relax rule to insert newlines in func signatures

In particular, in cases where a field list fits all in one line,
adding a newline at the end of the field list is clearly wrong.

Fixes #235.

Author: mvdan

format/format.go

@@ -546,12 +546,19 @@ func (f *fumpter) applyPre(c *astutil.Cursor) {
 
 			if f.Line(sign.Pos()) != endLine {
 				handleMultiLine := func(fl *ast.FieldList) {
+					// Refuse to insert a newline before the closing token
+					// if the list is empty or all in one line.
 					if fl == nil || len(fl.List) == 0 {
 						return
 					}
+					fieldOpeningLine := f.Line(fl.Opening)
+					fieldClosingLine := f.Line(fl.Closing)
+					if fieldOpeningLine == fieldClosingLine {
+						return
+					}
+
 					lastFieldEnd := fl.List[len(fl.List)-1].End()
 					lastFieldLine := f.Line(lastFieldEnd)
-					fieldClosingLine := f.Line(fl.Closing)
 					isLastFieldOnFieldClosingLine := lastFieldLine == fieldClosingLine
 					isLastFieldOnSigClosingLine := lastFieldLine == endLine
 

testdata/script/typeparams.txtar

@@ -36,6 +36,22 @@ type CombineEmbeds interface {
 func Caller() {
 	Foo[int,int](1,2)
 }
+
+func Issue235[K interface {
+	comparable
+	constraints.Ordered
+}, V any](m map[K]V) []K {
+	keys := maps.Keys(m)
+	slices.Sort(keys)
+	return keys
+}
+
+func multilineParams[V any](p1 V,
+	p2 V) {
+
+	println("body")
+
+}
 -- foo.go.golden --
 package p
 
@@ -65,3 +81,18 @@ type CombineEmbeds interface {
 func Caller() {
 	Foo[int, int](1, 2)
 }
+
+func Issue235[K interface {
+	comparable
+	constraints.Ordered
+}, V any](m map[K]V) []K {
+	keys := maps.Keys(m)
+	slices.Sort(keys)
+	return keys
+}
+
+func multilineParams[V any](p1 V,
+	p2 V,
+) {
+	println("body")
+}