Scope build_src_flags to project source compilation only

[huyhoang171106]

Summary

The current build flow applies build_src_flags too early (on a shared/base construction environment), which leaks those flags into library compilation (lib_deps). This breaks third-party libraries when users set strict flags like -Wpedantic in build_src_flags. The fix is to keep build_src_flags isolated and apply them only when compiling files from $PROJECT_SRC_DIR (and not to library builders, framework packages, or other dependency compilation units).

Files changed

• platformio/builder/tools/piobuild.py (modified)

Testing

• Not run in this environment.

Closes #5245

[Copilot]

Pull request overview

This PR aims to prevent user build_src_flags from leaking into third-party library (lib_deps) compilation by scoping those flags to compilation of sources under $PROJECT_SRC_DIR only.

Changes:

• Clone the project lib builder environment into a dedicated src_env for building project sources.
• Apply project-source-only flags on src_env before compiling $PROJECT_SRC_DIR.

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[Copilot]

build_src_flags is stored in the build env as SRC_BUILD_FLAGS (see platformio/project/options.py), but this code reads BUILD_SRC_FLAGS, so the option won’t be applied to project sources (and builds that rely on -D… in build_src_flags will break). Use SRC_BUILD_FLAGS here.

Suggested change

	src_env.ProcessFlags(src_env.get("BUILD_SRC_FLAGS"))
	src_env.ProcessFlags(src_env.get("SRC_BUILD_FLAGS"))

[Copilot]

If this is changed to use SRC_BUILD_FLAGS, note that ProjectAsLibBuilder already processes SRC_BUILD_FLAGS into plb.env during initialization (via ProjectAsLibBuilder.build_flags + LibBuilderBase.process_extra_options). Processing the same flags again on src_env would duplicate them. To truly scope build_src_flags to project source compilation, SRC_BUILD_FLAGS should be removed/avoided from plb.env and applied only on the dedicated env used to compile $PROJECT_SRC_DIR.

Suggested change

	src_env = plb.env.Clone()
	src_env.ProcessFlags(src_env.get("BUILD_SRC_FLAGS"))
	# Use a dedicated environment for project sources to avoid
	# re-processing source build flags that may already be applied in plb.env
	src_env = env.Clone()
	build_src_flags = plb.env.get("BUILD_SRC_FLAGS") or env.get("BUILD_SRC_FLAGS")
	if build_src_flags:
	src_env.ProcessFlags(build_src_flags)