check-abi: Minor UI improvements

tools/check-abi.sh

@@ -6,14 +6,16 @@ default_base_version="$(git describe --match "v*.*.*" --abbrev=0)"
 default_new_version="HEAD"
 
 display_help_and_exit() {
-    echo "Usage: $0 <base_ver> <new_ver>"
+    echo "Usage: $0 [<base_ver> [<new_ver>]]"
     echo ""
     echo "Description: This script uses the ABI Compliance Checker tool to determine if the ABI"
     echo "             of a new version of libsecp256k1 has changed in a backward-incompatible way."
     echo ""
     echo "Options:"
-    echo "  base_ver      Specify the base version (default: $default_base_version)"
-    echo "  new_ver       Specify the new version (default: $default_new_version)"
+    echo "  base_ver      Specify the base version as a git commit-ish"
+    echo "                  (default: most recent reachable tag matching \"v.*.*\", currently \"$default_base_version\")"
+    echo "  new_ver       Specify the new version as a git commit-ish"
+    echo "                  (default: $default_new_version)"
     echo "  -h, --help    Display this help message"
     exit 0
 }
@@ -23,9 +25,11 @@ if [ "$#" -eq 0 ]; then
     new_version="$default_new_version"
 elif [ "$#" -eq 1 ] && { [ "$1" = "-h" ] || [ "$1" = "--help" ]; }; then
     display_help_and_exit
-elif [ "$#" -eq 2 ]; then
+elif [ "$#" -eq 1 ] || [ "$#" -eq 2 ]; then
     base_version="$1"
-    new_version="$2"
+    if [ "$#" -eq 2 ]; then
+        new_version="$2"
+    fi
 else
     echo "Invalid usage. See help:"
     echo ""
@@ -52,10 +56,10 @@ checkout_and_build() {
 echo "Comparing $base_version (base version) to $new_version (new version)"
 echo
 
-base_source_dir=$(mktemp -d)
+base_source_dir="$(mktemp -d)"
 checkout_and_build "$base_source_dir" "$base_version"
 
-new_source_dir=$(mktemp -d)
+new_source_dir="$(mktemp -d)"
 checkout_and_build "$new_source_dir" "$new_version"
 
 abi-compliance-checker -lib libsecp256k1 -old "${base_source_dir}/build/ABI.dump" -new "${new_source_dir}/build/ABI.dump"