Match the pch source TU by resolved path so symlinked build dirs keep the pch

esphome/build_helpers/pch.py

@@ -212,6 +212,18 @@ _PCH_STRIP_FLAGS_WITH_ARG = frozenset({"-o", "-c", "-MT", "-MF", "-MQ"})
 _PCH_STRIP_FLAGS = frozenset({"-MD", "-MMD", "-MP", "-MM", "-M"})
 
 
+def _db_source_path(entry: dict, build_dir: Path) -> Path:
+    """A compile database entry's source file as a resolved absolute path."""
+    path = Path(entry["file"])
+    if not path.is_absolute():
+        directory = entry.get("directory")
+        base = (
+            Path(directory) if isinstance(directory, str) and directory else build_dir
+        )
+        path = base / path
+    return path.resolve()
+
+
 def pch_compile_command(
     build_dir: Path, header: Path, gch: Path
 ) -> tuple[list[str], Path] | None:
@@ -232,16 +244,17 @@ def pch_compile_command(
     if not isinstance(entries, list):
         _LOGGER.warning("Malformed compile database, skipping pch")
         return None
-    # Windows compile DBs use backslashes; normalize both sides
-    src_prefix = str(CORE.relative_src_path()).replace("\\", "/")
+    # CMake may spell paths through a symlink differently than CORE does
+    # (macOS /tmp vs /private/tmp), so compare resolved paths
+    src_root = Path(CORE.relative_src_path()).resolve()
     entry = next(
         (
             e
             for e in entries
             if isinstance(e, dict)
             and isinstance(e.get("file"), str)
-            and e["file"].replace("\\", "/").startswith(src_prefix)
             and e["file"].endswith(CXX_SOURCE_SUFFIXES)
+            and _db_source_path(e, build_dir).is_relative_to(src_root)
         ),
         None,
     )

tests/unit_tests/build_gen/test_espidf.py

@@ -657,6 +657,31 @@ def test_pch_compile_command_variants(tmp_path: Path) -> None:
     assert cmd_dir == build
 
 
+@pytest.mark.skipif(os.name == "nt", reason="symlinks need privileges on Windows")
+def test_pch_compile_command_matches_src_through_symlink(tmp_path: Path) -> None:
+    """Find the src TU when CMake spells paths through a different symlink (macOS /tmp)."""
+    from esphome.build_helpers.pch import pch_compile_command
+
+    real = tmp_path / "real"
+    (real / "src" / "esphome").mkdir(parents=True)
+    link = tmp_path / "link"
+    link.symlink_to(real, target_is_directory=True)
+    CORE.build_path = str(real)
+    build = real / "build"
+    build.mkdir()
+    header = build / "esphome_pch.h"
+    gch = build / "esphome_pch.h.gch"
+    src_file = str(link / "src" / "esphome" / "a.cpp")
+    (build / "compile_commands.json").write_text(
+        json.dumps([{"command": f"g++ -DX=1 -o a.obj -c {src_file}", "file": src_file}])
+    )
+
+    cmd, cmd_dir = pch_compile_command(build, header, gch)
+
+    assert cmd[:2] == ["g++", "-DX=1"]
+    assert cmd_dir == build
+
+
 def test_pch_compile_command_rejects_unusable_entries(tmp_path: Path) -> None:
     """Malformed DB shapes and command-less entries skip cleanly instead of
     producing a compiler-less argv retried every build."""