Do not export A in EAPI 9

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
avoids running into MAX_ARG_STRLEN when spawning a new child process.

This means that A is no longer exported in the ebuild and hence
unavaiable to child processes. However, A is mostly used as part of
the default_src_unpack function and there A does not need to be
exported.

Thanks to Zac Medico for helpful input on this change.

Closes: https://bugs.gentoo.org/721088
Signed-off-by: Florian Schmaus <[email protected]>

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 +10,11 @@ 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 "${PORTAGE_EBUILD_EXTRA_SOURCE}" || exit 1
+	unset PORTAGE_EBUILD_EXTRA_SOURCE
+fi
+
 source "${PORTAGE_BIN_PATH}/isolated-functions.sh" || exit 1
 
 # Set up the bash version compatibility level.  This does not disable

lib/portage/const.py

@@ -181,6 +181,7 @@
         "digest",
         "distcc",
         "distlocks",
+        "dont-export-a",
         "downgrade-backup",
         "ebuild-locks",
         "fail-clean",

lib/portage/eapi.py

@@ -1,4 +1,4 @@
-# Copyright 2010-2021 Gentoo Authors
+# Copyright 2010-2024 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 import collections
@@ -48,6 +48,10 @@ def eapi_supports_prefix(eapi: str) -> bool:
     return _get_eapi_attrs(eapi).prefix
 
 
+def eapi_exports_A(eapi: str) -> bool:
+    return _get_eapi_attrs(eapi).exports_A
+
+
 def eapi_exports_AA(eapi: str) -> bool:
     return _get_eapi_attrs(eapi).exports_AA
 
@@ -152,6 +156,7 @@ def eapi_has_sysroot(eapi: str) -> bool:
         "broot",
         "dosed_dohard",
         "empty_groups_always_true",
+        "exports_A",
         "exports_AA",
         "exports_EBUILD_PHASE_FUNC",
         "exports_ECLASSDIR",
@@ -198,6 +203,7 @@ class Eapi:
         "6",
         "7",
         "8",
+        "9",
     )
 
     _eapi_val: int = -1
@@ -231,6 +237,7 @@ def _get_eapi_attrs(eapi_str: Optional[str]) -> _eapi_attrs:
             broot=True,
             dosed_dohard=False,
             empty_groups_always_true=False,
+            exports_A=True,
             exports_AA=False,
             exports_EBUILD_PHASE_FUNC=True,
             exports_ECLASSDIR=False,
@@ -270,6 +277,7 @@ def _get_eapi_attrs(eapi_str: Optional[str]) -> _eapi_attrs:
             broot=eapi >= Eapi("7"),
             dosed_dohard=eapi <= Eapi("3"),
             empty_groups_always_true=eapi <= Eapi("6"),
+            exports_A=eapi <= Eapi("8"),
             exports_AA=eapi <= Eapi("3"),
             exports_EBUILD_PHASE_FUNC=eapi >= Eapi("5"),
             exports_ECLASSDIR=eapi <= Eapi("6"),

lib/portage/package/ebuild/doebuild.py

@@ -82,6 +82,7 @@
 )
 from portage.dep.libc import find_libc_deps
 from portage.eapi import (
+    eapi_exports_A,
     eapi_exports_KV,
     eapi_exports_merge_type,
     eapi_exports_replace_vars,
@@ -2133,9 +2134,37 @@ def spawn(
         logname_backup = mysettings.configdict["env"].get("LOGNAME")
         mysettings.configdict["env"]["LOGNAME"] = logname
 
+    eapi = mysettings["EAPI"]
+
+    unexported_env_vars = set()
+    if "dont-export-a" in mysettings.features or not eapi_exports_A(eapi):
+        unexported_env_vars.add("A")
+
+    if unexported_env_vars:
+        orig_env = mysettings.environ()
+        # Copy since we are potentially removing keys from the dict.
+        env = orig_env.copy()
+
+        t = env["T"]
+        if not os.path.isdir(t):
+            os.makedirs(t)
+
+        ebuildExtraSource = os.path.join(t, "portage-ebuild-extra-source")
+        with open(ebuildExtraSource, mode="w") as f:
+            for var_name in unexported_env_vars:
+                var_value = orig_env.get(var_name)
+                if var_value is None:
+                    continue
+                f.write(f"{var_name}='{var_value}'\n")
+                del env[var_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,