refactor: error handling to use exceptions (#1719)

* Refactor error handling to use exceptions

cibuildwheel has up until now handled most errors by printing an error message to sys.stderr and calling sys.exit. Others were handled using Logger.error, depending on the context. We also had return codes, but these weren't explicitly defined anywhere.

This makes that convention more explicit and codified. Now to halt the program, the correct thing to do is to throw a cibuildwheel.errors.FatalError exception - that is caught in main() and printed before exiting. The existing behaviour was kept - if an error occurs within a build step (probably something to do with the build itself), the Logger.error() method is used. Outside of a build step (e.g. a misconfiguration), the behaviour is still to print 'cibuildwheel: <message>'

I also took the opportunity to add a debugging option `--debug-traceback` (and `CIBW_DEBUG_TRACEBACK`), which you can enable to see a full traceback on errors.

(I've deactivated the flake8-errmsg lint rule, as it was throwing loads of errors and these error messages aren't generally seen in a traceback context)

* add noqa rule

* Apply suggestions from code review

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>

* Return to flake8-errmsg conformance

* Code review suggestions

* Subclass Exception rather than SystemExit

* apply error handling to new code and fix merge issues

* Apply review suggestion

* fix: merge issue

* Update cibuildwheel/errors.py

---------

Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>
Co-authored-by: mayeut <mayeut@users.noreply.github.com>

unit_test/main_tests/main_options_test.py

@@ -344,6 +344,28 @@ def test_before_all(before_all, platform_specific, platform, intercepted_build_a
     assert build_options.before_all == (before_all or "")
 
 
+@pytest.mark.parametrize("method", ["unset", "command_line", "env_var"])
+def test_debug_traceback(monkeypatch, method, capfd):
+    if method == "command_line":
+        monkeypatch.setattr(sys, "argv", [*sys.argv, "--debug-traceback"])
+    elif method == "env_var":
+        monkeypatch.setenv("CIBW_DEBUG_TRACEBACK", "TRUE")
+
+    # set an option that produces a configuration error
+    monkeypatch.setenv("CIBW_BUILD_FRONTEND", "invalid_value")
+
+    with pytest.raises(SystemExit) as exit:
+        main()
+    assert exit.value.code == 2
+
+    _, err = capfd.readouterr()
+
+    if method == "unset":
+        assert "Traceback (most recent call last)" not in err
+    else:
+        assert "Traceback (most recent call last)" in err
+
+
 def test_defaults(platform, intercepted_build_args):
     main()