fix Issue 15781 - Template type deduction failure with same-type vari…

…ables with different constness
dlang · Mar 15, 2016 · db7e4e1 · db7e4e1
1 parent bd4924b
commit db7e4e1
Show file tree

Hide file tree

Showing 2 changed files with 36 additions and 14 deletions.
diff --git a/src/dcast.d b/src/dcast.d
@@ -2476,23 +2476,22 @@ extern (C++) bool isVoidArrayLiteral(Expression e, Type other)
 // used by deduceType()
 extern (C++) Type rawTypeMerge(Type t1, Type t2)
 {
-    Type t1b = t1.toBasetype();
-    Type t2b = t2.toBasetype();
-
     if (t1.equals(t2))
-    {
         return t1;
-    }
-    else if (t1b.equals(t2b))
-    {
+    if (t1.equivalent(t2))
+        return t1.castMod(MODmerge(t1.mod, t2.mod));
+
+    auto t1b = t1.toBasetype();
+    auto t2b = t2.toBasetype();
+    if (t1b.equals(t2b))
         return t1b;
-    }
-    else
-    {
-        TY ty = cast(TY)impcnvResult[t1b.ty][t2b.ty];
-        if (ty != Terror)
-            return Type.basic[ty];
-    }
+    if (t1b.equivalent(t2b))
+        return t1b.castMod(MODmerge(t1b.mod, t2b.mod));
+
+    auto ty = cast(TY)impcnvResult[t1b.ty][t2b.ty];
+    if (ty != Terror)
+        return Type.basic[ty];
+
     return null;
 }
 

diff --git a/test/runnable/template9.d b/test/runnable/template9.d
@@ -4757,6 +4757,29 @@ void test15352()
     assert(is(typeof(s1) == typeof(s3)));
 }
 
+/******************************************/
+// 15781
+
+void test15781()
+{
+    static struct S
+    {
+        int value;
+    }
+
+    T foo(T)(T a, T b)
+    {
+        return T();
+    }
+
+    const S cs;
+          S ms;
+    static assert(is(typeof(foo(ms, ms)) ==       S));
+    static assert(is(typeof(foo(ms, cs)) == const S));
+    static assert(is(typeof(foo(cs, ms)) == const S));
+    static assert(is(typeof(foo(cs, cs)) == const S));
+}
+
 /******************************************/
 
 int main()