Drop duplicate ccache test, keep full compiler output at debug, guard empty compile-DB directory

esphome/build_helpers/pch.py

@@ -211,7 +211,7 @@ def pch_compile_command(
     if entry is None:
         _LOGGER.warning("No src C++ entry in the compile database, skipping pch")
         return None
-    cmd_dir = Path(entry.get("directory", build_dir))
+    cmd_dir = Path(entry.get("directory") or build_dir)
     tokens = expand_response_files(split_command(entry.get("command", "")), cmd_dir)
     # A DB recorded with ccache enabled prefixes the compiler with the
     # launcher; the .gch must be compiled directly
@@ -358,6 +358,8 @@ def prepare_pch(
         _LOGGER.warning(
             "Precompiled header failed; compiling without it: %s", error[:400]
         )
+        # This path latches, so keep the full compiler output recoverable
+        _LOGGER.debug("Full pch compile output: %s", error)
         discard_pch(build_dir)
         # Skip retries until a header/flag/backend-identity/command change
         failed_marker.write_text(checksum + "\n", encoding="utf-8")

tests/unit_tests/build_gen/test_espidf.py

@@ -675,6 +675,21 @@ def test_pch_compile_command_rejects_unusable_entries(tmp_path: Path) -> None:
     db.write_text(json.dumps(["just a string"]))
     assert pch_compile_command(build, header, gch) is None
 
+    # An empty-string directory must fall back to the build dir, not cwd
+    db.write_text(
+        json.dumps(
+            [
+                {
+                    "directory": "",
+                    "command": f"g++ -DX=1 -o a.obj -c {src_file}",
+                    "file": src_file,
+                }
+            ]
+        )
+    )
+    _, cmd_dir = pch_compile_command(build, header, gch)
+    assert cmd_dir == build
+
     # arguments-style entry (allowed by the spec, unused by CMake)
     db.write_text(
         json.dumps([{"arguments": ["g++", "-c", src_file], "file": src_file}])

tests/unit_tests/test_espidf_framework.py

@@ -1976,21 +1976,3 @@ def test_check_windows_path_length_long_path_warns(
     assert "long path support" in message
     # The install is global now; the remedy is the prefix env, not moving the project.
     assert "ESPHOME_ESP_IDF_PREFIX" in message
-
-
-def test_ccache_env_opt_in_with_usable_binary(
-    tmp_path: Path, caplog: pytest.LogCaptureFixture
-) -> None:
-    # Forced on with a runnable binary: no warning, full env exported.
-    p1, p2, p3 = _ccache_patches(tmp_path, "/usr/bin/ccache", tmp_path / "build")
-    with (
-        patch.dict("os.environ", {"IDF_CCACHE_ENABLE": "1"}, clear=True),
-        patch("esphome.espidf.framework.shutil.which", return_value="/usr/bin/ccache"),
-        patch("esphome.espidf.framework.tool_version_runs", return_value=True),
-        p1,
-        p2,
-        p3,
-    ):
-        env = _ccache_env()
-    assert env["IDF_CCACHE_ENABLE"] == "1"
-    assert not [r for r in caplog.records if r.levelno >= logging.WARNING]