Add an additional XCode + Rust project option

[bes]

I've been successfully using the "Swift Package" approach to build my swift-bridge library, but every time it's compiled XCode spends a long time refreshing the swift package(s), which can be tens of minutes!

There is another way though, and that is just adapting the XCode + Cargo variant to not build every time XCode builds, but rather do the rust build separately, with some additional scripts to copy things to the right place.

It's a very slight variation, but it's working for me.

[bes]

Here is the build script I'm using on the rust-project side:

#!/bin/bash

set -e

# Make the script run in its own directory instead of the caller's directory.
cd "$(cd -P -- "$(dirname -- "$0")" && pwd -P)" || exit 1

XCODE_IOS_DIR="../ios"
RUST_LIB_DIR="$XCODE_IOS_DIR/rust-lib"
# The library name of the Cargo project
RUST_CRATE_NAME="my-rust-lib"
RUST_LIB_NAME="libmy_rust_lib_ios.a"

if [ ! -d "$XCODE_IOS_DIR" ]; then
  echo "$XCODE_IOS_DIR does not exist."
fi
mkdir -p "./target/simulator-ios/release"
mkdir -p "./target/simulator-ios/debug"
# The directory for the source files
mkdir -p "$RUST_LIB_DIR/sources/$RUST_CRATE_NAME"
# The directory for the aarch64/arm64 lib
mkdir -p "$RUST_LIB_DIR/libs/arm64-ios"
# The directory for the simulator lib
mkdir -p "$RUST_LIB_DIR/libs/simulator-ios"
# The directory actually used by the compiler (XCode will use this directory)
mkdir -p "$RUST_LIB_DIR/libs/working-lib"

case "$1" in
  "ci")
    cargo build
    ;;
  "debug")
    cargo build --target aarch64-apple-ios
    cargo build --target x86_64-apple-ios
    cargo build --target aarch64-apple-ios-sim
    lipo \
        "./target/aarch64-apple-ios-sim/debug/$RUST_LIB_NAME" \
        "./target/x86_64-apple-ios/debug/$RUST_LIB_NAME" -create -output \
        "./target/simulator-ios/debug/$RUST_LIB_NAME"
    cp "./target/aarch64-apple-ios/debug/$RUST_LIB_NAME" "$RUST_LIB_DIR/libs/arm64-ios/"
    cp "./target/simulator-ios/debug/$RUST_LIB_NAME" "$RUST_LIB_DIR/libs/simulator-ios/"
    cp -R "./generated/" "$RUST_LIB_DIR/sources/"
    ;;
  "debug-arm64-only")
    cargo build --target aarch64-apple-ios
    cp "./target/aarch64-apple-ios/debug/$RUST_LIB_NAME" "$RUST_LIB_DIR/libs/arm64-ios/"
    cp -R "./generated/" "$RUST_LIB_DIR/sources/"
    ;;
  "release")
    cargo build --release --target aarch64-apple-ios
    cargo build --release --target x86_64-apple-ios
    cargo build --release --target aarch64-apple-ios-sim
    lipo \
        "./target/aarch64-apple-ios-sim/release/$RUST_LIB_NAME" \
        "./target/x86_64-apple-ios/release/$RUST_LIB_NAME" -create -output \
        "./target/simulator-ios/release/$RUST_LIB_NAME"
    cp "./target/aarch64-apple-ios/release/$RUST_LIB_NAME" "$RUST_LIB_DIR/libs/arm64-ios/"
    cp "./target/simulator-ios/release/$RUST_LIB_NAME" "$RUST_LIB_DIR/libs/simulator-ios/"
    cp -R "./generated/" "$RUST_LIB_DIR/sources/"
    ;;
  "release-arm64-only")
    cargo build --release --target aarch64-apple-ios
    cp "./target/aarch64-apple-ios/release/$RUST_LIB_NAME" "$RUST_LIB_DIR/libs/arm64-ios/"
    cp -R "./generated/" "$RUST_LIB_DIR/sources/"
    ;;
  *)
    echo "Must give option argument (debug | release)"
    exit 1
    ;;
esac

On the XCode side I have this build phase script

echo "Copying the correct version of the iOS library for platform $PLATFORM_NAME and architectures $ARCHS"
mkdir -p "$PROJECT_DIR/rust-lib/libs/working-lib"
if [[ "$PLATFORM_NAME" = "iphonesimulator" ]]; then
    cp "$PROJECT_DIR/rust-lib/libs/simulator-ios/libmy_rust_lib_ios.a" "$PROJECT_DIR/rust-lib/libs/working-lib/libmy_rust_lib_ios.a"
else
    cp "$PROJECT_DIR/rust-lib/libs/arm64-ios/libmy_rust_lib_ios.a" "$PROJECT_DIR/rust-lib/libs/working-lib/libmy_rust_lib_ios.a"
fi

Using those two scripts, most of the other XCode + Cargo steps still make sense.