dario.cat/mergo v1.0.1

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:golang/dario.cat/mergo@v1.0.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/dario.cat/mergo@v1.0.1

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:da1a5b2221aa399f463986b62f27ceed562df1b9acb139fbb2e77c054cab0233","contract":["mergo.Merge populates zero-value fields of a destination struct with non-zero values from a source struct while preserving existing destination values","mergo.Merge with mergo.WithOverride overrides non-empty destination fields with non-empty source fields","mergo.Merge with mergo.WithAppendSlice appends source slice elements to destination slice elements instead of leaving them unchanged"],"goal":"verify pkg:golang/dario.cat/mergo@v1.0.1","kind":"HOW","packages":["pkg:golang/dario.cat/mergo@v1.0.1"],"schemaVersion":1},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/dario.cat/mergo@v1.0.1"],"schemaVersion":1,"subject":"pkg:golang/dario.cat/mergo@v1.0.1","verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

require dario.cat/mergo v1.0.1

dario.cat/mergo v1.0.1 h1:Ra4+bf83h2ztPIQYNP99R6m+Y7KfnARDfID+a+vLl4s=
dario.cat/mergo v1.0.1/go.mod h1:uNxQE+84aUszobStD9th8a29P2fMDhsBdgRYvZOxGmk=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package main

import (
	"fmt"

	"dario.cat/mergo"
)

type ServerConfig struct {
	Host    string
	Port    int
	Timeout int
	Tags    []string
}

func main() {
	defaultConfig := ServerConfig{
		Host:    "localhost",
		Port:    8080,
		Timeout: 30,
	}

	userConfig := ServerConfig{
		Port: 9000,
		Tags: []string{"production", "api"},
	}

	if err := mergo.Merge(&userConfig, defaultConfig); err != nil {
		panic(err)
	}

	fmt.Printf("Final Config: Host=%s, Port=%d, Timeout=%d, Tags=%v\n",
		userConfig.Host, userConfig.Port, userConfig.Timeout, userConfig.Tags)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/dario.cat/mergo@v1.0.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/dario.cat/mergo@v1.0.1"
  ]
}

package main

import (
	"fmt"
	"os"
	"reflect"

	"dario.cat/mergo"
)

type Config struct {
	Host    string
	Port    int
	Timeout int
	Tags    []string
}

func main() {
	// Assertion 1: mergo.Merge populates zero-value fields of a destination struct with non-zero values from a source struct while preserving existing destination values
	dst1 := Config{
		Host: "example.org",
		Port: 8080,
	}
	src1 := Config{
		Host:    "fallback.org",
		Timeout: 60,
		Tags:    []string{"default"},
	}
	if err := mergo.Merge(&dst1, src1); err != nil {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: %v\n", err)
		os.Exit(1)
	}
	expected1 := Config{
		Host:    "example.org",
		Port:    8080,
		Timeout: 60,
		Tags:    []string{"default"},
	}
	if !reflect.DeepEqual(dst1, expected1) {
		fmt.Fprintf(os.Stderr, "assertion 1 failed: expected %+v, got %+v\n", expected1, dst1)
		os.Exit(1)
	}

	// Assertion 2: mergo.Merge with mergo.WithOverride overrides non-empty destination fields with non-empty source fields
	dst2 := Config{
		Host: "example.org",
		Port: 8080,
	}
	src2 := Config{
		Host: "override.org",
		Port: 9090,
	}
	if err := mergo.Merge(&dst2, src2, mergo.WithOverride); err != nil {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: %v\n", err)
		os.Exit(1)
	}
	expected2 := Config{
		Host: "override.org",
		Port: 9090,
	}
	if !reflect.DeepEqual(dst2, expected2) {
		fmt.Fprintf(os.Stderr, "assertion 2 failed: expected %+v, got %+v\n", expected2, dst2)
		os.Exit(1)
	}

	// Assertion 3: mergo.Merge with mergo.WithAppendSlice appends source slice elements to destination slice elements instead of leaving them unchanged
	dst3 := Config{
		Tags: []string{"tag1", "tag2"},
	}
	src3 := Config{
		Tags: []string{"tag3", "tag4"},
	}
	if err := mergo.Merge(&dst3, src3, mergo.WithAppendSlice); err != nil {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: %v\n", err)
		os.Exit(1)
	}
	expected3 := Config{
		Tags: []string{"tag1", "tag2", "tag3", "tag4"},
	}
	if !reflect.DeepEqual(dst3, expected3) {
		fmt.Fprintf(os.Stderr, "assertion 3 failed: expected %+v, got %+v\n", expected3, dst3)
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}