DO NOT MERGE: prove memory-impact no-common-platform fix in CI

Chained on top of the memory-impact fix to exercise it in real CI.

Changed components and their base-test platforms:
- const: variant-only test (test-display.esp32-s3-idf.yaml, no base test).
  --base-only cannot build it, so the fix must exclude it; it only injects
  an esp32-s3-idf platform hint.
- shelly_dimmer: base test esp8266-ard (real C++).
- daikin: base test esp8266-ard (real C++), the working third component.

Without the fix, the esp32-s3-idf hint (and const's variant counted as a
supported platform) selects esp32-s3-idf, which none of the three can build
under --base-only, yielding 0 builds and a failed memory extraction. With the
fix, const is excluded, the unbuildable hint is ignored in favor of the common
esp8266-ard platform, and shelly_dimmer + daikin generate memory impact.

esphome/components/daikin/daikin.cpp

@@ -1,3 +1,5 @@
+// DNM: do not merge. Trivial touch to mark daikin changed; this is the working
+// esp8266-ard component that should generate memory impact (see PR #16788).
 #include "daikin.h"
 #include "esphome/components/remote_base/remote_base.h"
 

esphome/components/shelly_dimmer/shelly_dimmer.cpp

@@ -1,3 +1,5 @@
+// DNM: do not merge. Trivial touch to mark shelly_dimmer changed so the
+// memory-impact CI job exercises the no-common-platform fix (see PR #16788).
 #include "esphome/core/defines.h"
 #include "esphome/core/helpers.h"
 

script/determine-jobs.py

@@ -70,6 +70,7 @@ from helpers import (
     get_changed_components,
     get_component_from_path,
     get_component_test_files,
+    get_component_test_platforms,
     get_components_with_dependencies,
     get_cpp_changed_components,
     get_fixture_to_test_files,
@@ -77,7 +78,6 @@ from helpers import (
     get_target_branch,
     git_ls_files,
     is_validate_only_file,
-    parse_test_filename,
     root_path,
 )
 from split_components_for_ci import create_intelligent_batches
@@ -169,24 +169,6 @@ MEMORY_IMPACT_FALLBACK_COMPONENT = "api"  # Representative component for core ch
 MEMORY_IMPACT_FALLBACK_PLATFORM = Platform.ESP32_IDF  # Most representative platform
 MEMORY_IMPACT_MAX_COMPONENTS = 40  # Max components before results become nonsensical
 
-# Platform-specific components that can only be built on their respective platforms
-# These components contain platform-specific code and cannot be cross-compiled
-# Regular components (wifi, logger, api, etc.) are cross-platform and not listed here
-PLATFORM_SPECIFIC_COMPONENTS = frozenset(
-    {
-        "esp32",  # ESP32 platform implementation
-        "esp8266",  # ESP8266 platform implementation
-        "rp2040",  # Raspberry Pi Pico / RP2040 platform implementation
-        "libretiny",  # LibreTiny base platform implementation
-        "bk72xx",  # Beken BK72xx platform implementation (uses LibreTiny)
-        "rtl87xx",  # Realtek RTL87xx platform implementation (uses LibreTiny)
-        "ln882x",  # Winner Micro LN882x platform implementation (uses LibreTiny)
-        "host",  # Host platform (for testing on development machine)
-        "nrf52",  # Nordic nRF52 platform implementation (uses Zephyr)
-        "zephyr",  # Zephyr RTOS platform implementation
-    }
-)
-
 # Platform preference order for memory impact analysis
 # This order is used when no platform-specific hints are detected from filenames
 # Priority rationale:
@@ -1006,23 +988,24 @@ def detect_memory_impact_config(
     ] = {}  # Track which platforms each component supports
 
     for component in sorted(changed_component_set):
-        # Look for test files on preferred platforms
-        test_files = get_component_test_files(component, all_variants=True)
-        if not test_files:
-            continue
-
-        # Check if component has tests for any preferred platform
-        available_platforms = [
-            platform
-            for test_file in test_files
-            if (platform := parse_test_filename(test_file)[1]) != "all"
-            and platform in MEMORY_IMPACT_PLATFORM_PREFERENCE
-        ]
+        # Discover the platforms this component has BASE tests for, using the
+        # same logic as the build runner (get_component_test_platforms wraps the
+        # shared get_component_test_files + parse_test_filename helpers). Base
+        # tests only: the memory impact CI build runs test_build_components.py
+        # with --base-only, which compiles base test.<platform>.yaml files but
+        # never variant test-<variant>.<platform>.yaml files. Counting
+        # variant-only platforms here would let us select a platform the build
+        # then has nothing to compile for, producing no memory output.
+        available_platforms = {
+            Platform(platform)
+            for platform in get_component_test_platforms(component)
+            if platform in MEMORY_IMPACT_PLATFORM_PREFERENCE
+        }
 
