Merge follow-through: discard the pch when its identity cannot be established

esphome/build_helpers/pch.py

@@ -294,16 +294,24 @@ def prepare_pch(
         .replace(effective_ccache_basedir(), "")
         .replace(str(CORE.build_path), "")
     )
-    checksum = pch_checksum(
-        CORE.relative_src_path(),
-        include_headers,
-        (
-            # The closure is sorted, so root order only enters via the text
-            pch_header_text(include_headers),
-            *extra,
-            cmd_id,
-        ),
-    )
+    try:
+        checksum = pch_checksum(
+            CORE.relative_src_path(),
+            include_headers,
+            (
+                # The closure is sorted, so root order only enters via the text
+                pch_header_text(include_headers),
+                *extra,
+                cmd_id,
+            ),
+        )
+    except OSError as err:
+        # Identity unknown: a stale cache entry must never be served
+        _LOGGER.warning(
+            "Could not establish the pch identity; compiling without it: %s", err
+        )
+        discard_pch(build_dir)
+        return
     if (
         gch.is_file()
         and sum_path.is_file()

tests/unit_tests/build_gen/test_espidf.py

@@ -1005,3 +1005,24 @@ def test_prepare_pch_keeps_user_force_includes(tmp_path: Path) -> None:
     cmd, _ = pch_compile_command(build, build / "esphome_pch.h", build / "x.gch")
     assert "user.h" in cmd
     assert "esphome_pch.h" not in " ".join(cmd[:-3])
+
+
+def test_prepare_pch_identity_unknown_discards(tmp_path: Path) -> None:
+    """An OSError from the checksum discards artifacts and skips the pch."""
+    from esphome.build_gen.espidf import prepare_pch
+
+    dev = _make_pch_device(tmp_path, "dev_i")
+    CORE.build_path = dev
+    stale = dev / "build" / "esphome_pch.h.gch"
+    stale.write_bytes(b"stale")
+    with (
+        patch.object(CORE, "name", "test"),
+        patch(
+            "esphome.build_helpers.pch.pch_checksum",
+            side_effect=OSError("stat failed"),
+        ),
+        patch("esphome.build_helpers.pch.subprocess.run", side_effect=AssertionError),
+    ):
+        prepare_pch()
+    assert not stale.exists()
+    assert not (dev / "build" / "esphome_pch.h.gch.sum").exists()