Support types from external packages (#33)

README.md

@@ -224,53 +224,83 @@ func (r *RateLimiter) Allow() bool {
 
 <br>
 
-- Linter only checks funcs with two return arguments, the last of which has `error` type.
+- Linter only checks functions with two return arguments, the last of which has `error` type.
 - Next types are checked:
   * pointers, functions & interfaces (`panic: invalid memory address or nil pointer dereference`);
   * maps (`panic: assignment to entry in nil map`);
   * channels (`fatal error: all goroutines are asleep - deadlock!`)
 - `uinptr` & `unsafe.Pointer` are not checked as a special case.
 - Supported only explicit `return nil, nil`.
-- Types from external packages are not supported.
 
 </details>
 
-## Check Golang source code
+## Check Go 1.22.2 source code
 
 <details>
   <summary>Click to expand</summary>
 
 ```shell
 $ cd $GOROOT/src
 $ nilnil ./...
-/usr/local/go/src/net/sockopt_posix.go:48:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/x509/parser.go:321:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/key_agreement.go:45:2: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/internal/bisect/bisect.go:196:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/fd_unix.go:71:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/fd_unix.go:79:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/fd_unix.go:156:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/iprawsock_posix.go:36:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/tcpsock_posix.go:38:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/udpsock_posix.go:37:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/unixsock_posix.go:92:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/key_agreement.go:46:2: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/ticket.go:355:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/ticket.go:359:3: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/database/sql/driver/types.go:157:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/database/sql/driver/types.go:231:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/database/sql/driver/types.go:262:4: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/debug/dwarf/entry.go:882:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/driver/types.go:232:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/driver/types.go:263:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/convert.go:548:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:205:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:231:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:257:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:284:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:311:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:337:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:363:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:389:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql.go:422:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/debug/dwarf/entry.go:884:3: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/debug/dwarf/line.go:146:3: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/debug/dwarf/line.go:153:3: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/debug/dwarf/typeunit.go:138:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/debug/pe/file.go:450:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/net/http/h2_bundle.go:8644:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/net/http/transfer.go:768:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/net/http/transfer.go:778:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/net/http/transfer.go:801:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/go/build/build.go:1404:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/go/build/build.go:1414:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/go/build/build.go:1419:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/debug/pe/file.go:470:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/http/h2_bundle.go:9530:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/http/transfer.go:765:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/http/transfer.go:775:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/http/transfer.go:798:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/go/build/build.go:1442:3: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/go/build/build.go:1453:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/internal/profile/legacy_profile.go:1087:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/go/build/build.go:1457:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/go/build/build.go:1491:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/go/internal/gccgoimporter/ar.go:125:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/image/jpeg/reader.go:622:5: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/image/png/reader.go:434:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/internal/profile/legacy_profile.go:1089:4: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/net/internal/socktest/switch.go:142:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/handshake_server_test.go:411:4: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/handshake_server_test.go:1012:3: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/handshake_server_test.go:1470:4: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/tls_test.go:747:4: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/tls_test.go:751:4: return both the `nil` error and invalid value: use a sentinel error instead
-/usr/local/go/src/crypto/tls/tls_test.go:755:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/handshake_client_test.go:2712:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/handshake_server_test.go:427:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/handshake_server_test.go:1029:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/handshake_server_test.go:1490:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/quic_test.go:390:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/tls_test.go:777:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/tls_test.go:781:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/tls_test.go:785:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/crypto/tls/tls_test.go:797:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/fakedb_test.go:1200:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql_test.go:938:2: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/database/sql/sql_test.go:942:2: return both the `nil` error and invalid value: use a sentinel error instead
 /usr/local/go/src/encoding/xml/xml_test.go:92:4: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/main_posix_test.go:48:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/net_test.go:338:3: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/http/transport_test.go:6234:85: return both the `nil` error and invalid value: use a sentinel error instead
+/usr/local/go/src/net/internal/socktest/main_test.go:48:61: return both the `nil` error and invalid value: use a sentinel error instead
 ```
 
 </details>

pkg/analyzer/analyzer.go

@@ -2,6 +2,7 @@ package analyzer
 
 import (
 	"go/ast"
+	"go/types"
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
@@ -40,29 +41,15 @@ func newNilNil() *nilNil {
 	}
 }
 
