Overview

This WIP project houses the hacky (but increasingly less so) scripts that I use to help with the maintenance of meta.mainProgram attributes for packages in nixpkgs, with the goal of increasing the number of packages that function with nix run.

Currently the project provides 3 primary scripts,

• add-mps
• add-mps-interactive
• rm-mps

all of which take two arguments, a path to nixpkgs on the local system, and an attribute path to a package set in nixpkg, e.g., '[ "perlPackages" ]'.

add-mps

Usage examples:

nix run .#add-mps -- ~/Code/nixpkgs '[ "pkgs" ]'

# or since it's the default package

nix run . -- ~/Code/nixpkgs '[ "pkgs" ]'

The add-mps script finds all packages in the given package set that don't have meta.mainProgram defined and then:

1. Checks whether the official binary cache contains the store path for each package using nix store ls; and
   • if it does, it retrieves the names of all executables located in bin/;
   • otherwise, it uses hydra check to see if the package failed to build on Hydra; and
     • if it didn't, and the store path for the package isn't listed in failed-builds.txt, it builds the package locally; and
       • if it succeeds, it retrieves the names of all executables located in bin/;
       • otherwise, it appends the store path of the package to failed-builds.txt.
2. If a single executable was found, and the name of that executable differs from the packages name (more specifically the result of builtins.parseDrvName name) or pname, it attempts to insert a meta.mainProgram definition into the appropriate file; and
   • if is succeeds, it prints a message to that effect;
   • otherwise, it prints a message with info helpful for trying to insert the meta.mainProgram definition manually.

Known issues:

• The meta attribute under which the script attempts to insert the meta.mainProgam definition spans multiple lines. In this case the script will insert the meta.mainProgam definition on the incorrect line producing a syntax error in the file.
• The meta attribute under which the script inserts the meta.mainProgam definition is in a meta block shared by unrelated packages. For example, it used to be the case that for packages in for perlPackages, if the package didn't have meta attributes defined, the script would insert the meta.mainProgam definition into pkgs/development/perl-modules/generic/default.nix, which applies to all packages in perlPackages. This case is now handled, but there are likely others that aren't.
• If the package definition is auto-generated, the inserted meta.mainProgram definition won't be helpful since it will be overwritten the next time the package definitions are generated. Exceptions are haskellPackages which the script explicitly skips, and nodePackages which has it's own mechanism for adding meta.mainProgram definitions which this script knows how to handle.
• Sometimes the executables available for a package differ between platforms, e.g., docker-credential-helpers provides a single executable on Darwin but multiple executables on Linux.
• Sometimes the name of an executable changes based on the packages definition. The most common example of this is when the executables name includes the specific version of the package. In these cases the meta.mainProgram definition should be manually edited to ensure it remains correct, e.g., mainProgram = "foo_${version}";.
• Sometimes a package includes a single executable whose name differs from the packages name or pname, but it really doesn't make sense at all for that executable the be the thing that would be run if someone tried to nix run the package. In these cases, the package should be added to lib/package-to-skip.nix.

As such, always make sure you review the changes made by this script to ensure they are valid. One way to catch problematic additions of meta.mainProgram definitions by this script, is to run rm-mps after running add-mps.

add-mps-interactive

The add-mps-interactive does the same thing as add-mps up to step 2, at which point it presents a selection prompt (if executables where found, and none of them matched the package's name or pname), that list all executables found as well as "Skip" and "Exclude". If the user selects,

• one of the listed executables, it then attempts to insert the meta.mainProgram definition into the appropriate file;
• "Skip", it does nothing an moves on to the next package;
• "Exclude", it adds an entry to lib/package-to-skip.nix for the package, which will cause that package to be excluded from future runs of the scripts in this project.

rm-mps

Usage example:

nix run .#rm-mps -- ~/Code/nixpkgs '[ "pkgs" ]'

The rm-mps script finds all packages in the given package set that have meta.mainProgram defined and then,

1. it attempts to finds all executables provided for each package in the same way as add-mps; and
2. if it could query the store path for the package; and
   • one of the following conditions is met:
     • the bin/ directory doesn't exist;
     • the bin/ directory is empty;
     • one of the executables in bin/ match the package's name or pname; or
     • none of the executables in bin/ match the defined mainProgram;
   • the meta.mainProgram line for the package is removed from the appropriate file.

Known issues:

• Sometimes multiple variations of packages exist in nixpkgs that are generated by, e.g., overriding a particular package, or calling a function that generates the package derivation with different arguments. In these cases, sometimes one of the packages' name or pname match an executable found in the bin/ triggering the removal of the meta.mainProgram for that package, which due to it being shared with other packages who's name or pname don't match for some reason, would cause those packages to stop working with nix run.

As such, always make sure you review the changes made by this script to ensure they are valid.