core/pkgs/build-support/fetchpatch/default.nix

# This function downloads and normalizes a patch/diff file.
# This is primarily useful for dynamically generated patches,
# such as GitHub's or cgit's, where the non-significant content parts
# often change with updating of git or cgit.
# stripLen acts as the -p parameter when applying a patch.

{ lib, fetchurl, patchutils }:

{ relative ? null, stripLen ? 0
, decode ? "cat" # custom command to decode patch e.g. base64 -d
, extraPrefix ? null, excludes ? [ ], includes ? [ ], revert ? false
, postFetch ? "", ... }@args:
let
  args' = if relative != null then {
    stripLen = 1 + lib.length (lib.splitString "/" relative) + stripLen;
    extraPrefix = lib.optionalString (extraPrefix != null) extraPrefix;
  } else {
    inherit stripLen extraPrefix;
  };
in let inherit (args') stripLen extraPrefix;
in lib.throwIfNot (excludes == [ ] || includes == [ ])
"fetchpatch: cannot use excludes and includes simultaneously" fetchurl ({
  postFetch = ''
    tmpfile="$TMPDIR/patch"

    if [ ! -s "$out" ]; then
      echo "error: Fetched patch file '$out' is empty!" 1>&2
      exit 1
    fi

    set +e
    ${decode} < "$out" > "$tmpfile"
    if [ $? -ne 0 ] || [ ! -s "$tmpfile" ]; then
        echo 'Failed to decode patch with command "'${
          lib.escapeShellArg decode
        }'"' >&2
        echo 'Fetched file was (limited to 128 bytes):' >&2
        od -A x -t x1z -v -N 128 "$out" >&2
        exit 1
    fi
    set -e
    mv "$tmpfile" "$out"

    "${patchutils}/bin/lsdiff" \
      ${
        lib.optionalString (relative != null)
        "-p1 -i ${lib.escapeShellArg relative}/'*'"
      } \
      "$out" \
    | sort -u | sed -e 's/[*?]/\\&/g' \
    | xargs -I{} \
      "${patchutils}/bin/filterdiff" \
      --include={} \
      --strip=${toString stripLen} \
      ${
        lib.optionalString (extraPrefix != null) ''
          --addoldprefix=a/${lib.escapeShellArg extraPrefix} \
          --addnewprefix=b/${lib.escapeShellArg extraPrefix} \
        ''
      } \
      --clean "$out" > "$tmpfile"

    if [ ! -s "$tmpfile" ]; then
      echo "error: Normalized patch '$tmpfile' is empty (while the fetched file was not)!" 1>&2
      echo "Did you maybe fetch a HTML representation of a patch instead of a raw patch?" 1>&2
      echo "Fetched file was:" 1>&2
      cat "$out" 1>&2
      exit 1
    fi

    ${patchutils}/bin/filterdiff \
      -p1 \
      ${
        builtins.toString
        (builtins.map (x: "-x ${lib.escapeShellArg x}") excludes)
      } \
      ${
        builtins.toString
        (builtins.map (x: "-i ${lib.escapeShellArg x}") includes)
      } \
      "$tmpfile" > "$out"

    if [ ! -s "$out" ]; then
      echo "error: Filtered patch '$out' is empty (while the original patch file was not)!" 1>&2
      echo "Check your includes and excludes." 1>&2
      echo "Normalized patch file was:" 1>&2
      cat "$tmpfile" 1>&2
      exit 1
    fi
  '' + lib.optionalString revert ''
    ${patchutils}/bin/interdiff "$out" /dev/null > "$tmpfile"
    mv "$tmpfile" "$out"
  '' + postFetch;
} // builtins.removeAttrs args [
  "relative"
  "stripLen"
  "decode"
  "extraPrefix"
  "excludes"
  "includes"
  "revert"
  "postFetch"
])