#4561: bison-3.5
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Reporter: bdubbs | Owner: lfs-book
Type: task | Status: new
Priority: normal | Milestone: 9.1
Component: Book | Version: SVN
Severity: normal | Resolution:
Keywords: |
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Comment (by bdubbs):
GNU Bison NEWS
Noteworthy changes in release 3.5 (2019-12-11) [stable]
* Backward incompatible changes
Lone carriage-return characters (aka \r or ^M) in the grammar files are
no
longer treated as end-of-lines. This changes the diagnostics, and in
particular their locations.
In C++, line numbers and columns are now represented as 'int' not
'unsigned', so that integer overflow on positions is easily checkable
via
'gcc -fsanitize=undefined' and the like. This affects the API for
positions. The default position and location classes now expose
'counter_type' (int), used to define line and column numbers.
* Deprecated features
The YYPRINT macro, which works only with yacc.c and only for tokens, was
obsoleted long ago by %printer, introduced in Bison 1.50 (November
2002).
It is deprecated and its support will be removed eventually.
* New features
* Lookahead correction in C++
The C++ deterministic skeleton (lalr1.cc) now supports LAC, via the
%define variable parse.lac.
* Variable api.token.raw: Optimized token numbers (all skeletons)
In the generated parsers, tokens have two numbers: the "external" token
number as returned by yylex (which starts at 257), and the "internal"
symbol number (which starts at 3). Each time yylex is called, a table
lookup maps the external token number to the internal symbol number.
When the %define variable api.token.raw is set, tokens are assigned
their
internal number, which saves one table lookup per token, and also saves
the generation of the mapping table.
The gain is typically moderate, but in extreme cases (very simple user
actions), a 10% improvement can be observed.
* Generated parsers use better types for states
Stacks now use the best integral type for state numbers, instead of
always
using 15 bits. As a result "small" parsers now have a smaller memory
footprint (they use 8 bits), and there is support for large automata (16
bits), and extra large (using int, i.e., typically 31 bits).
* Generated parsers prefer signed integer types
Bison skeletons now prefer signed to unsigned integer types when either
will do, as the signed types are less error-prone and allow for better
checking with 'gcc -fsanitize=undefined'. Also, the types chosen are
now
portable to unusual machines where char, short and int are all the same
width. On non-GNU platforms this may entail including <limits.h> and
(if
available) <stdint.h> to define integer types and constants.
* A skeleton for the D programming language
For the last few releases, Bison has shipped a stealth experimental
skeleton: lalr1.d. It was first contributed by Oliver Mangold, based on
Paolo Bonzini's lalr1.java, and was cleaned and improved thanks to
H. S. Teoh.
However, because nobody has committed to improving, testing, and
documenting this skeleton, it is not clear that it will be supported in
the future.
The lalr1.d skeleton *is functional*, and works well, as demonstrated in
examples/d/calc.d. Please try it, enjoy it, and... commit to support
it.
* Debug traces in Java
The Java backend no longer emits code and data for parser tracing if the
%define variable parse.trace is not defined.
* Diagnostics
* New diagnostic: -Wdangling-alias
String literals, which allow for better error messages, are (too)
liberally accepted by Bison, which might result in silent errors.
The -Wall option does not (yet?) include -Wdangling-alias.
* Better POSIX Yacc compatibility diagnostics
POSIX Yacc restricts %type to nonterminals. This is now diagnosed by
-Wyacc.
* Diagnostics with insertion
The diagnostics now display the suggestion below the underlined source.
Replacement for undeclared symbols are now also suggested.
* Diagnostics about long lines
Quoted sources may now be truncated to fit the screen.
* Changes
* Debugging glr.c and glr.cc
The glr.c skeleton always had asserts to check its own behavior (not the
user's). These assertions are now under the control of the parse.assert
%define variable (disabled by default).
* Clean up
Several new compiler warnings in the generated output have been avoided.
Some unused features are no longer emitted. Cleaner generated code in
general.
* Bug Fixes
Portability issues in the test suite.
In theory, parsers using %nonassoc could crash when reporting verbose
error messages. This unlikely bug has been fixed.
In Java, %define api.prefix was ignored. It now behaves as expected.
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