encoding/toml: decode syntax tree nodes with positions

Note that we don't do opening and closing token positions for table
structs and array table lists as they don't have delimiting tokens
in the original TOML, so we don't have any good position to use.
Moreover, it is faithful to the original syntax to use token.NoPos
to signal that delimiting tokens did not exist, and we are creating them
with only relative positions for the sake of good formatting.

Fixes #3379.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I71e659e5d597b72a3160f2837e606414b3284dc9
Dispatch-Trailer: {"type":"trybot","CL":1199938,"patchset":1,"ref":"refs/changes/38/1199938/1","targetBranch":"master"}

cmd/cue/cmd/testdata/script/vet_data.txtar

@@ -6,7 +6,6 @@ cmp stderr yaml-stderr
 
 # Ensure this also works for other encodings.
 
-# TODO(mvdan): note that TOML lacks position information still.
 ! exec cue vet schema.cue data.toml
 cmp stderr toml-stderr
 
@@ -42,3 +41,4 @@ languages.1.name: invalid value "dutch" (out of bound =~"^\\p{Lu}"):
 -- toml-stderr --
 languages.1.name: invalid value "dutch" (out of bound =~"^\\p{Lu}"):
     ./schema.cue:3:8
+    ./data.toml:5:8

encoding/toml/decode.go

@@ -102,14 +102,13 @@ type rootedKey = string
 
 // openTableArray records information about a declared table array.
 type openTableArray struct {
-	key       rootedKey
+	rkey      rootedKey
 	level     int // the level of nesting, 1 or higher, e.g. 2 for key="foo.bar"
 	list      *ast.ListLit
 	lastTable *ast.StructLit
 }
 
 // TODO(mvdan): support decoding comments
-// TODO(mvdan): support ast.Node positions
 
 // Decode parses the input stream as TOML and converts it to a CUE [*ast.File].
 // Because TOML files only contain a single top-level expression,
@@ -146,14 +145,17 @@ func (d *Decoder) Decode() (ast.Expr, error) {
 	return d.topFile, nil
 }
 
-func (d *Decoder) nodeErrf(tnode *toml.Node, format string, args ...any) error {
+func (d *Decoder) shape(tnode *toml.Node) toml.Shape {
 	if tnode.Raw.Length == 0 {
 		// Otherwise the Shape method call below happily returns a position like 1:1,
 		// which is worse than no position information as it confuses the user.
-		panic("Decoder.errf was given an empty toml.Node as position")
+		panic("Decoder.nodePos was given an empty toml.Node as position")
 	}
-	pos := d.parser.Shape(tnode.Raw).Start
-	return d.posErrf(pos, format, args...)
+	return d.parser.Shape(tnode.Raw)
+}
+
+func (d *Decoder) nodeErrf(tnode *toml.Node, format string, args ...any) error {
+	return d.posErrf(d.shape(tnode).Start, format, args...)
 }
 
 func (d *Decoder) posErrf(pos toml.Position, format string, args ...any) error {
@@ -198,7 +200,7 @@ func (d *Decoder) nextRootNode(tnode *toml.Node) error {
 
 	case toml.Table:
 		// Tables always begin a new line.
-		key, keyElems := decodeKey("", tnode.Key())
+		key, keyElems := d.decodeKey("", tnode.Key())
 		// All table keys must be unique, including for the top-level table.
 		if d.seenTableKeys[key] {
 			return d.nodeErrf(tnode.Child(), "duplicate key: %s", key)
@@ -208,33 +210,35 @@ func (d *Decoder) nextRootNode(tnode *toml.Node) error {
 		// We want a multi-line struct with curly braces,
 		// just like TOML's tables are on multiple lines.
 		d.currentTable = &ast.StructLit{
+			// No positions, as TOML doesn't have table delimiters.
 			Lbrace: token.NoPos.WithRel(token.Blank),
 			Rbrace: token.NoPos.WithRel(token.Newline),
 		}
 		array := d.findArrayPrefix(key)
 		if array != nil { // [last_array.new_table]
-			if array.key == key {
+			if array.rkey == key {
 				return d.nodeErrf(tnode.Child(), "cannot redeclare table array %q as a table", key)
 			}
 			subKeyElems := keyElems[array.level:]
-			topField, leafField := inlineFields(subKeyElems, token.Newline)
+			topField, leafField := d.inlineFields(subKeyElems, token.Newline)
 			array.lastTable.Elts = append(array.lastTable.Elts, topField)
 			leafField.Value = d.currentTable
 		} else { // [new_table]
-			topField, leafField := inlineFields(keyElems, token.Newline)
+			topField, leafField := d.inlineFields(keyElems, token.Newline)
 			d.topFile.Elts = append(d.topFile.Elts, topField)
 			leafField.Value = d.currentTable
 		}
 		d.currentTableKey = key
 
