From 97d75cb619e2bd83547ac6a7c899784d97af4401 Mon Sep 17 00:00:00 2001
From: Randy Eckenrode <randy@largeandhighquality.com>
Date: Sun, 29 Sep 2024 13:54:47 -0400
Subject: [PATCH] {bintools,cc}-wrapper: set up Darwin SDK paths
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Some compilers may know to check these paths when `SDKROOT` is set, but
it’s not assumed they do. `SDKROOT` is instead derived from the
`DEVELOPER_DIR`, and `NIX_CFLAGS_COMPILE` is set up with the sysroot and
necessary framework and include search paths.
---
 .../add-darwin-ldflags-before.sh               | 10 ++++++++++
 pkgs/build-support/cc-wrapper/add-flags.sh     | 18 +++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh b/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh
index 75d9484846a8..afcfce8ea9d5 100644
--- a/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh
+++ b/pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh
@@ -79,3 +79,13 @@ if [ ! "$havePlatformVersionFlag" ]; then
         extraBefore+=(-@darwinPlatform@_version_min "${@darwinMinVersionVariable@_@suffixSalt@:-@darwinMinVersion@}")
     fi
 fi
+
+mangleVarSingle DEVELOPER_DIR ${role_suffixes[@]+"${role_suffixes[@]}"}
+
+# Allow wrapped bintools to do something useful when no `DEVELOPER_DIR` is set, which can happen when
+# the compiler is run outside of a stdenv or intentionally in an environment with no environment variables set.
+DEVELOPER_DIR=${DEVELOPER_DIR_@suffixSalt@}
+
+# Darwin looks for frameworks in the SDK located at `DEVELOPER_DIR`.
+extraBefore+=("-F$DEVELOPER_DIR/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks")
+extraBefore+=("-L$DEVELOPER_DIR/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib")
diff --git a/pkgs/build-support/cc-wrapper/add-flags.sh b/pkgs/build-support/cc-wrapper/add-flags.sh
index 2c3dc8884023..6683337b77b9 100644
--- a/pkgs/build-support/cc-wrapper/add-flags.sh
+++ b/pkgs/build-support/cc-wrapper/add-flags.sh
@@ -78,12 +78,28 @@ if [ -e @out@/nix-support/cc-cflags-before ]; then
     NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@="$(< @out@/nix-support/cc-cflags-before) $NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@"
 fi
 
-# Only add darwin min version flag if a default darwin min version is set,
+# Only add darwin min version flag and set up `DEVELOPER_DIR` if a default darwin min version is set,
 # which is a signal that we're targetting darwin.
 if [ "@darwinMinVersion@" ]; then
     mangleVarSingle @darwinMinVersionVariable@ ${role_suffixes[@]+"${role_suffixes[@]}"}
 
     NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@="-m@darwinPlatformForCC@-version-min=${@darwinMinVersionVariable@_@suffixSalt@:-@darwinMinVersion@} $NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@"
+
+    # `DEVELOPER_DIR` is used to dynamically locate libSystem (and the SDK frameworks) based on the SDK at that path.
+    mangleVarSingle DEVELOPER_DIR ${role_suffixes[@]+"${role_suffixes[@]}"}
+
+    # Allow wrapped compilers to do something useful when no `DEVELOPER_DIR` is set, which can happen when
+    # the compiler is run outside of a stdenv or intentionally in an environment with no environment variables set.
+    DEVELOPER_DIR=${DEVELOPER_DIR_@suffixSalt@}
+
+    # xcbuild needs `SDKROOT` to be the name of the SDK, which it sets in its own wrapper,
+    # but compilers expect it to point to the absolute path.
+    SDKROOT="$DEVELOPER_DIR/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk"
+
+    # Set up various library paths since compilers may not support (or may have disabled) finding them in the sysroot.
+    NIX_CFLAGS_COMPILE_BEFORE_@suffixSalt@+=" -isysroot $SDKROOT"
+    NIX_CFLAGS_COMPILE_@suffixSalt@+=" -idirafter $SDKROOT/usr/include"
+    NIX_CFLAGS_COMPILE_@suffixSalt@+=" -iframework $SDKROOT/System/Library/Frameworks"
 fi
 
 # That way forked processes will not extend these environment variables again.