fix Issue 17123 - [REG 2.073] Issues with return @safe inference

src/func.d

@@ -2426,6 +2426,17 @@ extern (C++) class FuncDeclaration : Declaration
              */
             VarDeclaration v = new ThisDeclaration(loc, Type.tvoid.pointerTo());
             v.storage_class |= STCparameter;
+            if (type.ty == Tfunction)
+            {
+                TypeFunction tf = cast(TypeFunction)type;
+                if (tf.isreturn)
+                    v.storage_class |= STCreturn;
+                if (tf.isscope)
+                    v.storage_class |= STCscope;
+            }
+            if (flags & FUNCFLAGinferScope)
+                v.storage_class |= STCmaybescope;
+
             v.semantic(sc);
             if (!sc.insert(v))
                 assert(0);

src/mtype.d

@@ -781,7 +781,7 @@ extern (C++) abstract class Type : RootObject
                 goto Lnotcovariant;
         }
 
-        // We can subtract 'return' from 'this', but cannot add it
+        // We can subtract 'return ref' from 'this', but cannot add it
         else if (t1.isreturn && !t2.isreturn)
             goto Lnotcovariant;
 
@@ -6698,8 +6698,13 @@ extern (C++) final class TypeFunction : TypeNext
 
     override Type addStorageClass(StorageClass stc)
     {
+        //printf("addStorageClass(%llx) %d\n", stc, (stc & STCscope) != 0);
         TypeFunction t = cast(TypeFunction)Type.addStorageClass(stc);
-        if ((stc & STCpure && !t.purity) || (stc & STCnothrow && !t.isnothrow) || (stc & STCnogc && !t.isnogc) || (stc & STCsafe && t.trust < TRUSTtrusted))
+        if ((stc & STCpure && !t.purity) ||
+            (stc & STCnothrow && !t.isnothrow) ||
+            (stc & STCnogc && !t.isnogc) ||
+            (stc & STCscope && !t.isscope) ||
+            (stc & STCsafe && t.trust < TRUSTtrusted))
         {
             // Klunky to change these
             auto tf = new TypeFunction(t.parameters, t.next, t.varargs, t.linkage, 0);
@@ -6723,6 +6728,8 @@ extern (C++) final class TypeFunction : TypeNext
                 tf.isnogc = true;
             if (stc & STCsafe)
                 tf.trust = TRUSTsafe;
+            if (stc & STCscope)
+                tf.isscope = true;
 
             tf.deco = tf.merge().deco;
             t = tf;
@@ -7192,6 +7199,25 @@ extern (C++) final class TypeDelegate : TypeNext
         }
     }
 
+    override Type addStorageClass(StorageClass stc)
+    {
+        TypeDelegate t = cast(TypeDelegate)Type.addStorageClass(stc);
+        if (!global.params.vsafe)
+            return t;
+
+        /* The rest is meant to add 'scope' to a delegate declaration if it is of the form:
+         *  alias dg_t = void* delegate();
+         *  scope dg_t dg = ...;
+         */
+        auto n = t.next.addStorageClass(stc & STCscope);
+        if (n != t.next)
+        {
+            t.next = n;
+            t.deco = t.merge().deco;
+        }
+        return t;
+    }
+
     override d_uns64 size(Loc loc) const
     {
         return Target.ptrsize * 2;

test/fail_compilation/retscope.d

@@ -235,10 +235,10 @@ void* funretscope(scope dg_t ptr) @safe
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/retscope.d(249): Error: cannot implicitly convert expression (__lambda1) of type void* delegate() pure nothrow @nogc return @safe to void* delegate() @safe
-fail_compilation/retscope.d(249): Error: cannot implicitly convert expression (__lambda1) of type void* delegate() pure nothrow @nogc return @safe to void* delegate() @safe
-fail_compilation/retscope.d(250): Error: cannot implicitly convert expression (__lambda2) of type void* delegate() pure nothrow @nogc return @safe to void* delegate() @safe
-fail_compilation/retscope.d(250): Error: cannot implicitly convert expression (__lambda2) of type void* delegate() pure nothrow @nogc return @safe to void* delegate() @safe
+fail_compilation/retscope.d(249): Error: cannot implicitly convert expression (__lambda1) of type void* delegate() pure nothrow @nogc return scope @safe to void* delegate() scope @safe
+fail_compilation/retscope.d(249): Error: cannot implicitly convert expression (__lambda1) of type void* delegate() pure nothrow @nogc return scope @safe to void* delegate() scope @safe
+fail_compilation/retscope.d(250): Error: cannot implicitly convert expression (__lambda2) of type void* delegate() pure nothrow @nogc return scope @safe to void* delegate() scope @safe
+fail_compilation/retscope.d(250): Error: cannot implicitly convert expression (__lambda2) of type void* delegate() pure nothrow @nogc return scope @safe to void* delegate() scope @safe
 ---
 */
 
@@ -626,18 +626,6 @@ struct Result(R)
     n.empty();
 }
 
-/**********************************************/
-
-@safe void foo22()(ref char[] s)
-{
-    char[] a = s;
-}
-
-@safe void test22(scope char[] s)
-{
-    foo22(s);
-}
-
 /************************************************/
 
 // https://issues.dlang.org/show_bug.cgi?id=17117
@@ -660,3 +648,15 @@ int test21()
         return s;
 }
 
+/**********************************************/
+
+@safe void foo22()(ref char[] s)
+{
+    char[] a = s;
+}
+
+@safe void test22(scope char[] s)
+{
+    foo22(s);
+}
+

test/fail_compilation/retscope2.d

@@ -21,6 +21,19 @@ fail_compilation/retscope2.d(107): Error: address of variable s assigned to p wi
 
 /**********************************************/
 
+// https://issues.dlang.org/show_bug.cgi?id=17123
+
+void test200()
+{
+    char[256] buffer;
+
+    char[] delegate() read = () {
+        return buffer[];
+    };
+}
+
+/**********************************************/
+
 /*
 TEST_OUTPUT:
 ---
@@ -69,7 +82,6 @@ fail_compilation/retscope2.d(504): Error: scope variable c may not be returned
     return c;
 }
 
-
 /**********************************************/
 
 /*
@@ -99,3 +111,4 @@ fail_compilation/retscope2.d(614): Error: template instance retscope2.test600!(i
     test600(p, q);
 }
 
+