 	case toml.ArrayTable:
 		// Table array elements always begin a new line.
-		key, keyElems := decodeKey("", tnode.Key())
+		key, keyElems := d.decodeKey("", tnode.Key())
 		if d.seenTableKeys[key] {
 			return d.nodeErrf(tnode.Child(), "cannot redeclare key %q as a table array", key)
 		}
 		// Each struct inside a table array sits on separate lines.
 		d.currentTable = &ast.StructLit{
+			// No positions, as TOML doesn't have table delimiters.
 			Lbrace: token.NoPos.WithRel(token.Newline),
 			Rbrace: token.NoPos.WithRel(token.Newline),
 		}
@@ -248,26 +252,27 @@ func (d *Decoder) nextRootNode(tnode *toml.Node) error {
 			// We want a multi-line list with square braces,
 			// since TOML's table arrays are on multiple lines.
 			list := &ast.ListLit{
+				// No positions, as TOML doesn't have array table delimiters.
 				Lbrack: token.NoPos.WithRel(token.Blank),
 				Rbrack: token.NoPos.WithRel(token.Newline),
 			}
 			if array == nil {
 				// [[new_array]] - at the top level
-				topField, leafField := inlineFields(keyElems, token.Newline)
+				topField, leafField := d.inlineFields(keyElems, token.Newline)
 				d.topFile.Elts = append(d.topFile.Elts, topField)
 				leafField.Value = list
 			} else {
 				// [[last_array.new_array]] - on the last array element
 				subKeyElems := keyElems[array.level:]
-				topField, leafField := inlineFields(subKeyElems, token.Newline)
+				topField, leafField := d.inlineFields(subKeyElems, token.Newline)
 				array.lastTable.Elts = append(array.lastTable.Elts, topField)
 				leafField.Value = list
 			}
 
 			d.currentTableKey = key + ".0"
 			list.Elts = append(list.Elts, d.currentTable)
 			d.openTableArrays = append(d.openTableArrays, openTableArray{
-				key:       key,
+				rkey:      key,
 				level:     len(keyElems),
 				list:      list,
 				lastTable: d.currentTable,
@@ -281,18 +286,18 @@ func (d *Decoder) nextRootNode(tnode *toml.Node) error {
 }
 
 // decodeField decodes a single table key and its value as a struct field.
-func (d *Decoder) decodeField(key rootedKey, tnode *toml.Node, relPos token.RelPos) (*ast.Field, error) {
-	key, keyElems := decodeKey(key, tnode.Key())
-	if d.findArray(key) != nil {
-		return nil, d.nodeErrf(tnode.Child().Next(), "cannot redeclare table array %q as a table", key)
+func (d *Decoder) decodeField(rkey rootedKey, tnode *toml.Node, relPos token.RelPos) (*ast.Field, error) {
+	rkey, keyElems := d.decodeKey(rkey, tnode.Key())
+	if d.findArray(rkey) != nil {
+		return nil, d.nodeErrf(tnode.Child().Next(), "cannot redeclare table array %q as a table", rkey)
 	}
-	topField, leafField := inlineFields(keyElems, relPos)
+	topField, leafField := d.inlineFields(keyElems, relPos)
 	// All table keys must be unique, including inner table ones.
-	if d.seenTableKeys[key] {
-		return nil, d.nodeErrf(tnode.Child().Next(), "duplicate key: %s", key)
+	if d.seenTableKeys[rkey] {
+		return nil, d.nodeErrf(tnode.Child().Next(), "duplicate key: %s", rkey)
 	}
-	d.seenTableKeys[key] = true
-	value, err := d.decodeExpr(key, tnode.Value())
+	d.seenTableKeys[rkey] = true
+	value, err := d.decodeExpr(rkey, tnode.Value())
 	if err != nil {
 		return nil, err
 	}
@@ -301,9 +306,9 @@ func (d *Decoder) decodeField(key rootedKey, tnode *toml.Node, relPos token.RelP
 }
 
