avm2: Fix edge cases in RegExp constructor

core/src/avm2/globals/regexp.rs

@@ -1,6 +1,7 @@
 //! `RegExp` impl
 
 use crate::avm2::class::Class;
+use crate::avm2::error::type_error;
 use crate::avm2::method::{Method, NativeMethodImpl, ParamConfig};
 use crate::avm2::object::{regexp_allocator, ArrayObject, FunctionObject, Object, TObject};
 use crate::avm2::regexp::RegExpFlags;
@@ -27,16 +28,34 @@ pub fn instance_init<'gc>(
         activation.super_init(this, &[])?;
 
         if let Some(mut regexp) = this.as_regexp_mut(activation.context.gc_context) {
-            regexp.set_source(
-                args.get(0)
+            let source: AvmString<'gc> = match args.get(0) {
+                Some(Value::Undefined) => "".into(),
+                Some(Value::Object(Object::RegExpObject(o))) => {
+                    if !matches!(args.get(1), Some(Value::Undefined)) {
+                        return Err(Error::AvmError(type_error(
+                            activation,
+                            "Error #1100: Cannot supply flags when constructing one RegExp from another.",
+                            1100,
+                        )?));
+                    }
+                    let other = o.as_regexp().unwrap();
+                    regexp.set_source(other.source());
+                    regexp.set_flags(other.flags());
+                    return Ok(Value::Undefined);
+                }
+                arg => arg
                     .unwrap_or(&Value::String("".into()))
                     .coerce_to_string(activation)?,
-            );
+            };
 
-            let flag_chars = args
-                .get(1)
-                .unwrap_or(&Value::String("".into()))
-                .coerce_to_string(activation)?;
+            regexp.set_source(source);
+
+            let flag_chars = match args.get(1) {
+                Some(Value::Undefined) => "".into(),
+                arg => arg
+                    .unwrap_or(&Value::String("".into()))
+                    .coerce_to_string(activation)?,
+            };
 
             let mut flags = RegExpFlags::empty();
             for c in &flag_chars {
@@ -299,16 +318,8 @@ pub fn create_class<'gc>(activation: &mut Activation<'_, 'gc>) -> GcCell<'gc, Cl
             instance_init,
             "<RegExp instance initializer>",
             vec![
-                ParamConfig::optional(
-                    "re",
-                    Multiname::new(activation.avm2().public_namespace, "String"),
-                    "",
-                ),
-                ParamConfig::optional(
-                    "flags",
-                    Multiname::new(activation.avm2().public_namespace, "String"),
-                    "",
-                ),
+                ParamConfig::optional("re", Multiname::any(mc), Value::Undefined),
+                ParamConfig::optional("flags", Multiname::any(mc), Value::Undefined),
             ],
             false,
             mc,

tests/tests/swfs/avm2/regexp_constr/Test.as

@@ -14,8 +14,10 @@ trace("ignoreCase", re.ignoreCase);
 trace("multiline", re.multiline);
 trace("");
 
-function test(source:String, flags:String) {
-	trace("// new RegExp(\"" + source + "\", \"" + flags + "\");");
+function test(source:*, flags:*) {
+    var sourceStr = (typeof source === "string") ? "\"" + source + "\"" : source;
+    var flagsStr = (typeof flags === "string") ? "\"" + flags + "\"" : flags;
+    trace("// new RegExp(" + sourceStr + ", " + flagsStr + ");");
 	var re = new RegExp(source, flags);
 	trace(re);
 	trace(re.source == source);
@@ -38,3 +40,19 @@ test("all flags", "sxgim");
 test("invalid flags", "|%?-/.あa");
 test("uppercase flags", "SXGIM");
 test("duplicate flags", "ssgg");
+
+test(undefined, undefined);
+test(null, null);
+test(/#((.*))$/m, undefined);
+test(/empty flags/, undefined);
+test(/dotall embedded flags/s, undefined);
+try {
+    test(/empty string separate flag/s, "");
+} catch(e) {
+    trace(e);
+}
+try {
+    test(/dotall separate flags/s, "s");
+} catch(e) {
+    trace(e);
+}

tests/tests/swfs/avm2/regexp_constr/output.txt

@@ -97,3 +97,52 @@ global true
 ignoreCase false
 multiline false
 
+// new RegExp(undefined, undefined);
+//
+false
+dotall false
+extended false
+global false
+ignoreCase false
+multiline false
+
+// new RegExp(null, null);
+/null/
+false
+dotall false
+extended false
+global false
+ignoreCase false
+multiline false
+
+// new RegExp(/#((.*))$/m, undefined);
+/#((.*))$/m
+false
+dotall false
+extended false
+global false
+ignoreCase false
+multiline true
+
+// new RegExp(/empty flags/, undefined);
+/empty flags/
+false
+dotall false
+extended false
+global false
+ignoreCase false
+multiline false
+
+// new RegExp(/dotall embedded flags/s, undefined);
+/dotall embedded flags/s
+false
+dotall true
+extended false
+global false
+ignoreCase false
+multiline false
+
+// new RegExp(/empty string separate flag/s, "");
+TypeError: Error #1100: Cannot supply flags when constructing one RegExp from another.
+// new RegExp(/dotall separate flags/s, "s");
+TypeError: Error #1100: Cannot supply flags when constructing one RegExp from another.