Indented strings do not work with tabs

[piegamesde]

Is your feature request related to a problem? Please describe.

The manual says about indented strings:

This kind of string literal intelligently strips indentation from the start of each line. To be precise, it strips from each line a number of spaces equal to the minimal indentation of the string as a whole (disregarding the indentation of empty lines).

This is exclusive to spaces and won't work on files indented using tabs.

Describe the solution you'd like

I'd like to have it work with tabs as well.

Describe alternatives you've considered

• Create some helper functionality to convert between tabs and spaces
• Create some helper functionality to strip tabbed indented strings
• Resign and use soft tabs

Additional context

I use tabs for indentation. Programming languages should not force me to use spaces for some features to work.

[edolstra]

We can't change this because it would be incompatible (it could cause the result of evaluating a derivation to change).

[piegamesde]

If anyone else except me still wants to use tabs in their Nix files – this may help you:

stripTabs = text: let
	# Whether all lines start with a tab (or is empty)
	shouldStripTab = lines: builtins.all (line: (line == "") || (pkgs.lib.strings.hasPrefix "	" line)) lines;
	# Strip a leading tab from all lines
	stripTab = lines: builtins.map (line: pkgs.lib.strings.removePrefix "	" line) lines;
	# Strip tabs recursively until there are none
	stripTabs = lines: if (shouldStripTab lines) then (stripTabs (stripTab lines)) else lines;
in
	# Split into lines. Strip leading tabs. Concat back to string.
	builtins.concatStringsSep "\n" (stripTabs (pkgs.lib.strings.splitString "\n" text));

Usage:

myConfigExtraString = (stripTabs ''
	Some
		multiline
		text
'');

[JojOatXGME]

Other line terminators (i.e. CRLF) also prevent the removal of leading whitespace.

[piegamesde]

I think that warrants a reopen.

[ajs124]

Not really. For once I'll have to agree with @edolstra, this behavior cannot really be adjusted, as long as nix does not have any kind of language versioning or other process for breaking changes, because as he said "it could cause the result of evaluating a derivation to change".

[piegamesde]

@ajkovar Yes and no. Just because of this doesn't mean the issue cannot be resolved at all. Some possible alternative solutions off the hat:

• Add a helper function, preferably built-in and always in scope
• Emit a warning in Nix when encountering tabs or windows-style newlines in indented multi-line strings
• Add new Syntax to Nix that fixes the problem (triple quote strings?).

[piegamesde]

Actually, this has another, more severe implication: Some tools like git automatically adjust line endings to the preferred flavor of the host platform. With this behavior, this may silently change derivations.

[JojOatXGME]

I think adding new syntax or built-in functions just for this issue is over the top. However, I would like to see a warning in such cases, since such issues with whitespace are very subtle. It took a lot of time until I discovered that the line terminators were causing the problem.