mcp/internal/index/builder_test.go

package index

import (
	"os"
	"path/filepath"
	"testing"
)

// writeFixture lays down a single-module Einherjar-like repo under a temp root
// and returns the root path for Build to walk.
func writeFixture(t *testing.T) string {
	t.Helper()
	root := t.TempDir()
	modDir := filepath.Join(root, "demo")
	if err := os.MkdirAll(modDir, 0o755); err != nil {
		t.Fatal(err)
	}
	write := func(name, body string) {
		if err := os.WriteFile(filepath.Join(modDir, name), []byte(body), 0o644); err != nil {
			t.Fatal(err)
		}
	}
	write("go.mod", "module example.com/demo\n\ngo 1.26\n")
	write("demo.go", `// Package demo is a build fixture.
package demo

import "context"

// Config holds settings.
type Config struct {
	// Host is the bind address.
	Host string `+"`"+`env:"DEMO_HOST" envDefault:"0.0.0.0"`+"`"+`
	Port int    `+"`"+`env:"DEMO_PORT"`+"`"+`
	Inner
}

// Inner is embedded into Config.
type Inner struct {
	Name string
}

// Store reads values.
type Store interface {
	// Get fetches one value.
	Get(ctx context.Context, id string) (string, error)
	context.Context
}
`)
	return root
}

func findSymbol(t *testing.T, idx *Index, mod, name string) Symbol {
	t.Helper()
	m := idx.FindModule(mod)
	if m == nil {
		t.Fatalf("module %q not found", mod)
	}
	for _, s := range m.Symbols {
		if s.Name == name {
			return s
		}
	}
	t.Fatalf("symbol %q not found in module %q", name, mod)
	return Symbol{}
}

func TestBuildCapturesStructFields(t *testing.T) {
	idx, err := Build(writeFixture(t))
	if err != nil {
		t.Fatal(err)
	}

	cfg := findSymbol(t, idx, "demo", "Config")
	if cfg.Kind != "type" {
		t.Errorf("Config kind = %q, want type", cfg.Kind)
	}
	if len(cfg.Fields) != 3 {
		t.Fatalf("Config has %d fields, want 3: %+v", len(cfg.Fields), cfg.Fields)
	}

	host := cfg.Fields[0]
	if host.Name != "Host" || host.Type != "string" {
		t.Errorf("field[0] = %+v, want Host string", host)
	}
	if host.Tag != `env:"DEMO_HOST" envDefault:"0.0.0.0"` {
		t.Errorf("Host tag = %q, want the env/envDefault tag (backticks stripped)", host.Tag)
	}
	if host.Doc != "Host is the bind address." {
		t.Errorf("Host doc = %q", host.Doc)
	}

	if port := cfg.Fields[1]; port.Name != "Port" || port.Tag != `env:"DEMO_PORT"` {
		t.Errorf("field[1] = %+v, want Port with env tag", port)
	}

	if inner := cfg.Fields[2]; !inner.Embedded || inner.Name != "" || inner.Type != "Inner" {
		t.Errorf("field[2] = %+v, want embedded Inner", inner)
	}
}

func TestBuildCapturesInterfaceMethods(t *testing.T) {
	idx, err := Build(writeFixture(t))
	if err != nil {
		t.Fatal(err)
	}

	store := findSymbol(t, idx, "demo", "Store")
	if store.Kind != "interface" {
		t.Errorf("Store kind = %q, want interface", store.Kind)
	}
	if len(store.Methods) != 2 {
		t.Fatalf("Store has %d methods, want 2: %+v", len(store.Methods), store.Methods)
	}

	get := store.Methods[0]
	if get.Name != "Get" {
		t.Errorf("method[0] name = %q, want Get", get.Name)
	}
	if get.Signature != "Get(ctx context.Context, id string) (string, error)" {
		t.Errorf("Get signature = %q", get.Signature)
	}
	if get.Doc != "Get fetches one value." {
		t.Errorf("Get doc = %q", get.Doc)
	}

	if emb := store.Methods[1]; emb.Name != "" || emb.Signature != "context.Context" {
		t.Errorf("method[1] = %+v, want embedded context.Context", emb)
	}
}

// A struct must be discoverable by one of its struct tags — the failure mode
// that motivated capturing fields in the first place.
func TestSearchSymbolsByStructTag(t *testing.T) {
	idx, err := Build(writeFixture(t))
	if err != nil {
		t.Fatal(err)
	}

	got := idx.SearchSymbols("DEMO_HOST", 10)
	found := false
	for _, s := range got {
		if s.Name == "Config" {
			found = true
		}
	}
	if !found {
		t.Errorf("searching a struct tag did not surface its type; got %d results", len(got))
	}
}