Do not compile SConscripts with the future flags of SCons modules

CHANGES.txt

@@ -45,6 +45,16 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
       falls back to the <fm:Branch> field, which names the XSL-NS branch
       outright.
 
+  From Adam Matthews:
+    - SConstruct and SConscript files (including one read from stdin),
+      site_init.py and variables files are no longer compiled with the
+      future flags of the SCons module that runs them. Since
+      "from __future__ import annotations" was added to SConscript.py,
+      Main.py and Variables/__init__.py, annotations in those files had
+      become strings, which among other things stopped dataclasses from
+      recognising InitVar fields ("__post_init__() missing 1 required
+      positional argument").
+
   From Andrew Morrow:
     - Remove the legacy job scheduler and the "legacy_sched_deprecated"
       experimental feature flag.

NEWS.d/changes/NNNN.bugfix

@@ -0,0 +1,5 @@
+SConstruct and SConscript files, site_init.py and variables files are no
+longer compiled with the future flags of the SCons modules that run them.
+Since SCons 4.11 those modules use "from __future__ import annotations",
+which made annotations in build scripts strings and stopped dataclasses
+from recognising InitVar fields.

RELEASE.txt

@@ -65,6 +65,12 @@ FIXES
   CC="ccache clang". Generating the ninja file failed with "Could not find
   tool $CC".
 
+- SConstruct and SConscript files, site_init.py and variables files are no
+  longer compiled with the future flags of the SCons modules that run them.
+  Since SCons 4.11 those modules use "from __future__ import annotations",
+  which made annotations in build scripts strings and, for example, stopped
+  dataclasses from recognising InitVar fields.
+
 IMPROVEMENTS
 ------------
 

SCons/Script/Main.py

@@ -845,7 +845,8 @@ def _load_site_scons_dir(topdir, site_dir_name=None):
         with open(spec.origin) as f:
             code = f.read()
         try:
-            codeobj = compile(code, spec.name, "exec")
+            # dont_inherit: site_init.py must not pick up this module's future flags
+            codeobj = compile(code, spec.name, "exec", dont_inherit=True)
             exec(codeobj, site_m)
         except KeyboardInterrupt:
             raise

SCons/Script/SConscript.py

@@ -190,7 +190,12 @@ def _SConscript(fs: FS, *files: str | Node, **kw) -> Any | list[Any]:
         try:
             SCons.Script.sconscript_reading = SCons.Script.sconscript_reading + 1
             if fn == "-":
-                exec(sys.stdin.read(), call_stack[-1].globals)
+                # dont_inherit: SConscripts must not pick up this module's
+                # "from __future__ import annotations" (or any other future flag)
+                exec(
+                    compile(sys.stdin.read(), "<stdin>", 'exec', dont_inherit=True),
+                    call_stack[-1].globals,
+                )
             else:
                 if isinstance(fn, SCons.Node.Node):
                     f = fn
@@ -281,7 +286,10 @@ def _SConscript(fs: FS, *files: str | Node, **kw) -> Any | list[Any]:
                             _file_.close()
                             if SCons.Debug.sconscript_trace:
                                 print("scons: Entering "+str(scriptname))
-                            exec(compile(scriptdata, scriptname, 'exec'), call_stack[-1].globals)
+                            exec(
+                                compile(scriptdata, scriptname, 'exec', dont_inherit=True),
+                                call_stack[-1].globals,
+                            )
                             if SCons.Debug.sconscript_trace:
                                 print("scons: Exiting "+str(scriptname))
                         except SConscriptReturn:

SCons/Variables/__init__.py

@@ -284,7 +284,13 @@ def Update(self, env, args: dict | None = None) -> None:
                     temp_values['__name__'] = filename
                     with open(filename) as f:
                         contents = f.read()
-                    exec(contents, {}, temp_values)
+                    # dont_inherit: variables files must not pick up this
+                    # module's future flags
+                    exec(
+                        compile(contents, filename, 'exec', dont_inherit=True),
+                        {},
+                        temp_values,
+                    )
                 finally:
                     if dirname:
                         del sys.path[0]

test/SConscript/future-flags.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python
+#
+# MIT License
+#
+# Copyright The SCons Foundation
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be included
+# in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+"""
+Test that SConstruct, SConscript, site_init.py and variables files are not
+compiled with the future flags of the SCons modules that run them.
+
+SCons/Script/SConscript.py has "from __future__ import annotations". If a
+script inherits that flag, its annotations become strings, which among
+other things stops dataclasses from recognising InitVar fields.
+"""
+
+import TestSCons
+
+test = TestSCons.TestSCons()
+
+# reports whether an annotation in the script is a type or a string
+CHECK = """\
+def _f(x: int):
+    pass
+print("%s:", type(_f.__annotations__['x']).__name__)
+"""
+
+INITVAR = """\
+from dataclasses import InitVar, dataclass
+
+@dataclass
+class _C:
+    env: InitVar[int]
+    name: str
+
+    def __post_init__(self, env):
+        self.seen = env
+
+print("InitVar:", _C(env=1, name="n").seen)
+"""
+
+test.subdir('site_scons', 'sub')
+test.write(['site_scons', 'site_init.py'], CHECK % "site_init")
+test.write('vars.py', CHECK % "variables")
+test.write(['sub', 'SConscript'], CHECK % "SConscript" + INITVAR)
+test.write('SConstruct', CHECK % "SConstruct" + """\
+Environment(tools=[], variables=Variables('vars.py'))
+SConscript('sub/SConscript')
+""")
+
+# site_init.py is read before the SConscript files
+expect = "site_init: type\n" + test.wrap_stdout(
+    read_str="SConstruct: type\n"
+    "variables: type\n"
+    "SConscript: type\n"
+    "InitVar: 1\n",
+    build_str="scons: `.' is up to date.\n",
+)
+test.run(arguments='.', stdout=expect)
+
+# an SConstruct read from standard input
+expect = "site_init: type\n" + test.wrap_stdout(
+    read_str="stdin: type\n",
+    build_str="scons: `.' is up to date.\n",
+)
+test.run(arguments='-f - .', stdin=CHECK % "stdin", stdout=expect)
+
+test.pass_test()