Deprecate alias this for classes v2 (#14812)

changelog/dmd.deprecate-alias-this-for-classes.dd

@@ -0,0 +1,8 @@
+Alias this for classes is deprecated
+
+Using `alias this` for classes has not been clearly specified and the lookup rules in such circumstances are not defined. As a consequence, various failures or crashes may appear when `alias this` is used in conjunction with classes. Starting with this release, `alias this` for classes is being deprecated. As an alternative, getter/setter methods may be used to replace the `alias this`. This can be generically handled by:
+
+```d
+static foreach(member, __traits(allMembers, LeClass))
+    mixin("ref auto " ~ member() { return $field_name." ~ member ~ "; }");
+```

compiler/src/dmd/dsymbolsem.d

@@ -317,6 +317,11 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
             return;
         }
 
+        // @@@DEPRECATED_2.121@@@
+        // Deprecated in 2.101 - Can be removed in 2.121
+        if (ad.isClassDeclaration() || ad.isInterfaceDeclaration())
+            deprecation(dsym.loc, "alias this for classes/interfaces is deprecated");
+
         assert(ad.members);
         Dsymbol s = ad.search(dsym.loc, dsym.ident);
         if (!s)

compiler/src/dmd/dtoh.d

@@ -291,7 +291,21 @@ public:
 
     /// Informations about the current context in the AST
     Context context;
-    alias context this;
+
+    // Generates getter-setter methods to replace the use of alias this
+    // This should be replaced by a `static foreach` once the gdc tester
+    // gets upgraded to version 10 (to support `static foreach`).
+    private extern(D) static string generateMembers()
+    {
+        string result = "";
+        foreach(member; __traits(allMembers, Context))
+        {
+            result ~= "ref auto " ~ member ~ "() { return context." ~ member ~ "; }\n";
+        }
+        return result;
+    }
+
+    mixin(generateMembers());
 
     this(OutBuffer* fwdbuf, OutBuffer* donebuf, OutBuffer* buf) scope
     {

compiler/test/compilable/test21073.d

@@ -1,16 +0,0 @@
-// https://issues.dlang.org/show_bug.cgi?id=21073
-
-class C
-{
-    auto internal() const
-    {
-        return 5;
-    }
-    alias internal this;
-}
-
-void main() pure
-{
-    const c = new C;
-    auto r = cast(C)c;
-}

compiler/test/compilable/test21543.d

@@ -1,116 +0,0 @@
-// https://issues.dlang.org/show_bug.cgi?id=21543
-
-class B
-{
-    Nullable!B data;
-    alias data this;
-}
-
-void test1()
-{
-    B b;
-    Nullable!B n;
-}
-
-struct Nullable(T)
-{
-    T payload;
-
-    void opAssign()(T)
-    {
-        move(payload);
-    }
-
-    inout(T) get_() inout
-    {
-        return payload;
-    }
-
-    alias get_ this;
-}
-
-// another version with chain of 3 alias this
-
-struct C
-{
-    Nullable2 data;
-    alias data this;
-}
-
-void test2()
-{
-    C c;
-    Nullable2 n2 = &c;
-    Nullable3 n3 = &c;
-
-    // these are to check a sane -vcg-ast output
-    fn1(c);
-    fn1(n2);
-    fn1(n3);
-    fn2(c);
-    fn2(n2);
-    fn2(n3);
-    fn3(c);
-    fn3(n2);
-    fn3(n3);
-}
-
-void fn1(C x) {}
-
-void fn2(Nullable2 x) {}
-
-void fn3(Nullable3 x) {}
-
-struct Nullable2
-{
-    Nullable3 payload;
-
-    this(C* c)
-    {
-        payload = Nullable3(c);
-    }
-
-    void opAssign()(Nullable3)
-    {
-        move(payload);
-    }
-
-    inout(Nullable3) get_() inout
-    {
-        return payload;
-    }
-
-    alias get_ this;
-}
-
-struct Nullable3
-{
-    C* payload;
-
-    this(C* c)
-    {
-        payload = c;
-    }
-
-    void opAssign()(C)
-    {
-        move(payload);
-    }
-
-    inout(C) get_() inout
-    {
-        return *payload;
-    }
-
-    alias get_ this;
-}
-
-T move(T)(ref T source)
-{
-    return source;
-}
-
-T move(T)(T source)
-{
-    return source;
-}

