Route extra-script link flags and fail loudly on an unfulfilled provides() promise

Extra-script LINKFLAGS travel outside build.flags by design; the backend
now drains them into the library's link flags, matching the ESP-IDF
backend, instead of dropping a link-stage input silently. An unfulfilled
provides() promise raises by name (deduplicated) like the module's other
can-never-link checks, the vacuous end-to-end silence test is replaced
by a link-flags test that can fail, and a version-less dependency
assumed satisfied by manifest name alone warns like its backend twin
since the match is name-only evidence.

esphome/arduino/library.py

@@ -23,6 +23,8 @@ from esphome.platformio.extra_script import apply_extra_script
 from esphome.platformio.library import (
     DEFAULT_BUILD_INCLUDE_DIR,
     DEFAULT_BUILD_SRC_FILTER,
+    ESPHOME_DATA_KEY,
+    ESPHOME_DATA_LINK_FLAGS_KEY,
     LIBRARY_HEADER_SUFFIXES,
     SRC_FILE_EXTENSIONS,
     ConvertedLibrary,
@@ -317,20 +319,19 @@ def _external_short_name(name: str) -> str:
     return short.partition("#")[0].removesuffix(".git")
 
 
-def _warn_unfulfilled_provides(
+def _check_unfulfilled_provides(
     provided_requests: list[str], satisfied: set[str]
 ) -> None:
     """Reconcile the provides() promise: every dependency the walk skipped
     on the backend's word must have been added from the framework tree (or
-    knowingly satisfied by a converted/external library); an unfulfilled
-    promise would surface only as undefined symbols at link."""
-    for name in provided_requests:
-        if name not in satisfied:
-            _LOGGER.warning(
-                "provides() skipped dependency %s but nothing added it; "
-                "the build is missing a library",
-                name,
-            )
+    knowingly satisfied by a converted/external library). An unfulfilled
+    promise can only surface as undefined symbols at link, so it fails
+    here by name like the other can-never-link checks in this module."""
+    if missing := sorted(set(provided_requests) - satisfied):
+        raise EsphomeError(
+            "provides() skipped these dependencies but nothing added them: "
+            f"{', '.join(missing)}; the build is missing libraries"
+        )
 
 
 def resolve_libraries(
@@ -470,11 +471,18 @@ def resolve_libraries(
         )
         if isinstance(manifest_name := component.data.get("name"), str):
             converted_manifest_names.add(manifest_name)
-        converted.append(
-            _library_info(
-                component.get_require_name(), component.source_dir, component.data
+        lib = _library_info(
+            component.get_require_name(), component.source_dir, component.data
+        )
+        # Extra-script LINKFLAGS travel outside build.flags (see
+        # ESPHOME_DATA_LINK_FLAGS_KEY); dropping them would link wrong
+        # with no stated cause
+        lib.link_flags.extend(
+            component.data.get(ESPHOME_DATA_KEY, {}).get(
+                ESPHOME_DATA_LINK_FLAGS_KEY, []
             )
         )
+        converted.append(lib)
         _add_bundled_dependencies(component)
 
     backend = LibraryBackend(
@@ -503,7 +511,7 @@ def resolve_libraries(
         bundled_names.add(name)
         bundled.append(_bundled_library(framework_path, name))
 
-    _warn_unfulfilled_provides(
+    _check_unfulfilled_provides(
         backend.provided_requests,
         bundled_names | converted_manifest_names | external_short_names,
     )

esphome/platformio/library.py

@@ -943,9 +943,11 @@ def _warn_unsatisfied_versionless(
             continue
         if dep_name in resolved_manifest_names:
             # Name-only evidence: any resolved component with this manifest
-            # name counts, not just ones the requester can reach
-            _LOGGER.debug(
-                "Version-less dependency %s of %s satisfied by manifest name only",
+            # name counts, not just ones the requester can reach, so a
+            # coincidental name collision must stay visible
+            _LOGGER.warning(
+                "Version-less dependency %s of %s assumed satisfied by a "
+                "resolved library's manifest name only",
                 dep_name,
                 requester,
             )

tests/unit_tests/test_arduino_library.py

@@ -716,28 +716,34 @@ def test_bundled_dependency_dict_shorthand_prefers_bundled(tmp_path: Path) -> No
     assert "Wire" in [lib.name for lib in libs]
 
 
-def test_unfulfilled_provides_promise_warns(
-    tmp_path: Path, caplog: pytest.LogCaptureFixture
-) -> None:
-    """The walk records every provides()-skipped dependency; one nothing
-    added must warn instead of surfacing as link errors, while satisfied
-    ones stay silent."""
-    component._warn_unfulfilled_provides(["Wire", "Hash"], {"Hash"})
-    assert "provides() skipped dependency Wire but nothing added it" in caplog.text
-    assert "Hash" not in caplog.text
+def test_unfulfilled_provides_promise_raises(tmp_path: Path) -> None:
+    """A provides()-skipped dependency nothing added can only surface as
+    undefined symbols at link, so it fails here by name, deduplicated;
+    satisfied ones pass silently."""
+    with pytest.raises(EsphomeError, match="Wire") as err:
+        component._check_unfulfilled_provides(["Wire", "Wire", "Hash"], {"Hash"})
+    assert str(err.value).count("Wire") == 1
+    assert "Hash" not in str(err.value)
+    component._check_unfulfilled_provides(["Hash"], {"Hash"})
 
 
-def test_fulfilled_provides_promise_is_silent_end_to_end(
-    tmp_path: Path, caplog: pytest.LogCaptureFixture
-) -> None:
-    """The normal path: the walk records the skip and the backend adds the
-    bundled copy, so the reconciliation stays quiet."""
+def test_extra_script_link_flags_reach_the_library(tmp_path: Path) -> None:
+    """LINKFLAGS captured by an extra script travel outside build.flags and
+    must reach the library's link flags, matching the ESP-IDF backend."""
     framework = _make_framework(tmp_path)
-    converted = _webserver(tmp_path, {"build": {}, "dependencies": {"Wire": "*"}})
+    converted = _webserver(
+        tmp_path,
+        {
+            "build": {},
+            component.ESPHOME_DATA_KEY: {
+                component.ESPHOME_DATA_LINK_FLAGS_KEY: ["-Wl,--wrap=foo"]
+            },
+        },
+    )
     with _emitting_converter(converted):
         libs = _resolve(framework)
-    assert "Wire" in [lib.name for lib in libs]
-    assert "provides() skipped dependency" not in caplog.text
+    (webserver,) = (lib for lib in libs if "ESPAsyncWebServer" in lib.name)
+    assert "-Wl,--wrap=foo" in webserver.link_flags
 
 
 def test_bundled_dependency_platform_rejection_is_debug(
@@ -908,6 +914,8 @@ def test_dict_shorthand_dependency_skips_registry_through_real_converter(
     names = [lib.name for lib in libs]
     assert "Wire" in names
     assert any("locallib" in n.lower() for n in names)
+    # The walk populated provided_requests for the skip; the backend added
+    # the bundled copy, so the reconciliation passed without raising
 
 
 @pytest.mark.parametrize(