Merge pull request #1307 from gnembon/strict_and_null_initialization

Strict config and null initialization

docs/scarpet/api/Overview.md

@@ -40,8 +40,12 @@ apps `__on_close()` will execute once per app, and with `'player'` scoped apps,
 ### App config via `__config()` function
 
 If an app defines `__config` method, and that method returns a map, it will be used to apply custom settings 
-for this app. Currently the following options are supported:
+for this app. Currently, the following options are supported:
 
+* `'strict'` : if `true`, any use of an uninitialized variable will result in program failure. Defaults to `false` if 
+not specified. With `'strict'`you have to assign an initial value to any variable before using it. It is very useful 
+to use this setting for app debugging and for beginner programmers. Explicit initialization is not required for your 
+code to work, but mistakes may result from improper assumptions about initial variable values of `null`.
 * `'scope'`: default scope for global variables for the app, Default is `'player'`, which means that globals and defined 
 functions will be unique for each player so that apps for each player will run in isolation. This is useful in 
 tool-like applications, where behaviour of things is always from a player's perspective. With player scope the initial run 

src/main/java/carpet/script/CarpetScriptHost.java

@@ -100,6 +100,7 @@ public class CarpetScriptHost extends ScriptHost
         else if (parent != null)
         {
             persistenceRequired = ((CarpetScriptHost)parent).persistenceRequired;
+            strict = parent.strict;
         }
         appConfig = config;
         appArgTypes = argTypes;
@@ -306,6 +307,7 @@ public class CarpetScriptHost extends ScriptHost
             Map<Value, Value> config = ((MapValue) ret).getMap();
             setPerPlayer(config.getOrDefault(new StringValue("scope"), new StringValue("player")).getString().equalsIgnoreCase("player"));
             persistenceRequired = config.getOrDefault(new StringValue("stay_loaded"), Value.TRUE).getBoolean();
+            strict = config.getOrDefault(StringValue.of("strict"), Value.FALSE).getBoolean();
             // check requires
             Value loadRequirements = config.get(new StringValue("requires"));
             if (loadRequirements instanceof FunctionValue)

src/main/java/carpet/script/Expression.java

@@ -738,7 +738,7 @@ public class Expression
         }
         var = c.host.getGlobalVariable(module, name);
         if (var != null) return var;
-        var = (_c, _t ) -> Value.ZERO.reboundedTo(name);
+        var = (_c, _t ) -> _c.host.strict ? Value.UNDEF.reboundedTo(name) : Value.NULL.reboundedTo(name);
         setAnyVariable(c, name, var);
         return var;
     }

src/main/java/carpet/script/ScriptHost.java

@@ -36,6 +36,7 @@ public abstract class ScriptHost
     private final Map<Value, ThreadPoolExecutor> executorServices = new HashMap<>();
     private final Map<Value, Object> locks = new ConcurrentHashMap<>();
     protected boolean inTermination = false;
+    public boolean strict;
 
     private final Set<String> deprecations = new HashSet<>();
 
@@ -118,6 +119,7 @@ public abstract class ScriptHost
         this.main = code;
         this.perUser = perUser;
         this.user = null;
+        this.strict = false;
         ModuleData moduleData = new ModuleData(code);
         initializeModuleGlobals(moduleData);
         this.moduleData.put(code, moduleData);

src/main/java/carpet/script/value/NullValue.java

@@ -32,7 +32,7 @@ public class NullValue extends NumericValue // TODO check nonsingleton code
     {
         return new NullValue();
     }
-    private NullValue() {super(0);}
+    protected NullValue() {super(0);}
 
     @Override
     public boolean equals(final Object o)

src/main/java/carpet/script/value/UndefValue.java

@@ -0,0 +1,140 @@
+package carpet.script.value;
+
+import carpet.script.exception.InternalExpressionException;
+import com.google.gson.JsonElement;
+import net.minecraft.nbt.Tag;
+
+public class UndefValue extends NullValue {
+    public static final UndefValue UNDEF = new UndefValue();
+
+    private RuntimeException getError() {
+        return new InternalExpressionException("variable "+boundVariable+" was used before initialization under 'strict' app config");
+    }
+
+
+    @Override
+    public String getString()
+    {
+        throw getError();
+    }
+
+    @Override
+    public String getPrettyString()
+    {
+        return "undefined";
+    }
+
+    @Override
+    public boolean getBoolean()
+    {
+        throw getError();
+    }
+
+    @Override
+    public Value clone()
+    {
+        return new UndefValue();
+    }
+
+    @Override
+    public boolean equals(final Object o)
+    {
+        throw getError();
+    }
+
+    @Override
+    public Value slice(long fromDesc, Long toDesc) {
+        throw getError();
+    }
+
+    @Override
+    public NumericValue opposite() {
+        throw getError();
+    }
+
+    @Override
+    public int length() {
+        throw getError();
+    }
+
+    @Override
+    public int compareTo(Value o)
+    {
+        throw getError();
+    }
+
+    @Override
+    public Value in(Value value) {
+        throw getError();
+    }
+
+    @Override
+    public String getTypeString()
+    {
+        return "undef";
+    }
+
+    @Override
+    public int hashCode()
+    {
+        throw getError();
+    }
+
+    @Override
+    public Tag toTag(boolean force)
+    {
+        throw getError();
+    }
+
+    @Override
+    public Value split(Value delimiter) {
+        throw getError();
+    }
+
+    @Override
+    public JsonElement toJson()
+    {
+        throw getError();
+    }
+
+    @Override
+    public boolean isNull() {
+        throw getError();
+    }
+
+    @Override
+    public Value add(Value v) {
+        throw getError();
+    }
+
+    @Override
+    public Value subtract(Value v)
+    {
+        throw getError();
+    }
+
+    @Override
+    public Value multiply(Value v)
+    {
+        throw getError();
+    }
+
+    @Override
+    public Value divide(Value v)
+    {
+        throw getError();
+    }
+
+    @Override
+    public double readDoubleNumber()
+    {
+        throw getError();
+    }
+
+    @Override
+    public long readInteger()
+    {
+        throw getError();
+    }
+
+}

src/main/java/carpet/script/value/Value.java

@@ -21,6 +21,7 @@ public abstract class Value implements Comparable<Value>, Cloneable
     public static NumericValue ONE = new NumericValue(1);
 
     public static NullValue NULL = NullValue.NULL;
+    public static UndefValue UNDEF = UndefValue.UNDEF;
 
     public String boundVariable;