From 3ea4a8e237315a024ee04f37589d0d0628a2c770 Mon Sep 17 00:00:00 2001
From: AKhatskevich <avkhatskevich@gmail.com>
Date: Wed, 19 Sep 2018 00:36:16 +0300
Subject: [PATCH] Fix pattern cache key collision bug

Complex patterns are cached by this library to
speedup parsing.
In rare cases the parser was initialized with errors and did
not parse a valid string.

Factors which lead to the error:
1. The pattern cache is weak by value.
2. Intermediate syntax constructions are garbagecollected after
   those were used.
3. Key in the cache is a raw address sometimes.

There was possible the following case:
1. User defines grammar: `c = a + b`.
2. `c` is cached by addresses of `a` and `b`
3. `a` and `b` are garbagecollected
4. User defines grammar: `c1 = a1 + b1`.
5. There is a chance that `a1` and `b1` have got the
   same addresses as was `a` and `b`; in that case
   `c1` would be wrongly taken from the cache as its
   caching key is the same as for `c`.
6. Parser works wrong.

This commit introduces unique pattern ids, which are generated
by a counter. Cache key is then calculated based on those
values.
---
 src/API.lua          |  7 ++++---
 src/constructors.lua | 18 ++++++++++++------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/API.lua b/src/API.lua
index a3b58a7..2b5c877 100644
--- a/src/API.lua
+++ b/src/API.lua
@@ -212,14 +212,15 @@ do
 end
 
 
+-- Give a unique string for a combination of two patterns.
 local function nameify(a, b)
-    return tostring(a)..tostring(b)
+    return ('%s:%s'):format(a.id, b.id)
 end
 
 -- pt*pt
 local
 function choice (a, b)
-    local name = tostring(a)..tostring(b)
+    local name = nameify(a, b)
     local ch = Builder.ptcache.choice[name]
     if not ch then
         ch = factorize_choice(a, b) or constructors.binary("choice", a, b)
@@ -238,7 +239,7 @@ end
 
 local
 function sequence (a, b)
-    local name = tostring(a)..tostring(b)
+    local name = nameify(a, b)
     local seq = Builder.ptcache.sequence[name]
     if not seq then
         seq = factorize_sequence(a, b) or constructors.binary("sequence", a, b)
diff --git a/src/constructors.lua b/src/constructors.lua
index c6ddce8..8720cb4 100644
--- a/src/constructors.lua
+++ b/src/constructors.lua
@@ -86,6 +86,8 @@ local newpattern, pattmt
 -- This deals with the Lua 5.1/5.2 compatibility, and restricted
 -- environements without access to newproxy and/or debug.setmetatable.
 
+-- Augment a pattern with unique identifier.
+local next_pattern_id = 1
 if compat.proxies and not compat.lua52_len then 
     -- Lua 5.1 / LuaJIT without compat.
     local proxycache = weakkey{}
@@ -109,6 +111,8 @@ if compat.proxies and not compat.lua52_len then
         local pt = newproxy(baseproxy)
         setmetatable(cons, __index_LL)
         proxycache[pt]=cons
+        pt.id = "__ptid" .. next_pattern_id
+        next_pattern_id = next_pattern_id + 1
         return pt
     end
 else
@@ -122,6 +126,8 @@ else
     function LL.getdirect (p) return p end
 
     function newpattern(pt)
+        pt.id = "__ptid" .. next_pattern_id
+        next_pattern_id = next_pattern_id + 1
         return setmetatable(pt,LL)
     end
 end
@@ -230,13 +236,13 @@ end
 constructors["subpt"] = function(typ, pt)
     -- [[DP]]print("CONS: ", typ, pt, aux)
     local cache = ptcache[typ]
-    if not cache[pt] then
-        cache[pt] = newpattern{
+    if not cache[pt.id] then
+        cache[pt.id] = newpattern{
             pkind = typ,
             pattern = pt
         }
     end
-    return cache[pt]
+    return cache[pt.id]
 end
 
 constructors["both"] = function(typ, pt, aux)
@@ -246,15 +252,15 @@ constructors["both"] = function(typ, pt, aux)
         ptcache[typ][aux] = weakval{}
         cache = ptcache[typ][aux]
     end
-    if not cache[pt] then
-        cache[pt] = newpattern{
+    if not cache[pt.id] then
+        cache[pt.id] = newpattern{
             pkind = typ,
             pattern = pt,
             aux = aux,
             cache = cache -- needed to keep the cache as long as the pattern exists.
         }
     end
-    return cache[pt]
+    return cache[pt.id]
 end
 
 constructors["binary"] = function(typ, a, b)