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Bug in glr2.cc

From: Jot Dot
Subject: Bug in glr2.cc
Date: Fri, 24 Dec 2021 15:38:52 -0700 (MST)

I think I have found a bug when using glr2.cc
This does not occur when I switch to glr.cc

I am using:
bison (GNU Bison) 3.8.2

I have included my parser.y which causes a crash in the
generated parser code when I use certain input data.
The program crashes in yyremoveDeletes() on this line:

yylookaheadNeeds[j] = yylookaheadNeeds[i];

The vector 'yylookaheadNeeds' has size zero and the variable "i" is zero as 
thus a subscript out of range error occurs.

The relevant stack trace shows:
__int64 _Off) Line 2779  C++
genCompileTest.exe!`anonymous namespace'::glr_state_set::yyremoveDeletes() Line 
959     C++
genCompileTest.exe!`anonymous namespace'::state_stack::reduceToOneStack() Line 
1513     C++
genCompileTest.exe!gen::Parser::glr_stack::yyrecoverSyntaxError(gen::location * 
yylocp) Line 2158       C++
genCompileTest.exe!gen::Parser::glr_stack::parse() Line 2034    C++
genCompileTest.exe!gen::Parser::parse() Line 3113       C++
[External Code] 

I have spent a couple of hours slowly reducing my grammar to the point
where it is about as small as I can make it.

With the attached grammar, bison reports:
1>parser.y : warning : 2 shift/reduce conflicts [-Wconflicts-sr]
1>parser.y : warning : 2 reduce/reduce conflicts [-Wconflicts-rr]

It crashes with the input:
foo (*(*bar)())[]

[0:12-13] Error: syntax error, unexpected '(', expecting ')'

(Note: Yes, I know if 'foo' is a valid type, then the line should have been 
valid grammar - that's why I was debugging it.)

If I comment out line 100 in the grammar file, I get:
1>parser.y : warning : 1 shift/reduce conflict [-Wconflicts-sr]
1>parser.y : warning : 2 reduce/reduce conflicts [-Wconflicts-rr]

The app doesn't crash anymore:
foo (*(*bar)())[]

[0:12-13] Error: syntax error, unexpected '(', expecting ')'

If we leave line 100 uncommented but comment out line 135 instead, we still
have 2 S/R and 2 R/R but the program runs as above without crashing.
(I have placed comments at the end of those two lines for easy locating.)

I think this is as far as I can go.

Oh, btw: Seasons Greetings? Happy Holidays? Merry Christmas? (pick one or add 
Sorry to find it today (Dec 24) as this is a busy time for many people.


PS: Ignore the mess in my yylex code - if you recall (Akim) I modified
it to pass information to my %merge routines instead of passing data
with global variables.  Right now, in this sample code, I do not use
the %merge feature (but was planning on reintroducing it after).

I could remove this mess if we were able to make the %merge routines
as members of the Parser class. hint hint - just a gentle nudge :)

Attachment: parser.y
Description: Text Data

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