Improve make_component.sh

- "Exit immediately if a command exits with a non-zero status." (set -e)
- Fix incorrect `rm -rf COMPONENT_DIR` and add user prompt before deleting directory
- Suggest to run `mvn package` when simplelanguage.jar is not found
- Use pushd/popd in favor of `cd $COMPONENT_DIR || exit 1`
- Mark variables as `readonly`
- Minor consistency fixes

component/make_component.sh

@@ -1,23 +1,36 @@
 #!/usr/bin/env bash
+set -e
 
-COMPONENT_DIR="component_temp_dir"
-LANGUAGE_PATH="$COMPONENT_DIR/jre/languages/sl"
+readonly COMPONENT_DIR="component_temp_dir"
+readonly LANGUAGE_PATH="$COMPONENT_DIR/jre/languages/sl"
+readonly SIMPLE_LANGUAGE_JAR="../language/target/simplelanguage.jar"
 if [[ -f ../native/slnative ]]; then
     INCLUDE_SLNATIVE="TRUE"
 fi
 
-rm -rf COMPONENT_DIR
+if [[ -d "$COMPONENT_DIR" ]]; then
+    read -p "'$COMPONENT_DIR' already exists. Do you want to remove it? (y/N): " user_input
+    if [[ "${user_input}" != "y" ]]; then
+        exit 0
+    fi
+    rm -rf "$COMPONENT_DIR"
+fi
+
+if [[ ! -f "$SIMPLE_LANGUAGE_JAR" ]]; then
+    echo "Could not find '$SIMPLE_LANGUAGE_JAR'. Did you run mvn package?"
+    exit 1
+fi
 
 mkdir -p "$LANGUAGE_PATH"
-cp ../language/target/simplelanguage.jar "$LANGUAGE_PATH"
+cp "$SIMPLE_LANGUAGE_JAR" "$LANGUAGE_PATH"
 
 mkdir -p "$LANGUAGE_PATH/launcher"
 cp ../launcher/target/sl-launcher.jar "$LANGUAGE_PATH/launcher/"
 
 mkdir -p "$LANGUAGE_PATH/bin"
-cp ../sl $LANGUAGE_PATH/bin/
-if [[ $INCLUDE_SLNATIVE = "TRUE" ]]; then
-    cp ../native/slnative $LANGUAGE_PATH/bin/
+cp ../sl "$LANGUAGE_PATH/bin/"
+if [[ "$INCLUDE_SLNATIVE" = "TRUE" ]]; then
+    cp ../native/slnative "$LANGUAGE_PATH/bin/"
 fi
 
 mkdir -p "$COMPONENT_DIR/META-INF"
@@ -29,12 +42,11 @@ mkdir -p "$COMPONENT_DIR/META-INF"
     echo "x-GraalVM-Polyglot-Part: True"
 } > "$COMPONENT_DIR/META-INF/MANIFEST.MF"
 
-(
-cd $COMPONENT_DIR || exit 1
+pushd "$COMPONENT_DIR" > /dev/null
 jar cfm ../sl-component.jar META-INF/MANIFEST.MF .
 
 echo "bin/sl = ../jre/languages/sl/bin/sl" > META-INF/symlinks
-if [[ $INCLUDE_SLNATIVE = "TRUE" ]]; then
+if [[ "$INCLUDE_SLNATIVE" = "TRUE" ]]; then
     echo "bin/slnative = ../jre/languages/sl/bin/slnative" >> META-INF/symlinks
 fi
 jar uf ../sl-component.jar META-INF/symlinks
@@ -44,5 +56,6 @@ jar uf ../sl-component.jar META-INF/symlinks
     echo "jre/languages/sl/bin/slnative = rwxrwxr-x"
 } > META-INF/permissions
 jar uf ../sl-component.jar META-INF/permissions
-)
-rm -rf $COMPONENT_DIR
+popd > /dev/null
+
+rm -rf "$COMPONENT_DIR"