fix(document): rebuild set nodes and write documents back round-trip

Assisted-by: GLM 5.3

document.go

@@ -34,15 +34,31 @@ func (d *Document) Root() *Table {
 }
 
 // Map returns the value tree, the shape ParseMap gives. It is the tree the
-// document was parsed into, not a copy.
-func (d *Document) Map() map[string]any { return d.root.values }
+// document was parsed into, not a copy. A nil document or one with no root
+// holds no values.
+func (d *Document) Map() map[string]any {
+	if d == nil || d.root == nil {
+		return nil
+	}
+	return d.root.values
+}
 
 // Footer returns the comment lines that follow the last statement, and every
 // line of a document that holds no statement at all.
-func (d *Document) Footer() []string { return d.footer }
+func (d *Document) Footer() []string {
+	if d == nil {
+		return nil
+	}
+	return d.footer
+}
 
 // SetFooter replaces those lines.
-func (d *Document) SetFooter(lines []string) { d.footer = lines }
+func (d *Document) SetFooter(lines []string) {
+	if d == nil {
+		return
+	}
+	d.footer = lines
+}
 
 // The document-level convenience forms of the Table edit API; they act on
 // the root table.
@@ -87,6 +103,11 @@ type Table struct {
 	// rather than under a header or as a dotted key.
 	inline bool
 
+	// dotted records that a dotted key introduced the table, `a.b = 1`
+	// building the a around the leaf: the write side gives such a table back
+	// as dotted key lines, the form that holds the position of a line.
+	dotted bool
+
 	// comments are the lines above the table's header, trailing is the comment
 	// on the header's own line. Both are empty for a table a dotted key
 	// introduced, which has no line of its own.
@@ -98,8 +119,12 @@ func newTable(values map[string]any) *Table {
 	return &Table{values: values, index: map[string]*Entry{}}
 }
 
-// Keys returns the table's keys in the order they were written.
+// Keys returns the table's keys in the order they were written. A nil table
+// holds none, the answer a document without a root gives through Root.
 func (t *Table) Keys() []string {
+	if t == nil {
+		return nil
+	}
 	keys := make([]string, len(t.entries))
 	for i, e := range t.entries {
 		keys[i] = e.key
@@ -109,43 +134,75 @@ func (t *Table) Keys() []string {
 
 // Values returns the table's values, which is the map the value tree holds for
 // it.
-func (t *Table) Values() map[string]any { return t.values }
+func (t *Table) Values() map[string]any {
+	if t == nil {
+		return nil
+	}
+	return t.values
+}
 
 // Entries returns the table's entries in written order.
-func (t *Table) Entries() []*Entry { return t.entries }
+func (t *Table) Entries() []*Entry {
+	if t == nil {
+		return nil
+	}
+	return t.entries
+}
 
 // Get returns the entry for key, and whether the table has one.
 func (t *Table) Get(key string) (*Entry, bool) {
+	if t == nil {
+		return nil, false
+	}
 	e, ok := t.index[key]
 	return e, ok
 }
 
 // Inline reports whether the table was written as an inline table, `{…}`,
 // rather than under a header or introduced by a dotted key.
-func (t *Table) Inline() bool { return t.inline }
+func (t *Table) Inline() bool { return t != nil && t.inline }
 
 // Comments returns the comment lines above the table's header, or above the
 // key that introduced it. Lines carry no leading '#' and no surrounding space.
-func (t *Table) Comments() []string { return t.comments }
+func (t *Table) Comments() []string {
+	if t == nil {
+		return nil
+	}
+	return t.comments
+}
 
 // SetComments replaces those lines. Each line is written back with a "# " in
 // front of it, so a line should not carry one.
-func (t *Table) SetComments(lines []string) { t.comments = lines }
+func (t *Table) SetComments(lines []string) {
+	if t == nil {
+		return
+	}
+	t.comments = lines
+}
 
 // Trailing returns the comment on the header's own line, without the '#'.
-func (t *Table) Trailing() string { return t.trailing }
+func (t *Table) Trailing() string {
+	if t == nil {
+		return ""
+	}
+	return t.trailing
+}
 
 // SetTrailing replaces that comment.
-func (t *Table) SetTrailing(line string) { t.trailing = line }
+func (t *Table) SetTrailing(line string) {
+	if t == nil {
+		return
+	}
+	t.trailing = line
+}
 
-// addValue records a key of the table, in written order.
+// addValue records a key of the table, in written order. The caller gives
+// the entry a table node or element nodes when the value has that shape; a
+// map value left without a node writes as an inline table.
 func (t *Table) addValue(key string, val any, inline bool) *Entry {
 	e := &Entry{table: t, key: key, inline: inline}
 	t.entries = append(t.entries, e)
 	t.index[key] = e
-	if node, ok := val.(map[string]any); ok {
-		e.child = newTable(node)
-	}
 	return e
 }
 
@@ -178,6 +235,9 @@ func (t *Table) addElement(key string, values map[string]any) *Table {
 
