cmd/doc: don't log on constraint type elements

Fixes #50256

Change-Id: I2327a0b28f8173c801ed2946bec8083967667027
Reviewed-on: https://go-review.googlesource.com/c/go/+/373314
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/doc/doc_test.go

@@ -7,6 +7,7 @@ package main
 import (
 	"bytes"
 	"flag"
+	"log"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -125,6 +126,9 @@ var tests = []test{
 			`func MultiLineFunc\(x interface{ ... }\) \(r struct{ ... }\)`, // Multi line function.
 			`var LongLine = newLongLine\(("someArgument[1-4]", ){4}...\)`,  // Long list of arguments.
 			`type T1 = T2`,                                                 // Type alias
+			`type SimpleConstraint interface{ ... }`,
+			`type TildeConstraint interface{ ... }`,
+			`type StructConstraint interface{ ... }`,
 		},
 		[]string{
 			`const internalConstant = 2`,       // No internal constants.
@@ -199,6 +203,9 @@ var tests = []test{
 			`Comment about exported method`,
 			`type T1 = T2`,
 			`type T2 int`,
+			`type SimpleConstraint interface {`,
+			`type TildeConstraint interface {`,
+			`type StructConstraint interface {`,
 		},
 		[]string{
 			`constThree`,
@@ -822,13 +829,19 @@ var tests = []test{
 
 func TestDoc(t *testing.T) {
 	maybeSkip(t)
+	defer log.SetOutput(log.Writer())
 	for _, test := range tests {
 		var b bytes.Buffer
 		var flagSet flag.FlagSet
+		var logbuf bytes.Buffer
+		log.SetOutput(&logbuf)
 		err := do(&b, &flagSet, test.args)
 		if err != nil {
 			t.Fatalf("%s %v: %s\n", test.name, test.args, err)
 		}
+		if logbuf.Len() > 0 {
+			t.Errorf("%s %v: unexpected log messages:\n%s", test.name, test.args, logbuf.Bytes())
+		}
 		output := b.Bytes()
 		failed := false
 		for j, yes := range test.yes {

src/cmd/doc/pkg.go

@@ -865,6 +865,7 @@ func trimUnexportedFields(fields *ast.FieldList, isInterface bool) *ast.FieldLis
 		if len(names) == 0 {
 			// Embedded type. Use the name of the type. It must be of the form ident or
 			// pkg.ident (for structs and interfaces), or *ident or *pkg.ident (structs only).
+			// Or a type embedded in a constraint.
 			// Nothing else is allowed.
 			ty := field.Type
 			if se, ok := field.Type.(*ast.StarExpr); !isInterface && ok {
@@ -872,6 +873,7 @@ func trimUnexportedFields(fields *ast.FieldList, isInterface bool) *ast.FieldLis
 				// embedded types in structs.
 				ty = se.X
 			}
+			constraint := false
 			switch ident := ty.(type) {
 			case *ast.Ident:
 				if isInterface && ident.Name == "error" && ident.Obj == nil {
@@ -885,8 +887,12 @@ func trimUnexportedFields(fields *ast.FieldList, isInterface bool) *ast.FieldLis
 			case *ast.SelectorExpr:
 				// An embedded type may refer to a type in another package.
 				names = []*ast.Ident{ident.Sel}
+			default:
+				// An approximation or union or type
+				// literal in an interface.
+				constraint = true
 			}
-			if names == nil {
+			if names == nil && !constraint {
 				// Can only happen if AST is incorrect. Safe to continue with a nil list.
 				log.Print("invalid program: unexpected type for embedded field")
 			}

src/cmd/doc/testdata/pkg.go

@@ -238,3 +238,15 @@ type ExportedFormattedType struct {
 	// Text after pre-formatted block.
 	ExportedField int
 }
+
+type SimpleConstraint interface {
+	~int | ~float64
+}
+
+type TildeConstraint interface {
+	~int
+}
+
+type StructConstraint interface {
+	struct { F int }
+}