From 9543c479e2960014dad68632e6d6816786a0c63b Mon Sep 17 00:00:00 2001
From: Walter Bright <walter@walterbright.com>
Date: Sun, 26 Jul 2020 00:17:08 -0700
Subject: [PATCH] add support for Object.RTTypeid template

---
 src/dmd/dsymbolsem.d |  3 +++
 src/dmd/id.d         |  1 +
 src/dmd/mtype.d      |  1 +
 src/dmd/typinf.d     | 57 ++++++++++++++++++++++++++++++++++++--------
 4 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/src/dmd/dsymbolsem.d b/src/dmd/dsymbolsem.d
index 09a5003c7f0f..d5922f1408df 100644
--- a/src/dmd/dsymbolsem.d
+++ b/src/dmd/dsymbolsem.d
@@ -2719,6 +2719,9 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
         {
             if (tempdecl.ident == Id.RTInfo)
                 Type.rtinfo = tempdecl;
+
+            if (tempdecl.ident == Id.RTTypeid)
+                Type.rttypeid = tempdecl;
         }
 
         /* Remember Scope for later instantiations, but make
diff --git a/src/dmd/id.d b/src/dmd/id.d
index 2e3be17228b4..a7f1dcc5acd6 100644
--- a/src/dmd/id.d
+++ b/src/dmd/id.d
@@ -107,6 +107,7 @@ immutable Msgtable[] msgtable =
     { "outer" },
     { "Exception" },
     { "RTInfo" },
+    { "RTTypeid" },
     { "Throwable" },
     { "Error" },
     { "withSym", "__withSym" },
diff --git a/src/dmd/mtype.d b/src/dmd/mtype.d
index 436fb3e517d6..c9c52e9a4b67 100644
--- a/src/dmd/mtype.d
+++ b/src/dmd/mtype.d
@@ -473,6 +473,7 @@ extern (C++) abstract class Type : ASTNode
     extern (C++) __gshared ClassDeclaration typeinfowild;
 
     extern (C++) __gshared TemplateDeclaration rtinfo;
+    extern (C++) __gshared TemplateDeclaration rttypeid;
 
     extern (C++) __gshared Type[TMAX] basic;
 
diff --git a/src/dmd/typinf.d b/src/dmd/typinf.d
index d1a254f8b51c..5673caf2724f 100644
--- a/src/dmd/typinf.d
+++ b/src/dmd/typinf.d
@@ -11,15 +11,21 @@
 
 module dmd.typinf;
 
+import dmd.arraytypes;
 import dmd.declaration;
 import dmd.dmodule;
 import dmd.dscope;
 import dmd.dclass;
 import dmd.dstruct;
+import dmd.dsymbolsem;
+import dmd.dtemplate;
 import dmd.errors;
+import dmd.expressionsem;
 import dmd.globals;
 import dmd.gluelayer;
 import dmd.mtype;
+import dmd.semantic2;
+import dmd.semantic3;
 import dmd.visitor;
 import core.stdc.stdio;
 
@@ -56,16 +62,47 @@ void genTypeInfo(Loc loc, Type torig, Scope* sc)
     Type t = torig.merge2(); // do this since not all Type's are merge'd
     if (!t.vtinfo)
     {
-        if (t.isShared()) // does both 'shared' and 'shared const'
-            t.vtinfo = TypeInfoSharedDeclaration.create(t);
-        else if (t.isConst())
-            t.vtinfo = TypeInfoConstDeclaration.create(t);
-        else if (t.isImmutable())
-            t.vtinfo = TypeInfoInvariantDeclaration.create(t);
-        else if (t.isWild())
-            t.vtinfo = TypeInfoWildDeclaration.create(t);
-        else
-            t.vtinfo = getTypeInfoDeclaration(t);
+        if (Type.rttypeid)
+        {
+            // Evaluate: RTTypeid!t
+            auto tiargs = new Objects();
+            tiargs.push(t);
+            auto ti = new TemplateInstance(loc, Type.rttypeid, tiargs);
+
+            Scope* sc3 = ti.tempdecl._scope.startCTFE();
+            sc3.tinst = sc.tinst;
+            sc3.minst = sc.minst;
+            ti.dsymbolSemantic(sc3);
+            ti.semantic2(sc3);
+            ti.semantic3(sc3);
+            auto e = symbolToExp(ti.toAlias(), Loc.initial, sc3, false);
+
+            sc3.endCTFE();
+
+            e = e.ctfeInterpret();
+            t.vtinfo = cast(TypeInfoDeclaration) e.isVarExp();
+            /* Save this for when RTTypeid is fully operational
+            if (!t.vtinfo)
+            {
+                .error(loc, "`object.RTTypeid!T` did not return a TypeInfo variable");
+                fatal();
+            }
+            */
+        }
+
+        if (!t.vtinfo)
+        {
+            if (t.isShared()) // does both 'shared' and 'shared const'
+                t.vtinfo = TypeInfoSharedDeclaration.create(t);
+            else if (t.isConst())
+                t.vtinfo = TypeInfoConstDeclaration.create(t);
+            else if (t.isImmutable())
+                t.vtinfo = TypeInfoInvariantDeclaration.create(t);
+            else if (t.isWild())
+                t.vtinfo = TypeInfoWildDeclaration.create(t);
+            else
+                t.vtinfo = getTypeInfoDeclaration(t);
+        }
         assert(t.vtinfo);
 
         /* If this has a custom implementation in std/typeinfo, then