         if not available_platforms:
             continue
 
-        component_platforms_map[component] = set(available_platforms)
+        component_platforms_map[component] = available_platforms
         components_with_tests.append(component)
 
     # If no components have tests, don't run memory impact
@@ -1084,20 +1067,52 @@ def detect_memory_impact_config(
         )
         platform = _select_platform_by_count(platform_counts)
 
-    # Filter out platform-specific components that are incompatible with selected platform
-    # Platform components (esp32, esp8266, rp2040, etc.) can only build on their own platform
-    # Other components (wifi, logger, etc.) are cross-platform and can build anywhere
-    compatible_components = [
-        component
-        for component in components_with_tests
-        if component not in PLATFORM_SPECIFIC_COMPONENTS
-        or platform in component_platforms_map.get(component, set())
-    ]
+    # Keep only components that have a base test on the selected platform.
+    # The merged build runs test_build_components.py -t <platform> --base-only,
+    # so a component without a base test.<platform>.yaml compiles nothing and
+    # contributes no memory output. This also covers platform-specific
+    # components (esp32, esp8266, etc.), which only have tests on their own
+    # platform. When components don't share a common platform we build the
+    # largest subset that does, dropping the rest.
+    def components_supporting(target: Platform) -> list[str]:
+        return [
+            component
+            for component in components_with_tests
+            if target in component_platforms_map.get(component, set())
+        ]
+
+    compatible_components = components_supporting(platform)
+
+    # A platform hint (or no-common-platform fallback) can pick a platform that
+    # no changed component actually has a base test for, leaving nothing to
+    # build. In that case fall back to the platform supported by the most
+    # components, which by construction is backed by at least one base test.
+    if not compatible_components:
+        platform = _select_platform_by_count(
+            Counter(
+                p for platforms in component_platforms_map.values() for p in platforms
+            )
+        )
+        compatible_components = components_supporting(platform)
 
     # If no components are compatible with the selected platform, don't run
     if not compatible_components:
         return {"should_run": "false"}
 
+    # Log components dropped because they lack a base test on the selected
+    # platform so partial-subset builds are visible in CI logs.
+    dropped_components = [
+        component
+        for component in components_with_tests
+        if component not in compatible_components
+    ]
+    if dropped_components:
+        print(
+            f"Memory impact: Dropping components without a base test on "
+            f"{platform}: {dropped_components}",
+            file=sys.stderr,
+        )
+
     # Debug output
     print("Memory impact analysis:", file=sys.stderr)
     print(f"  Changed components: {sorted(changed_component_set)}", file=sys.stderr)

script/helpers.py

@@ -149,6 +149,31 @@ def get_component_test_files(
     return files
 
 
+def get_component_test_platforms(component: str, *, base_only: bool = True) -> set[str]:
+    """Return the set of platforms a component has compilable test files for.
+
+    Uses the same discovery as ``test_build_components.py`` (``get_component_test_files``
+    + ``parse_test_filename``) so callers agree with what the build runner would
+    actually compile. With ``base_only=True`` (the default, matching the
+    memory-impact build's ``--base-only``), only base ``test.<platform>.yaml``
+    files are considered; variant ``test-<variant>.<platform>.yaml`` files are
+    excluded. The ``"all"`` platform sentinel is excluded.
+
+    Args:
+        component: Component name (e.g. "wifi")
+        base_only: If True, only consider base test files (default).
+
+    Returns:
+        Set of platform identifiers (e.g. {"esp32-idf", "esp8266-ard"}).
+    """
+    platforms: set[str] = set()
+    for test_file in get_component_test_files(component, all_variants=not base_only):
+        platform = parse_test_filename(test_file)[1]
+        if platform != "all":
+            platforms.add(platform)
+    return platforms
+
+
 def is_validate_only_file(test_file: Path) -> bool:
     """Return True if the given path is a config-only validate file.
 

