Use the shared tool accessor for gcc, drop dead dataclass defaults, add a resolve test helper

toolchain_tool owns the bin path and Windows suffix now; _BuildConfig's
knob and MMU fields are required since the only constructor always
passes both; the tests' set-flags-then-resolve idiom collapses into one
_resolve helper (12 sites).

esphome/build_gen/arduino8266.py

@@ -15,13 +15,14 @@ from the build flags with the same precedence as the PlatformIO builder.
 from __future__ import annotations
 
 import contextlib
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 import logging
 import os
 from pathlib import Path
 import subprocess
 from typing import TYPE_CHECKING
 
+from esphome.arduino8266.framework import toolchain_tool
 from esphome.build_helpers.ninja import shell_token as _shell_token
 from esphome.components.esp8266 import build_surgery
 from esphome.core import CORE, EsphomeError
@@ -168,8 +169,8 @@ class _BuildConfig:
     exceptions: bool
     vtables: str
     fp_in_irom: bool
-    knob_defines: list[str] = field(default_factory=list)
-    mmu_defines: list[str] = field(default_factory=list)
+    knob_defines: list[str]
+    mmu_defines: list[str]
 
 
 def _lexed_build_flags() -> list[str]:
@@ -440,7 +441,7 @@ def generate_ld_scripts(
     rate-table DRAM relocation, and enlarged memory segments in testing mode.
     """
     framework = paths.framework
-    gcc = paths.toolchain / "bin" / "xtensa-lx106-elf-gcc"
+    gcc = toolchain_tool(paths.toolchain, "gcc")
     ld_dir = CORE.relative_pioenvs_path(CORE.name, "ld")
     mkdir_p(ld_dir)
 

tests/unit_tests/build_gen/test_arduino8266.py

@@ -59,12 +59,15 @@ def _set_flags(*flags: str) -> None:
     CORE.build_flags = set(flags)
 
 
+def _resolve(*flags: str):
+    """Set the build flags and resolve the knob config in one step."""
+    _set_flags(*flags)
+    return _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+
+
 def test_build_config_defaults() -> None:
 
-    _set_flags()
-    config = _resolve_build_config(
-        _flag_defines(set(), arduino8266._lexed_build_flags())
-    )
+    config = _resolve()
     assert config.nonosdk == "NONOSDK22x_190703"
     assert config.lwip_lib == "lwip2-536-feat"
     assert not config.exceptions
@@ -82,10 +85,7 @@ def test_build_config_esphome_lwip_knob() -> None:
     """The lwIP variant ESPHome selects maps to the same defines and library
     as the PlatformIO builder."""
 
-    _set_flags("-DPIO_FRAMEWORK_ARDUINO_LWIP2_HIGHER_BANDWIDTH_LOW_FLASH")
-    config = _resolve_build_config(
-        _flag_defines(set(), arduino8266._lexed_build_flags())
-    )
+    config = _resolve("-DPIO_FRAMEWORK_ARDUINO_LWIP2_HIGHER_BANDWIDTH_LOW_FLASH")
     assert config.lwip_lib == "lwip2-1460"
     assert "TCP_MSS=1460" in config.knob_defines
     assert "LWIP_FEATURES=0" in config.knob_defines
@@ -111,9 +111,8 @@ def test_build_config_knobs() -> None:
 
 def test_build_config_mmu_custom_requires_sizes() -> None:
 
-    _set_flags("-DPIO_FRAMEWORK_ARDUINO_MMU_CUSTOM")
     with pytest.raises(EsphomeError, match="MMU_IRAM_SIZE"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve("-DPIO_FRAMEWORK_ARDUINO_MMU_CUSTOM")
 
     _set_flags(
         "-DPIO_FRAMEWORK_ARDUINO_MMU_CUSTOM",
@@ -205,10 +204,7 @@ def test_build_config_lwip_variants(
 ) -> None:
     """Every lwIP knob maps to the same defines and library as the PIO builder."""
 
-    _set_flags(f"-D{knob}")
-    config = _resolve_build_config(
-        _flag_defines(set(), arduino8266._lexed_build_flags())
-    )
+    config = _resolve(f"-D{knob}")
     assert config.lwip_lib == lib
     assert f"TCP_MSS={mss}" in config.knob_defines
     assert f"LWIP_FEATURES={features}" in config.knob_defines
@@ -254,10 +250,7 @@ def test_build_config_mmu_variants(knob: str, expected: list[str]) -> None:
 
 def test_build_config_waveform_locked_phase() -> None:
 
-    _set_flags("-DPIO_FRAMEWORK_ARDUINO_WAVEFORM_LOCKED_PHASE", "-DFP_IN_IROM")
-    config = _resolve_build_config(
-        _flag_defines(set(), arduino8266._lexed_build_flags())
-    )
+    config = _resolve("-DPIO_FRAMEWORK_ARDUINO_WAVEFORM_LOCKED_PHASE", "-DFP_IN_IROM")
     assert "WAVEFORM_LOCKED_PHASE=1" in config.knob_defines
     assert config.fp_in_irom
 
