Warn about calling “env.BuildSources” in a POST-type script // Resolve #4385

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)

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=[