From d9ec4a20541adcce5c2624e8d209e77b1fce4613 Mon Sep 17 00:00:00 2001
From: Florian Schmaus <flow@gentoo.org>
Date: Tue, 2 Apr 2024 22:28:30 +0200
Subject: [PATCH] PoC: Do not export A

Instead of passing A as part of the process environment, we pass it
via a file. Since A is usually the greatest contributor to the process
environment, removing it from the process environment significantly
helps running into MAX_ARG_STRLEN when spawning a new child process.

This means that A is now unexported in the ebuild. However, A is
mostly used as part of the default_src_unpack function. And there A
does not need to be exported.

Proof-of-concept for https://bugs.gentoo.org/721088

Bug: https://bugs.gentoo.org/721088
Signed-off-by: Florian Schmaus <flow@gentoo.org>
---
 bin/ebuild.sh                          |  6 +++++-
 lib/portage/package/ebuild/doebuild.py | 30 +++++++++++++++++++++++++-
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/bin/ebuild.sh b/bin/ebuild.sh
index 8b1e0861a8..7ffb91e5a3 100755
--- a/bin/ebuild.sh
+++ b/bin/ebuild.sh
@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Copyright 1999-2021 Gentoo Authors
+# Copyright 1999-2024 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 # Prevent aliases from causing portage to act inappropriately.
@@ -10,6 +10,10 @@ unalias -a
 unset BASH_COMPAT
 declare -F ___in_portage_iuse >/dev/null && export -n -f ___in_portage_iuse
 
+if [[ -v PORTAGE_EBUILD_EXTRA_SOURCE ]]; then
+	source "${PORTAGE_EBUILD_EXTRA_SOURCE}" || exit 1
+fi
+
 source "${PORTAGE_BIN_PATH}/isolated-functions.sh" || exit 1
 
 # Set up the bash version compatibility level.  This does not disable
diff --git a/lib/portage/package/ebuild/doebuild.py b/lib/portage/package/ebuild/doebuild.py
index c7fa1d1e06..d34a14630c 100644
--- a/lib/portage/package/ebuild/doebuild.py
+++ b/lib/portage/package/ebuild/doebuild.py
@@ -2131,9 +2131,37 @@ def spawn(
         logname_backup = mysettings.configdict["env"].get("LOGNAME")
         mysettings.configdict["env"]["LOGNAME"] = logname
 
+    eapi = mysettings["EAPI"]
+
+    # TODO: Move into eapi.py
+    def eapi_does_not_export_a(eapi):
+        return eapi == "9"
+
+    dont_export_a = "dont-export-a" in mysettings.features or eapi_does_not_export_a(
+        eapi
+    )
+
+    if dont_export_a:
+        orig_env = mysettings.environ()
+        # Copy since we are potentially removing keys from the dict.
+        env = orig_env.copy()
+        t = env["T"]
+        if os.path.isdir(t):
+            ebuildExtraSource = os.path.join(t, "portage-ebuild-extra-source")
+            with open(ebuildExtraSource, mode="w") as f:
+                for name, value in orig_env.items():
+                    if name != "A":
+                        continue
+                    f.write(f"{name}='{value}'\n")
+                    del env[name]
+
+            env["PORTAGE_EBUILD_EXTRA_SOURCE"] = str(ebuildExtraSource)
+    else:
+        env = mysettings.environ()
+
     try:
         if keywords.get("returnpid") or keywords.get("returnproc"):
-            return spawn_func(mystring, env=mysettings.environ(), **keywords)
+            return spawn_func(mystring, env=env, **keywords)
 
         proc = EbuildSpawnProcess(
             background=False,