Add lvalue check for ref/out params with default arguments.

Move def arg check into semantic.

Move semantic check to FuncType.

Add more tests, do if check before assignment.

Separate fail tests.

toLvalue can take a scope. Add another test-case.

src/mtype.c

@@ -5584,6 +5584,11 @@ Type *TypeFunction::semantic(Loc loc, Scope *sc)
                     e = e->semantic(argsc);
                 }
                 e = e->implicitCastTo(argsc, fparam->type);
+
+                // default arg must be an lvalue
+                if (fparam->storageClass & (STCout | STCref))
+                    e = e->toLvalue(argsc, e);
+
                 fparam->defaultArg = e;
             }
 

test/fail_compilation/fail7603a.d

@@ -0,0 +1 @@
+void test(ref bool val = true) { }

test/fail_compilation/fail7603b.d

@@ -0,0 +1 @@
+void test(out bool val = true) { }

test/fail_compilation/fail7603c.d

@@ -0,0 +1,2 @@
+enum x = 3;
+void test(ref int val = x) { }

test/runnable/test7603.d

@@ -0,0 +1,30 @@
+void test7603()
+{
+    int g;
+    void foo(int n, ref int r = g) { r = n; }
+
+    int x;
+    foo(1, x);
+    assert(x == 1);
+
+    foo(2);
+    assert(g == 2);
+
+    int h = 100;
+    void bar(int n, out int r = h) { if (n != 0) r = n;  }
+
+    bar(0);
+    assert(h == 0);
+
+    bar(10);
+    assert(h == 10);
+
+    bar(10, x);
+    assert(x == 10);
+
+    bar(0, x);
+    assert(x == 0);
+
+}
+
+void main() { test7603(); }