-var (
-	types = []ast.Node{(*ast.TypeSpec)(nil)}
-
-	funcAndReturns = []ast.Node{
-		(*ast.FuncDecl)(nil),
-		(*ast.FuncLit)(nil),
-		(*ast.ReturnStmt)(nil),
-	}
-)
-
-type typeSpecByName map[string]typer
+var funcAndReturns = []ast.Node{
+	(*ast.FuncDecl)(nil),
+	(*ast.FuncLit)(nil),
+	(*ast.ReturnStmt)(nil),
+}
 
 func (n *nilNil) run(pass *analysis.Pass) (interface{}, error) {
 	insp := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
 
-	typeSpecs := typeSpecByName{
-		"any": newTyper(new(ast.InterfaceType)),
-	}
-	insp.Preorder(types, func(node ast.Node) {
-		t := node.(*ast.TypeSpec)
-		typeSpecs[t.Name.Name] = newTyper(t.Type)
-	})
-
 	var fs funcTypeStack
 	insp.Nodes(funcAndReturns, func(node ast.Node, push bool) (proceed bool) {
 		switch v := node.(type) {
@@ -88,12 +75,12 @@ func (n *nilNil) run(pass *analysis.Pass) (interface{}, error) {
 			}
 
 			fRes1, fRes2 := ft.Results.List[0], ft.Results.List[1]
-			if !(n.isDangerNilField(fRes1, typeSpecs) && n.isErrorField(fRes2)) {
+			if !(n.isDangerNilField(pass, fRes1) && n.isErrorField(pass, fRes2)) {
 				return false
 			}
 
 			rRes1, rRes2 := v.Results[0], v.Results[1]
-			if isNil(rRes1) && isNil(rRes2) {
+			if isNil(pass, rRes1) && isNil(pass, rRes2) {
 				pass.Reportf(v.Pos(), reportMsg)
 			}
 		}
@@ -104,55 +91,51 @@ func (n *nilNil) run(pass *analysis.Pass) (interface{}, error) {
 	return nil, nil //nolint:nilnil
 }
 
-func (n *nilNil) isDangerNilField(f *ast.Field, typeSpecs typeSpecByName) bool {
-	return n.isDangerNilType(f.Type, typeSpecs)
+func (n *nilNil) isDangerNilField(pass *analysis.Pass, f *ast.Field) bool {
+	return n.isDangerNilType(pass.TypesInfo.TypeOf(f.Type))
 }
 
-func (n *nilNil) isDangerNilType(t ast.Expr, typeSpecs typeSpecByName) bool {
+func (n *nilNil) isDangerNilType(t types.Type) bool {
 	switch v := t.(type) {
-	case *ast.StarExpr:
+	case *types.Pointer:
 		return n.checkedTypes.Contains(ptrType)
 
-	case *ast.FuncType:
+	case *types.Signature:
 		return n.checkedTypes.Contains(funcType)
 
-	case *ast.InterfaceType:
+	case *types.Interface:
 		return n.checkedTypes.Contains(ifaceType)
 
-	case *ast.MapType:
+	case *types.Map:
 		return n.checkedTypes.Contains(mapType)
 
-	case *ast.ChanType:
+	case *types.Chan:
 		return n.checkedTypes.Contains(chanType)
 
-	case *ast.Ident:
-		if t, ok := typeSpecs[v.Name]; ok {
-			return n.isDangerNilType(t.Type(), typeSpecs)
-		}
+	case *types.Named:
+		return n.isDangerNilType(v.Underlying())
 	}
 	return false
 }
 
-func (n *nilNil) isErrorField(f *ast.Field) bool {
-	return isIdent(f.Type, "error")
-}
+var errorIface = types.Universe.Lookup("error").Type().Underlying().(*types.Interface)
 
-func isNil(e ast.Expr) bool {
-	return isIdent(e, "nil")
+func (n *nilNil) isErrorField(pass *analysis.Pass, f *ast.Field) bool {
+	t := pass.TypesInfo.TypeOf(f.Type)
+	if t == nil {
+		return false
+	}
+
+	_, ok := t.Underlying().(*types.Interface)
+	return ok && types.Implements(t, errorIface)
 }
 
-func isIdent(n ast.Node, name string) bool {
-	i, ok := n.(*ast.Ident)
+func isNil(pass *analysis.Pass, e ast.Expr) bool {
+	i, ok := e.(*ast.Ident)
 	if !ok {
 		return false
 	}
-	return i.Name == name
-}
 
