github.com/imdario/mergo v0.3.12: 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@v0.3.12
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/imdario/mergo@v0.3.12
Demonstrate these symbols/APIs:
  - mergo.Map

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:sha256:7f36e11ea9a19ec773391022742979301450b1862b094659de699ad2f0c32f9c","contract":["mergo.Map merges map key-value pairs into matching struct fields without overwriting non-zero destination fields.","mergo.Map with mergo.WithOverride overwrites existing non-zero struct fields with values from the source map.","mergo.Map merges a source map into a destination map preserving existing non-overlapping keys.","mergo.Map returns an error when destination pointer is nil."],"goal":"verify pkg:golang/github.com/imdario/mergo@v0.3.12","kind":"HOW","packages":["pkg:golang/github.com/imdario/mergo@v0.3.12"],"schemaVersion":1,"symbols":["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@v0.3.12"],"schemaVersion":1,"subject":"pkg:golang/github.com/imdario/mergo@v0.3.12","symbols":["mergo.Map"],"verifierAdapter":"golang@1"}

module example.com/mergomap

go 1.22

require github.com/imdario/mergo v0.3.12

github.com/imdario/mergo v0.3.12 h1:b6R2BslTbIEToALKP7LxUvijTsNI9TAe80pLWN2g/HU=
github.com/imdario/mergo v0.3.12/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 AppConfig struct {
	Host    string
	Port    int
	Debug   bool
	Timeout int
}

func main() {
	cfg := AppConfig{
		Host: "127.0.0.1",
		Port: 8080,
	}

	overrides := map[string]interface{}{
		"Port":    9090,
		"Debug":   true,
		"Timeout": 30,
	}

	if err := mergo.Map(&cfg, overrides, mergo.WithOverride); err != nil {
		panic(err)
	}

	fmt.Printf("Host: %s, Port: %d, Debug: %t, Timeout: %d\n", cfg.Host, cfg.Port, cfg.Debug, cfg.Timeout)
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/imdario/mergo@v0.3.12",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/imdario/mergo@v0.3.12"
  ],
  "symbols": [
    "mergo.Map"
  ]
}

package test

import (
	"reflect"
	"testing"

	"github.com/imdario/mergo"
)

type Config struct {
	Host    string
	Port    int
	Debug   bool
	Timeout int
}

func TestMapToStructWithoutOverride(t *testing.T) {
	dst := Config{
		Host: "localhost",
		Port: 8080,
	}
	src := map[string]interface{}{
		"Port":    9000,
		"Debug":   true,
		"Timeout": 60,
	}

	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 != 8080 {
		t.Errorf("expected Port 8080 (preserved), got %d", dst.Port)
	}
	if !dst.Debug {
		t.Errorf("expected Debug true, got %v", dst.Debug)
	}
	if dst.Timeout != 60 {
		t.Errorf("expected Timeout 60, got %d", dst.Timeout)
	}
}

func TestMapToStructWithOverride(t *testing.T) {
	dst := Config{
		Host: "localhost",
		Port: 8080,
	}
	src := map[string]interface{}{
		"Port":    9000,
		"Timeout": 60,
	}

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

	if dst.Port != 9000 {
		t.Errorf("expected Port 9000 (overwritten), got %d", dst.Port)
	}
	if dst.Timeout != 60 {
		t.Errorf("expected Timeout 60, got %d", dst.Timeout)
	}
}

func TestMapToMap(t *testing.T) {
	dst := map[string]interface{}{
		"a": 1,
		"b": 2,
	}
	src := map[string]interface{}{
		"b": 20,
		"c": 3,
	}

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

	expected := map[string]interface{}{
		"a": 1,
		"b": 2,
		"c": 3,
	}
	if !reflect.DeepEqual(dst, expected) {
		t.Errorf("expected map %v, got %v", expected, dst)
	}
}

func TestMapNilDestination(t *testing.T) {
	var nilDst *Config
	src := map[string]interface{}{
		"Host": "localhost",
	}

	err := mergo.Map(nilDst, src)
	if err == nil {
		t.Errorf("expected error when mapping to nil dst, got nil")
	}
}