format: decl group allow first comment

fixes mvdan#212

format/format.go

@@ -316,13 +316,12 @@ func (f *fumpter) applyPre(c *astutil.Cursor) {
 	switch node := c.Node().(type) {
 	case *ast.File:
 		// Join contiguous lone var/const/import lines.
-		// Abort if there are empty lines or comments in between,
-		// including a leading comment, which could be a directive.
+		// Abort if there are empty lines or comments in between.
 		newDecls := make([]ast.Decl, 0, len(node.Decls))
 		for i := 0; i < len(node.Decls); {
 			newDecls = append(newDecls, node.Decls[i])
 			start, ok := node.Decls[i].(*ast.GenDecl)
-			if !ok || isCgoImport(start) || start.Doc != nil {
+			if !ok || isCgoImport(start) {
 				i++
 				continue
 			}

testdata/scripts/decl-group-many.txt

@@ -59,9 +59,8 @@ var v1 = "mixed"
 const c1 = "mixed"
 
 // comment, e.g. directive
-var v1 = 's'
-
 var (
+	v1 = 's'
 	v2 = 'd'
 	v3 = 'd'
 )