hcl/printer: format single line objects to not have newline between

Fixes hashicorp#161

See hashicorp#161 and test cases for examples.

hcl/printer/nodes.go

@@ -171,7 +171,15 @@ func (p *printer) output(n interface{}) []byte {
 
  buf.Write(p.output(t.Items[index]))
  if index != len(t.Items)-1 {
- buf.Write([]byte{newline, newline})
+ // Always write a newline to separate us from the next item
+ buf.WriteByte(newline)
+
+ // If the next item is an object that is exactly one line,
+ // then we don't output another newline.
+ next := t.Items[index+1]
+ if next.Pos().Line != t.Items[index].Pos().Line+1 || !p.isSingleLineObject(next) {
+ buf.WriteByte(newline)
+ }
  }
  index++
  }
@@ -683,6 +691,36 @@ func (p *printer) heredocIndent(buf []byte) []byte {
  return res
 }
 
+// isSingleLineObject tells whether the given object item is a single
+// line object such as "obj {}".
+//
+// A single line object:
+//
+// * has no lead comments (hence multi-line)
+// * has no assignment
+// * has no values in the stanza (within {})
+//
+func (p *printer) isSingleLineObject(val *ast.ObjectItem) bool {
+ // If there is a lead comment, can't be one line
+ if val.LeadComment != nil {
+ return false
+ }
+
+ // If there is assignment, we always break by line
+ if val.Assign.IsValid() {
+ return false
+ }
+
+ // If it isn't an object type, then its not a single line object
+ ot, ok := val.Val.(*ast.ObjectType)
+ if !ok {
+ return false
+ }
+
+ // If the object has no items, it is single line!
+ return len(ot.List.Items) == 0
+}
+
 func lines(txt string) int {
  endline := 1
  for i := 0; i < len(txt); i++ {

hcl/printer/printer_test.go

@@ -44,6 +44,7 @@ var data = []entry{
  {"empty_block.input", "empty_block.golden"},
  {"list_of_objects.input", "list_of_objects.golden"},
  {"multiline_string.input", "multiline_string.golden"},
+ {"object_singleline.input", "object_singleline.golden"},
  {"object_with_heredoc.input", "object_with_heredoc.golden"},
 }
 

hcl/printer/testdata/empty_block.golden

@@ -1,5 +1,4 @@
 variable "foo" {}
-
 variable "foo" {}
 
 variable "foo" {

hcl/printer/testdata/object_singleline.golden

@@ -0,0 +1,20 @@
+variable "foo" {}
+variable "bar" {}
+variable "baz" {}
+
+variable "qux" {}
+
+variable "foo" {
+ foo = "bar"
+}
+
+variable "foo" {}
+
+# lead comment
+variable "bar" {}
+
+# Purposeful newline check below:
+
+variable "foo" {}
+
+variable "purposeful-newline" {}

hcl/printer/testdata/object_singleline.input

@@ -0,0 +1,16 @@
+variable "foo" {}
+variable "bar" {}
+variable "baz" {}
+
+variable "qux" {}
+variable "foo" { foo = "bar" }
+
+variable "foo" {}
+# lead comment
+variable "bar" {}
+
+# Purposeful newline check below:
+
+variable "foo" {}
+
+variable "purposeful-newline" {}