-type typer interface {
-	Type() ast.Expr
+	_, ok = pass.TypesInfo.ObjectOf(i).(*types.Nil)
+	return ok
 }
-
-func newTyper(t ast.Expr) typer     { return typerImpl{t: t} } //
-type typerImpl struct{ t ast.Expr } //
-func (ti typerImpl) Type() ast.Expr { return ti.t }

pkg/analyzer/analyzer_test.go

@@ -11,6 +11,7 @@ import (
 func TestNilNil(t *testing.T) {
 	pkgs := []string{
 		"examples",
+		"strange",
 	}
 	analysistest.Run(t, analysistest.TestData(), analyzer.New(), pkgs...)
 }

pkg/analyzer/testdata/src/examples/negative.go

@@ -1,16 +1,58 @@
 package examples
 
 import (
+	"bytes"
 	"io"
 	"unsafe"
 )
 
+// Not checked at all.
+
 func withoutArgs()                                {}
 func withoutError1() *User                        { return nil }
 func withoutError2() (*User, *User)               { return nil, nil }
 func withoutError3() (*User, *User, *User)        { return nil, nil, nil }
 func withoutError4() (*User, *User, *User, *User) { return nil, nil, nil, nil }
 
+// Valid.
+
+func structPtrTypeValid() (*User, error) {
+	if false {
+		return nil, io.EOF
+	}
+	return new(User), nil
+}
+
+func primitivePtrTypeValid() (*int, error) {
+	if false {
+		return nil, io.EOF
+	}
+	return new(int), nil
+}
+
+func channelTypeValid() (ChannelType, error) {
+	if false {
+		return nil, io.EOF
+	}
+	return make(ChannelType), nil
+}
+
+func funcTypeValid() (FuncType, error) {
+	if false {
+		return nil, io.EOF
+	}
+	return func(i int) int {
+		return 0
+	}, nil
+}
+
+func ifaceTypeValid() (io.Reader, error) {
+	if false {
+		return nil, io.EOF
+	}
+	return new(bytes.Buffer), nil
+}
+
 // Unsupported.
 
 func invalidOrder() (error, *User)               { return nil, nil }
@@ -19,7 +61,6 @@ func withError4th() (*User, *User, *User, error) { return nil, nil, nil, nil }
 func unsafePtr() (unsafe.Pointer, error)         { return nil, nil }
 func uintPtr() (uintptr, error)                  { return 0, nil }
 func slice() ([]int, error)                      { return nil, nil }
-func ifaceExtPkg() (io.Closer, error)            { return nil, nil }
 
 func implicitNil1() (*User, error) {
 	err := (error)(nil)

pkg/analyzer/testdata/src/examples/positive.go

@@ -122,3 +122,12 @@ func deeplyNested() {
 		}
 	}
 }
+
+type MyError interface {
+	error
+	Code() string
+}
+
+func myError() (*User, MyError) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}

pkg/analyzer/testdata/src/examples/positive_external_types.go

@@ -0,0 +1,36 @@
+package examples
+
+import (
+	"go/token"
+	"io"
+	"net/http"
+	"os"
+
+	"somepkg"
+)
+
+func structPtrTypeExtPkg() (*os.File, error) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}
+
+func primitivePtrTypeExtPkg() (*token.Token, error) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}
+
+func channelTypeExtPkg() (somepkg.ChannelType, error) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}
+
+func funcTypeExtPkg() (http.HandlerFunc, error) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}
+
+func ifaceTypeExtPkg() (io.Closer, error) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}
+
+type closerAlias = io.Closer
+
+func ifaceTypeAliasedExtPkg() (closerAlias, error) {
+	return nil, nil // want "return both the `nil` error and invalid value: use a sentinel error instead"
+}

pkg/analyzer/testdata/src/somepkg/channel.go

@@ -0,0 +1,3 @@
+package somepkg
+
+type ChannelType chan int

pkg/analyzer/testdata/src/strange/aliases.go

@@ -0,0 +1,12 @@
+package strange
+
+type error = *int
+
+func myOwnError() (*int, error) {
+	return nil, nil
+}
+
+func myOwnNil() (*int, error) {
+	nil := new(int)
+	return nil, nil
+}