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

changelog/alias_from_trait.dd

@@ -0,0 +1,29 @@
+Aliases can be created directly from a `__trait`.
+
+Previously an `AliasSeq` was necessary in order to declare an alias based on a `__trait`.
+Now the grammar allows to write shorter declarations:
+
+---
+struct Foo
+{
+    int a;
+}
+
+alias oldWay = AliasSeq!(__traits(getMember, Foo, "a"))[0];
+alias newWay = __traits(getMember, Foo, "a");
+---
+
+To permit this it was more interesting to include `__trait` in the basic types
+instead of just changing the alias syntax, so as bonus,
+a new way of declaring the variables exists:
+
+---
+struct Foo { static struct Bar {} }
+const(__traits(getMember, Foo, "Bar")) fooBar;
+static assert(is(typeof(fooBar) == const(Foo.Bar)));
+---
+
+Despite of being a type from the syntax point of view and when used specifically for an `alias`
+the `getMember` trait can also represent symbols or even imports.
+This does not change the alias semantic since for example the same distinction
+was already done in case of an identifier chain.

src/dmd/astbase.d

@@ -4138,6 +4138,24 @@ 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/dsymbolsem.d

@@ -5976,6 +5976,21 @@ Laftersemantic:
 void aliasSemantic(AliasDeclaration ds, Scope* sc)
 {
     //printf("AliasDeclaration::semantic() %s\n", ds.toChars());
+    if (ds.type && ds.type.ty == Ttraits)
+    {
+        TypeTraits tt = cast(TypeTraits) ds.type;
+        if (auto t = typeSemantic(tt, tt.loc, sc))
+        {
+            ds.type = t;
+        }
+        else
+        {
+            if (tt.sym)
+                ds.aliassym = tt.sym;
+            // __trait(getMember) always returns alias-able stuff
+            // so at this point either we're good or traits sem has emitted an error
+        }
+    }
     if (ds.aliassym)
     {
         auto fd = ds.aliassym.isFuncLiteralDeclaration();

src/dmd/hdrgen.d

@@ -797,6 +797,12 @@ 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

@@ -285,6 +285,7 @@ enum ENUMTY : int
     Tvector,
     Tint128,
     Tuns128,
+    TTraits,
     TMAX,
 }
 
@@ -332,6 +333,7 @@ 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;
@@ -472,6 +474,7 @@ 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;
         }();
 
@@ -5017,6 +5020,43 @@ 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;
+    /// The symbol when exp doesn't represent a type.
+    Dsymbol sym;
+
+    final extern (D) this(Loc loc, TraitsExp exp)
+    {
+        super(Ttraits);
+        this.loc = loc;
+        this.exp = exp;
+    }
+
+    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/mtype.h

@@ -91,6 +91,7 @@ enum ENUMTY
     Tvector,
     Tint128,
     Tuns128,
+    TTraits,
     TMAX
 };
 typedef unsigned char TY;       // ENUMTY
@@ -580,6 +581,17 @@ class TypeDelegate : public TypeNext
     void accept(Visitor *v) { v->visit(this); }
 };
 
+class TypeTraits : public Type
+{
+    Loc loc;
+    /// The expression to resolve as type or symbol.
+    TraitsExp *exp;
+    /// The symbol when exp doesn't represent a type.
+    Dsymbol *sym;
+    Type *syntaxCopy();
+    void accept(Visitor *v) { v->visit(this); }
+};
+
 class TypeQualified : public Type
 {
 public:

src/dmd/parse.d

@@ -568,6 +568,7 @@ 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)
@@ -3719,6 +3720,27 @@ 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 give types and symbols");
+                t = new AST.TypeError;
+            }
+            else
+            {
+                t = new AST.TypeTraits(loc, te);
+            }
+            break;
+        }
+
         case TOK.const_:
             // const(type)
             nextToken();
@@ -5394,6 +5416,7 @@ final class Parser(AST) : Lexer
         case TOK.dot:
         case TOK.typeof_:
         case TOK.vector:
+        case TOK.traits:
             /* https://issues.dlang.org/show_bug.cgi?id=15163
              * If tokens can be handled as
              * old C-style declaration or D expression, prefer the latter.
@@ -5442,7 +5465,6 @@ final class Parser(AST) : Lexer
         case TOK.typeid_:
         case TOK.is_:
         case TOK.leftBracket:
-        case TOK.traits:
         case TOK.file:
         case TOK.fileFullPath:
         case TOK.line:
@@ -6905,6 +6927,25 @@ final class Parser(AST) : Lexer
                 goto Lfalse;
             goto L3;
 
+        case TOK.traits:
+            // __traits(getMember
+            t = peek(t);
+            if (t.value != TOK.leftParentheses)
+                goto Lfalse;
+            auto lp = t;
+            t = peek(t);
+            if (t.value != TOK.identifier || t.ident != Id.getMember)
+                goto Lfalse;
+            if (!skipParens(lp, &lp))
+                goto Lfalse;
+            // we are in a lookup for decl VS statement
+            // so we expect a declarator following __trait if it's a type.
+            // other usages wont be ambiguous (alias, template instance, type qual, etc.)
+            if (lp.value != TOK.identifier)
+                goto Lfalse;
+
+            break;
+
         case TOK.const_:
         case TOK.immutable_:
         case TOK.shared_:
@@ -8303,6 +8344,7 @@ final class Parser(AST) : Lexer
                         case TOK.function_:
                         case TOK.delegate_:
                         case TOK.typeof_:
+                        case TOK.traits:
                         case TOK.vector:
                         case TOK.file:
                         case TOK.fileFullPath:

src/dmd/parsetimevisitor.d

@@ -142,6 +142,7 @@ 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

@@ -121,6 +121,7 @@ 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

@@ -1645,6 +1645,20 @@ private extern (C++) final class TypeSemanticVisitor : Visitor
         result = t;
     }
 
+    override void visit(TypeTraits mtype)
+    {
+        import dmd.traits : semanticTraits;
+
+        result = null;
+        if (Expression e = semanticTraits(mtype.exp, sc))
+        {
+            if (Dsymbol ds = getDsymbol(e))
+                mtype.sym = ds;
+            else if (Type t = getType(e))
+                result = t.addMod(mtype.mod);
+        }
+    }
+
     override void visit(TypeReturn mtype)
     {
         //printf("TypeReturn::semantic() %s\n", toChars());

src/dmd/visitor.h

@@ -81,6 +81,7 @@ class TypeClass;
 class TypeTuple;
 class TypeSlice;
 class TypeNull;
+class TypeTraits;
 
 class Dsymbol;
 
@@ -427,6 +428,7 @@ class ParseTimeVisitor
     virtual void visit(TypeStruct *t) { visit((Type *)t); }
     virtual void visit(TypeNext *t) { visit((Type *)t); }
     virtual void visit(TypeQualified *t) { visit((Type *)t); }
+    virtual void visit(TypeTraits *t) { visit((Type *)t); }
 
     // TypeNext
     virtual void visit(TypeReference *t) { visit((TypeNext *)t); }

test/fail_compilation/e7804_1.d

@@ -0,0 +1,9 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/e7804_1.d(9): Error: invalid `__traits`, only `getMember` can give types and symbols
+---
+*/
+module e7804_1;
+
+__traits(farfelu, Aggr, "member") a;