[core] Log which source change triggered a rebuild (#18552)

tests/unit_tests/test_platformio_library.py

@@ -929,11 +929,11 @@ def test_split_flag_entry_non_string_is_clean() -> None:
 
 
 def test_source_kind_map_shape() -> None:
-    """The kind values the native compile rules key on, and the deliberate
-    AS/ASPP merge (.s and .S both map to asm)."""
+    """The kind values the native compile rules key on; the AS/ASPP split
+    matches SCons (.S preprocessed, .s plain assembler)."""
 
-    assert set(SOURCE_KIND_FOR_SUFFIX.values()) == {"c", "cxx", "asm"}
+    assert set(SOURCE_KIND_FOR_SUFFIX.values()) == {"c", "cxx", "asm", "aspp"}
     assert SOURCE_KIND_FOR_SUFFIX[".s"] == "asm"
-    assert SOURCE_KIND_FOR_SUFFIX[".S"] == "asm"
+    assert SOURCE_KIND_FOR_SUFFIX[".S"] == "aspp"
     assert SOURCE_KIND_FOR_SUFFIX[".c"] == "c"
     assert SOURCE_KIND_FOR_SUFFIX[".cpp"] == "cxx"

tests/unit_tests/test_writer.py

@@ -2441,3 +2441,39 @@ def test_copy_src_tree_ignores_removed_generated_file(
     # file was removed and regenerated, not that it triggered sources_changed.
     new_json = json.loads(build_info_json_path.read_text())
     assert new_json["config_hash"] == 0xDEADBEEF
+
+
+@pytest.mark.parametrize(
+    ("case", "content", "expected"),
+    [
+        ("files missing", None, True),
+        ("json missing", "ABSENT", True),
+        ("json unreadable", "not json", True),
+        # Valid JSON that is not an object is stale, not an AttributeError
+        ("json not an object", "[]", True),
+        ("hash mismatch", {"config_hash": 2, "esphome_version": "CURRENT"}, True),
+        ("version mismatch", {"config_hash": 1, "esphome_version": "0.0.0"}, True),
+        ("matching record", {"config_hash": 1, "esphome_version": "CURRENT"}, False),
+    ],
+)
+def test_build_info_stale_branches(
+    tmp_path: Path, case: str, content, expected: bool
+) -> None:
+    """Missing files, an unreadable JSON, a hash or version mismatch each
+    regenerate; a matching record does not."""
+    from esphome.const import __version__
+    from esphome.writer import _build_info_stale
+
+    h = tmp_path / "build_info_data.h"
+    cpp = tmp_path / "build_info_data.cpp"
+    info = tmp_path / "build_info.json"
+    if content is not None:
+        h.write_text("")
+        cpp.write_text("")
+    if isinstance(content, dict):
+        if content.get("esphome_version") == "CURRENT":
+            content["esphome_version"] = __version__
+        info.write_text(json.dumps(content))
+    elif isinstance(content, str) and content != "ABSENT":
+        info.write_text(content)
+    assert _build_info_stale(h, cpp, info, 1) is expected, case