Fix arm64 darwin install (#789)

* fix: workaround for lies from uname -m

On an arm64 mac, `uname -m` returns x86_64 which causes install script to install with the wrong architecture

* refactor: use same logic from rustup

* Tweak credit comment

* Prod ci

---------

Co-authored-by: oz <[email protected]>

nix-installer.sh

@@ -11,7 +11,7 @@
 # It runs on Unix shells like {a,ba,da,k,z}sh. It uses the common `local`
 # extension. Note: Most shells limit `local` to 1 var per line, contra bash.
 
-# This script is based off https://github.com/rust-lang/rustup/blob/8f6b53628ad996ad86f9c6225fa500cddf860905/rustup-init.sh
+# This script is based off https://github.com/rust-lang/rustup/blob/f8d7b3baba7a63237cb2b82ef49a68a37dd0633c/rustup-init.sh
 
 if [ "$KSH_VERSION" = 'Version JM 93t+ 2010-03-05' ]; then
     # The version of ksh93 that ships with many illumos systems does not
@@ -143,10 +143,30 @@ get_architecture() {
         fi
     fi
 
-    if [ "$_ostype" = Darwin ] && [ "$_cputype" = i386 ]; then
-        # Darwin `uname -m` lies
-        if sysctl hw.optional.x86_64 | grep -q ': 1'; then
-            _cputype=x86_64
+    if [ "$_ostype" = Darwin ]; then
+        # Darwin `uname -m` can lie due to Rosetta shenanigans. If you manage to
+        # invoke a native shell binary and then a native uname binary, you can
+        # get the real answer, but that's hard to ensure, so instead we use
+        # `sysctl` (which doesn't lie) to check for the actual architecture.
+        if [ "$_cputype" = i386 ]; then
+            # Handling i386 compatibility mode in older macOS versions (<10.15)
+            # running on x86_64-based Macs.
+            # Starting from 10.15, macOS explicitly bans all i386 binaries from running.
+            # See: <https://support.apple.com/en-us/HT208436>
+
+            # Avoid `sysctl: unknown oid` stderr output and/or non-zero exit code.
+            if sysctl hw.optional.x86_64 2> /dev/null || true | grep -q ': 1'; then
+                _cputype=x86_64
+            fi
+        elif [ "$_cputype" = x86_64 ]; then
+            # Handling x86-64 compatibility mode (a.k.a. Rosetta 2)
+            # in newer macOS versions (>=11) running on arm64-based Macs.
+            # Rosetta 2 is built exclusively for x86-64 and cannot run i386 binaries.
+
+            # Avoid `sysctl: unknown oid` stderr output and/or non-zero exit code.
+            if sysctl hw.optional.arm64 2> /dev/null || true | grep -q ': 1'; then
+                _cputype=arm64
+            fi
         fi
     fi