* Deal with mergeability outside of error comparison function
* Make `better_version_exists` function pure (don't halt other versions
as a side effect).
* Tweak error comparison logic
Signed-off-by: Rick Winfrey <rewinfrey@github.com>
The previous approach to error recovery relied on special error-recovery
states in the parse table. For each token T, there was an error recovery
state in which the parser looked for *any* token that could follow T.
Unfortunately, sometimes the set of tokens that could follow T contained
conflicts. For example, in JS, the token '}' can be followed by the
open-ended 'template_chars' token, but also by ordinary tokens like
'identifier'. So with the old algorithm, when recovering from an
unexpected '}' token, the lexer had no way to distinguish identifiers
from template_chars.
This commit drops the error recovery states. Instead, when we encounter
an unexpected token T, we recover from the error by finding a previous
state S in the stack in which T would be valid, popping all of the nodes
after S, and wrapping them in an error.
This way, the lexer is always invoked in a normal parse state, in which
it is looking for a non-conflicting set of tokens. Eliminating the error
recovery states also shrinks the lex state machine significantly.
Signed-off-by: Rick Winfrey <rewinfrey@github.com>
We previously maintained a set of individual productions that were
involved in conflicts, but that was subtly incorrect because
we don't compare productions themselves when comparing parse items;
we only compare the parse items properties that could affect the
final reduce actions.
SpyInput uses a fixed-size buffer and explicitly zeros memory which is good for
catching logic errors but defeats valgrind's memory tracking. Use a separate
buffer of exactly the correct size for each request. This correctly catches the
problem under valgrind:
```
==8694== Invalid read of size 2
==8694== at 0x54EFFB: utf16_iterate (utf16.c:10)
==8694== by 0x551126: ts_lexer__get_lookahead (lexer.c:54)
==8694== by 0x5515CD: ts_lexer_start (lexer.c:154)
==8694== by 0x54699F: parser(long,...)(long long) (parser.c:297)
==8694== by 0x54788A: parser__get_lookahead (parser.c:439)
==8694== by 0x54B2D3: parser__advance (parser.c:1150)
==8694== by 0x54C2AA: parser_parse (parser.c:1348)
==8694== by 0x53F063: ts_document_parse_with_options (document.c:136)
==8694== by 0x53EF43: ts_document_parse (document.c:107)
==8694== by 0x4AED11: {lambda()#1}::operator()() const::{lambda()#1}::operator()() const::{lambda()#4}::operator()() const::{lambda()#4}::operator()() const (document_test.cc:82)
==8694== by 0x4B56B6: std::_Function_handler<void (), {lambda()#1}::operator()() const::{lambda()#1}::operator()() const::{lambda()#4}::operator()() const::{lambda()#4}>::_M_invoke(std::_Any_data const&) (functional:1871)
==8694== by 0x40F8C5: std::function<void ()>::operator()() const (functional:2267)
==8694== Address 0x5d08be0 is 0 bytes inside a block of size 1 alloc'd
==8694== at 0x4C2E80F: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==8694== by 0x507C3E: SpyInput::read(void*, unsigned int*) (spy_input.cc:66)
==8694== by 0x55103D: ts_lexer__get_chunk (lexer.c:29)
==8694== by 0x5515B6: ts_lexer_start (lexer.c:152)
==8694== by 0x54699F: parser(long,...)(long long) (parser.c:297)
==8694== by 0x54788A: parser__get_lookahead (parser.c:439)
==8694== by 0x54B2D3: parser__advance (parser.c:1150)
==8694== by 0x54C2AA: parser_parse (parser.c:1348)
==8694== by 0x53F063: ts_document_parse_with_options (document.c:136)
==8694== by 0x53EF43: ts_document_parse (document.c:107)
==8694== by 0x4AED11: {lambda()#1}::operator()() const::{lambda()#1}::operator()() const::{lambda()#4}::operator()() const::{lambda()#4}::operator()() const (document_test.cc:82)
==8694== by 0x4B56B6: std::_Function_handler<void (), {lambda()#1}::operator()() const::{lambda()#1}::operator()() const::{lambda()#4}::operator()() const::{lambda()#4}>::_M_invoke(std::_Any_data const&) (functional:1871)
```
