macOS string.h shim and variant build fixes

builder/frameworks/arduino.py

@@ -23,6 +23,8 @@
 """
 
 import os
+import platform as host_platform
+import subprocess
 
 from SCons.Script import DefaultEnvironment
 
@@ -34,6 +36,77 @@
 FRAMEWORK_DIR = platform.get_package_dir("framework-portduino")
 assert os.path.isdir(FRAMEWORK_DIR)
 
+# On macOS, APFS is case-insensitive by default. The framework's
+# `cores/arduino/api/String.h` shadows libc's `<string.h>` when other code
+# does `#include <string.h>`, which breaks both libc++'s <cstring> machinery
+# and `extern "C" { #include <string.h> }` blocks in third-party libraries
+# (e.g., SparkFun ICM_20948_C.h) — under `extern "C"`, Arduino's String class
+# trips C-linkage rules and clang reports its `friend operator+` overloads
+# as "conflicting types".
+#
+# Trying to outrank `cores/arduino/api/` via `-I/path/to/sdk/...` doesn't
+# work because clang dedupes against its implicit search paths.
+# Instead, we materialize a tiny shim directory containing a *symlink* named
+# `string.h` -> libc++'s real `<string.h>` shim, and prepend that directory
+# to the include search path. Since the shim path is novel (not already
+# implicit), clang doesn't dedupe; `<string.h>` lookups find it first; the
+# shim's own `#include_next <string.h>` chains correctly to libc; and
+# Arduino's `String.h` is never reached via case-shadow.
+MACOS_STRING_SHIM_DIR = None
+if host_platform.system() == "Darwin":
+    try:
+        sdk_path = subprocess.check_output(
+            ["xcrun", "--show-sdk-path"], text=True
+        ).strip()
+        libc_string_h = os.path.join(sdk_path, "usr", "include", "string.h")
+        if os.path.isfile(libc_string_h):
+            shim_dir = os.path.join(
+                env.subst("$PROJECT_BUILD_DIR"),
+                "framework-portduino-darwin-shim",
+            )
+            os.makedirs(shim_dir, exist_ok=True)
+            shim_path = os.path.join(shim_dir, "string.h")
+            # Generate the shim content. We deliberately avoid `#include_next`
+            # because clang's `#include_next` searches relative to where the
+            # current file was *found* on the include path, not where it lives
+            # on disk — so if we routed through libc++'s shim via symlink,
+            # `#include_next` would continue searching from /our/shim/ and
+            # land on `cores/arduino/api/String.h` again. Instead, we
+            # explicitly:
+            #   1) define _LIBCPP_STRING_H so libc++'s <cstring> sees its
+            #      `<string.h>` shim "as if" it had been processed, and
+            #   2) absolute-include libc's real `<string.h>` to declare
+            #      memcpy/strlen/etc. at C linkage (which is also what every
+            #      `extern "C" { #include <string.h> }` block expects).
+            shim_content = (
+                "// Auto-generated by platform-native/builder/frameworks/"
+                "arduino.py.\n"
+                "// Routes <string.h> away from framework-portduino's "
+                "case-clashing\n"
+                "// `cores/arduino/api/String.h` on macOS APFS.\n"
+                "#pragma once\n"
+                "#ifndef _LIBCPP_STRING_H\n"
+                "#define _LIBCPP_STRING_H\n"
+                "#endif\n"
+                "#include \"%s\"\n" % libc_string_h
+            )
+            try:
+                existing = ""
+                if os.path.isfile(shim_path):
+                    with open(shim_path, "r") as f:
+                        existing = f.read()
+                if existing != shim_content:
+                    if os.path.lexists(shim_path):
+                        os.remove(shim_path)
+                    with open(shim_path, "w") as f:
+                        f.write(shim_content)
+            except OSError:
+                pass
+            if os.path.isfile(shim_path):
+                MACOS_STRING_SHIM_DIR = shim_dir
+    except (subprocess.CalledProcessError, FileNotFoundError):
+        pass
+
 env.Append(
     CPPDEFINES=[
         ("ARDUINO", 4403), # FIXME, find how these numbers are assigned!
@@ -46,7 +119,13 @@
     CCFLAGS=[
         "-w",
         "-Wall",
-        "-ggdb"
+        "-ggdb",
+        # Apple Clang 16+ promotes -Wenum-constexpr-conversion to a hard
+        # default error. The firmware uses 0xFF as an "unset" sentinel for
+        # several pb-generated enums whose declared range is smaller (e.g.
+        # MODEM_PRESET_END in mesh/MeshRadio.h). GCC has no equivalent
+        # warning, so this flag is harmless on Linux and necessary on macOS.
+        "-Wno-enum-constexpr-conversion",
     ],
 
     CXXFLAGS=[
@@ -78,6 +157,12 @@
     ]
 )
 
+# Darwin-only: prepend the macOS String.h shim directory so `<string.h>`
+# lookups find libc++'s shim first instead of case-shadowing onto Arduino's
+# `String.h` (see comment block at top).
+if MACOS_STRING_SHIM_DIR:
+    env.Prepend(CPPPATH=[MACOS_STRING_SHIM_DIR])
+
 #
 # Target: Build Core Library
 #
@@ -88,15 +173,26 @@
     variants_dir = os.path.join(
         "$PROJECT_DIR", board.get("build.variants_dir")) if board.get(
             "build.variants_dir", "") else os.path.join(FRAMEWORK_DIR, "variants")
-    env.Append(
-        CPPPATH=[
-            os.path.join(variants_dir, board.get("build.variant"))
-        ]
-    )
-    libs.append(env.BuildLibrary(
-        os.path.join("$BUILD_DIR", "FrameworkArduinoVariant"),
-        os.path.join(variants_dir, board.get("build.variant"))
-    ))
+    variant_path = os.path.join(variants_dir, board.get("build.variant"))
+    env.Append(CPPPATH=[variant_path])
+    # Skip BuildLibrary if the variant directory has no .c/.cpp/.S sources.
+    # macOS `ar` rejects archives with zero members ("ar: no archive members
+    # specified"); GNU ar on Linux silently produces an empty archive. The
+    # framework's bundled `variants/` is just a sentinel `.gitignore` for many
+    # boards, so we'd hit this on any host where `ar` is strict.
+    resolved_variant = env.subst(variant_path)
+    has_variant_sources = False
+    if os.path.isdir(resolved_variant):
+        for _, _, files in os.walk(resolved_variant):
+            if any(f.endswith((".c", ".cpp", ".cc", ".cxx", ".S", ".s"))
+                   for f in files):
+                has_variant_sources = True
+                break
+    if has_variant_sources:
+        libs.append(env.BuildLibrary(
+            os.path.join("$BUILD_DIR", "FrameworkArduinoVariant"),
+            variant_path
+        ))
 
 libs.append(env.BuildLibrary(
     os.path.join("$BUILD_DIR", "FrameworkArduino"),