Another question I was also stumbling into while working on this topic. Is there an idiomatic why to keep some trailing whitespace in indented strings? Let's consider the following code:

let
  markdown = ''
    **Headline:**

        code snippet
  '';
in
...

If I remove the first line of the markdown snipped (i.e. the "headline"), the additional indent of the code snippet gets trimmed. So instead of

    code snippet

the resulting string value would be:

code snippet

Is there some why to represent indented code block inside an indented string?

I guess I could do the following:

let
  markdown = ''
        code snippet
    ${""}'';
in
...

This would basically use the ${""} just in front on the closing quotes to mark the indent of the string. Not sure if there is a better way to do that in the Nix language. However, I guess this case might be rarely relevant. I currently consider to just kind of ignore this edge case for now.

In reply to @trudwin:matrix.org

I guess I could do the following:

let
  markdown = ''
        code snippet
    ${""}'';
in
...

This would basically use the ${""} just in front on the closing quotes to mark the indent of the string. Not sure if there is a better way to do that in the Nix language. However, I guess this case might be rarely relevant. I currently consider to just kind of ignore this edge case for now.

I personally choose not to use optionalAttrs in that way, instead choosing

  ${if cond then "foo" else null} = value;

xovidium has said that empty merges are free on new nix versions though