improve the initial install experience.

Made it easier to get up and running wit Rust, rather than relying entirely on one-time configuration that is hard to remember, later down the line.

.gitignore

@@ -62,3 +62,6 @@ fastlane/Preview.html
 fastlane/screenshots
 fastlane/test_output
 fastlane/readme.md
+
+# rust
+.cargo/

zcash-android-wallet-app/build.gradle.kts

@@ -6,7 +6,7 @@ buildscript {
         
     }
     dependencies {
-        classpath("com.android.tools.build:gradle:3.3.0-alpha13")
+        classpath("com.android.tools.build:gradle:3.4.0-alpha02")
         classpath(kotlin("gradle-plugin", version = "1.2.71"))
     }
 }

zcash-android-wallet-app/zcash-android-welding/build-ndk-standalone.sh

@@ -0,0 +1,60 @@
+#!/usr/bin/zsh
+
+# put this somewhere that's often ignored by git
+output_dir=out/ndk/standalone
+
+# check for NDK standalone 
+[[ -d "$output_dir" ]] && echo "Standalone NDK files found!" && exit 1
+
+standalone_script=$(find $ANDROID_HOME -name "*make_standalone_toolchain.py")
+
+# Try to find and print some info about the NDK based on the location of the toolchain script
+if [ ! -f "$standalone_script" ]; then
+	echo "NDK not found. Please make sure that ANDROID_HOME is set and the NDK has been installed there"
+else
+	echo "Standalone NDK files appear to be missing.\n    Attempting to install them..."
+	ndk_dir=$(dirname $(dirname $(dirname $standalone_script 2>/dev/null) 2>/dev/null) 2>/dev/null)
+	ndk_version=$(grep -oE "[0-9.]{5,}" /home/gmale/kg/setup/android/sdk/ndk-bundle/source.properties 2>/dev/null)
+	echo "        NDK version $ndk_version found at $ndk_dir"
+fi
+
+echo "        Installing the standalone NDK for x86|arm|arm64 into $output_dir"
+mkdir -p $output_dir
+"$standalone_script" --arch x86 --api 16 --install-dir "$output_dir/x86"
+"$standalone_script" --arch arm --api 16 --install-dir "$output_dir/arm"
+"$standalone_script" --arch arm64 --api 21 --install-dir "$output_dir/arm64"
+
+# check for our generated cargo file
+generated_cargo_config=../.cargo/config
+
+if [ -f "$generated_cargo_config" ]; then
+	backup_config_filename="config.$(date +%s).backup"
+	echo "    existing config found. Backing it up from $generated_cargo_config to $(dirname $generated_cargo_config)/$backup_config_filename"	
+	cp $generated_cargo_config $(dirname $generated_cargo_config)/$backup_config_filename
+fi
+
+echo "    generating cargo config at $generated_cargo_config"
+
+mkdir -p $(dirname $generated_cargo_config)
+
+awk -v SA_NDK=$output_dir -v SCRIPT_DIR=$PWD 'BEGIN{
+
+printf "#auto-generated by build-ndk-standalone.sh\n\n"
+
+printf "[target.i686-linux-android]\n"
+printf "ar = \"%s/%s/x86/bin/i686-linux-android-ar\"\n", SCRIPT_DIR, SA_NDK
+printf "linker = \"%s/%s/x86/bin/i686-linux-android-clang\"\n\n", SCRIPT_DIR, SA_NDK
+
+printf "[target.armv7-linux-androideabi]\n"
+printf "ar = \"%s/%s/arm/bin/arm-linux-androideabi-ar\"\n", SCRIPT_DIR, SA_NDK
+printf "linker = \"%s/%s/arm/bin/arm-linux-androideabi-clang\"\n\n", SCRIPT_DIR, SA_NDK
+
+printf "[target.aarch64-linux-android]\n"
+printf "ar = \"%s/%s/arm64/bin/aarch64-linux-android-ar\"\n", SCRIPT_DIR, SA_NDK
+printf "linker = \"%s/%s/arm64/bin/aarch64-linux-android-clang\"\n\n", SCRIPT_DIR, SA_NDK
+
+}' > $generated_cargo_config
+
+echo "Done"
+
+

zcash-android-wallet-app/zcash-android-welding/build-rust.sh

@@ -1,3 +1,32 @@
+#!/usr/bin/zsh
+
+# check for cargo installation
+if ! type -p ~/.cargo/bin/cargo > /dev/null; then
+	echo "Cargo appears to be missing.\nTry installing it with the following command:\n    curl https://sh.rustup.rs -sSf | sh"
+	echo "and then run this script again."
+	exit 1
+fi
+echo "Cargo found!"
+
+# check for android targets
+installed_android_target_count=$(~/.cargo/bin/rustup target list | grep android | grep installed | wc -l)
+if [ "$installed_android_target_count" -lt "3" ]; then
+	echo "The android targets do not appear to be installed."
+        echo "attempting to install them...\n    ~/.cargo/bin/rustup target add aarch64-linux-android armv7-linux-androideabi i686-linux-android"
+	~/.cargo/bin/rustup target add aarch64-linux-android armv7-linux-androideabi i686-linux-android
+	[[ $(~/.cargo/bin/rustup target list | grep android | grep installed | wc -l) -lt 3 ]] && echo "install failed. Aborting!" && exit 1
+	echo "Done."
+fi
+
+echo "Android targets found!" 
+
+# check for standalone  NDK
+./build-ndk-standalone.sh
+
+
+echo "Building..."
 cargo build --target aarch64-linux-android --release
 cargo build --target i686-linux-android --release
-cargo build --target armv7-linux-androideabi --release
+cargo build --target armv7-linux-androideabi --release
+
+echo "Done."