From dfffd5e97bb5370eeaea6ad035c9e268453e24c2 Mon Sep 17 00:00:00 2001
From: Ivan Kravets <me@ikravets.com>
Date: Mon, 8 Aug 2022 17:39:36 +0300
Subject: [PATCH] =?UTF-8?q?Warn=20about=20calling=20=E2=80=9Cenv.BuildSour?=
 =?UTF-8?q?ces=E2=80=9D=20in=20a=20POST-type=20script=20//=20Resolve=20#43?=
 =?UTF-8?q?85?=
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---
 HISTORY.rst                          | 1 +
 platformio/builder/tools/piobuild.py | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/HISTORY.rst b/HISTORY.rst
index b6bd269b..d51051d0 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -21,6 +21,7 @@ PlatformIO Core 6
 * Improved project dependency resolving when using the `pio project init --ide <https://docs.platformio.org/en/latest/core/userguide/project/cmd_init.html>`__ command
 * Upgraded build engine to the SCons 4.4.0 (`release notes <https://github.com/SCons/scons/releases/tag/4.4.0>`__)
 * Do not resolve project dependencies on for the ``cleanall`` target (`issue #4344 <https://github.com/platformio/platformio-core/issues/4344>`_)
+* Warn about calling "env.BuildSources" in a POST-type script (`issue #4385 <https://github.com/platformio/platformio-core/issues/4385>`_)
 * Fixed an issue when escaping macros/defines for IDE integration (`issue #4360 <https://github.com/platformio/platformio-core/issues/4360>`_)
 
 6.1.3 (2022-07-18)
diff --git a/platformio/builder/tools/piobuild.py b/platformio/builder/tools/piobuild.py
index 9652eabe..69359a32 100644
--- a/platformio/builder/tools/piobuild.py
+++ b/platformio/builder/tools/piobuild.py
@@ -341,6 +341,14 @@ def BuildLibrary(env, variant_dir, src_dir, src_filter=None, nodes=None):
 
 
 def BuildSources(env, variant_dir, src_dir, src_filter=None):
+    if env.get("PIOMAINPROG"):
+        sys.stderr.write(
+            "Error: The main program is already constructed and the inline "
+            "source files are not allowed. Please use `env.BuildLibrary(...)` "
+            "or PRE-type script instead."
+            )
+        env.Exit(1)
+
     nodes = env.CollectBuildFiles(variant_dir, src_dir, src_filter)
     DefaultEnvironment().Append(
         PIOBUILDFILES=[