github.com/imdario/mergo v0.3.11: Merge, Map

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/github.com/imdario/mergo@v0.3.11
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/imdario/mergo@v0.3.11

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:sha256:27d0ef61a9e7c7c26d3345a55114badf4a8ae41f54098deabe06bcf9993be862","contract":["mergo.Merge merges non-zero fields from a source struct into zero-value fields of a destination struct without overwriting non-zero destination fields.","mergo.Merge with mergo.WithOverride overwrites existing non-zero destination fields with source values.","mergo.Merge with mergo.WithAppendSlice appends source slice elements to destination slice elements.","mergo.Map merges map key-value pairs into matching zero-value struct fields without overwriting non-zero destination fields.","mergo.Merge returns an error when the destination pointer is nil."],"goal":"verify pkg:golang/github.com/imdario/mergo@v0.3.11","kind":"HOW","packages":["pkg:golang/github.com/imdario/mergo@v0.3.11"],"schemaVersion":1,"symbols":["mergo.Merge","mergo.Map"]},"contractCommand":["go","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/github.com/imdario/mergo@v0.3.11"],"schemaVersion":1,"subject":"pkg:golang/github.com/imdario/mergo@v0.3.11","symbols":["mergo.Merge","mergo.Map"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.22

require github.com/imdario/mergo v0.3.11

github.com/imdario/mergo v0.3.11 h1:3tnifQM4i+fbajXKBHXWEH+KvNHqojZ778UH75j3bGA=
github.com/imdario/mergo v0.3.11/go.mod h1:jmQim1M+e3UYxmgPu/WyfjB3N3VflVyUjjjwH0dnCYA=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v2 v2.3.0 h1:clyUAQHOM3G0M3f5vQj7LuJrETvjVot3Z5el9nffUtU=
gopkg.in/yaml.v2 v2.3.0/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

package main

import (
	"fmt"

	"github.com/imdario/mergo"
)

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

func main() {
	dst := ServerConfig{
		Port: 9000,
	}
	src := ServerConfig{
		Host:    "localhost",
		Port:    8080,
		Timeout: 30,
		Tags:    []string{"default"},
	}

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

	fmt.Printf("Host: %s, Port: %d, Timeout: %d, Tags: %v\n", dst.Host, dst.Port, dst.Timeout, dst.Tags)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/imdario/mergo@v0.3.11",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/imdario/mergo@v0.3.11"
  ]
}

package test

import (
	"reflect"
	"testing"

	"github.com/imdario/mergo"
)

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

func TestMergeDefaultWithoutOverwrite(t *testing.T) {
	dst := ServerConfig{
		Port: 9000,
	}
	src := ServerConfig{
		Host:    "localhost",
		Port:    8080,
		Timeout: 30,
		Tags:    []string{"web", "api"},
	}

	if err := mergo.Merge(&dst, src); err != nil {
		t.Fatalf("mergo.Merge failed: %v", err)
	}

	if dst.Host != "localhost" {
		t.Errorf("expected Host 'localhost', got %q", dst.Host)
	}
	if dst.Port != 9000 {
		t.Errorf("expected Port 9000, got %d", dst.Port)
	}
	if dst.Timeout != 30 {
		t.Errorf("expected Timeout 30, got %d", dst.Timeout)
	}
	if !reflect.DeepEqual(dst.Tags, []string{"web", "api"}) {
		t.Errorf("expected Tags [web api], got %v", dst.Tags)
	}
}

func TestMergeWithOverride(t *testing.T) {
	dst := ServerConfig{
		Host: "example.com",
		Port: 8080,
	}
	src := ServerConfig{
		Host: "localhost",
		Port: 9090,
	}

	if err := mergo.Merge(&dst, src, mergo.WithOverride); err != nil {
		t.Fatalf("mergo.Merge with WithOverride failed: %v", err)
	}

	if dst.Host != "localhost" {
		t.Errorf("expected Host 'localhost', got %q", dst.Host)
	}
	if dst.Port != 9090 {
		t.Errorf("expected Port 9090, got %d", dst.Port)
	}
}

func TestMergeWithAppendSlice(t *testing.T) {
	dst := ServerConfig{
		Tags: []string{"primary"},
	}
	src := ServerConfig{
		Tags: []string{"secondary", "backup"},
	}

	if err := mergo.Merge(&dst, src, mergo.WithAppendSlice); err != nil {
		t.Fatalf("mergo.Merge with WithAppendSlice failed: %v", err)
	}

	expected := []string{"primary", "secondary", "backup"}
	if !reflect.DeepEqual(dst.Tags, expected) {
		t.Errorf("expected Tags %v, got %v", expected, dst.Tags)
	}
}

func TestMapIntoStruct(t *testing.T) {
	dst := ServerConfig{
		Port: 9000,
	}
	src := map[string]interface{}{
		"host":    "localhost",
		"port":    8080,
		"timeout": 45,
	}

	if err := mergo.Map(&dst, src); err != nil {
		t.Fatalf("mergo.Map failed: %v", err)
	}

	if dst.Host != "localhost" {
		t.Errorf("expected Host 'localhost', got %q", dst.Host)
	}
	if dst.Port != 9000 {
		t.Errorf("expected Port 9000, got %d", dst.Port)
	}
	if dst.Timeout != 45 {
		t.Errorf("expected Timeout 45, got %d", dst.Timeout)
	}
}

func TestMergeNilArguments(t *testing.T) {
	var nilDst *ServerConfig
	src := ServerConfig{Host: "localhost"}

	if err := mergo.Merge(nilDst, src); err == nil {
		t.Errorf("expected error when merging into nil dst, got nil")
	}
}