Add public API boundary checks

internal/apicheck/main_test.go

@@ -0,0 +1,180 @@
+package main
+
+import (
+	"go/ast"
+	"go/importer"
+	"go/parser"
+	"go/token"
+	"go/types"
+	"strings"
+	"testing"
+)
+
+func TestExportedContractBoundaries(t *testing.T) {
+	tests := []struct {
+		name      string
+		source    string
+		wantError string
+	}{
+		{
+			name: "leaked implementation type",
+			source: `package facade
+import "example.com/implementation"
+func New() *implementation.State { return nil }
+`,
+			wantError: "exposes named type example.com/implementation.State",
+		},
+		{
+			name: "alias to implementation type",
+			source: `package facade
+import "example.com/implementation"
+type Alias = implementation.State
+`,
+			wantError: "exposes named type example.com/implementation.State",
+		},
+		{
+			name: "callback leaks implementation type",
+			source: `package facade
+import "example.com/implementation"
+type Callback func() *implementation.State
+`,
+			wantError: "exposes named type example.com/implementation.State",
+		},
+		{
+			name: "generic constraint leaks implementation type",
+			source: `package facade
+import "example.com/implementation"
+type Box[T interface{ Value() *implementation.State }] struct { value T }
+`,
+			wantError: "exposes named type example.com/implementation.State",
+		},
+		{
+			name: "generic instantiation leaks implementation type",
+			source: `package facade
+import "example.com/implementation"
+type Box[T any] struct { value T }
+func New() Box[implementation.State] { return Box[implementation.State]{} }
+`,
+			wantError: "exposes named type example.com/implementation.State",
+		},
+		{
+			name: "promoted implementation method",
+			source: `package facade
+import "example.com/implementation"
+type state = implementation.State
+type Handle struct { state }
+`,
+			wantError: "promotes method Promoted from example.com/implementation",
+		},
+		{
+			name: "promoted pointer implementation method",
+			source: `package facade
+import "example.com/implementation"
+type state = implementation.State
+type Handle struct { state }
+`,
+			wantError: "promotes method PointerPromoted from example.com/implementation",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			violations := checkFixture(t, test.source)
+			if !strings.Contains(strings.Join(violations, "\n"), test.wantError) {
+				t.Fatalf("checkExports() = %v, want an error containing %q", violations, test.wantError)
+			}
+		})
+	}
+}
+
+func TestPrivateImplementationFieldAndSelectedStandardTypes(t *testing.T) {
+	source := `package facade
+import (
+	"context"
+	"example.com/implementation"
+)
+type Handle struct { state *implementation.State }
+func Open(context.Context) *Handle { return nil }
+`
+	if violations := checkFixture(t, source); len(violations) != 0 {
+		t.Fatalf("private implementation field and selected standard type were rejected: %v", violations)
+	}
+}
+
+func TestActualRepositoryBoundaries(t *testing.T) {
+	if err := checkRepository(t.Context(), "../.."); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestInternalPackagesCannotImportPublicFacades(t *testing.T) {
+	packages := []listedPackage{
+		{ImportPath: modulePath + "/internal/operations", Imports: []string{modulePath}},
+		{ImportPath: modulePath},
+	}
+	err := checkImportDirections(packages)
+	if err == nil || !strings.Contains(err.Error(), "internal package "+modulePath+"/internal/operations imports public or command package "+modulePath) {
+		t.Fatalf("checkImportDirections() error = %v, want internal-to-facade violation", err)
+	}
+}
+
+func TestRuntimeFacadeCannotDependOnExternalPackages(t *testing.T) {
+	packages := []listedPackage{
+		{ImportPath: modulePath + "/buildinfo", Imports: []string{"example.com/runtime"}},
+		{ImportPath: "example.com/runtime"},
+	}
+	err := checkImportDirections(packages)
+	if err == nil || !strings.Contains(err.Error(), "buildinfo depends on non-runtime package example.com/runtime") {
+		t.Fatalf("checkImportDirections() error = %v, want runtime dependency violation", err)
+	}
+}
+
+func checkFixture(t *testing.T, facadeSource string) []string {
+	t.Helper()
+	fset := token.NewFileSet()
+	implementation := typecheck(t, fset, "example.com/implementation", `package implementation
+type State struct{}
+func (State) Promoted() {}
+func (*State) PointerPromoted() {}
+`)
+	fixtureImporter := singlePackageImporter{path: "example.com/implementation", pkg: implementation}
+	facade := typecheckWithImporter(t, fset, "example.com/facade", facadeSource, fixtureImporter)
+	return checkExports(facade)
+}
+
+type singlePackageImporter struct {
+	path string
+	pkg  *types.Package
+}
+
+func (i singlePackageImporter) Import(path string) (*types.Package, error) {
+	if path == i.path {
+		return i.pkg, nil
+	}
+	return importer.Default().Import(path)
+}
+
+func typecheck(t *testing.T, fset *token.FileSet, path, source string) *types.Package {
+	t.Helper()
+	return typecheckWithImporter(t, fset, path, source, importer.Default())
+}
+
+func typecheckWithImporter(t *testing.T, fset *token.FileSet, path, source string, imports types.Importer) *types.Package {
+	t.Helper()
+	file, err := parser.ParseFile(fset, path+".go", source, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var errors []error
+	config := types.Config{
+		Importer: imports,
+		Error: func(err error) {
+			errors = append(errors, err)
+		},
+	}
+	pkg, err := config.Check(path, fset, []*ast.File{file}, nil)
+	if err != nil {
+		t.Fatalf("typecheck %s: %v (%v)", path, err, errors)
+	}
+	return pkg
+}