build.sh: support -l opt to build for local arch

We might as well make it easy for people, rather than telling them to build for
aarch64 which may or may not be useful.

(Compare element-hq/element-x-android#4021)

Author: richvdh

README.md

@@ -20,23 +20,21 @@ Usage :
 
 ## Testing locally
 As the package vendors a pre-built binary of the SDK, all local development is done via the SDK's repo instead of this one.
-You can use the build script to generate the AAR file for testing. Be sure to have checkout the matrix-rust-sdk first.
-
-Usage:
+You can use the build script to generate the AAR file for testing. Be sure to have checked out the matrix-rust-sdk first.
 
+To build the main crate (eg, for Element-X):
 ```
-./scripts/build.sh -p matrix-rust-sdk-path -m sdk -t aarch64-linux-android
+./scripts/build.sh -p <matrix-rust-sdk-path> -m sdk -l
 ```
 
-To build just the crypto crate, use this instead:
-
+To build just the crypto crate (eg, for Element Android classic), use this instead:
 ```
-./scripts/build.sh -p matrix-rust-sdk-path -m crypto -t aarch64-linux-android
+./scripts/build.sh -p matrix-rust-sdk-path -m crypto -l
 ```
 
 Other useful flags:
 
-- `-o OUTPUT_DIR`: Writes the output AAR file to the dir `OUTPUT_DIR`.
+- `-o OUTPUT_DIR`: Moves the generated AAR file to the dir `OUTPUT_DIR`.
 - `-r`: Produces a release build instead of a development one.
 
 ## Prerequisites

scripts/build.sh

@@ -8,7 +8,8 @@ helpFunction() {
   echo -e "\t-o Optional output path with the expected name of the aar file"
   echo -e "\t-r Flag to build in release mode"
   echo -e "\t-m Option to select the gradle module to build. Default is sdk"
-  echo -e "\t-t Option to to select an android target to build against. Default will build for all targets."
+  echo -e "\t-t Select a target architecture to build for. Default will build for all known Android targets."
+  echo -e "\t-l Build for the local architecture. Incompatible with '-t'."
   exit 1
 }
 
@@ -20,14 +21,16 @@ scripts_dir=$(
 is_release='false'
 gradle_module='sdk'
 only_target=''
+local_target=''
 output=''
 
-while getopts ':rp:m:t:o:' 'opt'; do
+while getopts ':rp:m:t:lo:' 'opt'; do
   case ${opt} in
   'r') is_release='true' ;;
   'p') sdk_path="$OPTARG" ;;
   'm') gradle_module="$OPTARG" ;;
   't') only_target="$OPTARG" ;;
+  'l') local_target='true' ;;
   'o') output="$OPTARG" ;;
   ?) helpFunction ;;
   esac
@@ -38,6 +41,17 @@ if [ -z "$sdk_path" ]; then
   helpFunction
 fi
 
+if [ -n "$local_target" ]; then
+    if [ -n "$only_target" ]; then
+        echo "Cannot specifiy both '-l' and '-t'." >&2
+        exit 1
+    fi
+
+    only_target="$(uname -m)-linux-android"
+    # On ARM MacOS, `uname -m` returns arm64, but the toolchain is called aarch64
+    only_target="${only_target/arm64/aarch64}"
+fi
+
 if [ -z "$only_target" ]; then
   echo "no target provided, build for all targets"
   target_command=()