com/crossplane-contrib/function-kcl/issues/285

Mutating dictionaries/resources after creation causes function-kcl to create duplicate resources. This is a known bug in function-kcl's duplicate detection mechanism.

WRONG - Mutation Pattern:

# ❌ Creating resource then modifying it later
_deployment = {
    apiVersion = "apps/v1"
    kind = "Deployment"
    metadata = {
        name = _name
        annotations = {
            "base-annotation" = "value"
        }
    }
}

# ❌ MUTATION! This causes duplicates
if _deploymentReady:
    _deployment.metadata.annotations["krm.kcl.dev/ready"] = "True"

_items += [_deployment]

CORRECT - Inline Conditional Pattern:

# ✅ Using inline conditionals
_deployment = {
    apiVersion = "apps/v1"
    kind = "Deployment"
    metadata = {
        name = _name
        annotations = {
            "base-annotation" = "value"
            if _deploymentReady:
                "krm.kcl.dev/ready" = "True"  # ✅ Inline conditional
        }
    }
}
_items += [_deployment]

CORRECT - List Comprehension Pattern:

# ✅ List comprehensions with inline definitions
_items += [{
    apiVersion = "apps/v1"
    kind = "Deployment"
    metadata = {
        name = _name + "-" + db.name
        annotations = {
            "base-annotation" = "value"
            if _ready:
                "krm.kcl.dev/ready" = "True"
        }
    }
} for db in databases]

Safe patterns:

• Inline conditionals within dictionary literals
• List comprehensions with inline definitions
• Ternary operators returning complete dictionaries

Unsafe patterns (NEVER use):

• Post-creation field assignment: resource.field = value
• Post-creation nested assignment: resource.metadata.annotations["key"] = "value"
• Any mutation of resource variables after initial creation

Rule 2: Single-Line List Comprehensions

WRONG:

# ❌ Multi-line comprehension (will fail CI)
_ready = any_true([
    c.get("type") == "Available" and c.get("status") == "True"
    for c in conditions or []
])

CORRECT:

# ✅ Single-line comprehension
_ready = any_true([c.get("type") == "Available" and c.get("status") == "True" for c in conditions or []])

Rule 3: No Trailing Blank Lines

Remove extra blank lines between logical sections. The kcl fmt tool will catch these.

Pre-Commit Workflow

ALWAYS run before committing KCL changes:

# From repository root
./scripts/validate-kcl-compositions.sh

Expected output:

╔════════════════════════════════════════════════════════════════╗
║  KCL Crossplane Composition Validation                        ║
╚════════════════════════════════════════════════════════════════╝

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  Validating: app
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

📝 [1/3] Checking KCL formatting...
   ✅ Formatting is correct

🧪 [2/3] Validating KCL syntax and logic...
   ✅ KCL syntax valid

🎨 [3/3] Testing crossplane render...
   Testing: app-basic.yaml
   ✅ app-basic.yaml renders successfully
   Testing: app-complete.yaml
   ✅ app-complete.yaml renders successfully

✅ All checks passed for app

Target: Zero errors, minimal warnings.

Common Issues and Fixes

Issue: Code Reformatted by kcl fmt

Symptom: kcl fmt makes changes to your code

Fix:

1. Review the changes with git diff
2. Commit the formatted version
3. The formatting is now correct for CI

Issue: Syntax Errors

Symptom: kcl run fails with syntax error

Fix:

1. Read the error message carefully
2. Check the line number indicated
3. Common causes: missing commas, incorrect indentation, typos
4. Fix the syntax and re-run validation

Issue: Render Failures

Symptom: crossplane render fails

Fix:

1. Check that example files match composition schema
2. Verify functions.yaml is correctly configured
3. Ensure environmentconfig.yaml exists
4. Check function-kcl version compatibility

Issue: Duplicate Resources Created

Symptom: Multiple identical resources in rendered output

Fix:

1. Search for resource mutation patterns in code
2. Look for lines like: _resource.field = value
3. Refactor to use inline conditionals
4. See Rule 1 above for correct patterns

Quick Checklist

Before committing KCL changes, ensure:

• Run ./scripts/validate-kcl-compositions.sh from repo root
• All formatting checks pass (Stage 1)
• All syntax validations pass (Stage 2)
• All render tests pass (Stage 3)
• No resource mutation patterns in code
• List comprehensions are single-line
• No trailing blank lines

Additional Resources

• Mutation bug details: See reference.md in this skill folder
• Code patterns: See examples.md in this skill folder
• Quick reference: See quick-reference.md in this skill folder

Validation Targets

Modules validated:

• app - Application composition with progressive complexity
• cloudnativepg - PostgreSQL database instances
• eks-pod-identity - EKS Pod Identity for IAM roles

Example files tested:

• Basic examples (minimal configuration)
• Complete examples (production-ready with all features)

Success Criteria

Validation is successful when:

1. kcl fmt makes no changes (formatting correct)
2. kcl run executes without errors (syntax valid)
3. crossplane render succeeds for all examples (composition valid)
4. Zero errors reported by validation script
5. Minimal warnings (Docker availability only)