compiler/test/compilable/test5973.d

@@ -1,41 +0,0 @@
-// https://issues.dlang.org/show_bug.cgi?id=5973
-
-class A { int a = 1; }
-class B { int b = 2; }
-class C : A
-{
-    B obj;
-    alias obj this;
-    this(){ obj = new B(); }
-}
-class X : C {}
-
-class D
-{
-    int i;
-}
-
-class E
-{
-    D x;
-    alias x this;
-}
-
-class F : E
-{
-    void test()
-    {
-        i = 5;
-    }
-}
-
-void main()
-{
-    auto c = new C();
-    assert(c.a == 1);   // lookup C -> A, OK
-    assert(c.b == 2);   // lookup C => B, OK
-
-    auto x = new X();
-    assert(x.a == 1);   // lookup X -> C -> A, OK
-    assert(x.b == 2);   // lookup X -> C => B, NG (Line 17)
-}

compiler/test/compilable/test6777.d

@@ -1,11 +0,0 @@
-struct S {}
-
-class C {
-    S s;
-    alias s this;
-}
-
-void main() {
-    auto c = new C;
-    auto p = cast(void*) c;
-}

compiler/test/fail_compilation/fail5851.d

@@ -1,16 +0,0 @@
-/*
-TEST_OUTPUT:
----
-fail_compilation/fail5851.d(11): Error: alias this is not reachable as `Foo` already converts to `object.Object`
----
-*/
-
-class Foo
-{
-    Object o;
-    alias o this;
-}
-
-void main()
-{
-}

compiler/test/runnable/aliasthis.d

@@ -1,7 +1,16 @@
 /*
 TEST_OUTPUT:
 ---
+runnable/aliasthis.d(103): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(291): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(292): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(294): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(465): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(466): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(477): Deprecation: alias this for classes/interfaces is deprecated
+runnable/aliasthis.d(1013): Deprecation: alias this for classes/interfaces is deprecated
 false
+runnable/aliasthis.d(2100): Deprecation: alias this for classes/interfaces is deprecated
 [] = int
 [] = string
 [0] = int
@@ -10,6 +19,7 @@ false
 [] = int
 [1] = string
 [0] = int
+runnable/aliasthis.d(741): Deprecation: alias this for classes/interfaces is deprecated
 ---
 
 RUN_OUTPUT:

compiler/test/runnable/interpret.d

@@ -4,6 +4,7 @@ TEST_OUTPUT:
 true
 g
 &Test109S(&Test109S(<recursion>))
+runnable/interpret.d(3742): Deprecation: alias this for classes/interfaces is deprecated
 tfoo
 tfoo
 Crash!

compiler/test/runnable/test17684.d

@@ -1,3 +1,13 @@
+/*
+TEST_OUTPUT:
+---
+runnable/test17684.d(37): Deprecation: alias this for classes/interfaces is deprecated
+runnable/test17684.d(54): Deprecation: alias this for classes/interfaces is deprecated
+runnable/test17684.d(54): Deprecation: alias this for classes/interfaces is deprecated
+runnable/test17684.d(37): Deprecation: alias this for classes/interfaces is deprecated
+---
+*/
+
 struct StructField(T)
 {
     static T Field;

compiler/test/runnable/test19782.d

@@ -1,4 +1,12 @@
 // https://issues.dlang.org/show_bug.cgi?id=19782
+
+/*
+TEST_OUTPUT:
+---
+runnable/test19782.d(17): Deprecation: alias this for classes/interfaces is deprecated
+---
+*/
+
 class Inner
 {
     int a;