script/test_build_components.py

@@ -42,6 +42,7 @@ from script.analyze_component_buses import (
 from script.helpers import (
     get_component_test_files,
     is_validate_only_file,
+    parse_test_filename,
     split_conflicting_groups,
 )
 from script.merge_component_configs import merge_component_configs
@@ -122,21 +123,6 @@ def find_component_tests(
     return dict(component_tests)
 
 
-def parse_test_filename(test_file: Path) -> tuple[str, str]:
-    """Parse test filename to extract test name and platform.
-
-    Args:
-        test_file: Path to test file
-
-    Returns:
-        Tuple of (test_name, platform)
-    """
-    parts = test_file.stem.split(".")
-    if len(parts) == 2:
-        return parts[0], parts[1]  # test, platform
-    return parts[0], "all"
-
-
 def get_platform_base_files(base_dir: Path) -> dict[str, list[Path]]:
     """Get all platform base files.
 

tests/components/const/common.yaml

@@ -0,0 +1,37 @@
+display:
+  - platform: qspi_dbi
+    model: RM690B0
+    data_rate: 80MHz
+    spi_mode: mode0
+    dimensions:
+      width: 450
+      height: 600
+      offset_width: 16
+    color_order: rgb
+    invert_colors: false
+    brightness: 255
+    cs_pin: 11
+    reset_pin: 13
+    enable_pin: 9
+
+  - platform: qspi_dbi
+    model: CUSTOM
+    id: main_lcd
+    draw_from_origin: true
+    dimensions:
+      height: 240
+      width: 536
+    transform:
+      mirror_x: true
+      swap_xy: true
+    color_order: rgb
+    brightness: 255
+    cs_pin: 6
+    reset_pin: 17
+    enable_pin: 38
+    init_sequence:
+      - [0x3A, 0x66]
+      - [0x11]
+      - delay 120ms
+      - [0x29]
+      - delay 20ms

tests/components/const/test-display.esp32-s3-idf.yaml

@@ -0,0 +1,7 @@
+# DNM proof: this is a VARIANT test (test-display.*) with no base test.*.yaml.
+# The memory-impact build runs --base-only, so const has nothing buildable and
+# must be excluded; it only contributes an esp32-s3-idf platform hint.
+packages:
+  qspi: !include ../../test_build_components/common/qspi/esp32-s3-idf.yaml
+
+<<: !include common.yaml

tests/script/test_determine_jobs.py

@@ -1426,7 +1426,15 @@ def test_detect_memory_impact_config_core_python_only_changes(tmp_path: Path) ->
 
 @pytest.mark.usefixtures("mock_target_branch_dev")
 def test_detect_memory_impact_config_no_common_platform(tmp_path: Path) -> None:
-    """Test memory impact detection when components have no common platform."""
+    """Test memory impact detection when components have no common platform.
+
+    The merged build runs with --base-only on a single platform, so components
+    without a base test on the selected platform cannot be built and must be
+    dropped. We build the largest subset that shares the selected platform
+    rather than handing the runner components it has nothing to compile for
+    (which previously produced "0 passed, 0 failed" and a failed memory
+    extraction).
+    """
     # Create test directory structure
     tests_dir = tmp_path / "tests" / "components"
 
@@ -1453,12 +1461,70 @@ def test_detect_memory_impact_config_no_common_platform(tmp_path: Path) -> None:
 
         result = determine_jobs.detect_memory_impact_config()
 
