format: don't group interface members of different kinds

For instance, don't group exported and unexported methods,
nor methods with non-methods.

Fixes #168.

Author: mvdan

format/format.go

@@ -483,7 +483,11 @@ func (f *fumpter) applyPre(c *astutil.Cursor) {
 				f.removeLines(f.Line(node.Interface)+1, f.Line(removeToPos))
 
 			case len(f.commentsBetween(prev.End(), method.Pos())) > 0:
-				// continue
+				// comments in between; leave newlines alone
+			case len(prev.Names) != len(method.Names):
+				// don't group type unions with methods
+			case len(prev.Names) == 1 && token.IsExported(prev.Names[0].Name) != token.IsExported(method.Names[0].Name):
+				// don't group exported and unexported methods together
 			default:
 				f.removeLinesBetween(prev.End(), method.Pos())
 			}

testdata/scripts/interface.txt

@@ -15,6 +15,11 @@ type i1 interface {
 
 	c(x int) int
 
+	D()
+
+	E()
+
+	f()
 }
 
 type i2 interface {
@@ -103,6 +108,11 @@ type i1 interface {
 	a(x int) int
 	b(x int) int
 	c(x int) int
+
+	D()
+	E()
+
+	f()
 }
 
 type i2 interface {

testdata/scripts/typeparams.txt

@@ -22,11 +22,20 @@ type PredeclaredSignedInteger interface {
 }
 
 type StringableSignedInteger interface {
+
 	~int | ~int8 | ~int16 | ~int32 | ~int64
+
 	String() string
 
 }
 
+type CombineEmbeds interface {
+	fmt.Stringer
+	comparable | io.Reader
+
+	Foo()
+}
+
 func Caller() {
 	Foo[int,int](1,2)
 }
@@ -45,9 +54,17 @@ type PredeclaredSignedInteger interface {
 
 type StringableSignedInteger interface {
 	~int | ~int8 | ~int16 | ~int32 | ~int64
+
 	String() string
 }
 
+type CombineEmbeds interface {
+	fmt.Stringer
+	comparable | io.Reader
+
+	Foo()
+}
+
 func Caller() {
 	Foo[int, int](1, 2)
 }