compiler/test/runnable/test21039.d

@@ -1,5 +1,12 @@
 // https://issues.dlang.org/show_bug.cgi?id=21039
 
+/*
+TEST_OUTPUT:
+---
+runnable/test21039.d(14): Deprecation: alias this for classes/interfaces is deprecated
+---
+*/
+
 class Inner {}
 
 class Outer {

compiler/test/runnable/test23234.d

@@ -1,5 +1,12 @@
 // https://issues.dlang.org/show_bug.cgi?id=23234
 
+/*
+TEST_OUTPUT:
+---
+runnable/test23234.d(17): Deprecation: alias this for classes/interfaces is deprecated
+---
+*/
+
 class Bar
 {
 }

compiler/test/runnable/testaliascast.d

@@ -1,5 +1,13 @@
 // https://issues.dlang.org/show_bug.cgi?id=11294
 
+/*
+TEST_OUTPUT:
+---
+runnable/testaliascast.d(29): Deprecation: alias this for classes/interfaces is deprecated
+runnable/testaliascast.d(58): Deprecation: alias this for classes/interfaces is deprecated
+---
+*/
+
 string result;
 
 extern(C) void rt_finalize(void *ptr, bool det=true);

compiler/test/runnable/testassign.d

@@ -2,6 +2,8 @@
 REQUIRED_ARGS: -preview=rvaluerefparam
 TEST_OUTPUT:
 ---
+runnable/testassign.d(802): Deprecation: alias this for classes/interfaces is deprecated
+runnable/testassign.d(808): Deprecation: alias this for classes/interfaces is deprecated
 \	S1	S2a	S2b	S3a	S3b	S4a	S4b
 -	true	true	true	true	true	true	true
 Xa	true	true	true	true	true	true	true

compiler/test/runnable/traits_getPointerBitmap.d

@@ -1,4 +1,3 @@
-
 module traits_getPointerBitmap;
 
 import core.stdc.stdio;
@@ -76,19 +75,6 @@ template pOff(T)
     enum pOff = T.p.offsetof / bytesPerPtr;
 }
 
-class C(T, aliasTo = void)
-{
-    static if(!is(aliasTo == void))
-    {
-        aliasTo a;
-        alias a this;
-    }
-
-    size_t x;
-    T t = void;
-    void* p;
-}
-
 ///////////////////////////////////////
 
 void _testType(T)(size_t[] expected)
@@ -118,21 +104,6 @@ void testType(T)(size_t[] expected)
     // prepend string
     sexp[0] = (expected[0] << tOff!(S!(T, string))) | (1 << pOff!(S!(T, string))) | 2; // arr ptr
     _testType!(S!(T, string))(sexp);
-
-    // generate bit pattern for C!T
-    C!T ct = null;
-    size_t mutexBit = (RTInfoMark__Monitor ? 2 : 0);
-    size_t ctpOff = ct.p.offsetof / bytesPerPtr;
-    size_t cttOff = ct.t.offsetof / bytesPerPtr;
-    sexp[0] = (expected[0] << cttOff) | (1 << ctpOff) | mutexBit;
-    _testType!(C!(T))(sexp);
-
-    C!(T, string) cts = null;
-    size_t ctspOff = cts.p.offsetof / bytesPerPtr;
-    size_t ctstOff = cts.t.offsetof / bytesPerPtr;
-    // generate bit pattern for C!T
-    sexp[0] = (expected[0] << ctstOff) | (1 << ctspOff) | mutexBit | 0b1000; // arr ptr
-    _testType!(C!(T, string))(sexp);
 }
 
 ///////////////////////////////////////

compiler/test/runnable/xtest46.d

@@ -2,11 +2,14 @@
 //
 /* TEST_OUTPUT:
 ---
+runnable/xtest46.d(165): Deprecation: alias this for classes/interfaces is deprecated
 Boo!double
 Boo!int
 true
 int
 !! immutable(int)[]
+runnable/xtest46.d(2932): Deprecation: alias this for classes/interfaces is deprecated
+runnable/xtest46.d(2964): Deprecation: alias this for classes/interfaces is deprecated
 int(int i, long j = 7L)
 long
 C10390(C10390(C10390(<recursion>)))
@@ -19,6 +22,7 @@ string[]
 double[]
 double[]
 {}
+runnable/xtest46.d(4670): Deprecation: alias this for classes/interfaces is deprecated
 tuple("m")
 true
 TFunction1: extern (C) void function()

