Close the native CI trigger gap and log the remaining silent library skips

esphome/arduino8266/component.py

@@ -90,7 +90,16 @@ def _library_info(name: str, read_path: Path, data: dict) -> ArduinoLibrary:
         if tok.startswith("-I"):
             include_flags.append(tok[2:])
         elif tok.startswith("-L"):
-            lib.link_dirs.append((read_path / tok[2:]).resolve())
+            link_dir = (read_path / tok[2:]).resolve()
+            if not link_dir.is_dir():
+                # Kept anyway (the linker ignores missing -L dirs); the
+                # warning names the culprit before a bare "cannot find -lfoo"
+                _LOGGER.warning(
+                    "Library %s declares library dir %s which does not exist",
+                    name,
+                    tok[2:],
+                )
+            lib.link_dirs.append(link_dir)
         elif tok.startswith("-l"):
             lib.link_libs.append(tok[2:])
         elif tok.startswith("-Wl,"):

esphome/build_gen/arduino8266.py

@@ -15,6 +15,7 @@ from the build flags with the same precedence as the PlatformIO builder.
 from __future__ import annotations
 
 from dataclasses import dataclass, field
+import logging
 import os
 from pathlib import Path
 import re
@@ -41,6 +42,8 @@ from esphome.framework_helpers import get_project_cxx_compile_flags
 from esphome.helpers import mkdir_p, write_file_if_changed
 from esphome.platformio.library import join_flag_args
 
+_LOGGER = logging.getLogger(__name__)
+
 # Compile rule per source suffix; keys must cover SRC_FILE_EXTENSIONS so any
 # source a library manifest selects has a rule (pinned by a drift test).
 _RULE_FOR_SUFFIX = {
@@ -607,6 +610,12 @@ def write_project(paths: dict[str, Path]) -> bool:
 
     for lib in libraries:
         if not lib.sources:
+            # Header-only libraries are legitimate; the log makes an empty
+            # srcFilter or broken tree traceable before link errors do.
+            _LOGGER.debug(
+                "Library %s has no source files; contributing includes only",
+                lib.name,
+            )
             continue
         lib_root = _common_parent(lib.sources)
         objs = _ninja_compile_edges(