 // child returns the node of a table-valued key, or nil.
 func (t *Table) child(key string) *Table {
+	if t == nil {
+		return nil
+	}
 	if e, ok := t.index[key]; ok {
 		return e.child
 	}
@@ -239,6 +299,9 @@ func (e *Entry) SetTrailing(line string) { e.trailing = line }
 
 // GetString returns the string the key holds, and whether it holds one.
 func (t *Table) GetString(key string) (string, bool) {
+	if t == nil {
+		return "", false
+	}
 	v, ok := t.values[key]
 	s, ok := v.(string)
 	return s, ok
@@ -246,6 +309,9 @@ func (t *Table) GetString(key string) (string, bool) {
 
 // GetInt returns the integer the key holds, and whether it holds one.
 func (t *Table) GetInt(key string) (int64, bool) {
+	if t == nil {
+		return 0, false
+	}
 	v, ok := t.values[key]
 	i, ok := v.(int64)
 	return i, ok
@@ -253,6 +319,9 @@ func (t *Table) GetInt(key string) (int64, bool) {
 
 // GetFloat returns the float the key holds, and whether it holds one.
 func (t *Table) GetFloat(key string) (float64, bool) {
+	if t == nil {
+		return 0, false
+	}
 	v, ok := t.values[key]
 	f, ok := v.(float64)
 	return f, ok
@@ -260,6 +329,9 @@ func (t *Table) GetFloat(key string) (float64, bool) {
 
 // GetBool returns the boolean the key holds, and whether it holds one.
 func (t *Table) GetBool(key string) (bool, bool) {
+	if t == nil {
+		return false, false
+	}
 	v, ok := t.values[key]
 	b, ok := v.(bool)
 	return b, ok
@@ -267,6 +339,9 @@ func (t *Table) GetBool(key string) (bool, bool) {
 
 // GetArray returns the value array the key holds, and whether it holds one.
 func (t *Table) GetArray(key string) ([]any, bool) {
+	if t == nil {
+		return nil, false
+	}
 	v, ok := t.values[key]
 	a, ok := v.([]any)
 	return a, ok
@@ -282,9 +357,13 @@ func (t *Table) GetTable(key string) (*Table, bool) {
 // Set stores value under key. A key the table already has keeps its position
 // and its comments; a new one joins the end. A value of map[string]any
 // becomes a table node of its own, written under a header like any other
-// table; a Go map carries no order, so its keys take sorted order. A value
+// table, and replaces the node the key held, which belonged to the value the
+// key held; a Go map carries no order, so its keys take sorted order. A value
 // of []map[string]any becomes an array-of-tables node.
 func (t *Table) Set(key string, value any) {
+	if t == nil {
+		return
+	}
 	e, ok := t.index[key]
 	if !ok {
 		t.values[key] = value
@@ -303,11 +382,10 @@ func (t *Table) Set(key string, value any) {
 	t.values[key] = value
 	switch v := value.(type) {
 	case map[string]any:
-		if e.child == nil {
-			e.child = newOrderedTable(v)
-		} else {
-			e.child.values = v
-		}
+		// The node is rebuilt rather than patched: the entries and the index
+		// belong to the table the key held, and writing the new value
+		// through them would leave the old table's keys in the output.
+		e.child = newOrderedTable(v)
 		e.elements = nil
 	case []map[string]any:
 		e.child = nil
@@ -322,15 +400,30 @@ func (t *Table) Set(key string, value any) {
 }
 
 // newOrderedTable builds a table node for a value the caller set, its keys
-// entered as entries in sorted order, the order Marshal writes maps in.
+// entered in sorted order, the order Marshal writes maps in.
 func newOrderedTable(m map[string]any) *Table {
+	return orderedTable(m, 0)
+}
+
+// orderedTable is newOrderedTable's recursion. The depth bound is the value
+// encoder's: a cyclic map stopped here is written by the value writer, which
+// reports it instead of running the stack out.
+func orderedTable(m map[string]any, depth int) *Table {
 	t := newTable(m)
 	for _, k := range slices.Sorted(maps.Keys(m)) {
 		v := m[k]
-		_, isMap := v.(map[string]any)
 		e := t.addValue(k, v, false)
-		if isMap {
-			e.child = newOrderedTable(v.(map[string]any))
+		if depth >= maxEncodeDepth {
+			continue
+		}
+		switch val := v.(type) {
+		case map[string]any:
+			e.child = orderedTable(val, depth+1)
+		case []map[string]any:
+			e.elements = make([]*Table, len(val))
+			for i, item := range val {
+				e.elements[i] = orderedTable(item, depth+1)
+			}
 		}
 	}
 	return t
@@ -338,6 +431,9 @@ func newOrderedTable(m map[string]any) *Table {
 
 // Delete removes key and everything it holds.
 func (t *Table) Delete(key string) {
+	if t == nil {
+		return
+	}
 	if _, ok := t.values[key]; !ok {
 		return
 	}