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

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.ErrDifferentArgumentsTypes 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.ErrDifferentArgumentsTypes

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:sha256:6f0db9578aca12fcdf8a91b190c7ebe0bdc738ee15dc088fba3ce41c6eb9d65d","contract":["mergo.Merge returns mergo.ErrDifferentArgumentsTypes when destination and source arguments are different struct types.","mergo.Merge returns mergo.ErrDifferentArgumentsTypes when destination is a struct pointer and source is a primitive type.","mergo.Merge returns mergo.ErrDifferentArgumentsTypes when destination and source maps have different value types.","mergo.ErrDifferentArgumentsTypes error message equals \"src and dst must be of same type\"."],"goal":"verify github.com/imdario/mergo.ErrDifferentArgumentsTypes 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.ErrDifferentArgumentsTypes"]},"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.ErrDifferentArgumentsTypes"],"verifierAdapter":"golang@1"}

module example.com/mergoerrdifferentargumentstypes

go 1.22

require (
	github.com/imdario/mergo v0.3.8
	gopkg.in/yaml.v2 v2.4.0 // indirect
)

github.com/imdario/mergo v0.3.8 h1:CGgOkSJeqMRmt0D9XLWExdT4m4F1vd3FV3VPt+0VxkQ=
github.com/imdario/mergo v0.3.8/go.mod h1:2EnlNZ0deacrJVfApfmtdGgDfMuh/nq6Ok1EcJh5FfA=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=
gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=

package main

import (
	"errors"
	"fmt"

	"github.com/imdario/mergo"
)

type ConfigA struct {
	Host string
	Port int
}

type ConfigB struct {
	Endpoint string
	Timeout  int
}

func main() {
	dst := ConfigA{Host: "localhost", Port: 8080}
	src := ConfigB{Endpoint: "example.com", Timeout: 30}

	err := mergo.Merge(&dst, src)
	if errors.Is(err, mergo.ErrDifferentArgumentsTypes) || err == mergo.ErrDifferentArgumentsTypes {
		fmt.Printf("Detected expected ErrDifferentArgumentsTypes: %v\n", err)
	} else if err != nil {
		fmt.Printf("Unexpected error: %v\n", err)
	} else {
		fmt.Println("Merge unexpectedly succeeded")
	}
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/imdario/mergo.ErrDifferentArgumentsTypes 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.ErrDifferentArgumentsTypes"
  ]
}

package test

import (
	"errors"
	"testing"

	"github.com/imdario/mergo"
)

type ServerConfig struct {
	Host string
	Port int
}

type ClientConfig struct {
	Endpoint string
	Timeout  int
}

func TestErrDifferentArgumentsTypesWithDistinctStructs(t *testing.T) {
	dst := ServerConfig{Host: "localhost", Port: 8080}
	src := ClientConfig{Endpoint: "example.com", Timeout: 30}

	err := mergo.Merge(&dst, src)
	if err == nil {
		t.Fatal("expected error when merging different struct types, got nil")
	}
	if !errors.Is(err, mergo.ErrDifferentArgumentsTypes) && err != mergo.ErrDifferentArgumentsTypes {
		t.Fatalf("expected ErrDifferentArgumentsTypes, got: %v", err)
	}
}

func TestErrDifferentArgumentsTypesWithStructAndPrimitive(t *testing.T) {
	dst := ServerConfig{Host: "localhost", Port: 8080}
	src := 42

	err := mergo.Merge(&dst, src)
	if err == nil {
		t.Fatal("expected error when merging struct pointer with primitive, got nil")
	}
	if !errors.Is(err, mergo.ErrDifferentArgumentsTypes) && err != mergo.ErrDifferentArgumentsTypes {
		t.Fatalf("expected ErrDifferentArgumentsTypes, got: %v", err)
	}
}

func TestErrDifferentArgumentsTypesErrorMessage(t *testing.T) {
	expectedMsg := "src and dst must be of same type"
	if mergo.ErrDifferentArgumentsTypes.Error() != expectedMsg {
		t.Fatalf("expected error message %q, got %q", expectedMsg, mergo.ErrDifferentArgumentsTypes.Error())
	}
}

func TestErrDifferentArgumentsTypesWithDifferentMapValueTypes(t *testing.T) {
	dst := map[string]int{"count": 1}
	src := map[string]string{"name": "test"}

	err := mergo.Merge(&dst, src)
	if err == nil {
		t.Fatal("expected error when merging maps of different types, got nil")
	}
	if !errors.Is(err, mergo.ErrDifferentArgumentsTypes) && err != mergo.ErrDifferentArgumentsTypes {
		t.Fatalf("expected ErrDifferentArgumentsTypes, got: %v", err)
	}
}