-    # Should pick the most frequently supported platform
+    # No common platform: pick the most preferred platform among those supported
+    # (esp8266-ard outranks esp32-idf in the preference list) and build only the
+    # components that have a base test on it. wifi (esp32-idf only) is dropped.
     assert result["should_run"] == "true"
-    assert set(result["components"]) == {"wifi", "logger"}
-    # When no common platform, picks most commonly supported
-    # esp8266-ard is preferred over esp32-idf in the preference list
-    assert result["platform"] in ["esp32-idf", "esp8266-ard"]
+    assert result["platform"] == "esp8266-ard"
+    assert result["components"] == ["logger"]
+    assert result["use_merged_config"] == "true"
+
+
+def test_detect_memory_impact_config_variant_only_platform_excluded(
+    tmp_path: Path,
+) -> None:
+    """Regression test for the const + shelly_dimmer memory-impact failure.
+
+    Reproduces https://github.com/esphome/esphome/actions/runs/26746938473
+    where a platform hint selected esp32-idf even though neither changed
+    component had a base test.esp32-idf.yaml. The merged --base-only build then
+    found nothing to compile ("0 passed, 0 failed") and memory extraction
+    failed. Also covers a component whose only esp32-idf test is a *variant*
+    (test-*.esp32-idf.yaml): --base-only never compiles variants, so it must
+    not count toward platform availability.
+    """
+    tests_dir = tmp_path / "tests" / "components"
+
+    # const: base test only on esp32-s3-idf
+    const_dir = tests_dir / "const"
+    const_dir.mkdir(parents=True)
+    (const_dir / "test.esp32-s3-idf.yaml").write_text("test: const")
+
+    # shelly_dimmer: base test only on esp8266-ard
+    shelly_dir = tests_dir / "shelly_dimmer"
+    shelly_dir.mkdir(parents=True)
+    (shelly_dir / "test.esp8266-ard.yaml").write_text("test: shelly_dimmer")
+
+    # mdns: only a VARIANT test on esp32-idf (no base test.esp32-idf.yaml).
+    # --base-only would never build it, so it must be excluded entirely.
+    mdns_dir = tests_dir / "mdns"
+    mdns_dir.mkdir(parents=True)
+    (mdns_dir / "test-min.esp32-idf.yaml").write_text("test: mdns")
+
+    with (
+        patch.object(determine_jobs, "root_path", str(tmp_path)),
+        patch.object(helpers, "root_path", str(tmp_path)),
+        patch.object(determine_jobs, "changed_files") as mock_changed_files,
+    ):
+        # The "_esp32" filename yields an esp32-idf platform hint, reproducing
+        # the original bug where the hint picked a platform no component could
+        # build as a base test.
+        mock_changed_files.return_value = [
+            "esphome/components/const/const.cpp",
+            "esphome/components/shelly_dimmer/shelly_dimmer_esp32.cpp",
+            "esphome/components/mdns/mdns.cpp",
+        ]
+
+        result = determine_jobs.detect_memory_impact_config()
+
+    # The esp32-idf hint is unbuildable (no base test), so we fall back to the
+    # platform supported by the most components, broken by preference order:
+    # esp8266-ard (shelly_dimmer) outranks esp32-s3-idf (const). Only the
+    # component with a base test on the selected platform is returned; the
+    # variant-only mdns is excluded entirely.
+    assert result["should_run"] == "true"
+    assert result["platform"] == "esp8266-ard"
+    assert result["components"] == ["shelly_dimmer"]
     assert result["use_merged_config"] == "true"
 
 
@@ -1545,12 +1611,16 @@ def test_detect_memory_impact_config_includes_base_bus_components(
 
 
 @pytest.mark.usefixtures("mock_target_branch_dev")
-def test_detect_memory_impact_config_with_variant_tests(tmp_path: Path) -> None:
-    """Test memory impact detection for components with only variant test files.
+def test_detect_memory_impact_config_variant_only_components_skipped(
+    tmp_path: Path,
+) -> None:
+    """Components with only variant tests are skipped for memory impact.
 
-    This verifies that memory impact analysis works correctly for components like
-    improv_serial, ethernet, mdns, etc. which only have variant test files
-    (test-*.yaml) instead of base test files (test.*.yaml).
+    Components like improv_serial and ethernet only have variant test files
+    (test-*.yaml), no base test.<platform>.yaml. The memory-impact build runs
+    test_build_components.py with --base-only, which never compiles variants, so
+    these components have nothing buildable and must not be selected. Selecting
+    them previously produced "0 passed, 0 failed" and a failed memory extraction.
     """
     # Create test directory structure
     tests_dir = tmp_path / "tests" / "components"
@@ -1581,12 +1651,8 @@ def test_detect_memory_impact_config_with_variant_tests(tmp_path: Path) -> None:
 
         result = determine_jobs.detect_memory_impact_config()
 
-    # Should detect both components even though they only have variant tests
-    assert result["should_run"] == "true"
-    assert set(result["components"]) == {"improv_serial", "ethernet"}
-    # Both components support esp32-idf
-    assert result["platform"] == "esp32-idf"
-    assert result["use_merged_config"] == "true"
+    # Neither component has a base test, so nothing is buildable under --base-only
+    assert result["should_run"] == "false"
 
 
 # Tests for clang-tidy split mode logic