lib.escapeRegex: fix with boost::regex implementation

[9999years]

NixOS/nix#7762 switched nix to use the boost::regex implementation, which expects that all literal braces are escaped. That is, the regex \{crate} no longer parses. We modify lib.escapeRegex to accommodate this change. Fortunately, the old regex implementation doesn't mind if closing braces are escaped as well, so this is backwards compatible and we don't need to worry about version-gating it.

Here's how nix works without this patch:

Old regex implementation:

$ nix repl nixpkgs
Welcome to Nix 2.18.1. Type :? for help.

Loading installable 'flake:nixpkgs#'...
Added 5 variables.
nix-repl> builtins.match (lib.escapeRegex "{}") "{}"
[ ]

$ ~/nix/result/bin/nix repl nixpkgs
Welcome to Nix 2.20.0pre20231130_dirty. Type :? for help.

boost::regex implementation:

$ ~/nix/result/bin/nix repl nixpkgs
Welcome to Nix 2.20.0pre20231130_dirty. Type :? for help.

Loading installable 'flake:nixpkgs#'...
Added 5 variables.
nix-repl> builtins.match (lib.escapeRegex "{}") "{}"
error:
       … while calling the 'match' builtin

         at «string»:1:1:

            1| builtins.match (lib.escapeRegex "{}") "{}"
             | ^

       error: invalid regular expression '\{}'

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

Priorities

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[infinisil]

This is a Nix regression that should just get reverted. Nixpkgs is the best test suite we have for Nix, if there's a regression for Nixpkgs there will also be regressions for third-parties.

I submitted a revert PR here: NixOS/nix#9508

[9999years]

But the fix is back-compatible -- why not just roll forward?

[infinisil]

@9999years The problem is that Nix broke backwards compatibility. Older versions of Nixpkgs should always work with newer Nix versions.

[infinisil]

Revert in NixOS/nix#9508 was merged, it also includes your report as a test case, so this shouldn't be a problem going forward :)