[cmd/mdatagen] Generate required fields validation for go config structs

[jkoronaAtCisco]

Description

This PR adds automatic generation of Validate() methods for Go config structs produced by mdatagen, based on the JSON Schema config metadata.

When a config field is marked required in the config schema, the generated Validate() method emits the appropriate nil/empty check, handling all field kinds:

• IsPointer → nil check
• IsOptional (configoptional) → .HasValue() check
• string → empty string check
• array → len() == 0 check
• object (map) → nil or empty map check

Validation is also propagated recursively — if a field is an embedded struct, map, or slice whose element type itself has required fields, the generated Validate() calls the child type's Validate() method. Internal $ref and allOf references are resolved through internal $defs and validated the same way.

Example

Given a metadata.yaml with:

config:
  type: object
  required: [targets]
  properties:
    targets:
      type: array
      items:
        type: object
        required: [url]
        properties:
          url:
            type: string

The generated code produces:

func (c *TargetsItem) Validate() error {
  var err error

  if c.URL == "" {
      err = errors.Join(err, errors.New("URL is required"))
  }

  return err
}

func (c *Config) Validate() error {
  var err error

  if len(c.Targets) == 0 {
      err = errors.Join(err, errors.New("Targets is required"))
  }
  for _, value := range c.Targets {
      err = errors.Join(err, value.Validate())
  }

  return err
}

Link to tracking issue

#14563

Testing

1. Unit tests
2. Added use cases to samplescraper and samplereceiver

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 7 untouched benchmarks
⏩ 76 skipped benchmarks¹

---

_{Comparing jkoronaAtCisco:go_validators_mdatagen (3dce9ee) with main (16844a7)}

Footnotes

1. 76 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

❌ Patch coverage is 54.68750% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.33%. Comparing base (16844a7) to head (3dce9ee).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/mdatagen/internal/cfggen/generation.go	74.46%	9 Missing and 3 partials ⚠️
...datagen/internal/samplescraper/generated_config.go	0.00%	12 Missing ⚠️
...atagen/internal/samplereceiver/generated_config.go	0.00%	5 Missing ⚠️

❌ Your patch status has failed because the patch coverage (54.68%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14768      +/-   ##
==========================================
- Coverage   91.38%   91.33%   -0.05%     
==========================================
  Files         695      697       +2     
  Lines       44405    44456      +51     
==========================================
+ Hits        40579    40604      +25     
- Misses       2690     2714      +24     
- Partials     1136     1138       +2     

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[dmitryax]

IsOptional (configoptional) → .HasValue() check

This is not needed. optional and required are contradictory

[jkoronaAtCisco]

IsOptional (configoptional) → .HasValue() check

This is not needed. optional and required are contradictory

Makes sense. I removed it.