github.com/imdario/mergo v0.3.8: ErrNilArguments

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 github.com/imdario/mergo.ErrNilArguments in pkg:golang/github.com/imdario/mergo@v0.3.8
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/imdario/mergo@v0.3.8
Demonstrate these symbols/APIs:
  - github.com/imdario/mergo.ErrNilArguments

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:d41b938d19a18d6213b1468d729ee88e930c0cfd57bef5bf861a6d659276f49f","contract":["mergo.Merge returns mergo.ErrNilArguments when destination argument is nil.","mergo.Merge returns mergo.ErrNilArguments when source argument is nil.","mergo.Merge returns mergo.ErrNilArguments when both destination and source arguments are nil.","mergo.ErrNilArguments error string equals \"src and dst must not be nil\".","mergo.Map returns mergo.ErrNilArguments when destination or source map argument is nil."],"goal":"verify github.com/imdario/mergo.ErrNilArguments in pkg:golang/github.com/imdario/mergo@v0.3.8","kind":"HOW","packages":["pkg:golang/github.com/imdario/mergo@v0.3.8"],"schemaVersion":1,"symbols":["github.com/imdario/mergo.ErrNilArguments"]},"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@v0.3.8"],"schemaVersion":1,"subject":"pkg:golang/github.com/imdario/mergo@v0.3.8","symbols":["github.com/imdario/mergo.ErrNilArguments"],"verifierAdapter":"golang@1"}

module example.com/mergonilarguments

go 1.22

require github.com/imdario/mergo v0.3.8

github.com/imdario/mergo v0.3.8 h1:CGgOkSJeqMRmt0D9XLWExdT4m4F1vd3FV3VPt+0VxkQ=
github.com/imdario/mergo v0.3.8/go.mod h1:2EnlNZ0deacrJVfApfmtdGgDfMuh/nq6Ok1EcJh5FfA=

package main

import (
	"errors"
	"fmt"

	"github.com/imdario/mergo"
)

type Config struct {
	Port int
	Host string
}

func main() {
	cfg := Config{Port: 8080}

	err := mergo.Merge(&cfg, nil)
	if errors.Is(err, mergo.ErrNilArguments) {
		fmt.Printf("mergo returned expected ErrNilArguments: %v\n", err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/imdario/mergo.ErrNilArguments in pkg:golang/github.com/imdario/mergo@v0.3.8",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/imdario/mergo@v0.3.8"
  ],
  "symbols": [
    "github.com/imdario/mergo.ErrNilArguments"
  ]
}

package test

import (
	"errors"
	"testing"

	"github.com/imdario/mergo"
)

type Config struct {
	Port int
	Host string
}

func TestMergeNilDestinationReturnsErrNilArguments(t *testing.T) {
	src := Config{Port: 8080}
	err := mergo.Merge(nil, src)
	if err == nil {
		t.Fatal("expected error when dst is nil, got nil")
	}
	if !errors.Is(err, mergo.ErrNilArguments) {
		t.Fatalf("expected ErrNilArguments, got %v", err)
	}
	if err != mergo.ErrNilArguments {
		t.Fatalf("expected exact ErrNilArguments sentinel error, got %v", err)
	}
}

func TestMergeNilSourceReturnsErrNilArguments(t *testing.T) {
	dst := Config{Port: 8080}
	err := mergo.Merge(&dst, nil)
	if err == nil {
		t.Fatal("expected error when src is nil, got nil")
	}
	if !errors.Is(err, mergo.ErrNilArguments) {
		t.Fatalf("expected ErrNilArguments, got %v", err)
	}
	if err != mergo.ErrNilArguments {
		t.Fatalf("expected exact ErrNilArguments sentinel error, got %v", err)
	}
}

func TestMergeBothNilReturnsErrNilArguments(t *testing.T) {
	err := mergo.Merge(nil, nil)
	if err == nil {
		t.Fatal("expected error when both arguments are nil, got nil")
	}
	if !errors.Is(err, mergo.ErrNilArguments) {
		t.Fatalf("expected ErrNilArguments, got %v", err)
	}
	if err != mergo.ErrNilArguments {
		t.Fatalf("expected exact ErrNilArguments sentinel error, got %v", err)
	}
}

func TestErrNilArgumentsErrorMessage(t *testing.T) {
	expectedMsg := "src and dst must not be nil"
	if mergo.ErrNilArguments.Error() != expectedMsg {
		t.Fatalf("expected %q, got %q", expectedMsg, mergo.ErrNilArguments.Error())
	}
}

func TestMapNilArgumentsReturnsErrNilArguments(t *testing.T) {
	m := map[string]interface{}{"port": 8080}
	if err := mergo.Map(nil, m); !errors.Is(err, mergo.ErrNilArguments) {
		t.Fatalf("expected ErrNilArguments when dst is nil, got %v", err)
	}
	if err := mergo.Map(&m, nil); !errors.Is(err, mergo.ErrNilArguments) {
		t.Fatalf("expected ErrNilArguments when src is nil, got %v", err)
	}
}