From eea088c5f59610ce7cd966d1f9c53e032de39f3d Mon Sep 17 00:00:00 2001
From: florian <florian@freepascal.org>
Date: Sun, 14 Oct 2018 07:38:13 +0000
Subject: [PATCH] * allow nil to be assigned to generic types, resolves #34037
 * niln is also a constant node

git-svn-id: trunk@39934 -
---
 .gitattributes          |  1 +
 compiler/defcmp.pas     |  3 ++-
 compiler/node.pas       |  8 +++++---
 compiler/pexpr.pas      |  2 +-
 tests/webtbs/tw34037.pp | 21 +++++++++++++++++++++
 5 files changed, 30 insertions(+), 5 deletions(-)
 create mode 100644 tests/webtbs/tw34037.pp

diff --git a/.gitattributes b/.gitattributes
index 9925c4b539..eb81fe1a94 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -16378,6 +16378,7 @@ tests/webtbs/tw33840.pp -text svneol=native#text/pascal
 tests/webtbs/tw33898.pp -text svneol=native#text/pascal
 tests/webtbs/tw3402.pp svneol=native#text/plain
 tests/webtbs/tw34021.pp -text svneol=native#text/pascal
+tests/webtbs/tw34037.pp svneol=native#text/pascal
 tests/webtbs/tw3411.pp svneol=native#text/plain
 tests/webtbs/tw34124.pp svneol=native#text/pascal
 tests/webtbs/tw3418.pp svneol=native#text/plain
diff --git a/compiler/defcmp.pas b/compiler/defcmp.pas
index 3f5882f762..af4b40d931 100644
--- a/compiler/defcmp.pas
+++ b/compiler/defcmp.pas
@@ -289,7 +289,8 @@ implementation
              if assigned(tstoreddef(def_from).genconstraintdata) or
                  assigned(tstoreddef(def_to).genconstraintdata) then
                begin
-                 if def_from.typ<>def_to.typ then
+                 { constants could get another deftype (e.g. niln) }
+                 if (def_from.typ<>def_to.typ) and not(fromtreetype in nodetype_const) then
                    begin
                      { not compatible anyway }
                      doconv:=tc_not_possible;
diff --git a/compiler/node.pas b/compiler/node.pas
index b8600000bf..21b421107c 100644
--- a/compiler/node.pas
+++ b/compiler/node.pas
@@ -197,11 +197,13 @@ interface
           'specializen');
 
       { a set containing all const nodes }
-      nodetype_const = [ordconstn,
+      nodetype_const = [niln,
+                        ordconstn,
                         pointerconstn,
                         stringconstn,
                         guidconstn,
-                        realconstn];
+                        realconstn,
+                        setconstn];
 
     type
        { all boolean field of ttree are now collected in flags }
@@ -657,7 +659,7 @@ implementation
 
     function is_constnode(p : tnode) : boolean;
       begin
-        is_constnode:=(p.nodetype in [niln,ordconstn,realconstn,stringconstn,setconstn,pointerconstn,guidconstn]);
+        is_constnode:=(p.nodetype in nodetype_const);
       end;
 
 
diff --git a/compiler/pexpr.pas b/compiler/pexpr.pas
index 56374d89ef..e6f99ba68e 100644
--- a/compiler/pexpr.pas
+++ b/compiler/pexpr.pas
@@ -1939,7 +1939,7 @@ implementation
                       not is_objectpascal_helper(tdef(srsymtable.defowner)) then
                     internalerror(2013011401);
                   { convert const node to temp node of the extended type }
-                  if node.nodetype in (nodetype_const+[niln,addrn]) then
+                  if node.nodetype in (nodetype_const+[addrn]) then
                     begin
                       extdef:=tobjectdef(srsymtable.defowner).extendeddef;
                       newstatement:=nil;
diff --git a/tests/webtbs/tw34037.pp b/tests/webtbs/tw34037.pp
new file mode 100644
index 0000000000..2d7ffbfe64
--- /dev/null
+++ b/tests/webtbs/tw34037.pp
@@ -0,0 +1,21 @@
+program project1;
+{$mode objfpc}{$H+}
+
+uses
+  Classes, FGL;
+
+type
+  TBaseClass = class (TObject)
+  end;
+
+  generic TFPGObjectListEx<T: TBaseClass> = class (specialize TFPGObjectList<T>)
+    function GetItemByID(AID: Integer): T;
+  end;
+
+function TFPGObjectListEx.GetItemByID(AID: Integer): T;
+begin
+  Result:=nil; //T(nil);
+end;
+
+begin
+end.