go/analysis/passes/composite: update for generics

Warn about unkeyed composite literals via literals of type parameter
type.

Updates golang/go#48704

Change-Id: Ia75139b56cb73288c133bd547d71664464015813
Reviewed-on: https://go-review.googlesource.com/c/tools/+/357756
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Tim King <taking@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

go/analysis/passes/composite/composite.go

@@ -14,6 +14,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 const Doc = `check for unkeyed composite literals
@@ -67,41 +68,52 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			// skip whitelisted types
 			return
 		}
-		under := typ.Underlying()
-		for {
-			ptr, ok := under.(*types.Pointer)
-			if !ok {
-				break
+		terms, err := typeparams.StructuralTerms(typ)
+		if err != nil {
+			return // invalid type
+		}
+		for _, term := range terms {
+			under := deref(term.Type().Underlying())
+			if _, ok := under.(*types.Struct); !ok {
+				// skip non-struct composite literals
+				continue
 			}
-			under = ptr.Elem().Underlying()
-		}
-		if _, ok := under.(*types.Struct); !ok {
-			// skip non-struct composite literals
-			return
-		}
-		if isLocalType(pass, typ) {
-			// allow unkeyed locally defined composite literal
-			return
-		}
-
-		// check if the CompositeLit contains an unkeyed field
-		allKeyValue := true
-		for _, e := range cl.Elts {
-			if _, ok := e.(*ast.KeyValueExpr); !ok {
-				allKeyValue = false
-				break
+			if isLocalType(pass, term.Type()) {
+				// allow unkeyed locally defined composite literal
+				continue
 			}
-		}
-		if allKeyValue {
-			// all the composite literal fields are keyed
+
+			// check if the CompositeLit contains an unkeyed field
+			allKeyValue := true
+			for _, e := range cl.Elts {
+				if _, ok := e.(*ast.KeyValueExpr); !ok {
+					allKeyValue = false
+					break
+				}
+			}
+			if allKeyValue {
+				// all the composite literal fields are keyed
+				continue
+			}
+
+			pass.ReportRangef(cl, "%s composite literal uses unkeyed fields", typeName)
 			return
 		}
-
-		pass.ReportRangef(cl, "%s composite literal uses unkeyed fields", typeName)
 	})
 	return nil, nil
 }
 
+func deref(typ types.Type) types.Type {
+	for {
+		ptr, ok := typ.(*types.Pointer)
+		if !ok {
+			break
+		}
+		typ = ptr.Elem().Underlying()
+	}
+	return typ
+}
+
 func isLocalType(pass *analysis.Pass, typ types.Type) bool {
 	switch x := typ.(type) {
 	case *types.Struct:
@@ -112,6 +124,8 @@ func isLocalType(pass *analysis.Pass, typ types.Type) bool {
 	case *types.Named:
 		// names in package foo are local to foo_test too
 		return strings.TrimSuffix(x.Obj().Pkg().Path(), "_test") == strings.TrimSuffix(pass.Pkg.Path(), "_test")
+	case *typeparams.TypeParam:
+		return strings.TrimSuffix(x.Obj().Pkg().Path(), "_test") == strings.TrimSuffix(pass.Pkg.Path(), "_test")
 	}
 	return false
 }

go/analysis/passes/composite/composite_test.go

@@ -9,9 +9,14 @@ import (
 
 	"golang.org/x/tools/go/analysis/analysistest"
 	"golang.org/x/tools/go/analysis/passes/composite"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 func Test(t *testing.T) {
 	testdata := analysistest.TestData()
-	analysistest.Run(t, testdata, composite.Analyzer, "a")
+	pkgs := []string{"a"}
+	if typeparams.Enabled {
+		pkgs = append(pkgs, "typeparams")
+	}
+	analysistest.Run(t, testdata, composite.Analyzer, pkgs...)
 }

go/analysis/passes/composite/testdata/src/typeparams/lib/lib.go

@@ -0,0 +1,9 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package lib
+
+type Struct struct{ F int }
+type Slice []int
+type Map map[int]int