 // findArray returns an existing table array if one exists at exactly the given key.
-func (d *Decoder) findArray(key rootedKey) *openTableArray {
+func (d *Decoder) findArray(rkey rootedKey) *openTableArray {
 	for i, arr := range d.openTableArrays {
-		if arr.key == key {
+		if arr.rkey == rkey {
 			return &d.openTableArrays[i]
 		}
 	}
@@ -312,18 +317,18 @@ func (d *Decoder) findArray(key rootedKey) *openTableArray {
 
 // findArray returns an existing table array if one exists at exactly the given key
 // or as a prefix to the given key.
-func (d *Decoder) findArrayPrefix(key rootedKey) *openTableArray {
+func (d *Decoder) findArrayPrefix(rkey rootedKey) *openTableArray {
 	// TODO(mvdan): see the performance TODO on [Decoder.openTableArrays].
 
 	// Prefer an exact match over a relative prefix match.
-	if arr := d.findArray(key); arr != nil {
+	if arr := d.findArray(rkey); arr != nil {
 		return arr
 	}
 	// The longest relative key match wins.
 	maxLevel := 0
 	var maxLevelArr *openTableArray
 	for i, arr := range d.openTableArrays {
-		if strings.HasPrefix(key, arr.key+".") && arr.level > maxLevel {
+		if strings.HasPrefix(rkey, arr.rkey+".") && arr.level > maxLevel {
 			maxLevel = arr.level
 			maxLevelArr = &d.openTableArrays[i]
 		}
@@ -334,20 +339,28 @@ func (d *Decoder) findArrayPrefix(key rootedKey) *openTableArray {
 	return nil
 }
 
+// tomlKey represents a name with a position which forms part of a TOML dotted key,
+// such as "foo" from "[foo.bar.baz]".
+type tomlKey struct {
+	name  string
+	shape toml.Shape
+}
+
 // decodeKey extracts a rootedKey from a TOML node key iterator,
 // appending to the given parent key and returning the unquoted string elements.
-func decodeKey(key rootedKey, iter toml.Iterator) (rootedKey, []string) {
-	var elems []string
+func (d *Decoder) decodeKey(rkey rootedKey, iter toml.Iterator) (rootedKey, []tomlKey) {
+	var elems []tomlKey
 	for iter.Next() {
-		name := string(iter.Node().Data)
+		node := iter.Node()
+		name := string(node.Data)
 		// TODO(mvdan): use an append-like API once we have benchmarks
-		if len(key) > 0 {
-			key += "."
+		if len(rkey) > 0 {
+			rkey += "."
 		}
-		key += quoteLabelIfNeeded(name)
-		elems = append(elems, name)
+		rkey += quoteLabelIfNeeded(name)
+		elems = append(elems, tomlKey{name, d.shape(node)})
 	}
-	return key, elems
+	return rkey, elems
 }
 
 // inlineFields constructs a single-line chain of CUE fields joined with structs,
@@ -361,15 +374,15 @@ func decodeKey(key rootedKey, iter toml.Iterator) (rootedKey, []string) {
 //
 // The "top" field, in this case "foo", can then be added as an element to a struct.
 // The "leaf" field, in this case "zzz", leaves its value as nil to be filled out.
-func inlineFields(names []string, relPos token.RelPos) (top, leaf *ast.Field) {
+func (d *Decoder) inlineFields(tkeys []tomlKey, relPos token.RelPos) (top, leaf *ast.Field) {
 	curField := &ast.Field{
-		Label: label(names[0], token.NoPos.WithRel(relPos)),
+		Label: d.label(tkeys[0], relPos),
 	}
 
