Fix BackendDispatcher syntax error and validate toolchain flags

[swayam-2003]

Summary

• Remove duplicate else in BackendDispatcher.configure() that caused a SyntaxError and blocked importing the package.
• Unknown backends now raise RuntimeError consistently in configure()/build().
• Validate toolchain.extra_cflags and toolchain.extra_ldflags as string lists so scalar YAML values cannot silently split into per-character flags.

Approach

Followed existing target-field validation patterns in config.py and regression tests in tests/unit/test_dispatch.py.

Testing

python -m pip install -e ".[dev]"
python -m pytest tests/unit/test_dispatch.py tests/ebuild/test_config_validation.py -v

21 tests passed locally.

DCO

Signed-off-by: Swayam Nayak 154440440+swayam-2003@users.noreply.github.com

[Copilot]

🟡 Changes recommended

Existing repo tests still assert ValueError for unknown backends and the build() error message currently presents a contradictory supported-backend list for ninja, so the test suite and messaging need alignment.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Fixes a Python syntax error in BackendDispatcher.configure() that prevented importing the package, and tightens config parsing so toolchain flag fields are validated as lists of strings (avoiding accidental per-character flag splitting from scalar YAML values).

Changes:

• Remove the duplicate else path in BackendDispatcher.configure() and standardize unknown/unhandled backend failures to raise RuntimeError in configure()/build().
• Add toolchain.extra_cflags / toolchain.extra_ldflags validation in load_config to require list[str].
• Add regression tests for toolchain flag type validation and document the behavior in the changelog.

File summaries

File	Description
tests/ebuild/test_config_validation.py	Adds regression tests ensuring toolchain flag fields are lists of strings.
ebuild/core/config.py	Validates extra_cflags/extra_ldflags types before constructing ToolchainConfig.
ebuild/build/dispatch.py	Fixes configure() syntax error and changes unknown/unhandled backend failures to RuntimeError.
CHANGELOG.md	Documents the dispatcher import fix and new toolchain flag validation rules.

Review details

Suppressed comments (1)

ebuild/build/dispatch.py:131

• configure() now raises RuntimeError for unhandled/unknown backends, but the existing tests/ebuild/test_dispatch.py::TestUnknownBackend suite still asserts ValueError for unknown backend names (e.g. bazel, gradle, scons). Unless those tests are intentionally deprecated, this change will break the default pytest run (pytest.ini discovers tests/**/test_*.py). Please update that test suite (and any docs/docstrings that still mention ValueError) to match the new exception type/contract.

        else:
            raise RuntimeError(
                f"BackendDispatcher cannot configure backend '{backend}'. "
                "This dispatcher only handles cmake, meson, and cargo "
                "(make/kbuild need no configure step). ebuild's own ninja "

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Lite

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[srpatcha]

The flags validation is the valuable half, and I confirmed it

extra_cflags: -O2 -Wall is the natural thing to write, and YAML gives you a string. ToolchainConfig annotates the field List[str] and nothing enforces it, so the string is passed straight through to code that iterates it:

YAML gives:        '-O2 -Wall'  (str)
iterating it:      ['-', 'O', '2', ' ', '-', 'W', 'a', 'l', ...]

Every character becomes a separate compiler flag. The build then fails with something about an unrecognised option -, which points at nothing the developer wrote. A type annotation is documentation, not a check, and this is the case that shows the difference.

Rejecting it at load with a message naming the field is right. It is the same treatment #73 gives a malformed packages: section, and the same class as several others in this repo: a value of the wrong shape silently accepted, and the consequence surfacing somewhere unrelated.

The dispatcher half is superseded

Three PRs fix the same SyntaxError: #66, #70 and this one. I have approved #66 — it came first and is the wider change. My own #70 I have marked superseded for the same reason.

Standardising on RuntimeError for unknown backends is correct and is what #66 does too, so that part lands either way.

What I would like

Rebase onto #66 and reduce this to the config.py validation plus its tests. That should be a small branch with no conflicts, and I will merge it — the flags bug is not fixed by #66 or by anything else open, and it is the piece that would otherwise be lost.

Worth extending while you are there, if you want: extra_ldflags and extra_cflags are not the only List[str] fields that a scalar would break. sources, includes, defines and depends on a target have the same shape, and sources: src/main.c is at least as easy to write as the list form.

Verification

Confirmed the scalar-splitting behaviour on current master with a direct YAML load. Not verified this branch merged — it conflicts with #66 in dispatch.py, which is the overlap described above.