cue/format: ensure a newline after every comment

This is similar to the nooverride whiteSpace flag,
but only enforces the newline whitespace token to be printed.

Fixes #2567.

Co-authored-by: Daniel Martí <mvdan@mvdan.cc>
Co-authored-by: Noam Dolovich <noam.tzvi.dolovich@gmail.com>
Signed-off-by: Noam Dolovich <noam.tzvi.dolovich@gmail.com>
Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I83bebcca9aeba14f84cbcf4c4befa0677da3fb0f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1195628
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

cue/format/format.go

@@ -331,6 +331,7 @@ func (f *formatter) printComment(cg *ast.CommentGroup) {
 		f.Print(c.Slash)
 		f.Print(c)
 		if isEnd {
+			f.printingComment = true
 			f.Print(newline)
 			if cg.Doc {
 				f.Print(nooverride)

cue/format/printer.go

@@ -46,6 +46,12 @@ type printer struct {
 	spaceBefore      bool
 	prevLbraceOnLine bool // true if a '{' has been written on the current line
 
+	// TODO(mvdan): This is similar to nooverride but used only for comments,
+	// to ensure that we always print a newline after them.
+	// We should fix our logic with whiteSpace instead, but for now this ensures
+	// we don't break the syntax by omitting the newline after a comment.
+	printingComment bool
+
 	errs errors.Error
 }
 
@@ -231,6 +237,9 @@ func (p *printer) Print(v interface{}) {
 				case token.NewSection:
 					requested |= newsection
 				}
+				if p.printingComment {
+					requested |= newline
+				}
 				p.writeWhitespace(requested)
 				p.allowed = 0
 				p.requested = 0
@@ -247,6 +256,7 @@ func (p *printer) Print(v interface{}) {
 	p.writeWhitespace(p.allowed)
 	p.allowed = 0
 	p.requested = 0
+	p.printingComment = false
 	p.writeString(data, isLit)
 	p.allowed = nextWS
 	_ = impliedComma // TODO: delay comment printings

cue/format/testdata/comments.golden

@@ -135,3 +135,12 @@ funcArg3: foo(
 	)
 
 //	comment including		some tabs
+
+// issue #2567
+foo: [
+	bar["baz"], //some comment
+]
+
+[
+	if true {}, // inline comment
+]

cue/format/testdata/comments.input

@@ -145,3 +145,13 @@ funcArg3: foo(
 )
 
 //	comment including		some tabs
+
+
+// issue #2567
+foo: [
+ 	bar["baz"], //some comment
+]
+
+[
+	if true // inline comment
+	{}]