[WIP] fix issue 7804 - Allow __traits(getMember) as a BasicType

src/dmd/astbase.d

@@ -4085,6 +4085,24 @@ struct ASTBase
         }
     }
 
+    extern (C++) class TypeTraits : Type
+    {
+        TraitsExp exp;
+        Loc loc;
+
+        extern (D) this(Loc loc, TraitsExp exp)
+        {
+            super(Tident);
+            this.loc = loc;
+            this.exp = exp;
+        }
+
+        override void accept(Visitor v)
+        {
+            v.visit(this);
+        }
+    }
+
     extern (C++) final class TypeIdentifier : TypeQualified
     {
         Identifier ident;

src/dmd/dmangle.d

@@ -102,6 +102,7 @@ private immutable char[TMAX] mangleChar =
     Tslice       : '@',
     Treturn      : '@',
     Tvector      : '@',
+    Ttraits      : '@',
 ];
 
 unittest

src/dmd/hdrgen.d

@@ -784,6 +784,12 @@ public:
         buf.writestring(t.dstring);
     }
 
+    override void visit(TypeTraits t)
+    {
+        //printf("TypeBasic::toCBuffer2(t.mod = %d)\n", t.mod);
+        visit(t.exp);
+    }
+
     override void visit(TypeVector t)
     {
         //printf("TypeVector::toCBuffer2(t.mod = %d)\n", t.mod);

src/dmd/mtype.d

@@ -334,6 +334,7 @@ enum ENUMTY : int
     Tvector,
     Tint128,
     Tuns128,
+    TTraits,
     TMAX,
 }
 
@@ -381,6 +382,7 @@ alias Tnull = ENUMTY.Tnull;
 alias Tvector = ENUMTY.Tvector;
 alias Tint128 = ENUMTY.Tint128;
 alias Tuns128 = ENUMTY.Tuns128;
+alias Ttraits = ENUMTY.TTraits;
 alias TMAX = ENUMTY.TMAX;
 
 alias TY = ubyte;
@@ -512,6 +514,7 @@ extern (C++) abstract class Type : RootObject
             sizeTy[Terror] = __traits(classInstanceSize, TypeError);
             sizeTy[Tnull] = __traits(classInstanceSize, TypeNull);
             sizeTy[Tvector] = __traits(classInstanceSize, TypeVector);
+            sizeTy[Ttraits] = __traits(classInstanceSize, TypeTraits);
             return sizeTy;
         }();
 
@@ -5240,6 +5243,41 @@ extern (C++) final class TypeDelegate : TypeNext
     }
 }
 
+/**
+ * This is a shell containing a TraitsExp that can be
+ * either resolved to a type or to a symbol.
+ *
+ * The point is to allow AliasDeclarationY to use `__traits(getMember)`
+ * directly (VS using a library helper in the past).
+ */
+extern (C++) final class TypeTraits : Type
+{
+    Loc loc;
+
+    /// The expression to resolve as type or symbol.
+    TraitsExp exp;
+
+    final extern (D) this(Loc loc, TraitsExp exp)
+    {
+        super(Ttraits);
+        this.loc = loc;
+        this.exp = exp;
+    }
+
+    final override Type syntaxCopy()
+    {
+        TraitsExp te = cast(TraitsExp) exp.syntaxCopy();
+        TypeTraits tt = new TypeTraits(loc, te);
+        tt.mod = mod;
+        return tt;
+    }
+
+    override void accept(Visitor v)
+    {
+        v.visit(this);
+    }
+}
+
 /***********************************************************
  */
 extern (C++) abstract class TypeQualified : Type

src/dmd/parse.d

@@ -513,6 +513,7 @@ final class Parser(AST) : Lexer
             case TOK.union_:
             case TOK.class_:
             case TOK.interface_:
+            case TOK.traits:
             Ldeclaration:
                 a = parseDeclarations(false, pAttrs, pAttrs.comment);
                 if (a && a.dim)
@@ -3495,6 +3496,28 @@ final class Parser(AST) : Lexer
             t = parseVector();
             break;
 
