allow ref on locals, globals, and statics

changelog/dmd.reflocal.dd

@@ -0,0 +1,12 @@
+`ref` can now be applied to local, static, extern, and global variables
+
+For example, one can now write:
+```
+void main()
+{
+    int i;
+    ref int r = i;
+    r = 3;
+    assert(i == 3);
+}
+```

compiler/src/dmd/dsymbolsem.d

@@ -1001,9 +1001,9 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
             }
         }
 
-        if ((dsym.storage_class & (STC.ref_ | STC.parameter | STC.foreach_ | STC.temp | STC.result)) == STC.ref_ && dsym.ident != Id.This)
+        if ((dsym.storage_class & (STC.ref_ | STC.field)) == (STC.ref_ | STC.field) && dsym.ident != Id.This)
         {
-            .error(dsym.loc, "%s `%s` - only parameters, functions and `foreach` declarations can be `ref`", dsym.kind, dsym.toPrettyChars);
+            .error(dsym.loc, "%s `%s` - field declarations cannot be `ref`", dsym.kind, dsym.toPrettyChars);
         }
 
         if (dsym.type.hasWild())

compiler/test/fail_compilation/diag9679.d

@@ -1,13 +1,46 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/diag9679.d(11): Error: variable `diag9679.main.n` - only parameters, functions and `foreach` declarations can be `ref`
-fail_compilation/diag9679.d(12): Error: variable `diag9679.main.n` - storage class `auto` has no effect if type is not inferred, did you mean `scope`?
+fail_compilation/diag9679.d(15): Error: variable `diag9679.main.n` - storage class `auto` has no effect if type is not inferred, did you mean `scope`?
+fail_compilation/diag9679.d(16): Error: variable `diag9679.main.S.a` - field declarations cannot be `ref`
+fail_compilation/diag9679.d(23): Error: returning `r` escapes a reference to local variable `r`
+fail_compilation/diag9679.d(30): Error: returning `r` escapes a reference to local variable `r`
 ---
 */
 
+
 void main()
 {
     if (ref n = 1) {}
     if (auto int n = 1) {}
+    struct S { ref int a; }
+}
+
+ref int test2()
+{
+    int i;
+    ref r = i;
+    return r;
+}
+
+ref int test3()
+{
+    extern int i;
+    ref r = i;
+    return r;
+}
+
+struct S { int a; }
+
+void test4()
+{
+    S s;
+    ref int r1 = s.a;
+    r1 = 3;
+    __gshared S t2;
+    ref int r2 = t2.a;
+    static S t3;
+    ref int r3 = t3.a;
+    extern S t4;
+    ref int r4 = t4.a;
 }