Require adjacent auto ref keywords

changelog/dmd.auto-ref-adjacent.dd

@@ -0,0 +1,18 @@
+`auto ref` variables must have adjacent keywords `auto` and `ref`
+
+It's now deprecated to declare `auto ref` parameters without putting those two keywords next to eachother.
+This way it's clear that `auto ref` semantics are intended, rather than `ref` and `auto` semantics separately.
+For the newly introduced `ref` local / global variables, it's an error immediately.
+
+---
+void t()(ref const auto int x) // Deprecation
+{
+    ref auto y = x; // Error
+}
+
+// Correction:
+void t()(auto ref const int x)
+{
+    auto ref y = x;
+}
+---

compiler/src/dmd/dsymbolsem.d

@@ -616,7 +616,13 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
             dsym.storage_class |= ad.storage_class & STC.TYPECTOR;
 
         if ((dsym.storage_class & STC.auto_) && (dsym.storage_class & STC.ref_))
+        {
+            if (!(dsym.storage_class & STC.autoref))
+            {
+                .error(dsym.loc, "%s `%s` - `auto ref` variable must have `auto` and `ref` adjacent", dsym.kind, dsym.toChars());
                 dsym.storage_class |= STC.autoref;
+            }
+        }
 
         /* If auto type inference, do the inference
          */

compiler/src/dmd/parse.d

@@ -651,6 +651,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
 
             case TOK.auto_:
                 stc = STC.auto_;
+                if (peekNext() == TOK.ref_)
+                    stc |= STC.autoref;
                 goto Lstc;
 
             case TOK.scope_:
@@ -2935,6 +2937,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
 
                 case TOK.auto_:
                     stc = STC.auto_;
+                    if (peekNext() == TOK.ref_)
+                        stc |= STC.autoref;
                     goto L2;
 
                 case TOK.return_:
@@ -2952,8 +2956,10 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
                         // if stcx is not a power of 2
                         if (stcx & (stcx - 1) && !(stcx == (STC.in_ | STC.ref_)))
                             error("incompatible parameter storage classes");
-                        //if ((storageClass & STC.scope_) && (storageClass & (STC.ref_ | STC.out_)))
+
-                            //error("scope cannot be ref or out");
+                        // Deprecated in 2.111
+                        if ((storageClass & STC.auto_) && (storageClass & STC.ref_) && !(storageClass & STC.autoref))
+                            deprecation("`auto` and `ref` storage classes should be adjacent");
 
                         const tv = peekNext();
                         Loc loc;
@@ -4259,6 +4265,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
 
             case TOK.auto_:
                 stc = STC.auto_;
+                if (peekNext() == TOK.ref_)
+                    stc |= STC.autoref;
                 goto L1;
 
             case TOK.scope_:
@@ -5079,7 +5087,7 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
                 {
                     // function auto ref (parameters) { statements... }
                     // delegate auto ref (parameters) { statements... }
-                    stc = STC.auto_ | STC.ref_;
+                    stc = STC.auto_ | STC.ref_ | STC.autoref;
                     nextToken();
                 }
                 else
@@ -5121,7 +5129,7 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
                 {
                     // auto ref (parameters) => expression
                     // auto ref (parameters) { statements... }
-                    stc = STC.auto_ | STC.ref_;
+                    stc = STC.auto_ | STC.ref_ | STC.autoref;
                     nextToken();
                 }
                 else
@@ -5678,6 +5686,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
 
             case TOK.auto_:
                 stc = STC.auto_;
+                if (peekNext() == TOK.ref_)
+                    stc |= STC.autoref;
                 break;
 
             case TOK.const_:

compiler/test/fail_compilation/diag9679.d

@@ -1,6 +1,8 @@
 /* REQUIRED_ARGS: -verrors=0
 TEST_OUTPUT:
 ---
+fail_compilation/diag9679.d(93): Deprecation: `auto` and `ref` storage classes should be adjacent
+fail_compilation/diag9679.d(93): Deprecation: `auto` and `ref` storage classes should be adjacent
 fail_compilation/diag9679.d(15): Error: rvalue `1` cannot be assigned to `ref n`
 fail_compilation/diag9679.d(16): Error: variable `diag9679.main.n` - storage class `auto` has no effect if type is not inferred, did you mean `scope`?
 fail_compilation/diag9679.d(17): Error: variable `diag9679.main.S.a` - field declarations cannot be `ref`
@@ -8,8 +10,6 @@ fail_compilation/diag9679.d(24): Error: returning `r` escapes a reference to loc
 ---
 */
 
-
-
 void main()
 {
     if (ref n = 1) {}
@@ -56,11 +56,11 @@ fail_compilation/diag9679.d(77): Error: type `immutable(int)` cannot be assigned
 fail_compilation/diag9679.d(84): Error: returning `x` escapes a reference to local variable `x`
 fail_compilation/diag9679.d(89): Error: variable `diag9679.test9.x` - void initializer not allowed for `ref` variable
 fail_compilation/diag9679.d(90): Error: variable `diag9679.test9.y` - void initializer not allowed for `ref` variable
+fail_compilation/diag9679.d(96): Error: variable `x` - `auto ref` variable must have `auto` and `ref` adjacent
 ---
 */
 
 
-
 void test5()
 {
     ref int r5;
@@ -89,3 +89,9 @@ void test9()
     ref int x = void;
     auto ref int y = void;
 }
+
+void testKeywordOrder()(ref auto int x, auto const ref float y) {}
+void testKeywordOrder()
+{
+    ref auto int x = 3;
+}

druntime/src/core/lifetime.d

@@ -1699,7 +1699,7 @@ template forward(args...)
         {
             x_ = forward!x;
         }
-        this()(auto const ref X x)
+        this()(auto ref const X x)
         {
             x_ = forward!x;
         }