Do not export PMS variables

Instead of passing PMS variables as part of the process environment,
we pass them via a file that is later sourced by the ebuild's
bash.

Since, for example, 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 and other PMS variables are 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.

This started as a change that only unexported A, but was later
extended to most PMS variables as suggested by ulm in
https://bugs.gentoo.org/721088#c23.

Thanks to Zac Medico for helpful input on this change, and to Eli
Schwartz for suggesting that (bash) helpers should simply source the
environment file introduced by this change.

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

bin/isolated-functions.sh

@@ -8,6 +8,11 @@ if ___eapi_has_version_functions; then
 	source "${PORTAGE_BIN_PATH}/eapi7-ver-funcs.sh" || exit 1
 fi
 
+if [[ -v PORTAGE_EBUILD_EXTRA_SOURCE ]]; then
+	source "${PORTAGE_EBUILD_EXTRA_SOURCE}" || exit 1
+	unset PORTAGE_EBUILD_EXTRA_SOURCE
+fi
+
 # We need this next line for "die" and "assert". It expands
 # It _must_ preceed all the calls to die and assert.
 shopt -s expand_aliases

lib/portage/const.py

@@ -181,6 +181,7 @@
         "digest",
         "distcc",
         "distlocks",
+        "dont-export-pms-vars",
         "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_pms_vars(eapi: str) -> bool:
+    return _get_eapi_attrs(eapi).exports_pms_vars
+
+
 def eapi_exports_AA(eapi: str) -> bool:
     return _get_eapi_attrs(eapi).exports_AA
 
@@ -157,6 +161,7 @@ def eapi_has_sysroot(eapi: str) -> bool:
         "exports_ECLASSDIR",
         "exports_KV",
         "exports_merge_type",
+        "exports_pms_vars",
         "exports_PORTDIR",
         "exports_replace_vars",
         "feature_flag_test",
@@ -198,6 +203,7 @@ class Eapi:
         "6",
         "7",
         "8",
+        "9",
     )
 
     _eapi_val: int = -1
@@ -236,6 +242,7 @@ def _get_eapi_attrs(eapi_str: Optional[str]) -> _eapi_attrs:
             exports_ECLASSDIR=False,
             exports_KV=False,
             exports_merge_type=True,
+            exports_pms_vars=True,
             exports_PORTDIR=True,
             exports_replace_vars=True,
             feature_flag_test=False,
@@ -275,6 +282,7 @@ def _get_eapi_attrs(eapi_str: Optional[str]) -> _eapi_attrs:
             exports_ECLASSDIR=eapi <= Eapi("6"),
             exports_KV=eapi <= Eapi("3"),
             exports_merge_type=eapi >= Eapi("4"),
+            exports_pms_vars=eapi <= Eapi("8"),
             exports_PORTDIR=eapi <= Eapi("6"),
             exports_replace_vars=eapi >= Eapi("4"),
             feature_flag_test=False,

lib/portage/package/ebuild/doebuild.py

@@ -84,6 +84,7 @@
 from portage.eapi import (
     eapi_exports_KV,
     eapi_exports_merge_type,
+    eapi_exports_pms_vars,
     eapi_exports_replace_vars,
     eapi_has_required_use,
     eapi_has_src_prepare_and_src_configure,
@@ -189,6 +190,57 @@
     "RESTRICT",
 )
 
+# The following is a set of PMS § 11.1 and § 7.4 without
+# - TMPDIR
+# - HOME
+# because these variables are often assumed to be exported and
+# therefore consumed by child processes.
+_unexported_pms_vars = frozenset(
+    # fmt: off
+    [
+        # PMS § 11.1 Defined Variables
+        "P",               # NOT-EXPORTED: tendency to break Makefiles when exported
+        "PF",
+        "PN",
+        "CATEGORY",
+        "PV",
+        "PR",
+        "PVR",
+        "A",               # NOT-EXPORTED: largest contributor to process environment when exported
+        "AA",              # NOT-EXPORTED: unused after EAPI 4
+        "FILESDIR",
+        "DISTDIR",
+        "WORKDIR",
+        "S",
+        "PORTDIR",
+        "ECLASSDIR",
+        "ROOT",
+        "EROOT",
+        "SYSROOT",
+        "ESYSROOT",
+        "BROOT",
+        "T",
+#        "TMPDIR",        # EXPORTED: often assumed to be exported and available to child processes
+#        "HOME",          # EXPORTED: often assumed to be exported and available to child processes
+        "EPREFIX",
+        "D",              # NOT-EXPORTED: tendency to break Makefiles when exported
+        "ED",
+        "DESTTREE",
+        "INSDESTTREE",
+        "EBUILD_PHASE",
+        "EBUILD_PHASE_FUNC",
+        "KV",
+        "MERGE_TYPE",
+        "REPLACING_VERSIONS",
+        "REPLACED_BY_VERSION",
+        # PMS 7.4 Magic Ebuild-defined Variables
+        "ECLASS",
+        "INHERITED",
+        "DEFINED_PHASES",
+    ]
+    # fmt: on
+)
+
 
 def _doebuild_spawn(phase, settings, actionmap=None, **kwargs):
     """
@@ -2133,9 +2185,37 @@ def spawn(
         logname_backup = mysettings.configdict["env"].get("LOGNAME")
         mysettings.configdict["env"]["LOGNAME"] = logname
 
+    eapi = mysettings["EAPI"]
+
+    unexported_env_vars = None
+    if "dont-export-pms-vars" in mysettings.features or not eapi_exports_pms_vars(eapi):
+        unexported_env_vars = _unexported_pms_vars
+
+    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,