Issue 9999 - Integer literal 0 and 1 should prefer integer type in overload resolution

src/mtype.c

@@ -5855,8 +5855,25 @@ MATCH TypeFunction::callMatch(Type *tthis, Expressions *args, int flag)
         {
             //printf("%s of type %s implicitConvTo %s\n", arg->toChars(), targ->toChars(), tprm->toChars());
             if (flag)
+            {
                 // for partial ordering, value is an irrelevant mockup, just look at the type
-                m = targ->implicitConvTo(tprm);
+#if DMDV2
+                /* Special rule for partial ordering between bool and non-bool integral types.
+                 * In basic, bool is more specialized than other integers.
+                 * But partial ordering should prefer integer parameters for integer literal arguments.
+                 * So reverse match result in here - bool is less specialized than other integer types.
+                 * See Bugzilla 9999.
+                 */
+                Type *tba = targ->toBasetype();
+                Type *tbp = tprm->toBasetype();
+                if (tba->ty == Tbool && (tbp->ty != Tbool && tbp->isintegral()))
+                    m = MATCHnomatch;
+                else if ((tba->ty != Tbool && tba->isintegral()) && tbp->ty == Tbool)
+                    m = MATCHconvert;
+                else
+#endif
+                    m = targ->implicitConvTo(tprm);
+            }
             else
                 m = arg->implicitConvTo(tprm);
             //printf("match %d\n", m);

test/runnable/overload.d

@@ -166,6 +166,56 @@ void test9410()
     assert(foo(1, S()) == 2); // Fails with: Error: S() is not an lvalue
 }
 
+/***************************************************/
+// 9999
+
+auto foo9999(bool) { return 1; }
+auto foo9999(long) { return 2; }
+
+void test9999()
+{
+    enum int  x0 = 0, x1 = 1, x2 = 2;
+    enum byte b0 = 0, b1 = 1, b2 = 2;
+
+    assert(foo9999(true) == 1);
+    assert(foo9999(false) == 1);
+    assert(foo9999(0) == 2);
+    assert(foo9999(1) == 2);
+    assert(foo9999(2) == 2);
+    assert(foo9999(x0) == 2);
+    assert(foo9999(x1) == 2);
+    assert(foo9999(x2) == 2);
+    assert(foo9999(b0) == 2);
+    assert(foo9999(b1) == 2);
+    assert(foo9999(b2) == 2);
+    assert(foo9999('\0') == 2);
+    assert(foo9999('\1') == 2);
+    assert(foo9999('\2') == 2);
+
+    void fooInt(int) {}
+    void fooLong(long) {}
+    void fooBool(bool) {}
+
+    // bool value matches to integer types
+    bool f;
+    fooInt(true);
+    fooInt(false);
+    fooInt(f);
+    fooLong(true);
+    fooLong(false);
+    fooLong(f);
+
+    // Integer literal 0 and 1 matches to bool
+    fooBool(0);
+    fooBool(1);
+    // from core.stdc.windows.windows
+    enum : int { FALSE = 0, TRUE = 1 }
+    fooBool(FALSE);
+    fooBool(TRUE);
+    // other integer literals don't match to bool
+    static assert(!__traits(compiles, fooBool(2)));
+}
+
 /***************************************************/
 
 int main()
@@ -176,6 +226,7 @@ int main()
     test8668();
     test8943();
     test9410();
+    test9999();
 
     printf("Success\n");
     return 0;