Make symbol unflags pair-aware on the link line, drop the dead KEY_FLASH_MODE

esphome/build_gen/arduino8266.py

@@ -446,6 +446,22 @@ def _resolve_build_config(defines: dict[str, str]) -> _BuildConfig:
 _INCOMPLETE_INSTALL = "Arduino toolchain install is incomplete"
 
 
+def _filter_link_flags(unflags: set[str]) -> list[str]:
+    """_LINKFLAGS minus ``unflags``, pair-aware: unflagging a symbol also
+    drops the ``-u`` that carried it, so no dangling operand-less flag
+    reaches ld as the next token's consumer."""
+    out: list[str] = []
+    it = iter(_LINKFLAGS)
+    for tok in it:
+        if tok == "-u":
+            symbol = next(it)
+            if symbol not in unflags:
+                out += [tok, symbol]
+        elif tok not in unflags:
+            out.append(tok)
+    return out
+
+
 def _active_flash_ld_name(flash_ld_name: str) -> str:
     """The flash linker-script filename the link uses (testing mode renames
     the surgically patched copy)."""
@@ -979,10 +995,10 @@ def write_project(paths: InstalledPaths, ccache: str | None) -> bool:
             f"build_unflags cannot remove plain linker flag(s) "
             f"{', '.join(plain)}; unflag the full -Wl, form or the symbol"
         )
-    cflags, cxxflags, asflags, link_flags = (
-        [f for f in flags if f not in unflags]
-        for flags in (cflags, cxxflags, asflags, _LINKFLAGS)
+    cflags, cxxflags, asflags = (
+        [f for f in flags if f not in unflags] for flags in (cflags, cxxflags, asflags)
     )
+    link_flags = _filter_link_flags(unflags)
     if esp8266_data[KEY_SCANF_FLOAT]:
         link_flags += ["-u", "_scanf_float"]
     link_flags += project_link_flags

esphome/components/esp8266/const.py

@@ -16,7 +16,6 @@ KEY_WAVEFORM_REQUIRED = "waveform_required"
 KEY_SERIAL_REQUIRED = "serial_required"
 KEY_SERIAL1_REQUIRED = "serial1_required"
 # Set for the native (non-PlatformIO) toolchain's build generator
-KEY_FLASH_MODE = "flash_mode"
 KEY_SCANF_FLOAT = "scanf_float"
 
 # esp8266 namespace is already defined by arduino, manually prefix esphome

tests/unit_tests/build_gen/test_arduino8266.py

@@ -688,6 +688,23 @@ def test_build_config_nonosdk_precedence() -> None:
     assert _resolve_build_config(_defines()).nonosdk == "NONOSDK221"
 
 
+def test_write_project_unflagged_symbol_takes_its_dash_u(tmp_path: Path) -> None:
+    """Unflagging a -u symbol drops the -u that carried it; a dangling -u
+    would consume the next token and hand ld a symbol as an input file."""
+    paths = _make_framework(tmp_path)
+    _set_flags()
+    CORE.build_unflags = {"_printf_float"}
+    content = _write_ninja(paths)
+    link_line = next(
+        line for line in content.splitlines() if line.startswith("linkflags = ")
+    )
+    assert "_printf_float" not in link_line
+    assert "-u -u" not in link_line
+    # The neighbors survive as intact pairs
+    assert "-u app_entry" in link_line
+    assert "-u _DebugExceptionVector" in link_line
+
+
 def test_write_project_build_unflags_apply_to_framework_flags(tmp_path: Path) -> None:
     """build_unflags removes flags from the framework sets, as PlatformIO does."""
     paths = _make_framework(tmp_path)