go/analysis/passes/composite/testdata/src/typeparams/typeparams.go

@@ -0,0 +1,27 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typeparams
+
+import "typeparams/lib"
+
+type localStruct struct { F int }
+
+func F[
+	T1 ~struct{ f int },
+	T2a localStruct,
+	T2b lib.Struct,
+	T3 ~[]int,
+	T4 lib.Slice,
+	T5 ~map[int]int,
+	T6 lib.Map,
+]() {
+	_ = T1{2}
+	_ = T2a{2}
+	_ = T2b{2} // want "unkeyed fields"
+	_ = T3{1,2}
+	_ = T4{1,2}
+	_ = T5{1:2}
+	_ = T6{1:2}
+}

internal/typeparams/normalize.go

@@ -5,6 +5,7 @@
 package typeparams
 
 import (
+	"errors"
 	"fmt"
 	"go/types"
 	"os"
@@ -65,6 +66,44 @@ func NormalizeInterface(iface *types.Interface) (*types.Interface, error) {
 	return types.NewInterfaceType(methods, embeddeds), nil
 }
 
+var ErrEmptyTypeSet = errors.New("empty type set")
+
+// StructuralTerms returns the normalized structural type restrictions of a
+// type, if any. For types that are not type parameters, it returns term slice
+// containing a single non-tilde term holding the given type. For type
+// parameters, it returns the normalized term list of the type parameter's
+// constraint. See NormalizeInterface for more information on the normal form
+// of a constraint interface.
+//
+// StructuralTerms returns an error if the structural term list cannot be
+// computed. If the type set of typ is empty, it returns ErrEmptyTypeSet.
+func StructuralTerms(typ types.Type) ([]*Term, error) {
+	switch typ := typ.(type) {
+	case *TypeParam:
+		iface, _ := typ.Constraint().(*types.Interface)
+		if iface == nil {
+			return nil, fmt.Errorf("constraint is %T, not *types.Interface", typ)
+		}
+		tset, err := computeTermSet(iface, make(map[types.Type]*termSet), 0)
+		if err != nil {
+			return nil, err
+		}
+		if tset.terms.isEmpty() {
+			return nil, ErrEmptyTypeSet
+		}
+		if tset.terms.isAll() {
+			return nil, nil
+		}
+		var terms []*Term
+		for _, term := range tset.terms {
+			terms = append(terms, NewTerm(term.tilde, term.typ))
+		}
+		return terms, nil
+	default:
+		return []*Term{NewTerm(false, typ)}, nil
+	}
+}
+
 // A termSet holds the normalized set of terms for a given type.
 //
 // The name termSet is intentionally distinct from 'type set': a type set is

internal/typeparams/typeparams_go117.go

@@ -164,19 +164,25 @@ func NamedTypeOrigin(named *types.Named) types.Type {
 	return named
 }
 
-// Term is a placeholder type, as type parameters are not supported at this Go
-// version. Its methods panic on use.
-type Term struct{}
+// Term holds information about a structural type restriction.
+type Term struct {
+	tilde bool
+	typ   types.Type
+}
 
-func (*Term) Tilde() bool            { unsupported(); return false }
-func (*Term) Type() types.Type       { unsupported(); return nil }
-func (*Term) String() string         { unsupported(); return "" }
-func (*Term) Underlying() types.Type { unsupported(); return nil }
+func (m *Term) Tilde() bool      { return m.tilde }
+func (m *Term) Type() types.Type { return m.typ }
+func (m *Term) String() string {
+	pre := ""
+	if m.tilde {
+		pre = "~"
+	}
+	return pre + m.typ.String()
+}
 
 // NewTerm is unsupported at this Go version, and panics.
 func NewTerm(tilde bool, typ types.Type) *Term {
-	unsupported()
-	return nil
+	return &Term{tilde, typ}
 }
 
 // Union is a placeholder type, as type parameters are not supported at this Go