compiler/test/runnable/xtest46_gc.d

@@ -3,11 +3,14 @@ REQUIRED_ARGS: -lowmem -Jrunnable -preview=rvaluerefparam
 EXTRA_FILES: xtest46.d
 TEST_OUTPUT:
 ---
+runnable/xtest46_gc.d-mixin-33(197): Deprecation: alias this for classes/interfaces is deprecated
 Boo!double
 Boo!int
 true
 int
 !! immutable(int)[]
+runnable/xtest46_gc.d-mixin-33(2964): Deprecation: alias this for classes/interfaces is deprecated
+runnable/xtest46_gc.d-mixin-33(2996): Deprecation: alias this for classes/interfaces is deprecated
 int(int i, long j = 7L)
 long
 C10390(C10390(<recursion>))
@@ -20,6 +23,7 @@ string[]
 double[]
 double[]
 {}
+runnable/xtest46_gc.d-mixin-33(4702): Deprecation: alias this for classes/interfaces is deprecated
 tuple("m")
 true
 TFunction1: extern (C) void function()

druntime/src/object.d

@@ -2927,25 +2927,6 @@ void clear(Value, Key)(Value[Key]* aa)
     assert("k1" !in aa);
 }
 
-// Issue 20559
-@system unittest
-{
-    static class Foo
-    {
-        int[string] aa;
-        alias aa this;
-    }
-
-    auto v = new Foo();
-    v["Hello World"] = 42;
-    v.clear;
-    assert("Hello World" !in v);
-
-    // Test for T*
-    static assert(!__traits(compiles, (&v).clear));
-    static assert( __traits(compiles, (*(&v)).clear));
-}
-
 /***********************************
  * Reorganizes the associative array in place so that lookups are more
  * efficient.
@@ -4278,44 +4259,6 @@ void destroy(bool initialize = true, T)(T obj) if (is(T == interface))
     destroy!true(new C());
 }
 
-@system unittest
-{
-    // class with an `alias this`
-    class A
-    {
-        static int dtorCount;
-        ~this()
-        {
-            dtorCount++;
-        }
-    }
-
-    class B
-    {
-        A a;
-        alias a this;
-        this()
-        {
-            a = new A;
-        }
-        static int dtorCount;
-        ~this()
-        {
-            dtorCount++;
-        }
-    }
-    auto b = new B;
-    assert(A.dtorCount == 0);
-    assert(B.dtorCount == 0);
-    destroy(b);
-    assert(A.dtorCount == 0);
-    assert(B.dtorCount == 1);
-
-    auto a = new A;
-    destroy(a);
-    assert(A.dtorCount == 1);
-}
-
 @system unittest
 {
     interface I { }
@@ -4529,43 +4472,6 @@ if (__traits(isStaticArray, T))
     }
 }
 
-// https://issues.dlang.org/show_bug.cgi?id=19218
-@system unittest
-{
-    static struct S
-    {
-        static dtorCount = 0;
-        ~this() { ++dtorCount; }
-    }
-
-    static interface I
-    {
-        ref S[3] getArray();
-        alias getArray this;
-    }
-
-    static class C : I
-    {
-        static dtorCount = 0;
-        ~this() { ++dtorCount; }
-
-        S[3] a;
-        alias a this;
-
-        ref S[3] getArray() { return a; }
-    }
-
-    C c = new C();
-    destroy(c);
-    assert(S.dtorCount == 3);
-    assert(C.dtorCount == 1);
-
-    I i = new C();
-    destroy(i);
-    assert(S.dtorCount == 6);
-    assert(C.dtorCount == 2);
-}
-
 /// ditto
 void destroy(bool initialize = true, T)(ref T obj)
     if (!is(T == struct) && !is(T == interface) && !is(T == class) && !__traits(isStaticArray, T))