@@ -478,9 +471,8 @@ def test_build_config_custom_mmu_without_knob_raises() -> None:
     layout the linker script does not implement; refuse instead of warning
     (PlatformIO warns, but its defaults win the compile line; ours would
     not)."""
-    _set_flags("-DMMU_IRAM_SIZE=0xC000")
     with pytest.raises(EsphomeError, match="PIO_FRAMEWORK_ARDUINO_MMU_CUSTOM"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve("-DMMU_IRAM_SIZE=0xC000")
 
 
 def test_flag_defines_lexes_quoted_single_tokens() -> None:
@@ -602,15 +594,13 @@ def test_flag_defines_respects_unflags() -> None:
 def test_vtables_unknown_raises() -> None:
     """A typo'd knob would win the sorted pick and die in the SDK header's
     #error; fail by name at generation instead."""
-    _set_flags("-DVTABLES_IN_BANANA")
     with pytest.raises(EsphomeError, match="Unknown VTABLES_IN_.*BANANA"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve("-DVTABLES_IN_BANANA")
 
 
 def test_vtables_conflicting_raises() -> None:
-    _set_flags("-DVTABLES_IN_DRAM", "-DVTABLES_IN_IRAM")
     with pytest.raises(EsphomeError, match="Conflicting VTABLES_IN_"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve("-DVTABLES_IN_DRAM", "-DVTABLES_IN_IRAM")
 
 
 def test_project_flags_empty_lib_flags_warn(
@@ -653,26 +643,21 @@ def test_generate_ld_scripts_surfaces_preprocessor_warnings(
 def test_build_config_mmu_knob_with_raw_mmu_flag_raises() -> None:
     """A variant knob plus a raw MMU_* define would split the compile line
     from the linker script; refuse like the no-knob case."""
-    _set_flags("-DPIO_FRAMEWORK_ARDUINO_MMU_CACHE16_IRAM48", "-DMMU_IRAM_SIZE=0x4000")
     with pytest.raises(EsphomeError, match="MMU_IRAM_SIZE conflict with .*CACHE16"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve("-DPIO_FRAMEWORK_ARDUINO_MMU_CACHE16_IRAM48", "-DMMU_IRAM_SIZE=0x4000")
 
 
 def test_build_config_raw_lwip_define_raises() -> None:
     """TCP_MSS/LWIP_* belong to the lwIP knobs: a raw value would win the
     compile line while the prebuilt library stays the knob's."""
-    _set_flags("-DTCP_MSS=1024")
     with pytest.raises(EsphomeError, match="TCP_MSS are set by the .*LWIP2"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve("-DTCP_MSS=1024")
 
 
 def test_build_config_mmu_defines_do_not_alias_the_table() -> None:
     """The resolved list must be a copy; mutating it must not corrupt the
     module table for later builds in the same process."""
-    _set_flags("-DPIO_FRAMEWORK_ARDUINO_MMU_CACHE16_IRAM48")
-    config = _resolve_build_config(
-        _flag_defines(set(), arduino8266._lexed_build_flags())
-    )
+    config = _resolve("-DPIO_FRAMEWORK_ARDUINO_MMU_CACHE16_IRAM48")
     config.mmu_defines.append("MMU_BOGUS")
     again = _resolve_build_config(
         _flag_defines(set(), arduino8266._lexed_build_flags())
@@ -760,14 +745,13 @@ def test_generate_ld_scripts_surgery_failure_is_named(tmp_path: Path) -> None:
 def test_build_config_mmu_conflict_names_the_variant_knob_with_custom() -> None:
     """With MMU_CUSTOM also set, the actionable fix is dropping the variant
     knob, not setting the knob the user already set."""
-    _set_flags(
-        "-DPIO_FRAMEWORK_ARDUINO_MMU_CACHE16_IRAM48",
-        "-DPIO_FRAMEWORK_ARDUINO_MMU_CUSTOM",
-        "-DMMU_IRAM_SIZE=0xC000",
-        "-DMMU_ICACHE_SIZE=0x4000",
-    )
     with pytest.raises(EsphomeError, match="drop PIO_FRAMEWORK_ARDUINO_MMU_CACHE16"):
-        _resolve_build_config(_flag_defines(set(), arduino8266._lexed_build_flags()))
+        _resolve(
+            "-DPIO_FRAMEWORK_ARDUINO_MMU_CACHE16_IRAM48",
+            "-DPIO_FRAMEWORK_ARDUINO_MMU_CUSTOM",
+            "-DMMU_IRAM_SIZE=0xC000",
+            "-DMMU_ICACHE_SIZE=0x4000",
+        )
 
 
 def test_generate_ld_scripts_testing_surgery_failure_is_named(