Fix Issue 20178 - Add TypeInfo_Class/TypeInfo_Interface.isBaseOf

Equivalent to C#/Java isAssignableFrom. Naming the method
"isAssignableFrom" would be more familiar to people coming from C#/Java
but is potentially misleading: "alias this" and overloadable opAssign
mean that this would not actually indicate whether values of one type
could be assigned to another.

Adding qualifiers to rt.cast_ functions.

src/object.d

@@ -959,6 +959,8 @@ class TypeInfo_Delegate : TypeInfo
 }
 
 private extern (C) Object _d_newclass(const TypeInfo_Class ci);
+private extern (C) int _d_isbaseof(scope TypeInfo_Class child,
+    scope const TypeInfo_Class parent) @nogc nothrow pure @safe; // rt.cast_
 
 /**
  * Runtime type information about a class.
@@ -1102,6 +1104,24 @@ class TypeInfo_Class : TypeInfo
         }
         return o;
     }
+
+   /**
+    * Returns true if the class described by `child` derives from the class
+    * described by this `TypeInfo_Class`.
+    *
+    * Params:
+    *  child = TypeInfo for some class
+    * Returns:
+    *  true if the class described by `child` derives from the
+    *  class described by this `TypeInfo_Class`.
+    */
+    bool isBaseOf(scope const TypeInfo_Class child) const @nogc nothrow pure @trusted
+    {
+        for (auto ti = cast() child; ti !is null; ti = ti.base)
+            if (ti is this)
+                return true;
+        return false;
+    }
 }
 
 alias ClassInfo = TypeInfo_Class;
@@ -1191,6 +1211,38 @@ class TypeInfo_Interface : TypeInfo
     override @property uint flags() nothrow pure const { return 1; }
 
     TypeInfo_Class info;
+
+   /**
+    * Returns true if the class described by `child` derives from the interface
+    * described by this `TypeInfo_Interface`.
+    *
+    * Params:
+    *  child = TypeInfo for some class
+    * Returns:
+    *  true if the class described by `child` derives from the
+    *  interface described by this `TypeInfo_Interface`.
+    */
+    bool isBaseOf(scope const TypeInfo_Class child) const @nogc nothrow pure @trusted
+    {
+        auto child_ = cast() child;
+        return cast(bool) _d_isbaseof(child_, this.info);
+    }
+
+   /**
+    * Returns true if the interface described by `child` derives from the
+    * the interface described by this `TypeInfo_Interface`.
+    *
+    * Params:
+    *  child = TypeInfo for some interface
+    * Returns:
+    *  true if the interface described by `child` derives from the
+    *  interface described by this `TypeInfo_Interface`.
+    */
+    bool isBaseOf(scope const TypeInfo_Interface child) const @nogc nothrow pure @trusted
+    {
+        auto child_ = cast() child;
+        return child !is null && cast(bool) _d_isbaseof(child_.info, this.info);
+    }
 }
 
 class TypeInfo_Struct : TypeInfo

src/rt/cast_.d

@@ -14,6 +14,9 @@
 module rt.cast_;
 
 extern (C):
+@nogc:
+nothrow:
+pure:
 
 /******************************************
  * Given a pointer:
@@ -74,7 +77,7 @@ void* _d_dynamic_cast(Object o, ClassInfo c)
     return res;
 }
 
-int _d_isbaseof2(ClassInfo oc, ClassInfo c, ref size_t offset)
+int _d_isbaseof2(scope ClassInfo oc, scope const ClassInfo c, scope ref size_t offset) @safe
 {
     if (oc is c)
         return true;
@@ -101,7 +104,7 @@ int _d_isbaseof2(ClassInfo oc, ClassInfo c, ref size_t offset)
     return false;
 }
 
-int _d_isbaseof(ClassInfo oc, ClassInfo c)
+int _d_isbaseof(scope ClassInfo oc, scope const ClassInfo c) @safe
 {
     if (oc is c)
         return true;

test/typeinfo/Makefile

@@ -1,6 +1,6 @@
 include ../common.mak
 
-TESTS:=comparison
+TESTS:=comparison isbaseof
 
 .PHONY: all clean
 all: $(addprefix $(ROOT)/,$(addsuffix .done,$(TESTS)))

test/typeinfo/src/isbaseof.d

@@ -0,0 +1,35 @@
+// https://issues.dlang.org/show_bug.cgi?id=20178
+
+interface I {}
+interface J : I {}
+class C1 : I {}
+class C2 : C1 {}
+class C3 : J {}
+
+void main() @nogc nothrow pure @safe
+{
+    assert(typeid(C1).isBaseOf(typeid(C1)));
+    assert(typeid(C1).isBaseOf(typeid(C2)));
+
+    assert(!typeid(C2).isBaseOf(typeid(C1)));
+    assert(typeid(C2).isBaseOf(typeid(C2)));
+
+    assert(!typeid(C1).isBaseOf(typeid(Object)));
+    assert(!typeid(C2).isBaseOf(typeid(Object)));
+    assert(typeid(Object).isBaseOf(typeid(C1)));
+    assert(typeid(Object).isBaseOf(typeid(C2)));
+
+    assert(typeid(I).isBaseOf(typeid(I)));
+    assert(typeid(I).isBaseOf(typeid(J)));
+    assert(typeid(I).isBaseOf(typeid(C1)));
+    assert(typeid(I).isBaseOf(typeid(C2)));
+    assert(typeid(I).isBaseOf(typeid(C3)));
+    assert(!typeid(I).isBaseOf(typeid(Object)));
+
+    assert(!typeid(J).isBaseOf(typeid(I)));
+    assert(typeid(J).isBaseOf(typeid(J)));
+    assert(!typeid(J).isBaseOf(typeid(C1)));
+    assert(!typeid(J).isBaseOf(typeid(C2)));
+    assert(typeid(J).isBaseOf(typeid(C3)));
+    assert(!typeid(J).isBaseOf(typeid(Object)));
+}