+        case TOK.traits:
+        {
+            AST.TraitsExp te = cast(AST.TraitsExp) parsePrimaryExp();
+            if (!te)
+            {
+                // error already emitted while parsing primary
+                t = new AST.TypeError;
+            }
+            else if (te.ident != Id.getMember)
+            {
+                // even if this is not a grammar error, it's not worth continuing.
+                error("invalid `__traits`, only `getMember` can be aliased and not `%s`",
+                    te.ident.toChars);
+                t = new AST.TypeError;
+            }
+            else
+            {
+                t = new AST.TypeTraits(loc, te);
+            }
+            break;
+        }
+
         case TOK.const_:
             // const(type)
             nextToken();
@@ -6502,6 +6525,16 @@ final class Parser(AST) : Lexer
                 goto Lfalse;
             goto L3;
 
+        case TOK.traits:
+            // __traits(getMember
+            t = peek(t);
+            if (t.value != TOK.leftParentheses)
+                goto Lfalse;
+            t = peek(t);
+            if (t.value != TOK.identifier || t.ident != Id.getMember)
+                goto Lfalse;
+            break;
+
         case TOK.const_:
         case TOK.immutable_:
         case TOK.shared_:

src/dmd/parsetimevisitor.d

@@ -138,6 +138,7 @@ public:
     void visit(AST.TypeStruct t) { visit(cast(AST.Type)t); }
     void visit(AST.TypeNext t) { visit(cast(AST.Type)t); }
     void visit(AST.TypeQualified t) { visit(cast(AST.Type)t); }
+    void visit(AST.TypeTraits t) { visit(cast(AST.Type)t); }
 
     // TypeNext
     void visit(AST.TypeReference t) { visit(cast(AST.TypeNext)t); }

src/dmd/strictvisitor.d

@@ -120,6 +120,7 @@ extern(C++) class StrictVisitor(AST) : ParseTimeVisitor!AST
     override void visit(AST.TypeAArray) { assert(0); }
     override void visit(AST.TypeSArray) { assert(0); }
     override void visit(AST.TypeQualified) { assert(0); }
+    override void visit(AST.TypeTraits) { assert(0); }
     override void visit(AST.TypeIdentifier) { assert(0); }
     override void visit(AST.TypeReturn) { assert(0); }
     override void visit(AST.TypeTypeof) { assert(0); }

src/dmd/transitivevisitor.d

@@ -459,6 +459,11 @@ package mixin template ParseVisitMethods(AST)
         t.upr.accept(this);
     }
 
+    override void visit(AST.TypeTraits t)
+    {
+        t.exp.accept(this);
+    }
+
 //      Miscellaneous
 //========================================================
 

src/dmd/typesem.d

@@ -1307,6 +1307,21 @@ private extern (C++) final class TypeSemanticVisitor : Visitor
         result = t;
     }
 
+    override void visit(TypeTraits mtype)
+    {
+        import dmd.traits : semanticTraits;
+        import dmd.dtemplate : getType;
+
+        result = null;
+        if (Expression e = semanticTraits(mtype.exp, sc))
+            if (Type t = getType(e))
+                result = t.addMod(mtype.mod);
+        //if (result) printf("TypeTraits found to be %s\n".ptr, result.toChars);
+        if (result is null)
+            mtype.error(loc, "`%s` cannot be resolved to a valid type",
+                mtype.toChars());
+    }
+
     override void visit(TypeReturn mtype)
     {
         //printf("TypeReturn::semantic() %s\n", toChars());

test/fail_compilation/e7804_1.d

@@ -0,0 +1,9 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/e7804_1.d(9): Error: invalid `__traits`, only `getMember` can be aliased and not `farfelu`
+---
+*/
+module e7804_1;
+
+__traits(farfelu, Aggr, "member") a;

test/runnable/e7804.d

@@ -0,0 +1,32 @@
+module e7804;
+
+struct Bar {static struct B{}}
+alias BarB = __traits(getMember, Bar, "B");
+static assert(is(BarB == Bar.B));
+static assert(is(const(__traits(getMember, Bar, "B")) == const(Bar.B)));
+
+
+struct Foo {alias MyInt = int;}
+alias FooInt = __traits(getMember, Foo, "MyInt");
+static immutable FooInt fi = 42;
+static assert(fi == 42);
+
+
+enum __traits(getMember, Foo, "MyInt") a0 = 12;
+static assert(is(typeof(a0) == int));
+static assert(a0 == 12);
+
+
+const __traits(getMember, Foo, "MyInt") a1 = 46;
+static this(){assert(a1 == 46);}
+
+
+__traits(getMember, Foo, "MyInt") a2 = 78;
+static this(){assert(a2 == 78);}
+
+
+const(__traits(getMember, Foo, "MyInt")) a3 = 63;
+static this(){assert(a3 == 63);}
+
+
+void main(){}