Add assertion and fix AST identity that had broken by template instan…

…tiation

src/struct.c

@@ -655,6 +655,15 @@ void StructDeclaration::semantic(Scope *sc)
         deferred->semantic2(sc);
         deferred->semantic3(sc);
     }
+
+#if 0
+    if (type->ty == Tstruct && ((TypeStruct *)type)->sym != this)
+    {
+        printf("this = %p %s\n", this, this->toChars());
+        printf("type = %d %s, sym = %p\n", type->ty, type->toChars(), ((TypeStruct *)type)->sym);
+    }
+#endif
+    assert(type->ty != Tstruct || ((TypeStruct *)type)->sym == this);
 }
 
 Dsymbol *StructDeclaration::search(Loc loc, Identifier *ident, int flags)

src/template.c

@@ -5050,7 +5050,11 @@ void TemplateInstance::semantic(Scope *sc, Expressions *fargs)
 #endif
 
     // Copy the syntax trees from the TemplateDeclaration
-    members = Dsymbol::arraySyntaxCopy(tempdecl->members);
+    if (members && speculative)
+    {}  // Don't copy again so they were previously created.
+    else
+        members = Dsymbol::arraySyntaxCopy(tempdecl->members);
+
     // todo for TemplateThisParameter
     for (size_t i = 0; i < tempdecl->parameters->dim; i++)
     {
@@ -6511,7 +6515,10 @@ void TemplateMixin::semantic(Scope *sc)
     }
 
     // Copy the syntax trees from the TemplateDeclaration
-    members = Dsymbol::arraySyntaxCopy(tempdecl->members);
+    if (scx && members)
+    {}  // Don't copy again so they were previously created.
+    else
+        members = Dsymbol::arraySyntaxCopy(tempdecl->members);
     if (!members)
         return;