Ports: Port gn

This requires allowing ports to override fetch() since tar.gz sha256sums
from googlesource.com are not deterministic.

Ports/.port_include.sh

@@ -310,7 +310,8 @@ do_download_file() {
     fi
 }
 
-fetch() {
+# FIXME: Don't allow overriding fetch, support multiple protocols instead. See #20004
+func_defined fetch || fetch() {
     pre_fetch
 
     tried_download_again=0

Ports/AvailablePorts.md

@@ -94,6 +94,7 @@ This list is also available at [ports.serenityos.net](https://ports.serenityos.n
 | [`gltron`](gltron/)                                 | GLTron                                                          | 0.70                      | http://gltron.org                                                              |
 | [`glu`](glu/)                                       | Mesa GLU                                                        | 9.0.2                     | https://gitlab.freedesktop.org/mesa/glu                                        |
 | [`gmp`](gmp/)                                       | GNU Multiple Precision Arithmetic Library (GMP)                 | 6.2.1                     | https://gmplib.org/                                                            |
+| [`gn`](gn/)                                         | GN Meta Build System                                            | 2023.07.12                | https://gn.googlesource.com/gn/                                                |
 | [`gnuapl`](gnuapl/)                                 | GNU APL                                                         | 1.8                       | https://www.gnu.org/software/apl/                                              |
 | [`gnucobol`](gnucobol/)                             | GnuCOBOL                                                        | 3.1.2                     | https://gnucobol.sourceforge.io/                                               |
 | [`gnupg`](gnupg/)                                   | GnuPG                                                           | 2.3.0                     | https://gnupg.org/software/index.html                                          |

Ports/gn/package.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port='gn'
+workdir='gn'
+version='2023.07.12'
+repository='https://gn.googlesource.com/gn'
+git_rev='fae280eabe5d31accc53100137459ece19a7a295'
+useconfigure='true'
+# FIXME: The files and auth_type are lies here. See #20004
+files=('git')
+auth_type='sha256'
+depends=(
+    'ninja'
+    'python3'
+)
+
+fetch() {
+    if [ ! -d ${workdir} ]; then
+        git clone ${repository} ${workdir}
+    fi
+    run git checkout ${git_rev}
+}
+
+configure() {
+    run python3 build/gen.py --platform='serenity' --allow-warnings
+}
+
+build() {
+    run ninja -C out
+}
+
+install() {
+    run mkdir -p "${SERENITY_INSTALL_ROOT}/usr/local/bin"
+    run cp out/gn "${SERENITY_INSTALL_ROOT}/usr/local/bin"
+    run cp out/gn_unittests "${SERENITY_INSTALL_ROOT}/usr/local/bin"
+}