From 636c9a8042787d0c790d676595f3d56e672ce9f5 Mon Sep 17 00:00:00 2001
From: Akim Demaille <akim.demaille@gmail.com>
Date: Fri, 25 Dec 2020 08:53:31 +0100
Subject: [PATCH] glr2.cc: beware of self-assignment

In yycompressStack:

    while (yyr != YY_NULLPTR)
      {
        nextFreeItem->check_ ();
        yyr->check_();
        nextFreeItem->setState(*yyr);
        glr_state& nextFreeState = nextFreeItem->getState();
        yyr = yyr->pred();
        nextFreeState.setPred(&(nextFreeItem - 1)->getState());
        setFirstTop(&nextFreeState);
        ++nextFreeItem;
      }

it is possible that nextFreeItem and yyr are actually the same state.
In which case `nextFreeItem->setState(*yyr)` does really bad things.

* data/skeletons/glr2.cc (glr_stack_item::setState): Beware of
self-assignment.
---
 data/skeletons/glr2.cc | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/data/skeletons/glr2.cc b/data/skeletons/glr2.cc
index 5af9f6ae..e76a376a 100644
--- a/data/skeletons/glr2.cc
+++ b/data/skeletons/glr2.cc
@@ -896,6 +896,12 @@ public:
     return asItem(this);
   }
 
+  const glr_stack_item* asItem () const
+  {]b4_parse_assert_if([[
+    check_ ();]])[
+    return asItem (this);
+  }
+
  private:
   template <typename T>
   static const glr_stack_item* asItem (const T* state)
@@ -1272,12 +1278,15 @@ public:
   {]b4_parse_assert_if([[
     check_ ();
     state.check_ ();]])[
-    // FIXME: What about the previous content?  Shouldn't it be freed?
-    // It might be useful to have an explicit "void" state when this item
-    // is in unused state (in the list of free items), when parse.assert
-    // is set.
-    is_state_ = true;
-    new (&raw_) glr_state (state);
+    if (this != state.asItem ())
+      {
+        is_state_ = true;
+        // FIXME: What about the previous content?  Shouldn't it be
+        // freed?  It might be useful to have an explicit "void" state
+        // when this item is in unused state (in the list of free
+        // items), when parse.assert is set.
+        new (&raw_) glr_state (state);
+      }
   }
 
   glr_state& getState ()