 	topField := curField
-	for _, elem := range names[1:] {
+	for _, tkey := range tkeys[1:] {
 		nextField := &ast.Field{
-			Label: label(elem, token.NoPos.WithRel(token.Blank)), // on the same line
+			Label: d.label(tkey, token.Blank), // on the same line
 		}
 		curField.Value = &ast.StructLit{Elts: []ast.Decl{nextField}}
 		curField = nextField
@@ -391,47 +404,49 @@ func quoteLabelIfNeeded(name string) string {
 // This means a quoted string literal for the key "_", as TOML never means "top",
 // as well as for any keys beginning with an underscore, as we don't want to hide any fields.
 // cue/format knows how to quote any other identifiers correctly.
-func label(name string, pos token.Pos) ast.Label {
-	if strings.HasPrefix(name, "_") {
+func (d *Decoder) label(tkey tomlKey, relPos token.RelPos) ast.Label {
+	pos := d.tokenFile.Pos(tkey.shape.Start.Offset, relPos)
+	if strings.HasPrefix(tkey.name, "_") {
 		return &ast.BasicLit{
 			ValuePos: pos,
 			Kind:     token.STRING,
-			Value:    literal.String.Quote(name),
+			Value:    literal.String.Quote(tkey.name),
 		}
 	}
 	return &ast.Ident{
 		NamePos: pos,
-		Name:    name,
+		Name:    tkey.name,
 	}
 }
 
 // decodeExpr decodes a single TOML value expression, found on the right side
 // of a `key = value` line.
-func (d *Decoder) decodeExpr(key rootedKey, tnode *toml.Node) (ast.Expr, error) {
+func (d *Decoder) decodeExpr(rkey rootedKey, tnode *toml.Node) (ast.Expr, error) {
 	// TODO(mvdan): we currently assume that TOML basic literals (string, int, float)
 	// are also valid CUE literals; we should double check this, perhaps via fuzzing.
 	data := string(tnode.Data)
+	var expr ast.Expr
 	switch tnode.Kind {
 	case toml.String:
-		return ast.NewString(data), nil
+		expr = ast.NewString(data)
 	case toml.Integer:
-		return ast.NewLit(token.INT, data), nil
+		expr = ast.NewLit(token.INT, data)
 	case toml.Float:
-		return ast.NewLit(token.FLOAT, data), nil
+		expr = ast.NewLit(token.FLOAT, data)
 	case toml.Bool:
-		return ast.NewBool(data == "true"), nil
+		expr = ast.NewBool(data == "true")
 	case toml.Array:
 		list := &ast.ListLit{}
 		elems := tnode.Children()
 		for elems.Next() {
-			key := key + "." + strconv.Itoa(len(list.Elts))
+			key := rkey + "." + strconv.Itoa(len(list.Elts))
 			elem, err := d.decodeExpr(key, elems.Node())
 			if err != nil {
 				return nil, err
 			}
 			list.Elts = append(list.Elts, elem)
 		}
-		return list, nil
+		expr = list
 	case toml.InlineTable:
 		strct := &ast.StructLit{
 			// We want a single-line struct, just like TOML's inline tables are on a single line.
@@ -441,15 +456,21 @@ func (d *Decoder) decodeExpr(key rootedKey, tnode *toml.Node) (ast.Expr, error)
 		elems := tnode.Children()
 		for elems.Next() {
 			// Inline table fields are on the same line.
-			field, err := d.decodeField(key, elems.Node(), token.Blank)
+			field, err := d.decodeField(rkey, elems.Node(), token.Blank)
 			if err != nil {
 				return nil, err
 			}
 			strct.Elts = append(strct.Elts, field)
 		}
-		return strct, nil
+		expr = strct
 	// TODO(mvdan): dates and times
 	default:
 		return nil, fmt.Errorf("encoding/toml.Decoder.decodeExpr: unknown %s %#v", tnode.Kind, tnode)
 	}
+	// TODO(mvdan): some go-toml nodes such as Kind=toml.Bool do not seem to have a Raw Range
+	// which would let us grab their position information; fix this upstream.
+	if tnode.Raw.Length > 0 {
+		ast.SetPos(expr, d.tokenFile.Pos(d.shape(tnode).Start.Offset, token.NoRelPos))
+	}
+	return expr, nil
 }