fix(ebuild): validate toolchain extra_cflags/extra_ldflags at config load

[furqan72672]

Summary

load_config() now validates toolchain.extra_cflags and toolchain.extra_ldflags in build.yaml, rejecting non-list values and lists containing non-string items at config load time instead of letting them leak into toolchain resolution / build generation.

Type of Change

• fix — Bug fix
• test — Add or fix tests

Issue being addressed

toolchain.extra_cflags / extra_ldflags were accepted verbatim. A scalar string (e.g. extra_cflags: -mcpu=cortex-m4) would silently become a list of characters when the value is later treated as a sequence, producing malformed compiler arguments.

Approach

Validate the two fields the same way target flag fields (cflags, ldflags, sources, etc.) are already validated: require a list, and require every item to be a string, otherwise raise ConfigError. Failing fast at parse time is consistent with the existing parser behaviour.

Changes

• Added _parse_toolchain_flag_list() in ebuild/core/config.py, mirroring the existing target-field validation style.
• _parse_toolchain() now validates both flag fields before constructing ToolchainConfig.
• Added 4 parametrized regression tests in tests/ebuild/test_config_validation.py covering scalar and non-string cases for both fields.

Testing

• py -m pytest tests/ebuild/test_config_validation.py -q → 18 passed
• py -m flake8 ebuild/core/config.py tests/ebuild/test_config_validation.py → no new violations (3 pre-existing E501s remain, unrelated)
• py -m pytest tests/ebuild/test_smoke_imports.py -q → 45 passed, 1 failed (pre-existing SyntaxError in ebuild/build/dispatch.py, see below)

Pre-Submission Checklist

• New tests added for new functionality
• Commit message follows type(scope): description convention
• DCO sign-off included
• All existing tests pass — blocked by pre-existing dispatch.py issue

Additional Notes / Limitations

• Behaviour change: existing build.yaml files that used a scalar string for these fields will now fail fast. Intentional, and consistent with the target flag fields.
• While running the smoke import check I found a pre-existing defect in ebuild/build/dispatch.py (duplicate unreachable else: causing a SyntaxError at line 133). It is out of scope here and recorded in TASKS.md as T-002. It also surfaces a conflict between tests/ebuild/test_dispatch.py (expects ValueError) and tests/unit/test_dispatch.py (expects RuntimeError), which needs a design decision before it can be fixed.

[Copilot]

🟢 Approval recommended

The changes are small, consistent with existing target-field validation patterns, and are covered by focused regression tests for the newly enforced constraints.

Pull request overview

This PR tightens configuration validation in load_config() by rejecting invalid toolchain.extra_cflags / toolchain.extra_ldflags values at parse time, preventing scalar strings (and other non-list / non-string cases) from later being misinterpreted as sequences and producing malformed compiler/linker arguments.

Changes:

• Added _parse_toolchain_flag_list() to validate toolchain flag fields as list[str] and raise ConfigError on invalid input.
• Updated _parse_toolchain() to use the new validation for extra_cflags and extra_ldflags.
• Added parametrized regression tests ensuring both fields reject non-lists and lists containing non-strings.

Verification

• Reviewer: NOT RUN (no tests or linters executed in this review).
• Author-reported (from PR description): tests/ebuild/test_config_validation.py and tests/ebuild/test_smoke_imports.py were run; the remaining failure is described as pre-existing and out of scope.

File summaries

File	Description
ebuild/core/config.py	Adds parse-time validation for toolchain extra flag lists and wires it into toolchain parsing.
tests/ebuild/test_config_validation.py	Adds regression coverage for invalid toolchain extra flag field types/contents.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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