Modifying the AST before printing?

[brikis98]

Is there a way to use this HCL library to:

1. Parse a file that contains HCL (e.g. main.tf) to get back an AST.
2. Modify the AST in memory.
3. Write the result back out.

It seems like this should be easy, but it falls apart due to the logic in token.Pos. In particular, if you add a node somewhere to the AST, then all the line and offset values in the rest of the AST are wrong; and if you modify an existing node in the AST, then all the column and offset values in the rest of the AST are wrong. As a result, when you print the AST back out, you get all sorts of mangled code, especially related to comments.

Am I using this library wrong or is this just a current limitation?

[apparentlymart]

Hi @brikis98!

The HCL printer code is primarily intended for pretty-printing a parsed, unmodified AST. I expect the mangling you saw was related to how comments get re-inserted into the stream in order to write out the result, since comments are not normally part of the main AST.

[brikis98]

@apparentlymart Got it. I'll see if I can hack something up to properly update line/column/offset values for my use case.

[VladRassokhin]

My suggestion is to add comments to AST so there would be no need to insert them back into the stream. And user could then even modify not only logic but comments too. Is it doable?

[sean-zou]

+1