cue/format: avoid indenting a lone leading comment

We would often precede a comment with a vertical tab for alignment,
even when a comment began at the start of the line,
where vertical alignment is completely pointless.

This was largely harmless, except in a few edge cases such as
a single comment followed by a declaration, where we would indent.

Instead, only add the vertical tab if the comment does not begin
at the start of the line, resolving these issues.

Note that this change requires no longer using internal.NewComment
for top-level comments in a file, as the API always sets either of
the Doc or Line booleans in ast.Comment, causing extra and unwanted
blank spaces or newlines. A lone comment at the start of a file
is neither a doc comment nor a line (inline) comment.

Fixes #722.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: If9f1afb3f3e6dbdf65d5ee28c76a0f279c97aa49
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196134
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Aram Hăvărneanu <aram@cue.works>

cmd/cue/cmd/get_go.go

@@ -529,7 +529,9 @@ func (e *extractor) extractPkg(root string, p *packages.Package) error {
 		addDoc(f.Doc, pkg)
 
 		f := &cueast.File{Decls: []cueast.Decl{
-			internal.NewComment(false, "Code generated by cue get go. DO NOT EDIT."),
+			&cueast.CommentGroup{List: []*cueast.Comment{
+				{Text: "// Code generated by cue get go. DO NOT EDIT."},
+			}},
 			&cueast.CommentGroup{List: []*cueast.Comment{
 				{Text: "//cue:generate cue get go " + args},
 			}},

cue/ast/astutil/sanitize_test.go

@@ -101,7 +101,7 @@ a: bar.Min()
 			spec2 := ast.NewImport(nil, "foo/bar")
 			spec3 := ast.NewImport(ast.NewIdent("bar"), "foo")
 			return &ast.File{Decls: []ast.Decl{
-				internal.NewComment(false, "File comment"),
+				&ast.CommentGroup{List: []*ast.Comment{{Text: "// File comment"}}},
 				&ast.Package{Name: ast.NewIdent("pkg")},
 				&ast.Field{
 					Label: ast.NewIdent("a"),

cue/format/format.go

@@ -313,13 +313,12 @@ func (f *formatter) visitComments(until int8) {
 func (f *formatter) printComment(cg *ast.CommentGroup) {
 	f.Print(cg)
 
-	printBlank := false
 	if cg.Doc && len(f.output) > 0 {
 		f.Print(newline)
-		printBlank = true
 	}
 	for _, c := range cg.List {
-		if !printBlank {
+		if f.pos.Column > 1 {
+			// Vertically align inline comments.
 			f.Print(vtab)
 		}
 		f.Print(c.Slash)

cue/format/testdata/comments.txtar

@@ -334,10 +334,10 @@ foo: [
 -- comment_alone.golden --
 // Just one comment on its own.
 -- comment_field.input --
-// Just one comment on a field. TODO(mvdan): do not indent.
+// Just one comment on a field.
 foo: string
 -- comment_field.golden --
-	// Just one comment on a field. TODO(mvdan): do not indent.
+// Just one comment on a field.
 foo: string
 -- comments_alone.input --
 // Just a few comments

cue/format/testdata/expressions.txtar

@@ -589,7 +589,7 @@ _foo: {
 	// skip_create_image: true
 }
 -- issue2496.golden --
-		// TODO(mvdan): we indent the list elements too much.
+// TODO(mvdan): we indent the list elements too much.
 machine_type: [
 		if arch == "amd" {"n2-standard-2"},
 		if arch == "arm" {"t2a-standard-2"},

encoding/protobuf/jsonpb/testdata/decoder/null.txtar

@@ -88,7 +88,7 @@ a9: null
 // comment a10
 a10: null
 -- out/jsonpb/data.yaml --
-	// comment a0
+// comment a0
 a0: 0
 
 // comment a1
@@ -121,7 +121,7 @@ a9: true
 // comment a10
 a10: null
 -- out/jsonpb/data.cue --
-	// comment a0
+// comment a0
 a0: 0
 
 // comment a1

internal/core/export/testdata/main/disjunction.txtar

@@ -4,7 +4,7 @@ a: *1 | int
 b: *2 | int
 c: *(a & b) | 3
 -- out/definition --
-	// Issue #950
+// Issue #950
 a: *1 | int
 b: *2 | int
 c: *(a & b) | 3

internal/core/export/testdata/selfcontained/import.txtar

@@ -137,7 +137,7 @@ diff old new
 +++ new
 @@ -1,10 +1,7 @@
  import "tool/exec"
-
+ 
  // Can be inlined.
 -v: {
 -	x: 3

pkg/math/testdata/mult.txtar

@@ -12,7 +12,7 @@ f1: math.MultipleOf(5555555, 2)
 f2: math.MultipleOf(100.01, 4)
 
 -- out/math --
-	// should be true
+// should be true
 t1: true
 t2: true
 t3: true