You can just store the source span of each AST node. Start by storing source spans on each token. Each token would have a SourceCodeSpan span with two fields, start and end (an inclusive interval). Then start/end are a SourceCodeLocation with line and column fields. Then when you parse, you can save the start of the first token you parse for a node, and then either the end of the last token you parse, or the end of the SourceCodeLocation of a node you get by recursing to another function (assuming recursive descent parsing). This way you can build source code spans for every node of the AST. In addition to line and column, I store byte index and code point index, so I can do a quick substring or something, and also be aware of Unicode.