Fix for JVM backend

Wrong argument was passed into `CoercionHOW::coerce`.

- Added `COERCE` candidate to Str to handle native strings
- Fixed a `nqp::die` in `CoercionHOW::coerce`

src/Perl6/Metamodel/CoercionHOW.nqp

@@ -202,11 +202,13 @@ class Perl6::Metamodel::CoercionHOW
                             ~ (nqp::defined($coerced_decont) ?? "an instance of" !! "a type object")
                             ~ " " ~ $coerced_name;
             }
-            if %ex {
+            unless nqp::isnull(%ex) {
                 %ex<X::Coerce::Impossible>($target_type_name, $value_type_name, $hint)
             }
-            nqp::die("Impossible coercion from " ~ $value_type.HOW.name($value_type_name)
-                        ~ " into " ~ $target_type_name ~ ": " ~ $hint);
+            nqp::die("Impossible coercion from "
+                        ~ $value_type_name
+                        ~ " into " ~ $target_type_name
+                        ~ ": " ~ $hint);
         }
 
         $coerced_value

src/core.c/Str.pm6

@@ -62,6 +62,11 @@ my class Str does Stringy { # declared in BOOTSTRAP
     multi method Stringy(Str:D:) { self }
     multi method DUMP(Str:D: --> Str:D) { self.raku }
 
+    proto method COERCE(|) {*}
+    multi method COERCE(Mu \s) {
+        self.new(:value(nqp::p6box_s(s)))
+    }
+
     method Int(Str:D: --> Int:D) {
         nqp::istype((my $n := self.Numeric),Int) || nqp::istype($n,Failure)
           ?? $n

src/vm/jvm/runtime/org/raku/rakudo/Binder.java

@@ -379,7 +379,7 @@ else if (desiredNative == 0) {
         boolean didHLLTransform = false;
         SixModelObject paramType = param.get_attribute_boxed(tc, gcx.Parameter, "$!type", HINT_type);
         SixModelObject ContextRef = null;
-        SixModelObject HOW = null;
+        SixModelObject HOW = paramType.st.HOW;
         if (flag == CallSiteDescriptor.ARG_OBJ && !(is_rw && desiredNative != 0)) {
             /* We need to work on the decontainerized value. */
             decontValue = Ops.decont(arg_o, tc);
@@ -390,14 +390,12 @@ else if (desiredNative == 0) {
             if (decontValue != beforeHLLize)
                 didHLLTransform = true;
 
-
             /* Skip nominal type check if not needed. */
             if (!noNomTypeCheck) {
                 /* Is the nominal type generic and in need of instantiation? (This
                  * can happen in (::T, T) where we didn't learn about the type until
                  * during the signature bind.) */
                 if ((paramFlags & SIG_ELEM_TYPE_GENERIC) != 0) {
-                    HOW = paramType.st.HOW;
                     SixModelObject ig = Ops.findmethod(HOW,
                         "instantiate_generic", tc);
                     ContextRef = tc.gc.ContextRef;
@@ -514,9 +512,8 @@ else if (Ops.istype_nd(decontValue, gcx.PositionalBindFailover, tc) != 0) {
                 return BIND_RESULT_FAIL;
             }
 
-            HOW = paramType.st.HOW;
             SixModelObject coerceMeth = Ops.findmethod(HOW, "coerce", tc);
-            Ops.invokeDirect(tc, coerceMeth, genIns, new Object[] { HOW, paramType, origArg });
+            Ops.invokeDirect(tc, coerceMeth, genIns, new Object[] { HOW, paramType, arg_o });
             arg_o = Ops.result_o(tc.curFrame);
             decontValue = Ops.decont(arg_o, tc);
         }