fix(cfg): give the lines of each duplicate config key instead of crashing

tests/commands/test_cfg.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from click.testing import CliRunner
+
+from unshackle.commands import cfg as cfg_module
+
+
+@pytest.fixture
+def config_file(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
+    path = tmp_path / "unshackle.yaml"
+    monkeypatch.setattr(cfg_module, "get_config_path", lambda: path)
+    return path
+
+
+def test_a_duplicate_key_names_its_lines_but_no_key_or_value(config_file: Path) -> None:
+    config_file.write_text(
+        "theme: rainbow\ncredentials:\n  EXAMPLE: first-secret\n  OTHER: other\n  EXAMPLE: second-secret\n"
+        "serve:\n  users:\n    key-secret: {tier: a}\n    key-secret: {tier: b}\n",
+        encoding="utf-8",
+    )
+    result = CliRunner().invoke(cfg_module.cfg, ["theme"])
+    assert isinstance(result.exception, SystemExit), result.exception  # a ClickException, not a crash
+    assert result.exit_code == 1
+    text = " ".join(result.output.replace("│", " ").split())  # the error panel wraps its lines
+    assert "unshackle.yaml: duplicate key on lines 3 and 5, lines 8 and 9. Unshackle uses the later one." in text
+    assert "secret" not in result.output
+    assert "EXAMPLE" not in result.output
+
+
+def test_a_duplicate_key_blocks_a_write(config_file: Path) -> None:
+    original = "theme: rainbow\ncredentials:\n  EXAMPLE: a\n  EXAMPLE: b\n"
+    config_file.write_text(original, encoding="utf-8")
+    result = CliRunner().invoke(cfg_module.cfg, ["theme", "plain"])
+    assert result.exit_code == 1
+    assert config_file.read_text(encoding="utf-8") == original
+
+
+def test_a_valid_config_still_reads_a_key(config_file: Path) -> None:
+    config_file.write_text("theme: rainbow\n", encoding="utf-8")
+    result = CliRunner().invoke(cfg_module.cfg, ["theme"])
+    assert result.exit_code == 0, result.output
+    assert "rainbow" in result.output
+
+
+def test_duplicate_key_lines_follows_aliases_without_looping() -> None:
+    from ruamel.yaml import YAML
+
+    root = YAML().compose("base: &b\n  x: 1\n  x: 2\n  self: *b\nother: *b\nlist:\n  - y: 1\n    y: 2\n")
+    assert cfg_module.duplicate_key_lines(root) == [(2, 3), (7, 8)]
+
+
+def test_a_duplicate_only_ruamel_sees_still_gives_its_line(config_file: Path) -> None:
+    config_file.write_text("a: 1\n1: x\n0x1: y\n", encoding="utf-8")
+    result = CliRunner().invoke(cfg_module.cfg, ["a"])
+    assert "unshackle.yaml: duplicate key on line 3." in " ".join(result.output.replace("│", " ").split())