Merge branch 'esp8266-native-pch' into esp32-idf-pch

esphome/platformio/pch.py.script

@@ -117,12 +117,18 @@ def _compile_gch(cxx, flags, header: Path, gch: Path, proj_dir: Path):
         raise OSError(f"compiler killed by signal {-result.returncode}")
     if result.returncode != 0:
         return result.stderr
+    # -MF is only legal alongside a dependency flag; pass it solely to
+    # redirect a depfile that -MD/-MMD in the flags would otherwise write
+    dep_redirect = (
+        ["-MF", os.devnull]
+        if any(f in ("-MD", "-MMD", "-M", "-MM") for f in flags)
+        else []
+    )
     probe = subprocess.run(  # noqa: PLW1510
         [
             cxx,
             *flags,
-            "-MF",
-            os.devnull,
+            *dep_redirect,
             "-Winvalid-pch",
             "-include",
             str(header),

tests/unit_tests/test_platformio_pch_script.py

@@ -100,7 +100,9 @@ def _fake_cxx(
         body += f"echo {fail_msg or 'boom'} >&2\nexit 1\n"
     else:
         # Only the c++-header compile has a -o; the load probe has none
-        body += 'out=""; prev=""\nfor a in "$@"; do [ "$prev" = "-o" ] && out="$a"; prev="$a"; done\n'
+        body += 'out=""; prev=""; mf=0; dep=0\nfor a in "$@"; do [ "$prev" = "-o" ] && out="$a"; prev="$a"; [ "$a" = "-MF" ] && mf=1; case "$a" in -M|-MM|-MD|-MMD) dep=1;; esac; done\n'
+        # Real cc1plus rejects -MF without a dependency flag
+        body += 'if [ "$mf" = 1 ] && [ "$dep" = 0 ]; then echo "cc1plus: error: to generate dependencies you must specify either \x27-M\x27 or \x27-MM\x27" >&2; exit 1; fi\n'
         body += '[ -n "$out" ] && echo gch > "$out"\n'
         if reject_pch:
             body += 'case " $* " in *c++-header*) ;; *) echo "warning: esphome_pch.h.gch: had text segment at different address" >&2;; esac\n'