在 nixpkgs 中，如何在不重新编译的情况下覆盖包的文件？

问题描述

对于需要很长时间构建的 nixpkgs 包，如何在不引起完全重建的情况下进行一些简单的文件更改？

示例用法：

添加/删除一些文件
更改一些 shell 脚本
添加丢失的 pkgconfig .pc 文件

解决方法

创建一个新的派生，复制或符号链接原始包的所有文件（例如，使用 cp），然后根据需要修改文件。

这是一个完整注释的示例：

# This snippet shows how to override a nix package by copying all of the
# files of an already-built package,and then modifying some of them,# thus avoiding a full rebuild.
#
# Example usage:
#
# Build the package:
#     nix-build --no-out-link change-file-after-build-example.nix
# See our replacement worked:
#     $ $(nix-build --no-out-link change-file-after-build-example.nix)/share/git/contrib/fast-import/git-import.sh
#     USAGE: git-import branch import-message
{
  pkgs ? import <nixpkgs> {},lib ? pkgs.lib,}:
let
  originalPackage = pkgs.git;

  # We use `overrideAttrs` instead of defining a new `mkDerivation` to keep
  # the original package's `output`,`passthru`,and so on.
  myOverriddenGitPackage = originalPackage.overrideAttrs (old: {
    name = "git-overridden";

    # Using `buildCommand` replaces the original packages build phases.
    buildCommand = ''
      set -euo pipefail

      ${
        # Copy original files,for each split-output (`out`,`dev` etc.).
        # E.g. `${package.dev}` to `$dev`,and so on. If none,just "out".
        # Symlink all files from the original package to here (`cp -rs`),# to save disk space.
        # We could alternatiively also copy (`cp -a --no-preserve=mode`).
        lib.concatStringsSep "\n"
          (map
            (outputName:
              ''
                echo "Copying output ${outputName}"
                set -x
                cp -rs --no-preserve=mode "${originalPackage.${outputName}}" "''$${outputName}"
                set +x
              ''
            )
            (old.outputs or ["out"])
          )
      }

      # Example change:
      # Change `usage:` to `USAGE:` in a shell script.
      # Make the file to be not a symlink by full copying using `install` first.
      # This also makes it writable (files in the nix store have `chmod -w`).
      install -v "${originalPackage}"/share/git/contrib/fast-import/git-import.sh "$out"/share/git/contrib/fast-import/git-import.sh
      sed -i -e 's/usage:/USAGE:/g' "$out"/share/git/contrib/fast-import/git-import.sh
    '';

  });
in
  myOverriddenGitPackage

nix nix